Research on the Application of Biochar in Carbon Sequestration: A Bibliometric Analysis

Abstract

Driven by global carbon neutrality goals, biochar has gained significant attention due to its stable carbon sequestration capabilities and environmental benefits. This research employs bibliometric tools such as VOSviewer 1.6.16, Citespace 6.2 R6, and Scimago Graphica to systematically analyze 2076 publications from the Web of Science Core Collection between 2007 and 2024, aiming to clarify the evolutionary trajectory, research hotspots, and international collaboration patterns of biochar carbon sequestration research while identifying future knowledge gaps for innovation. Research results reveal a three-stage developmental characteristic: 2007–2014 was a slow accumulation period for fundamental mechanism exploration, 2015–2020 was an accelerated expansion period driven by policies like the Paris Agreement, and 2021 to the present marks an exponential growth phase of interdisciplinary integration due to global carbon market consolidation. China and the United States are core producing countries, though inter-institutional deep collaboration remains insufficient. Research hotspots have progressively shifted from early biochar preparation and carbon stability to multiple waste materials (such as rice straw and urban carbon sequestration waste) and co-pyrolysis technologies (significantly emerging since 2022), with machine learning applications in process optimization becoming a nascent direction. The study recommends increasing cross-disciplinary research funding, establishing biochar raw material pollution standards, and promoting coordinated policies that combine biochar carbon sequestration with agricultural efficiency to support global carbon reduction objectives. Notably, the research’s reliance on the Web of Science Core Collection may limit coverage of non-English literature and regional studies. By quantitatively analyzing technological evolution and collaboration networks, this study provides a data-driven framework for optimizing biochar carbon sequestration strategies, helping bridge the gap between laboratory potential and actual climate emission reduction, and offering focused action pathways for policymakers and researchers.

1. Introduction

In recent years, under the combined influence of human activities and natural factors, global climate change has been intensifying, with frequent extreme climate events posing a severe challenge to the sustainable development of ecosystems and human society, prompting countries worldwide to actively explore countermeasures [1,2,3]. The 2015 Paris Agreement proposed controlling the global average temperature rise to within 2 °C compared to pre-industrial levels, and striving to limit it to 1.5 °C [4], which requires a significant reduction in greenhouse gas emissions [5,6].

Carbon sequestration technology, as a key negative emission strategy to mitigate greenhouse gas emissions, shows significant differences among various technological paths in terms of the sequestration cycle, cost-effectiveness, and environmental synergy. Geological sequestration, while having a large-capacity advantage, faces challenges in leak monitoring [7,8]. Mineral carbonation can permanently fix Carbon dioxide (CO₂) without leakage risks, but its slow reaction speed and high energy consumption limit widespread application [9,10]. Ocean sequestration has enormous capacity but may cause ecological risks [11,12]. In comparison, biochar is reshaping the carbon sequestration technology landscape with its unique closed-loop carbon cycle characteristics. Biochar is formed through pyrolysis of biomass under oxygen-limited conditions, creating a stable aromatic carbon structure [13], with high carbon content and thermal stability [14]. It can store CO₂ for hundreds of years [15] and achieve high cost-effectiveness with relatively low energy requirements [16]. Research indicates that converting 373 million tons of annual agricultural waste into biochar could capture approximately 550 million tons of CO₂ [17], highlighting its undeniable potential in carbon cycle regulation. Moreover, biochar can improve soil structure, enhance nutrient retention capabilities, and regulate microbial activity, facilitating a win–win scenario for carbon sequestration and agricultural sustainable development [18,19].

Over the past two decades, biochar has garnered widespread attention in the field of environmental remediation as an eco-friendly and multifunctional material [20,21,22,23]. However, existing research has primarily focused on its role in improving soil fertility and enhancing soil carbon sequestration, with a notable lack of systematic and comprehensive analysis of biochar in carbon storage [15]. Biochar is often merely described as a supplement to soil improvement characteristics, with insufficient in-depth exploration of its potential as a critical carbon fixation method. As global demand for reducing carbon dioxide emissions becomes increasingly urgent, and the potential of biochar in reducing greenhouse gas emissions gains recognition, a review of systematic applications, international research status, hotspots, and development trends in biochar carbon fixation has become particularly necessary. Against this background, this study employs bibliometric analysis methods to provide a unique perspective and comprehensive understanding of the biochar carbon fixation field, charting a course for future research.

As a crucial tool for quantitatively analyzing the scientific literature structure and evolutionary patterns [24], bibliometrics can precisely identify research hotspot evolution, core knowledge producers, and interdisciplinary interaction modes through high-frequency keyword co-occurrence, collaborative network analysis, and temporal mapping [25]. Compared to methods like meta-analysis focusing on parameter quantitative integration, bibliometrics’ core advantage lies in its macro-scale analysis capability to systematically reveal knowledge network characteristics of technological development trajectories (such as knowledge flow direction and interdisciplinary nodes) and social network attributes (like institutional collaboration patterns and national competitiveness landscapes), rather than being limited to statistical parameter inference.

This panoramic analysis method is particularly suitable for revealing technological evolution paths and innovation ecosystem requirements in the biochar carbon sequestration field. This study integrates global literature from the Web of Science core database, utilizing VOSviewer, Citespace, and Scimago Graphica to construct co-occurrence networks and timeline maps for institutions, countries, authors, and keywords. The method of selection is primarily based on two considerations: first, while quantitative analyses of parameters like biochar application range and pH effects have been established through existing meta-research, unstructured issues such as technological adoption barriers and research hotspot migration still require bibliometric revelation; second, technical innovation for agricultural, waste-source, and nano-structured biochar necessitates establishing a technological evolution analysis framework from three dimensions: knowledge production subjects, knowledge transmission carriers, and knowledge dissemination networks.

The research results will provide a theoretical basis for optimizing biochar carbon sequestration strategies; offer decision-making support for policymakers in balancing technological feasibility, economic costs, and ecological risks; and identify key interdisciplinary knowledge integration nodes to guide technological innovation.

2. Materials and Methods

2.1. Data Sources and Retrieval Strategy

This research used the Web of Science Core Collection (WoSCC) as the data source, as it indexes over 9000 high-impact journals globally [26], covering core fields such as environmental science and soil science, and is one of the most widely used databases in bibliometric research. Compared to other databases like Scopus and PubMed, it is widely considered the most comprehensive and reliable bibliometric analysis database [27,28]. Although databases like Scopus can provide Supplementary Information, Web of Science has advantages in cross-disciplinary literature coverage and data standardization, making it suitable for constructing a systematic bibliometric analysis framework. The search strategy was as follows: TS = ((“biochar” OR “bio-char”) AND (“carbon sequestration” OR “carbon storage” OR “carbon sink” OR “carbon removal” OR “CO₂ sequestration” OR “CO₂ storage”)) NOT TS = (“geological sequestration” OR “enhanced oil recovery”). The search was conducted on 22 April 2025.

