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Review

Tracing the Research Pulse: A Bibliometric Analysis and Systematic Review of Hydrogen Production Through Gasification

by
Satyanarayana Narra
and
Eliasu Ali
*
Material and Energy Valorisation of Biogenous Residues, Department of Waste and Resource Management, University of Rostock, 18059 Rostock, Germany
*
Author to whom correspondence should be addressed.
Processes 2025, 13(6), 1847; https://doi.org/10.3390/pr13061847
Submission received: 9 May 2025 / Revised: 28 May 2025 / Accepted: 3 June 2025 / Published: 11 June 2025
(This article belongs to the Special Issue Studies on Waste Resource Utilization and Its Processing Technologies)
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Abstract

:
Clean hydrogen is expected to play a crucial role in the future decarbonized energy mix. This places the gasification of biomass as a critical conversion pathway for hydrogen production, owing to its carbon neutrality. However, there is limited research on the direction of the body of literature on this subject matter. Utilising the Bibliometrix package R, this paper conducts a systematic review and bibliometric analysis of the literature on gasification-derived hydrogen production over the previous three decades. The results show a decade-wise spike in hydrogen research, mostly contributed by China, the United States, and Europe, whereas the scientific contribution of Africa on the topic is limited, with less than 6% of the continent’s research output on the subject matter sponsored by African institutions. The current trend of the research is geared towards alignment with the Paris Agreement through feedstock diversification to include renewable sources such as biomass and municipal solid waste and decarbonising the gasification process through carbon-capture technologies. This review reveals a gap in the experimental evaluation of heterogenous organic municipal solid waste for hydrogen production through gasification within the African context. The study provides an incentive for policy actors and researchers to advance the green hydrogen economy in Africa.

1. Introduction

Amidst concerted global efforts to mitigate the climate crisis, the energy landscape is undergoing a profound transformation. Energy demand continues to grow, influenced mainly by demand growth in emerging economies [1]. Hydrogen is theoretically expected to play a critical role in meeting this growing energy and is projected to supply 18% of global energy demand by the mid-century [2]. The gas is abundantly available in nature and possesses the highest gravimetric energy density compared to any known fuel, thus positioning it as a promising choice for energy storage and for applications in energy-intensive industries [3]. Perhaps the most significant attraction of hydrogen in the transition economy is its low carbon footprint, as it releases only water vapour when combusted, making it a plausible addition to the net zero-energy mix [4].
Various technological pathways have been developed and explored for hydrogen production, including water splitting, mainly through electrolysis, thermochemical conversion through pyrolysis and gasification, and biological processes photolysis [3]. The environmental friendliness of hydrogen is largely hinged on its method of production and feedstocks from which it is derived, thus giving rise to what is popularly termed the hydrogen rainbow [5]. Table 1. Illustrates the different types of hydrogen by their colour codes.
Even though water electrolysis using renewable energy has gained prominence in the literature because of its environmental benefits (denoted in green, as shown in Table 1), electrolysis is constraint by economic and infrastructure concerns. For instance, while hydrogen generated from electrolysis is estimated to cost about 4–6 USD/kg, biomass gasification is estimated to generate hydrogen at a cost of about 2.68 USD/kg of hydrogen [8].
The literature is, therefore, increasingly replete with biomass gasification as a viable alternative to conventional means of hydrogen production. Through a thermo-chemical process, gasification converts biogenous feedstocks into hydrogen-rich synthetic gas and offers a circular economy pathway for valorising biogenous resources and some plastics into energy fuel [9,10]. The diversity of feed stocks available for gasification and the limited electricity supply in Sub-Saharan Africa makes the region an ideal geography for biomass gasification [8]. Gasification is also distinguished by its flexibility, efficiency, and carbon neutrality, with a potential for significant emission reduction through carbon capture techniques and reliance on sustainable sources of biomass [10,11]. For instance, Armoo et al. [12] reported a carbon saving of 2.3 kg CO2eq for pyrolysis of waste as compared to landfilling.
With emerging techniques such as super-critical water gasification (SCWG), biomass is conveniently converted without the need for intensive drying, thus further lowering the cost curve of the gasification-driven hydrogen economy [13]. However, the commercial deployment of gasification as a sustainable pathway for hydrogen production remains constraint by limited policy incentives and high feedstock costs [2]. This notwithstanding, the positive drivers of gasification research include the climate-related imperative to decarbonize the global energy mix and growing affordability of gasification technologies [14,15].
Even though the literature demonstrates a growing consensus on biomass gasification as a viable pathway for clean or green hydrogen production, knowledge remains fragmented, despite some attempts to synthesise the existing literature. Many of these reviews have either been skewed towards the gasification of biomass feedstock or do not target research with a focus on hydrogen production [16,17]. Other reviews, such as that of [18], have sought to conduct a comparative analysis of food-waste-to-energy thermochemical conversion pathways. Their study identified incineration, pyrolysis, and gasification as inefficient technologies based on their energy yields. However, in view of the improvements in technological efficiency over time, some caution must be exercised in lending contemporary relevance to this decade-old study. Their findings, for instance, sharply contrast those of ref. [15], who, barely a year later, reported gasification as the most efficient thermochemical process and increasingly the most cost-effective.
This context points to a gap in the synthesised knowledge of hydrogen production through gasification across scales, feedstock diversity, and bibliometric trends. The objectives of the study are, therefore, as follows:
  • To map the evolution of thermochemical pathways for hydrogen production through gasification for the past three (3) decades.
  • To examine regional and institutional distribution of hydrogen-focused gasification research output.
  • To provide future research directions for policymakers, researchers, and industry actors interested in advancing low-carbon hydrogen production through gasification.