2.2. Screening Criteria

Based on a systematic retrieval strategy, the earliest retrievable literature dates back to 2007. Up to now, 2245 related papers have been obtained. Since 2025 data have not yet been fully included, we excluded 2025 data. We limited the results to “Article” and “Review Article” published between 2007 and 2024. Because the number of non-English articles in the literature is very small and lacks representativeness, the language was set to English. This selection process ultimately formed a core dataset containing 2076 literature references, laying the foundation for final analysis. The search and analysis process is shown in Figure 1.

2.3. Data Analysis

This research adopts a multi-tool collaborative analysis method, achieving data visualization through three bibliometric tools. VOSviewer 1.6.16 was selected for co-occurrence network visualization, leveraging its proven stability in processing large-scale bibliometric datasets and interpretability advantages in traditional keyword clustering [29]. Although advanced artificial intelligence support tools excel in processing unstructured data and predicting research trends, VOSviewer remains irreplaceable in transparent, rule-based co-occurrence analysis, which is crucial for reproducible bibliometric research. Complementing VOSviewer is CiteSpace, a Java application developed by Professor Chen Chaomei’s team, which demonstrates outstanding value in revealing discipline evolution paths and research hotspot transitions through its longitudinal analysis advantages [30]. Therefore, the article specifically employs CiteSpace 6.2 R6’s journal overlay mapping, keyword emergence intensity detection, and cited literature emergence intensity detection functions to systematically reveal the knowledge diffusion trajectory of the research field. To optimize international collaboration networks, this research introduced Scimago Graphica for spatial processing, which exhibits significant professional advantages in visualization layout and interactive analysis of complex networks. Through the collaborative application of these three tools, co-occurrence networks of institutions, countries, authors, and keywords, as well as timeline maps, were constructed.

3. Results

3.1. Annual Publication Volume Analysis

The development status, knowledge accumulation, and maturity of a research field can be measured by changes in its literature output [31]. This study systematically retrieved and counted the annual publication volume of the literature related to biochar carbon sequestration in the Web of Science Core Collection (WoSCC) from 2007 to 2024, selecting a total of 2075 papers. Figure 2A shows that the number of papers in the literature exhibits significant staged characteristics. During the initial accumulation period from 2007 to 2014, academic interest in this field showed a moderate growth trend, with an average annual publication of 34.89 papers. After entering 2015, the annual publication volume entered an acceleration period, with the average annual growth rate increasing by approximately 256% compared to the previous stage, while maintaining a steady upward trend. Since 2021, the data curve has demonstrated a notable exponential growth characteristic, with the annual publication volume breaking through 200 papers, and it is expected to continue growing. The citation frequency of the literature also shows a steady growth trend. To better display the increment trend, a fitting method was used to calculate the relationship between the number of publications and years (Y = 1.275X² − 5122.35X + 5144823.975, R² = 0.9856). According to this equation, the number of articles will continue to increase (Figure 2B).

3.2. Journal Analysis

The 2075 literature references are distributed across 376 journals, with significant variations in publication volume. Based on Bradford’s Law, a cluster analysis of the journal distribution in the biochar carbon sequestration technology field identified 12 core journals (

Table 1. Top 10 Publication Sources.

Rank	Journal	Number of Documents	IF (2024)	Publishers	Core Research Directions
1st	Science of the Total Environment	164	8.2	Elsevier	Environmental Science; Pollution Control
2nd	Journal of Environmental Management	67	8.0	Academic	Environmental Management; Sustainability Policies
3rd	Journal of Cleaner Production	64	9.7	Elsevier	Cleaner Production Technologies; Circular Economy
4th	Agronomy-Basel	59	3.3	MDPI	Agronomy; Sustainable Agriculture
5th	Sustainability	58	3.3	MDPI	Comprehensive Sustainability Studies
6th	Global Change Biology Bioenergy	48	5.9	Wiley	Climate Change and Bioenergy
7th	Chemosphere	41	8.8	Elsevier	Environmental Chemistry; Pollutant Studies
8th	Bioresource Technology	40	9.7	Elsevier	Bioresource Technology; Bioenergy
9th	Biochar	39	13.1	Springer Nature	Biochar Applications; Soil Amendment
10th	Geoderma	39	5.6	Elsevier	Soil Science; Land Management
11	Bioresource Technology	39	9.7	Elsevier	Biological Resource Conversion and Environmental Biotechnology
12	Agriculture Ecosystems & Environment	38	3.9	Elsevier	Agricultural Ecosystem Sustainability

). Science of the Total Environment, with 167 published articles, emerged as the most productive journal, far surpassing others. It primarily publishes research on comprehensive environmental studies, environmental pollution and remediation, and environmental technologies and applications, and is considered a top-tier environmental science journal. Among these journals, 58% have an impact factor (IF) ≥ 5, indicating a high quality level. The publishers are predominantly from Elsevier, accounting for 58.3% of the publications. From a disciplinary perspective, the included journals cover environmental science, soil science, energy and fuels, agronomy, environmental engineering, and green sustainable science and technology (Figure 3). Environmental science journals published the highest number of articles, serving as the primary platform for research findings and innovative ideas in this field.

Dual mapping overlay is a visualization analysis technique aimed at analyzing, comparing, and contrasting publication portfolio characteristics [32]. This method enables cross-disciplinary attributes between research sources and targets and has been widely applied in bibliometric research [30]. The journal dual mapping overlay represents the thematic distribution of journals (Figure 4), with citing journals on the left, cited journals on the right, and colored paths indicating citation relationships [33,34]. The journal dual mapping overlay analysis reveals the interdisciplinary knowledge dissemination pattern of biochar in carbon sequestration research. Three main citation pathways were identified, reflecting interactions across different disciplines. The citing journals’ domains are (Veterinary, Animal, Science), while the cited journals are (Plant, Ecology, Zoology), (Environmental, Toxicology, Nutrition), and (Chemistry, Materials, Physics), with cited journals converging towards citing journals. Beyond these mainstream citation pathways, other citation paths exist, albeit with weaker associations. This suggests that biochar research is developing in a multidisciplinary direction.

3.3. Institutional Analysis

Network analysis of the collaboration among 2464 global research institutions reveals that in the 2076 literature entries analyzed, 15 institutions contributing over 15 papers accounted for 29.3% of the total literature volume (

Table 2. Top 15 Publishing Institutions.

Rank	Institution	Countries/ Regions	Publication	Citation	Citation per Publication	TLS
1st	Chinese Academy of Sciences	China	116	5492	47.34	104
2nd	Zhejiang University	China	60	4872	81.20	45
3rd	Northwest A&F University	China	52	1713	32.94	27
4th	Nanjing Agricultural University	China	48	2525	52.60	34
5th	University of Chinese Academy of Sciences	China	44	2115	48.07	60
6th	University of Edinburgh	England	38	3248	85.47	30
7th	China Agricultural University	China	30	1235	41.17	29
8th	Zhejiang A&F University	China	30	1933	64.34	22
9th	King Saud University	Saudi Arabia	29	2392	82.48	15
10th	Shanghai Jiao Tong University	China	29	2546	87.79	21
11th	University of Florida	U.S.	28	4433	158.32	14
12th	University of Western Australia	Australia	28	2444	87.29	35
13th	Chinese Academy of Agricultural Sciences	China	27	768	28.44	24
14th	Aarhus University	Denmark	27	1249	46.25	19
15th	Cornell University	U.S.	25	5853	234.12	22

). Furthermore, 9 of the top 15 institutions are from China. Taking the Chinese Academy of Sciences (CAS) as an example, it comprehensively leads with 116 published papers, 5492 citations, and a Total Link Strength (TLS) of 104. Total Link Strength represents the sum of link intensities between a node (such as keywords, authors, countries) and all other nodes, and in institutional collaboration network analysis, it indicates the total number of joint publications between institutions, serving as a core metric for measuring network node association intensity.

Notably, while 3/5 of the top 15 institutions by publication volume are Chinese universities, Chinese institutions generally have lower citation rates. For instance, Cornell University from the United States, despite having only 25 papers, has 5853 citations, with the highest citation per paper rate of 234.12 among all institutions.

From the institutional overlay visualization map (Figure 5), among the 37 institutions with ≥15 papers, the Chinese Academy of Sciences has the largest node with dense connection lines, demonstrating high productivity and strong collaborative attributes. Institutions like Zhejiang University, Nanjing Agricultural University, and Northwest A&F University form a regional research cluster around the Chinese Academy of Sciences, with most of these high-intensity collaborations being domestic institutions. Chinese institutions have relatively less collaboration with high-productivity U.S. institutions such as University of Florida, University of Massachusetts, Iowa State University, and USDA ARS. In terms of spatio-temporal evolution, U.S. institutions generally emerged earlier in the research, while Chinese institutions typically emerged later.

3.4. National Analysis

A total of 100 countries have published articles in the field of carbon sequestration, with 48 institutions screening out ≥10 articles. China is the country with the most publications, with a total of 811 papers, followed by the United States (395 papers), Australia (174 papers), Germany (156 papers), India (154 papers), Canada (100 papers), Italy (94 papers), United Kingdom (87 papers), Pakistan (84 papers), and Republic of Korea (82 papers), with developed countries accounting for 70% (Figure 6). In terms of H-index, the United States (102) ranks first, followed by China (97), Australia (64), Germany (54), Canada (46), India (45), United Kingdom (41), Italy (38), Republic of Korea (36), and Pakistan (35). In terms of average citations per paper, the top three countries are Republic of Korea (128.54 citations), Canada (119.3 citations), and Australia (109.67 citations), while the United States (105.31 citations), United Kingdom (95.46 citations), and Germany (82.37 citations) also demonstrate high research impact (Figure 6). However, China has the lowest number of citations among the top 10 countries in terms of publication volume (only 51.72).

As shown in Figure 7, China had a low publication volume in the early stage, with a relatively slow article growth rate from 2010 to 2015. After 2015, it entered a growth phase, especially after 2020, showing exponential growth. The United States demonstrates a steady growth trend, reaching its peak in 2023, with a slight decrease in 2024. Australia, Germany, and India had relatively low publication volumes but experienced small explosive growth after 2021.

Figure 8 displays the overall landscape of global research collaboration, visualizing the intensity and nature of cooperation between countries. Countries are represented by circles, with size indicating the number of published papers. Connection line colors range from yellow to red, with redder colors indicating higher cooperation intensity. China and the United States are the two core players, with their interconnecting line being extremely red, demonstrating the highest cooperation intensity in the global research network. China’s total cooperation intensity is 634, while the United States’ total connection intensity is 439, reflecting a leading international research collaboration. China collaborates closely with countries like Republic of Korea, Saudi Arabia, and Australia, mostly geographically proximate nations, with a tendency towards regional research collaboration, as indicated by the reddish connection lines. Countries collaborating with the United States span across Asia, Europe, and South America, with a more extensive and international collaboration nature, as shown by connection lines varying from yellow to red. Both China and the United States maintain close cooperation with Republic of Korea, with reddish lines highlighting the tight trilateral collaboration. Europe is the most densely connected collaboration network, with connection lines among many countries rich in color and predominantly reddish, reflecting high-intensity multilateral research cooperation, closely related to geographical proximity and deep academic exchange traditions.

Figure 9’s country time overlay network reveals that the United States and Australia were the earliest countries to research this field, followed by developed countries like the United Kingdom, Denmark, and Germany. Developing countries such as China, India, and Pakistan entered the field more recently.

3.5. Author Analysis

The study included a total of 8943 authors. According to the screening criteria (≥10 publications and ≥100 citations), 29 core authors were ultimately identified. After removing isolated nodes lacking cooperative relationships, the cooperation network contained 27 authors, forming four research clusters with distinctive characteristics (Figure 10). Based on Price’s law for selecting core authors, if an author’s number of papers $M=0.749\sqrt{P_{max}}$, they belong to the core author group, where Pmax represents the number of papers by the most productive author. Therefore,

Table 3. Top 4 Authors by Publication Volume.

Ranking	Author	Publications	Citations	H-Index	Affiliated Institution
1st	Yong Sik Ok	30	7795	145	Korea University
2nd	Ondřej Mašek	24	1544	49	University of Edinburgh
3rd	Tsang, Daniel C. W.	19	1537	129	Hong Kong University of Science and Technology
4th	Cao, Xinde	19	2429	78	Shanghai Jiao Tong University

lists the top 4 authors by publication volume. Among these four authors, Yong Sik Ok from a Korean university has the highest H-index and the most citations, indicating his greatest influence.

The interaction and collaboration between different clusters are not tight-knit, with the green cluster showing the most cohesive collaborative relationships, primarily focusing on research about biochar applications in rice fields and agricultural production [35,36,37,38]. The red cluster exhibits relatively low internal collaboration, with its representative scholar Lehmann Johannes dedicating long-term research to biochar in soil improvement [39,40]. He and Professor Yong Sik Ok are the only authors with collaborations spanning all four clusters. The yellow cluster centers around Professor Yong Sik Ok, characterized by notably interdisciplinary research [41,42]. This scholar has not only promoted the technological transformation of biochar across multiple industries but has also recently optimized the biochar functional design through machine learning [43,44,45]. His academic impact indicators, including publication volume, citation frequency, and H-index, are at the top level (Figure 11, Table 3). Several authors in the blue cluster have relatively frequent collaborations, with their research primarily oriented towards biochar applications in water purification and heavy metal adsorption [46,47].

3.6. Keyword Co-Occurrence

To ensure the accuracy and consistency of research result analysis and avoid potential biases caused by subtle differences in terminology usage, this study standardized the keywords found in the retrieved literature. “CO₂ storage” and “CO₂ sequestration” were jointly merged into “carbon sequestration”; “CO₂” was merged into “carbon dioxide”; “climate” and “climate change” were integrated into “climate-change”; and “life cycle assessment” was merged into “life-cycle assessment”.