2. Materials and Methods

This systematic literature review approach follows the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020), as shown in Figure 1. The search terms and the bibliometric database used for the search, as well as the inclusion and exclusion strategies for the sourced literature, are discussed subsequently. The data analysis and visualisation tools are also discussed below.

2.1. Search Querry

The literature search was conducted on 1 May 2025, using the Scopus database. Scopus is considered one of the most comprehensive and credible indexes for peer-reviewed scientific papers [19,20]. The search term (gasification AND “bio-hydrogen”) OR (gasification AND “clean hydrogen”) OR (gasification AND “green hydrogen”) OR (gasification AND hydrogen) was used.

2.2. Inclusion and Exclusion Criteria

The initial search using the search terms described above yielded 11,743 documents from the Scopus database. The documents were filtered for documents published from 1995 to 2025 to consider the evolution of the literature over the past 30 years and a decade post the Paris Agreement, which marked the world’s greatest diplomatic success on climate change [21]. Document types were limited to finalised publications comprising articles, conference papers, reviews, books, and book chapters, and were further limited to only documents published in the English language. The documents were further filtered to include only the literature from the energy, environmental science, chemical engineering, engineering, physics, chemistry, mathematics, materials science, agricultural and biological sciences, computer science, decision science, and economics and econometrics subject areas.
The Boolean logic used for the study is shown as follows: “TITLE-ABS-KEY ((gasification AND “bio-hydrogen”) OR (gasification AND “clean hydrogen”) OR (gasification AND “green hydrogen”) OR (gasification AND hydrogen)) AND PUBYEAR > 1994 AND PUBYEAR < 2026 AND (EXCLUDE (EXACTKEYWORD, “Article”)) AND (LIMIT-TO (DOCTYPE, “ar”) OR LIMIT-TO (DOCTYPE, “cp”) OR LIMIT-TO (DOCTYPE, “re”) OR LIMIT-TO (DOCTYPE, “ch”) OR LIMIT-TO (DOCTYPE, “bk”)) AND (LIMIT-TO (SUBJAREA, “ENER”) OR LIMIT-TO (SUBJAREA, “CENG”) OR LIMIT-TO (SUBJAREA, “ENGI”) OR LIMIT-TO (SUBJAREA, “ENVI”) OR LIMIT-TO (SUBJAREA, “CHEM”) OR LIMIT-TO (SUBJAREA, “PHYS”) OR LIMIT-TO (SUBJAREA, “MATE”) OR LIMIT-TO (SUBJAREA, “MATH”) OR LIMIT-TO (SUBJAREA, “AGRI”) OR LIMIT-TO (SUBJAREA, “COMP”) OR LIMIT-TO (SUBJAREA, “ECON”) OR LIMIT-TO (SUBJAREA, “DECI”)) AND (LIMIT-TO (LANGUAGE, “English”))”.
The resulting documents from the foregoing inclusion and exclusion criteria were screened by manual reading of titles and abstracts to exclude documents that did not directly address or focus on gasification and hydrogen production. This resulted in a total of 8440 studies considered in this review. The PRISMA-compliant approach [22] is summarised in Figure 1.