High-frequency and high-ranking keywords directly reflect the core research content and hot issues in the field. By tracking the changes in keyword frequency over time, research hotspots can be captured and traced.

Table 4. Top 15 Keywords.

Rank	Keywords	Occurrences	Total Link Strength
1st	biochar	1208	10,736
2nd	carbon sequestration	878	8004
3rd	pyrolysis	388	3560
4th	black carbon	341	3345
5th	biomass	319	3048
6th	soil	301	2705
7th	carbon	237	2050
8th	charcoal	214	2040
9th	nitrogen	213	2018
10th	pyrolysis temperature	209	2072
11th	stability	202	1948
12th	organic—matter	202	1880
13th	greenhouse—gas emissions	184	1856
14th	temperature	184	1768
15th	adsorption	172	1564

shows the top 15 keywords, with biochar being the most frequent, appearing 1208 times, with a total connection intensity of 10,736, followed by carbon sequestration, appearing 878 times, with a total connection intensity of 8004.

There were 7238 keywords in total. When the keyword threshold was below 15, there were three clusters, but the large number of keywords was not conducive to in-depth analysis. Setting the keyword appearance threshold to over 25 times still resulted in three clusters, but with significantly different keyword distributions. When the threshold was set between 30 and 60 times, the clusters reduced to two. Upon further increasing the keyword appearance threshold to 70 times, the keyword clusters returned to three, with significantly reduced interference keywords. At this point, only core keywords in the carbon sequestration field related to biochar emerged, with a total of 54 high-frequency terms identified. Carbon sequestration and biochar were the most focused keywords. Based on keyword co-occurrence clustering, current biochar research directions can be divided into three categories: the red area’s main keywords include biochar, carbon sequestration, pyrolysis, adsorption, carbon, soil, biomass, waste, etc., indicating biochar technology development and application; the blue area focuses on black carbon stability mechanisms, with high-frequency keywords like black carbon, stability, oxidation, mineralization, and mechanisms; the green area’s keywords include organic carbon, microbial community, greenhouse gas emissions, and climate change, primarily reflecting organic carbon dynamics and climate feedback mechanisms (Figure 12A).

To reveal the temporal evolution trend of research themes, an overlay visualization map was constructed (Figure 12B). Purple indicates keywords that appeared relatively early, while yellow represents recently emerging keywords. The overlay visualization map shows that keywords like charcoal, black carbon, sorption, oxidation, and chemical properties appear in purple, indicating they emerged earlier; keywords such as removal, waste, water, straw, quality, and soil organic carbon appear in yellow–green; greenhouse gas emissions and mechanisms appear in bright yellow, indicating these themes have recently attracted increasing attention.

Keyword citation burst refers to keywords with rapidly increasing citation volumes. Burst detection is a useful analytical method for discovering keywords of special focus from relevant scientific communities during a specific period [48]. The red portion represents the time period of citation bursts [49], and keywords with strong burst intensity can represent research hotspots and frontiers [50]. Using CiteSpace to explore keywords with strong burst intensity from 2007 to 2024, Figure 13 lists the top 25 keywords in the biochar carbon sequestration field. These represent rapidly growing topics in biochar research. By analyzing the 25 high-burst-intensity keywords between 2007 and 2024, a clear evolutionary path in carbon sequestration research emerges. Early research centered on black carbon and charcoal, with burst intensities of 51.98 and 47.05, respectively, reflecting the academic community’s strong interest in carbon stability mechanisms. Keywords like oxidation (intensity 12.92) and bioavailability further revealed black carbon’s resistance to decomposition in the environment. These foundational studies provided theoretical support for subsequent applications.

From the early 2010s, the research focus gradually shifted to agricultural practices. Keywords like soil carbon and soil amendment significantly increased in frequency, indicating biochar research transitioned from laboratory stages to field trials. Scientists conducted application research on straw biochar in rice field systems, verifying carbon sequestration effects and collecting scalable application data. Between 2022 and 2024, keywords like rice straw, municipal solid waste, and co-pyrolysis remained active, showing research moving towards multi-waste collaborative conversion. Specific examples include co-pyrolysis technologies applying rice straw biochar with municipal waste. Simultaneously, keywords like sorption and aggregate stability continued to appear, involving optimization of biochar’s physicochemical properties. Early high-frequency terms like bioenergy and chemical property had relatively shorter active periods. Current research expanded to exploring microbial community influences on organic carbon decomposition and observing relationships between biochar application and greenhouse gas emissions, encompassing comprehensive ecosystem-level impact assessments.

3.7. Co-Citation Analysis

When two papers appear simultaneously in the citations of a third paper, they are considered to have a co-citation relationship [51]. Important publications typically attract significant attention and interest, which can be reflected through citations [52], and co-citation analysis serves as a crucial method for detecting specific domain structures and evolutionary pathways [53]. This article generated a literature co-citation visualization map using VOSviewer software (Figure 14) and listed the top 10 co-cited papers using Cite Space (

Table 5. Top 10 Co-Cited References.

First Author	Article	Journal	Year	Co-Citation	Total Citation
Tomczyk, A. [54]	Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects	Environmental Science and Bio/Technology	2020	115	1606
Wang, J.Y. [55]	Biochar stability in soil: meta-analysis of decomposition and priming effects	Global Change Biology Bioenergy	2016	105	897
Lehmann, J. [40]	Biochar effects on soil biota—A review	Soil Biology and Biochemistry	2011	101	4017
Lehmann, J. [56]	Biochar in climate change mitigation	Nature Geoscience	2021	93	433
Leng, L.J. [57]	Biochar stability assessment methods: A review	Science of The Total Environment	2019	76	469
El-Naggar, A. [41]	Biochar application to low fertility soils: A review of current status, and future prospects	Geoderma	2019	75	727
Smith, P. [58]	Soil carbon sequestration and biochar as negative emission technologies	Global Change Biology	2016	70	658
Borchard, N. [59]	Biochar, soil and land-use interactions that reduce nitrate leaching and N2O emissions: A meta-analysis	Science of the Total Environment,	2021	69	361
Jeffery, S. [60]	A quantitative review of the effects of biochar application to soils on crop productivity using meta-analysis	Agriculture, Ecosystems & Environment	2011	65	1917
Woolf, D. [61]	Sustainable biochar to mitigate global climate change	Nature Communications	2010	65	1761

), with only the first authors cited. In the biochar research field, a series of foundational literature collectively constructs the knowledge landscape. While all these papers are related to biochar, they focus on different perspectives.

Tomczyk et al. (2020) [54] systematically revealed the influence of pyrolysis temperature (300–700 °C) and raw material type on biochar’s physicochemical properties, finding that high temperatures significantly enhance specific surface area and ash content while reducing volatile matter and CEC. Woody material-based biochar demonstrates higher carbon sequestration and pollutant adsorption potential due to high carbon content and porous structure, while manure-based biochar is more suitable for soil improvement due to high ash content and CEC. Wang et al. (2016) [55] conducted a meta-analysis of 128 isotope tracing studies, revealing biochar’s dual-pool decomposition mode in soil, showing an overall negative priming effect on soil organic carbon mineralization but significantly promoting mineralization in sandy soils, quantifying biochar’s long-term carbon sequestration potential and environmental factors’ impact on its stability.

Lehmann’s team, from a microbial ecology perspective, first unveiled biochar’s porous structure’s regulatory mechanism on rhizosphere microbiota, discovering its promotion of beneficial microbial colonization through allelopathic substance adsorption [56]. Leng et al. (2019) [57] systematically reviewed biochar stability assessment methods, proposing a multi-dimensional evaluation system combining elemental analysis, thermal oxidation stability, and molecular markers, finding high correlation between H/C ratio and mineralization model results, and recommending thermal oxidation stability indicators to improve prediction accuracy.

El-Naggar, through field trials and meta-analysis, systematically demonstrated biochar’s potential to enhance nutrient utilization efficiency in low-fertility soils, innovatively proposing the “designed biochar” concept to optimize material performance [38]. Smith et al. (2016) [58] examined biochar from a negative emissions technology perspective, proving its synergistic benefits in carbon sequestration and soil improvement through life cycle assessment. Borchard et al. (2019) [59] meta-analyzed 88 studies, finding biochar can reduce N₂O emissions by 38% and NO₃⁻ leaching by 13%, with particularly significant effects in paddy and sandy soils, though diminishing over time.

Jeffery et al. (2011) [60] meta-analyzed 16 studies, discovering biochar generally increases crop yield by 10% on average, with effects significantly influenced by soil pH and texture. Poultry manure-based biochar showed the best performance (28%), while solid biochar demonstrated negative effects. Woolf et al. (2010) [61] proposed that biochar, through sustainable biomass pyrolysis and soil sequestration, could achieve an annual 12% greenhouse gas emission reduction potential, with century-long benefits significantly higher than direct biomass power generation.

All research focuses on biochar’s carbon sequestration potential and its environmental/agricultural synergistic benefits, serving climate change mitigation and sustainable development goals.

3.8. Analysis of Highly Cited References

Highly cited literature is a direct reflection of academic recognition of research achievements. According to Price’s law and ESI database standards (top 1% in citation frequency), such literature often possesses high theoretical innovation or practical guidance value. By analyzing the citation networks of these publications, one can reveal knowledge diffusion paths and the formation mechanism of academic influence. Therefore, this article selected the top 20 publications (top 1% in citation frequency) for analysis (Table 6). Among these, 10 are review articles and 10 are research articles, with review articles ranking relatively high.

From the temporal distribution perspective, research on biochar began in 2007, with research enthusiasm significantly increasing around 2010 (five papers in 2010). That year had a high number of related publications. Research remained active in 2014–2015 (three papers in 2014, three papers in 2015) and continued to follow up until 2020, indicating sustained attention to biochar research over the past decade. In terms of research content, numerous publications extensively discussed biochar applications in environmental and agricultural fields. On one hand, they focused on its function as an adsorbent in treating soil and water pollutants, with some of the literature specifically exploring biochar’s application in soil and water pollution management [42,62,63]. On the other hand, they examined how preparation conditions (such as pyrolysis temperature) influence its physicochemical properties [54,64]. Simultaneously, many publications analyzed biochar’s effects as a soil amendment on soil properties, plant growth, and microbial communities, including the agronomic value of green waste biochar as a soil improver [65,66,67,68,69,70,71]. Additionally, several review articles systematically summarized biochar’s preparation, modification, properties, and environmental applications, reviewing research progress and future directions [72,73,74,75,76].

The overall research formed a coherent narrative from fundamental property exploration to practical application potential, consistently focusing on biochar’s applications in pollution management and soil improvement, providing solid theoretical support and directional guidance for subsequent in-depth research.

Reference literature burst detection is another method to track and capture research hotspots. References with the highest citation counts indicate special attention during a specific period and are typically considered the foundational research frontier of a field [77]. Figure 15 shows the top 25 references with the strongest citation bursts. The article “Bio-char Sequestration in Terrestrial Ecosystems—A Review” has the earliest burst time, while “Biochar effects on soil biota—A review” has the highest burst intensity. Both are from the same author; Lehmann J. Tomczyk’s work “Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects” began bursting in 2020 and continues until 2024.

Table 6. Top 20 Most Cited References.

First Author	Article	Journal	Year	Cited Times	Document Type
Ahmad, M. [42]	Biochar as a sorbent for contaminant management in soil and water: A review	Chemosphere	2014	3762	Review
Keiluweit, M. [78]	Dynamic Molecular Structure of Plant Biomass-Derived Black Carbon (Biochar)	Environmental Science & Technology	2010	2453	Article
Mohan, D. [62]	Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent—A critical review	Bioresource Technology	2014	1985	Review
Wang, J.L. [72]	Preparation, modification and environmental application of biochar: A review	Journal of Cleaner Production	2019	1684	Review
Tomczyk, A. [54]	Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects	Environmental Science and Bio/Technology	2020	1671	Review
Tan, X.F. [63]	Application of biochar for the removal of pollutants from aqueous solutions	Chemosphere	2015	1618	Review
Atkinson, C.J. [66]	Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review	Plant and Soil	2010	1582	Review
Chan, K.Y. [65]	Agronomic values of greenwaste biochar as a soil amendment greenwaste	Australian Journal of Soil Research	2007	1579	Article
Lehmann, J. [79]	Bio-energy in the black	Frontiers in Ecology and the Environment	2007	1563	Article
Biederman, L.A. [76]	Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis	Global Change Biology Bioenergy	2013	1361	Review
Kambo, H.S. [73]	A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications	Renewable and Sustainable Energy Reviews	2015	1283	Review
Warnock, D.D. [80]	Mycorrhizal responses to biochar in soil—concepts and mechanisms	Plant and Soil	2007	1133	Article
Gul, S. [74]	Physico-chemical properties and microbial responses in biochar-amended soils: Mechanisms and future directions	Agriculture, Ecosystems & Environment	2015	1113	Review
Mukherjee, A. [81]	Surface chemistry variations among a series of laboratory-produced biochars	Geoderma	2011	1013	Article
Fuss, S. [75]	Negative emissions-Part 2: Costs, potentials and side effects	Environmental Research Letters	2018	970	Review
Joseph, S.D. [69]	An investigation into the reactions of biochar in soil	Australian Journal of Soil Research	2010	952	Article
Gaskin, J.W. [67]	EFFECT OF LOW-TEMPERATURE PYROLYSIS CONDITIONS ON BIOCHAR FOR AGRICULTURAL USE	Transactions of the ASABE	2008	944	Article
Singh, B. [68]	Characterisation and evaluation of biochars for their application as a soil amendment	Australian Journal of Soil Research	2010	896	Article
Al-Wabel, M.I. [64]	Pyrolysis temperature induced changes in characteristics and chemical composition of biochar produced from conocarpus wastes	Bioresource Technology	2013	868	Article
Chan, K.Y. [70]	Using poultry litter biochars as soil amendments	Australian Journal of Soil Research	2008	864	Article

Table 6. Top 20 Most Cited References.