2.3. Analysis and Visualisation Tools

The Scopus-extracted data were exported in BibTeX format and analysed using the R Version 4.5.0 (2025-04-11 ucrt) software developed by the R Core Team based in Vienna, Austria. The specific R package used was Bibliometrix, developed by Aria & Cuccurullo [23] and its graphic user interface, Biblioshiny. Bibliometrix is the most popular R package for the systematic review and visualisation of large volumes of the literature, which, coupled with the Biblioshiny package, provides a user-friendly web-based interface to identify and graphically present the main themes of the literature [24].

3. Results

3.1. Analysis of Scientific Research Output

The results (see Figure 2) show an increasing trend in the production output of research on gasification focused on hydrogen production over the past three decades, with over 60% of the research published between 1995 and 2025, peaking in 2024, with over 880 documents published on this topic. The trend also shows spikes in 2006, 2017, and 2024. This trend, although anecdotal, points to a ten-year cycle of increasing interest in hydrogen research. In fact, the International Energy Agency (IEA)’s 2024 Global Hydrogen Review shows that most hydrogen projects are expected to be delivered in 2027 [1], demonstrating a possible surge in hydrogen research from 2027 to 2030. The COVID-19 pandemic may have influenced the marginal spike observed in 2019, as overall global research output increased due to increased remote worktimes under lockdown orders [25,26].
Figure 3 and Figure 4 illustrate the most globally cited documents and the most relevant authors, respectively.
With a citation of over 2397, the paper by ref. [15] is by far the most cited document on the topic under review. Their paper provided a comprehensive overview of hydrogen production processes, including thermochemical methods such as gasification. They concluded that gasification was among the most cost-competitive and efficient means of producing hydrogen (at a production cost of between USD 1.34 and USD 2.27/kg). Ref. [27], whose paper emerged as the second most cited in the literature, evaluated the conversion of biomass to biofuels through catalysis and provided early support for the conversion of sugars to renewable hydrogen. The third most widely cited document, although focused on thermochemical conversion techniques, displays a slight deviation from the heavy emphasis of the literature on biomass, rather choosing to assess the feasibility of hydrogen generation from solid plastic gasification [28].
The next most cited paper conducted a comprehensive assessment of hydrogen production methods, concluding that gasification and other thermochemical processes were preferred as long as efficiency was a priority [29]. Ref. [13] corroborated the cost-competitiveness of gasification for hydrogen production, with a distinct endorsement of biomass feedstocks, and highlighted the prospects of super-critical water gasification (SCWG) to further enhance efficiency.
A state-of-the-art overview of biomass technology [30] with 804 citations reported that biomass gasification was a cost-effective means of producing hydrogen but concluded that a comprehensive review of the literature was missing. Other widely cited papers in the literature have reviewed gasification technology either with respect to different feedstocks, environmental impacts, or the state of the technology [14,18,31,32,33,34,35,36].
The top destinations for documents pertaining to the topic were published in the International Journal of Hydrogen Energy and Energy, accounting for 1107 publications (representing nearly 13% of the literature) as shown in Table 2. The distribution of publication on the subject matter supports Bradford’s law of scattering, which states that “if scientific journals are arranged in order of decreasing productivity of articles on a given subject, they may be divided into a nucleus of periodicals more particularly devoted to the subject and several groups or zones containing the same articles as the nucleus, when the number of periodicals in the nucleus and succeeding zones will be as 1: n: n2, where “n” is a multiplier” [37]. This law effectively posits that articles are majorly published in a concentrated few journals and that the rest are distributed over a large number of journals (see Table 3).