First Author	Article	Journal	Year	Cited Times	Document Type
Ahmad, M. [42]	Biochar as a sorbent for contaminant management in soil and water: A review	Chemosphere	2014	3762	Review
Keiluweit, M. [78]	Dynamic Molecular Structure of Plant Biomass-Derived Black Carbon (Biochar)	Environmental Science & Technology	2010	2453	Article
Mohan, D. [62]	Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent—A critical review	Bioresource Technology	2014	1985	Review
Wang, J.L. [72]	Preparation, modification and environmental application of biochar: A review	Journal of Cleaner Production	2019	1684	Review
Tomczyk, A. [54]	Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects	Environmental Science and Bio/Technology	2020	1671	Review
Tan, X.F. [63]	Application of biochar for the removal of pollutants from aqueous solutions	Chemosphere	2015	1618	Review
Atkinson, C.J. [66]	Potential mechanisms for achieving agricultural benefits from biochar application to temperate soils: a review	Plant and Soil	2010	1582	Review
Chan, K.Y. [65]	Agronomic values of greenwaste biochar as a soil amendment greenwaste	Australian Journal of Soil Research	2007	1579	Article
Lehmann, J. [79]	Bio-energy in the black	Frontiers in Ecology and the Environment	2007	1563	Article
Biederman, L.A. [76]	Biochar and its effects on plant productivity and nutrient cycling: a meta-analysis	Global Change Biology Bioenergy	2013	1361	Review
Kambo, H.S. [73]	A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications	Renewable and Sustainable Energy Reviews	2015	1283	Review
Warnock, D.D. [80]	Mycorrhizal responses to biochar in soil—concepts and mechanisms	Plant and Soil	2007	1133	Article
Gul, S. [74]	Physico-chemical properties and microbial responses in biochar-amended soils: Mechanisms and future directions	Agriculture, Ecosystems & Environment	2015	1113	Review
Mukherjee, A. [81]	Surface chemistry variations among a series of laboratory-produced biochars	Geoderma	2011	1013	Article
Fuss, S. [75]	Negative emissions-Part 2: Costs, potentials and side effects	Environmental Research Letters	2018	970	Review
Joseph, S.D. [69]	An investigation into the reactions of biochar in soil	Australian Journal of Soil Research	2010	952	Article
Gaskin, J.W. [67]	EFFECT OF LOW-TEMPERATURE PYROLYSIS CONDITIONS ON BIOCHAR FOR AGRICULTURAL USE	Transactions of the ASABE	2008	944	Article
Singh, B. [68]	Characterisation and evaluation of biochars for their application as a soil amendment	Australian Journal of Soil Research	2010	896	Article
Al-Wabel, M.I. [64]	Pyrolysis temperature induced changes in characteristics and chemical composition of biochar produced from conocarpus wastes	Bioresource Technology	2013	868	Article
Chan, K.Y. [70]	Using poultry litter biochars as soil amendments	Australian Journal of Soil Research	2008	864	Article

4. Discussion

4.1. Evolutionary Stages of Biochar Technology

In this era of information explosion, keeping up with industry frontiers and understanding the latest research findings is increasingly challenging [82]. To present a global scientific output study of biochar from 2007 to 2024, this paper employs bibliometric analysis to provide a novel method for organizing the knowledge structure of specific research.

The literature growth in this field exhibits a clear three-stage characteristic (Figure 2): The initial stage (2007–2014) had an average annual publication volume of less than 29 papers, reflecting that technological R&D was still in the exploratory stage. The research focus during this period was on basic scientific verification, such as the launch of the CSIRO farmland carbon sequestration experiment in Australia in 2007 [83]. The release of the European Union’s White Paper “Biochar Climate Mitigation Potential” in 2009 [84] led to a year-on-year surge of 225% in the number of publications in 2010, reflecting the academic community’s systematic exploration of biochar carbon sequestration mechanisms driven by policy.

The acceleration stage (2015–2020) saw an average annual output increase to 117 papers, a threefold increase compared to the previous stage. This shift is significantly correlated with the implementation of the Paris Agreement. In 2015, the Paris Agreement listed biochar as a negative emission technology option [4], and the literature growth entered an accelerated channel. Key industrialization events such as the breakthrough in pyrolysis technology by Germany’s Pyreg company in 2016 [85] and the development of Cool Terra nano-char in the United States in 2017 [86] promoted the extension of research topics to engineering optimization and carbon metrology methodologies. The establishment of the AgriProve carbon trading platform in 2018 further triggered explosive growth in carbon credit accounting model research. The significant increase in citation frequency during this stage further confirms the strengthening effect of technological maturity on academic influence.

During the outbreak stage (2020–2024), the accelerated integration of the global carbon market after 2021 directly triggered high-speed growth in the number of publications. Combining the annual growth trend chart of the top 5 countries (Figure 7), it is not difficult to find that China contributed the main growth momentum. This is directly related to the top-level design of the “dual carbon” strategy—special central government financial support, green financial policy innovation, and the directed allocation of scientific research resources [87,88,89,90,91] have formed systematic support for technological breakthroughs. This institutional advantage may provide sustained momentum for the development of the field.

4.2. Heterogeneity and Institutional Logic of Sino–U.S. Scientific Research Output

China and the United States far surpass other countries in scientific paper output, being the most productive nations in the field. While their overall collaboration frequency ranks high, deep cooperation between core research institutions remains limited (Figure 9). The Chinese Academy of Sciences, despite establishing a broad international collaboration network, primarily concentrates its cooperation intensity with domestic top-tier universities. Collaboration with U.S. institutions like University of Florida, University of Massachusetts, Iowa State University, and USDA ARS is comparatively minimal (Figure 5), a “shallow collaboration” phenomenon potentially linked to differences in research evaluation systems and institutional technology transfer mechanisms.

The two countries contribute approximately 60% of global research outcomes but demonstrate differentiated development paths. Chinese research institutions have achieved scale superiority in total paper volume, yet the United States maintains leadership in research impact (such as the H-index) (Figure 7). Examining average citation frequencies, China ranks relatively low internationally. While China leads in total paper count, each paper receives fewer citations compared to the U.S., primarily due to four factors: Extensive Chinese research faces barriers from language limitations and insufficient international promotion, struggling to enter global academic systems. Chinese institutions have low representation in top-tier international journals, and domestic scholars tend to cite domestic literature, constraining international citation volume. International collaborations remain concentrated among few elite institutions, and Sino–U.S. cooperation has diminished due to policy influences, narrowing knowledge exchange channels [92]. High retraction rates in international journals, data fabrication issues, and domestic evaluation systems emphasizing paper quantity further impact international credibility [93].