3.2. Keyword Tree Map

Figure 5 shows the prevalence of the keywords in the literature, demonstrating that the words “gasification”, “hydrogen production”, “hydrogen”, and “biomass” emerge as the most prevalent keywords, with “gasification” comprising 12% and the next top three prevalent keywords making up 7% of the keywords in the literature, respectively. The next most occurring keywords are “carbon dioxide” (5%), “synthetic gas”(4%), and “biomass gasification”(3%). Apart from the fact that these dominant keywords may be attributed to their use in direct search terms, the dominance of “gasification” and ‘hydrogen production” in the literature is also due to the positive prospects of biomass gasification as an efficient means of producing green hydrogen [38,39].
On the other hand, “coal combustion”, “feedstocks”, “water gas shift gasification”, “hydrogen fuels”, “fuel cells”, “super-critical water”, and “gas emissions” are among the least prevalent keywords in the literature, accounting for 1% each of the keywords. This depicts either a decline or the emergence of studies on these topics. For instance, while the low prevalence of “coal combustion” in the literature may be plausibly attributed to a declining interest in coal as a feedstock post-Paris Agreement [40], the low prevalence of “feedstocks” could be attributed to the recent interest in exploring renewable feedstocks as alternatives to fossil fuels for gasification-derived bio-hydrogen [41,42].
It is observed that, while bio-hydrogen is gaining momentum as a sustainable and competitive alternative to fossil-derived hydrogen [43,44], the term “bio-hydrogen” does not occur in the tree map in Figure 5. This is because, even though “bio-hydrogen” was part of the search term, this study focuses on hydrogen derived from gasification (a thermochemical process), whereas “bio-hydrogen” is a term often associated with hydrogen derived from biological processes such as anaerobic microbial digestion or fermentation [45,46].

3.3. Co-Occurrence Analysis

A co-occurrence network analysis (see Table 4) reveals four main clusters. Cluster 1 shows the co-occurrence of keywords such as “biomass gasification”, “hydrogen production”, “biomass”, “steam gasification”, “chemical reactions”, and “syngas”, reflecting a focus on the process-oriented literature and revealing the strong interlinkage between gasification processes and hydrogen production in the literature. Some papers with a focus on feedstock have assessed the feasibility of Athabasca bitumen as a feedstock for hydrogen generation through super-critical water gasification, reporting significant hydrogen yields [47]. Similarly, ref. [48] reported the viability of biomass as an alternative feedstock for hydrogen production through gasification.
Cluster 2 comprises keywords such as “carbon dioxide”, “hydrogen”, “carbon monoxide”, “methane”, “synthetic gas”, “oxygen”, “gases”, and “gas generators”. This clearly illustrates a strong focus on the diverse products and bio-products of gasification processes.
Cluster 3 emphasises process optimisation techniques for improved efficiency. Keywords here include “catalysts”, “catalysts activity”, “supercritical water”, and “nickel”. Research with these keywords seeks to investigate the utility of various catalysts to improve biofuel yields and process efficiency. For instance, ref. [49] reported increased hydrogen yield (90%) under optimised conditions of (360 °C, 0.5 g Ni-La catalyst loading, 0.5 g biomass and 10 min), emphasising the importance of an Ni-L catalyst in the gasification process. Other studies have also assessed the effect of various catalysts on optimising the gasification process for improved hydrogen yield [50,51].
The fourth cluster of keywords focuses on environmental assessment and cost–benefit analyses, featuring keywords such as “energy efficiency”, “economic analysis”, and “exergy”. Works in this cluster seek to evaluate the cost-competitiveness of using various feedstocks to produce hydrogen through gasification (see [52,53,54]). Predictably, keywords on greenhouse gas emission analysis co-occur with keywords such as “coal combustion” and “natural gas”, as the literature here seeks to evaluate the emission profiles of fossil fuel feedstocks and their mitigation approaches.
The co-occurrence analysis, therefore, reveals four clusters of the literature on the subject matter: (1) the fundamentals of the gasification process for hydrogen production and the feasible feedstocks, as seen in [18,33,55,56,57]; (2) the evaluation of products and bio-products of the gasification process, as reported by [36]; (3) the thermochemical process optimisation for hydrogen production, as reported by refs. [58,59]; and (4) the emission and economic evaluation of the gasification process (see refs. [60,61,62,63,64,65,66,67,68,69,70]).