Improvement requires multiple approaches: expanding international collaboration networks by deepening engagement with European and American institutions, exploring partnerships with emerging research countries like India and Brazil, and encouraging scholars with international backgrounds. Increasing English-language paper proportions, supporting internationalized journals like Research (co-established by the Chinese Academy of Sciences and U.S. partners), and utilizing open-access platforms to enhance paper visibility are further approaches. Additional approaches include reforming research evaluation standards by reducing paper quantity assessments, increasing support for originality and long-term research, and strengthening academic integrity oversight.

4.3. Insufficient Author Collaboration Seriously Impedes Knowledge Dissemination

The current author collaboration network in the biochar carbon sequestration field exhibits significant clustering characteristics, accompanied by insufficient cross-cluster cooperation. Through author co-occurrence analysis (Figure 10), it can be seen that 27 core authors form four relatively independent research clusters. However, except for a few core scholars like Professor Yong Sik Ok and Lehmann Johannes, inter-cluster collaboration lines are sparse. Research teams have relatively close internal cooperation, but there is little interaction and collaboration between different teams, with knowledge mostly circulating within their own small circles and cross-team interaction and knowledge sharing being relatively limited.

This collaborative mode’s limitations have created a dual impediment to field development. First, knowledge dissemination faces barriers, making it difficult to achieve cross-fusion of frontier achievements in specific sub-domains, such as biochar stability mechanisms, pyrolysis process optimization, and machine learning-driven material design, through inter-cluster collaboration. Second, the risk of redundant research increases, as each cluster independently explores common methodological issues like carbon sequestration efficiency assessment and environmental risk modeling, failing to establish a standardized research framework.

To address the problem of insufficient collaboration between author clusters, a routine collaborative network can be established, leveraging regional advantageous research institutions. For example, using institutions like the Chinese Academy of Sciences and Cornell University as pivots, regional alliances can be formed by combining universities and research institutes in Asia, North America, and other regions. By regularly hosting “Interdisciplinary Biochar Forums” and other activities, geographical and disciplinary boundaries can be broken down, promoting face-to-face communication among authors from agriculture, materials, environmental, and other clusters. This approach can help new discoveries in soil microbiology and frontier achievements in machine learning material design collide and generate collaborative innovation, effectively resolving knowledge dissemination barriers and redundant research challenges.

4.4. Technical Hotspots and Trends in Biochar Carbon Sequestration

In keyword burst detection (Figure 13), black carbon and charcoal show particularly high burst intensities, with values quite close to each other. Their colors are also the darkest in the keyword time overlay graph (Figure 12B), indicating an especially early appearance. By consulting the literature, this may be because in early biochar research (2007–2016), the “biochar” concept was not yet unified and was often mixed with terms like “charcoal” and “black carbon”. For example, historically remaining combustion residues in natural soil (such as black carbon) were once classified as precursors of biochar [94]. Their outbreaks ended in 2016 and 2017, respectively, which may be related to the publication of the “Standardized Product Definition and Product Testing Guidelines for Biochar for Soil” (Version 2.1) by the IBI in 2015 (International Biochar Initiative. Standardized Product Definition and Product Testing Guidelines for Biochar That Is Used in Soil) [95]. This guideline specified the organic carbon content, preparation conditions, and functional uses of biochar from a technical standard level, marking the definition of biochar as authoritative and globally applicable.

The basic principle of biochar carbon sequestration is to convert unstable organic carbon in biomass into highly stable aromatic structures through thermochemical conversion, and reduce its decomposition and release in the environment through physical and chemical interactions, thereby achieving long-term carbon storage [96]. Laboratory cultivation experiments show that biochar’s mean residence time (MRT) is 617–2829 years, with a half-life of approximately 1400 years [97], but the actual carbon sequestration age is significantly influenced by field environmental aging, microbial activity, and soil heterogeneity [98]. For instance, in a long-term field trial in Germany, high-dose biochar (40 Mg ha⁻¹) was applied to sandy soil, combined with digestate or compost. Results showed that initial soil organic carbon (SOC) storage increased by 61 Mg ha⁻¹; but after four years, due to insufficient soil physical protection, 38 Mg ha⁻¹ of SOC disappeared. Nine years later, SOC storage in biochar-improved soil was only 7 Mg ha⁻¹ higher than the control group, and black carbon storage almost returned to its original level [99]. This indicates that in sandy soil, biochar’s physical stability is insufficient for long-term carbon sequestration, and the actual carbon sequestration effect may be far lower than theoretical expectations.

In the keyword overlay diagram, the highlight yellow of “climate change” and “greenhouse gas emissions” demonstrates that biochar production and improvement have been increasingly applied to mitigate global climate change, a trend driven by the international policy of the 2015 Paris Agreement [3], as well as China’s growing influence in global climate governance. China’s proposal of the “dual carbon” target (carbon peaking and carbon neutrality) in 2020 further promoted the practical application of biochar in climate governance. Biochar’s function in achieving carbon neutrality is primarily through carbon fixation and emission reduction [100,101].

Combining keyword burst detection (Figure 13) and keyword network co-occurrence (Figure 12A), biochar stability has long been a focus of attention. The preparation raw materials are a crucial factor affecting biochar stability [102]. Keyword burst detection shows that keywords like “wood”, “rice straw”, “waste water treatment”, and “municipal solid waste” burst after 2017 (Figure 13), with “straw biochar” specifically bursting after 2022. This indicates that biochar raw materials are currently transitioning from single sources to diverse waste materials, including crop residues [103], forestry residues [104], municipal solid waste [105], sewage sludge, manure [106], and biomass oil distillation residues [107]. This transformation is driven by rapid industrialization, widespread environmental pollution concerns, and the need for proper waste disposal. In 2015, the United Nations Environment Programme (UNEP) proposed integrating lifecycle methods with circular economy [108], emphasizing policy tools that cover the entire chain. This compelled cities to seek alternative treatment solutions, with biochar production being preferred due to its carbon sequestration and resource recycling functions. Through comparison with other recent bibliometric analyses on biochar, we found that Karki (2024) [109] and Hao et al. (2025) [110] both proposed applications of biochar in waste management, although they only studied biochar’s application in specific types of waste. Particularly, Hao et al. (2025) focused on tea leaf waste, which was not detected in our keyword co-occurrence network (Figure 12A) or keyword burst detection (Figure 13). However, their findings are consistent with our current conclusions, both discovering that biochar has received widespread attention and significant enhancement in applications across various waste types.