3.4. Most Relevant Affiliations

The bibliometric analysis in Table 5 reveals that the top 10 affiliations are Xi’an Jiaotong University (China), Huazhong University of Science and Technology (China), King Fahd University of Petroleum and Minerals (Saudi Arabia), Universiti Teknologic Petronas (Malaysia), Chulalongkorn University (Thailand), National Energy Technology Laboratory (United States of America), the University of Tehran (Iran), Southeast University (China), Tsinghua University (China), and Zhejiang University (China). This trend points to a concentration of researcher affiliations with institutions in Asia and the Middle East, with only one of the top 10 institutions with the most author affiliations located outside Asia and the Middle East, i.e., The National Energy Technology Laboratory of the U.S.A. The proliferation of countries that may be characterised as petro-states, such as Saudi Arabia and Iran, in the top 10 list of the most affiliated institutions can be explained in terms of the fact that petro-states have an increased incentive, and are actually making efforts in research and development, to diversify away from petroleum, and thus view hydrogen as a convenient alternative in the long-term [64,65].

3.5. Scientific Production and Collaboration by Country

Figure 6 illustrates the comparative scientific research output on hydrogen production through gasification. The map shows that the research output on the subject matter is concentrated within a few countries, illustrated by the dark shades. Thus, China, the United States of America, Germany, India, and the United Kingdom register substantial research outputs. The map conversely shows large parts of Africa, Central Asia, and some portions of Latin America in grey, signifying limited research activity on the subject matter. African countries with marginal research output include South Africa, Egypt, and Nigeria.
The concertation of research outputs in China and Europe is reflected in their hydrogen infrastructure maturity, as the two regions collectively host over 70% of global hydrogen capacity [1].
A country collaboration map (see Figure 7) shows that countries with the highest density of research outputs tend to also exhibit the most collaborative links across the globe. Therefore, China, the United States, and countries in Europe host the densest research links, whereas the Global South demonstrates limited research collaborations, both inwardly and outwardly.
The limited research output in Africa may be attributed to the continent’s starved investment in research and development. For instance, Africa’s Gross Expenditure on R&D (GERD) is about 0.5% of GDP compared to a global average of 2.2% [66]. Also, the number of researchers per million people in Africa (100 researchers per million) is far less than the global average of 1100 researchers per million people [67]. This funding deficit is reflected in the continent’s heavy reliance on external funding sources to meet its research and development needs. Only 8 out of the 134 funding sponsors of Scopus-indexed African research output on the subject matter are located in Africa, namely the University of South Africa, the University of Johannesburg, Durban University of Technology (South Africa), Tshwane University of Technology (South Africa), the University of Cape Town (South Africa), the Council for Scientific and Industrial Research (South Africa), North-West University (South Africa), and the Kwame Nkrumah University of Science and Technology (Ghana). The remainder (including the top 10 funding institutions, as shown in Table 6) are non-African.
This funding gap and limited research output notwithstanding, there are over one hundred (100) hydrogen projects at various phases of operation in Algeria, Angola, the Democratic Republic of Congo, Djibouti, Egypt, Kenya, Mauritania, Morocco, Mozambique, Namibia, Niger, South Africa, Uganda, and Zimbabwe. However, these projects are mainly focused on electrolytic water-splitting technology (95% of the projects), without any operational biomass-based hydrogen project as of 2024 [68]. Comparatively, there are over 50 biomass-based hydrogen projects globally as of 2024, according to the International Energy Agency (see Figure 8).