However, this transformation also has drawbacks. The diversification of raw materials means varying pyrolysis temperatures and carbon fixation capabilities [111], leading to wide-ranging pH, specific surface area, and ash content indicators [112,113], making it challenging to develop universal industry standards. More seriously, it may risk pollutant migration. For instance, biochar produced from urban wastewater and municipal solid waste may contain excessive heavy metals [114], which could cause soil pollution when applied as fertilizer [102,115]. While the International Biochar Initiative (IBI) emphasizes raw material sustainability, it has not clearly defined pollutant thresholds [116].

In the highly cited literature, several articles investigate the impact of pyrolysis on physicochemical property stability (Table 6). The latest burst in literature detection is Professor Tomczyk A’s article “Biochar physicochemical properties: pyrolysis temperature and feedstock kind effects”, which is still ongoing (Figure 15). This indicates that the academic community has recently been particularly focused on pyrolysis technology. Co-pyrolysis, with the latest keyword burst (Figure 13), suggests that co-pyrolysis technology for biochar has received significant attention in recent years. This is likely closely related to the diversification of biochar raw materials. Co-pyrolysis is a technique of heating multiple biomass or waste materials under oxygen-deficient conditions, which can significantly improve biochar quality, including enhanced carbon fixation capacity [117,118]. Márquez et al. (2024) [119] conducted a bibliometric analysis of pyrolysis and concluded that co-pyrolysis has become a hot topic of comprehensive research since 2018, a conclusion consistent with ours.

However, we did not find co-pyrolysis literature among highly cited references. This may be because co-pyrolysis is a recently emerging technology, and the literature citations take time to accumulate. Despite this, it remains an emerging technology currently constrained by raw material complexity, pollution risks, yield and energy efficiency trade-offs, and technological promotion challenges [120], requiring further process optimization and long-term benefit verification.

Soil is the largest terrestrial carbon reservoir [121,122], with surface soil storing about two-thirds (approximately 1500 Pg) of global carbon, which is three times the atmospheric carbon pool [55,123]. Therefore, any slight changes in the soil carbon reservoir can have tremendous impacts on global greenhouse gas emissions [124]. The co-occurrence keyword graph showing connections between biochar and soil, soil organic carbon (Figure 12A) demonstrates that biochar is a core technology for soil carbon sequestration, making significant contributions. Numerous studies indicate that biochar application can reduce soil greenhouse gas emissions [87]. When applied as a fertilizer, biochar can also suppress methane (CH₄) and nitrous oxide (N₂O) release.

In addition to preserving substantial carbon sinks, the keyword burst detection (Figure 13) reveals that keywords like Soil, Soil carbon, amendments, and fertility emerged around 2010, with high burst duration and intensity. This suggests that biochar applications in soil were among the earliest areas of focus. The burst time of bioavailability coincides with soil, indicating scholars’ particular interest in biochar’s impact on soil microbial communities. Wang et al. (2024) [125] pointed out that new eco-fertilizers prepared from organic raw materials have attracted widespread attention and application in recent years. As a soil amendment, biochar can enhance soil carbon sequestration capacity [126], making it a continuing research hotspot. The dark-blue keywords related to soil in the keyword time overlay diagram (Figure 12A) further confirmed this perspective.

Gross’ meta-analysis synthesizing 64 studies and 736 treatments demonstrated that biochar application increases soil organic carbon storage by an average of 29% (field trials), with even higher carbon storage in experiments lasting over 5 years [127]. However, Han et al. (2013) [128] found that while biochar application can provide significant soil carbon sequestration, it also involves considerable uncertainty. The mechanisms underlying biochar’s initial effects on soil carbon sequestration remain unclear [129].

Biochar technology represents an emerging interdisciplinary frontier and trend. Its disciplinary distribution spans environmental science, soil science, energy and fuel, agronomy, environmental engineering, and green sustainable science and technology, with environmental science being the most prominent (Figure 3). The biochar analysis in Figure 4 reveals deep interactions across environmental science, chemistry, and earth sciences, and even includes limited pathways involving psychology, education, socioeconomics, economics, and political science. This indicates a shift from single technological research towards comprehensive eco-economic system regulation.

Professor Yong Sik Ok from a Korean university has become a core leader in biochar research through exceptional publication volume, citation frequency, and H-index (Table 3). With the highest collaboration intensity, his emerging research directions potentially represent future development trends. His team has recently focused on machine learning (ML)-driven biochar technology optimization [43,44,45]. In the current era of internet big data and artificial intelligence (AI), machine learning demonstrates significant potential in biochar preparation process optimization, performance prediction, and application scenario expansion, marking an important future development direction.

5. Conclusions

This study employs bibliometric analysis to assess the current status and research prospects of international cooperation in biochar carbon sequestration. The analysis includes a comprehensive evaluation of the distribution of publication years and the identification of prolific authors and their institutions, international collaboration patterns, publication sources, high-frequency keywords, and related citation rates. This method aids in identifying and exploring research hotspots and emerging trends in the field. Future research directions should closely address the key gaps identified through bibliometric analysis: (1) Focus on the growth potential of research related to “biochar-microorganism interactions” and form interdisciplinary teams, leveraging the high-producing author groups identified through quantitative analysis, to elucidate the underlying microscopic mechanisms, thereby filling the current knowledge gap. (2) Biochar carbon sequestration research has progressively advanced from early mechanistic exploration to engineering applications, currently focusing on waste resource utilization and technological innovation. However, constrained by factors such as raw material diversity and the imperfect long-term carbon sequestration monitoring system, the field faces practical challenges such as a lack of standards. In the future, researchers can utilize improved machine learning models to assist in biochar preparation and conduct tests in complex soil systems to screen for biochar suited to specific application scenarios. This will help to thoroughly clarify the mechanisms and influencing factors of biochar carbon sequestration, and then accurately predict the environmental impact of biochar’s life cycle. (3) At the policy level, there is a need to expedite the establishment of thresholds for heavy metals and other pollutants in raw materials, support “biochar + agriculture” demonstration projects, and promote it as an important technical pathway to achieve carbon neutrality.

Researchers should leverage these insights to prioritize high-impact collaborations, advocate for standardized assessment frameworks, and involve policymakers in scaling biochar from pilot studies to climate mitigation strategies. By bridging these gaps, the field can transition from fragmented findings to systematic, globally coordinated carbon sequestration solutions.

6. Limitations

This research has certain limitations in terms of data sources and analytical methods. On the data source side, the study is based solely on the Web of Science database, without incorporating Scopus, patent databases, or regional academic resources. This approach may overlook research outcomes from non-English or non-mainstream journals, and the data are limited to 2024, with non-English literature excluded, which affects the comprehensiveness, timeliness, and cultural diversity of the conclusions. Additionally, the international collaboration network analysis relies exclusively on bibliometric data, without integrating non-literature factors such as funding support or policy guidance, thus providing limited insight into the driving mechanisms of collaboration modes. Furthermore, while widely used analysis software like Vosviewer and Citespace were employed, these methods cannot fully exploit the data potential as digital technologies advance. Future research could consider developing or utilizing more advanced analysis software and Supplementing Data from alternative databases or custom data sources to optimize the study.