3.6. Research Trends

Figure 9 illustrates the evolution of research from 1995 to 2025. Four thematic timelines emerge in the literature, discussed below.
Fundamentals of thermochemical processes (1995–2002)
The literature within this period is characterised by keywords such as “sulphidation”, “pressure drop”, “combustion”, “high temperature effects”, and “gasifiers”. This emphasises a focus on technical feasibility and unravelling the science behind thermochemical processes. For instance, ref. [69] developed a reduced nitrogen oxides model for industrial coal-firing boilers. Their study reports that the latter stages of the gasification process (such as gasification) were important for the formation of hydro-carbon radicals from leftover char. Also, ref. [70] reported that the ammonia content in the resulting producer gas from a gasification process were most sensitive to the nitrogen content of the gasification fuel. Similar studies within this period assessed hydro-carbon yield from pyrolysis and gasification processes [71], while other studies assessed the effects of various gasifying agents on the gasification process [72,73].
Notwithstanding the focus of the literature within the period on the thermodynamic fundamentals of gasification technology, the earliest appearance of the word “hydrogen” in the published literature within the period was in 1995, when ref. [74] discussed the emergence of carbon as a hydrogen carrier. Their study expressed optimism about the generation of hydrogen from fossil fuels.
Process Optimisation and Feedstock Diversification (2003–2015).
This period represents the longest run where the trend shows a growing popularity of keywords such as “catalysts”, “concentration”, “thermal effects”, “mathematical modelling”, “biological materials”, “renewable energy resources”, and “reaction kinetics”. These keywords represent an evolution of the literature towards technical process optimisation and feedstock diversification beyond fossil fuel resources. Mathematical models and experimental set-ups have been designed to assess the effects of different operating conditions on the chemical properties of the resulting producer gas [75,76,77,78]. Some of these studies have established a positive correlation between temperature and hydrogen output from gasification processes, with CaO also reported to increase hydrogen yield by over 16% [75]. Under high-pressure conditions, hydrogen yield is also reportedly increased using Ca(OH)2 as a CO2 absorbent [79]. The absence of third-generation feedstocks, such as “algae”, in keyword evolution is largely because such feedstocks are usually treated through biochemical processes in lieu of the thermo-chemical (gasification) focus of this study, which is best suited for first- and second-generation feedstocks [80,81].
This period also demonstrates that the interest in diversifying the feedstock away from fossil fuels precedes the Paris Agreement, given the early, albeit limited, emergence of the literature seeking to assess the viability of renewable resources for hydrogen production via gasification [75,76].
Post-Paris Agreement Alignment (2016–2022).
The literature post-Paris Agreement sees a strong emergence of keywords such as “biomass gasification”, “municipal solid waste” (MSW), “hydrogen production”, and “economic analysis”. Improvements in gasification technology and incentives to transition to a low-carbon economy make municipal solid waste increasingly suitable and attractive for use in the thermo-chemical conversion of heterogenous waste such as municipal solid waste to hydrogen-rich syngas [82,83,84,85], with the possibility of reaching an energy efficiency of 57% [84]. For instance, ref. [85] reported that the organic component of municipal solid waste in parts of Western Norway can generate 2700 tonnes of hydrogen via gasification. Similarly, ref. [86] found that waste generation in a typical city in Ghana (Cape Coast) has the potential of generating over 780,000 kg of bio-hydrogen, with the waste generated projected to increase by over 70% in the next 29 years.
Despite this enormous potential of MSW for hydrogen production, unsustainable waste management practices pose a major barrier [86]. Lessons may be drawn from a four-stage strategy proposal for the management of crop residue encompassing stakeholder engagement, education, and capacity building and the development of integrated systems for the collection, storage, and transportation of biomass resources for hydrogen production [87].
As established in the case of the gasification of other biomass feedstocks, higher gasification temperatures tend to improve hydrogen yield from MSW gasification. Ref. [88] found that the gasification of municipal solid waste at higher temperatures (600 °C–800 °C) increases the hydrogen yield by 30–40 percent. An oxygen-steam gasifying agent, rather than pure oxygen, is advised for hydrogen-rich syngas production from MSW gasification [88,89]. Similarly, metal- and calcite-based catalysts, such as marbles, have proven to be effective in improving hydrogen yield from MSW gasification [88,89,90].
Decarbonisation (2023–2025).
This period marks a deep decarbonisation focus. The keywords prevalent here include “carbon capture and utilisation” (CCU), “direct capture”, “Kyoto protocol”, “clean energy”, and “greenhouse gas emissions”. Whilst the earliest emergence of the literature on CCU-coupled hydrogen production from gasification between 1995 and 2025 was recorded in 2011 [91], the period from 2023 to 2025 is particularly replete with the literature on the use of CCU as a carbon-abating approach in the thermochemical production of hydrogen from biomass. Thus, several studies have been performed on the lifecycle assessment (LCA) of bioenergy carbon capture and storage (BECCS) [92,93,94,95,96]. A key finding from this emerging theme is the need for a standardised approach to conducting LCA on bioenergy production with CCS [96].

3.7. Research Gaps

The review of the literature on hydrogen production through gasification reveals a scarcity of research on the specific context of Africa. This is demonstrated by the light colourisation of the region, as shown in Figure 6 and Figure 7. This is particularly relevant because the MSW generated in most African cities is composed of over 60% organic components [97], whereas only about 44–60% of this waste is collected [98] and only 1% of this waste is recovered [87]. Comparatively, over 96% of MSW is reportedly collected in advanced countries [99]. This gap provides an incentive for increased research to advance the hydrogen economy in emerging economies such as Africa.
Furthermore, while the literature features some studies on the evaluation of MSW gasification, most of the studies have treated MSW as a homogeneous resource, often overlooking the heterogeneity of MSW. For instance, some studies have focused on food waste [18], while others have focused on livestock manure [34] and crop residues [87] as raw materials for hydrogen production via gasification. This calls for expansive studies to broaden the body of knowledge on the thermodynamic, chemical, and operational enablers of increased hydrogen production from municipal solid waste gasification.

4. Conclusions

The post-Paris Agreement energy landscape is increasingly defined by an urgent demand for decarbonized energy systems. Hydrogen has emerged as a plausible alternative to carbon-intensive fossil fuels. As a result, thermochemical processes, such as gasification, have gained traction as competitive pathways for hydrogen production, particularly utilising biomass and other biogenous substances as feedstock.
This study systematically maps the evolution of thermochemical pathways for hydrogen production through gasification for the past three decades (from 1995 to 2025). This review reveals an increasing trend in research output on the subject matter, with spikes occurring approximately every ten (10) years. An institutional and geographical analysis of the research field reveals that the top contributing researchers are affiliated with institutions in Asia and the Middle East, predominantly in China, Saudi Arabia, and Iran. This demonstrates a peculiar incentive of petrostates to diversify their economies from fossil fuels, with hydrogen as a prospective alternative. This study also shows that the most extensive collaboration links are observed running from China to the rest of the world. The United States also demonstrates strong research collaboration links. However, research collaborations among and with African researchers on the subject matter have been modest.
A trend analysis of the literature shows a shift towards climate change mitigation in hydrogen production through thermochemical processes using carbon capture techniques. The most consistent research of interest, however, has been on the use of renewable biomass for hydrogen production through gasification.
Importantly, this study identifies a research gap on the sparsity of knowledge resources on the subject matter in the African context and the techno-economic feasibility of hydrogen production from heterogenous municipal solid-waste gasification. Bridging this research gap would enhance policy-relevant research to diversify the green hydrogen economy in Africa beyond electrolytic means. This would potentially address the energy access gap while solving the municipal solid waste problem on the continent.

5. Limitations of This Study

While this study leverages the peer-reviewed literature from the largest indexing database, Scopus, the scope of the literature available in Scopus largely excludes grey literature such as technical reports and industry intel. However, this study references reports from key multilateral agencies, such as the International Energy Agency (IEA) and the Global Hydrogen Review, to draw policy insights.
Furthermore, the language inclusion criterion for this review only considers the literature published in the English Language. The choice of English was based on its status as the most popular language for scientific research and the inability to translate the literature published in other languages due to time and resource constraints. Notwithstanding the limitation to the English literature, non-English speaking regions such as Asia have not been excluded from this discourse, as demonstrated by the concentration of author affiliations and publications relevant to the search terms in the region.
However, it would be interesting to replicate this study to encompass both peer-reviewed and grey literature, as well as other languages besides the English language.

Author Contributions

Conceptualization, S.N. and E.A.; methodology, S.N. and E.A.; software, E.A.; validation, S.N.; formal analysis, S.N. and E.A.; investigation, E.A.; resources, S.N.; data curation, E.A.; writing—original draft preparation, E.A.; writing—review and editing, E.A.; visualization, E.A.; supervision, S.N.; project administration, E.A.; funding acquisition, S.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Deutscher Akademischer Austauschdienst (DAAD) (grant number 57730835) and the APC was funded by University of Rostock.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Abbreviations

IEAInternational Energy Agency
PVPhotovoltaic
USDUnited States Dollars
SCWGSuper-critical water gasification
PRISMAPreferred Reporting Items for Systematic Reviews and Meta-Analyses
MSWMunicipal solid waste
CCUCarbon capture and utilisation
CCSCarbon capture and storage
AEMAnion exchange membrane
ALKAlkaline electrolysis
PEMProton exchange membrane electrolysis
SOECSolid oxide electrolysis cells

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Processes 13 01847 g001
Figure 1. 2020 PRISMA flow chart.
Figure 1. 2020 PRISMA flow chart.
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Figure 2. Annual production of studies.
Figure 2. Annual production of studies.
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Figure 3. Most globally cited documents.
Figure 3. Most globally cited documents.
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Figure 4. Most relevant authors.
Figure 4. Most relevant authors.
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Figure 5. Tree map of keywords.
Figure 5. Tree map of keywords.
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Figure 6. Scientific production by country.
Figure 6. Scientific production by country.
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Figure 7. Research collaboration map.
Figure 7. Research collaboration map.
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Figure 8. Hydrogen projects by technology type globally (based on [68]).
Figure 8. Hydrogen projects by technology type globally (based on [68]).
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Figure 9. Research trend.
Figure 9. Research trend.
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Table 1. The hydrogen rainbow.
Table 1. The hydrogen rainbow.
Energy Source MaterialHydrogen Production TechnologyHydrogen Type Produced
BiomassConversion (Thermochemical/Biochemical)Green Hydrogen
Direct SolarElectricity for ElectrolysisGreen Hydrogen
Direct Water SplittingGreen Hydrogen
Electricity for ElectrolysisGreen Hydrogen
Solar PVElectricity for ElectrolysisGreen Hydrogen
HydroElectricity for ElectrolysisGreen Hydrogen
WindElectricity for ElectrolysisGreen Hydrogen
Geo-ThermalElectricity for ElectrolysisGreen Hydrogen
Nuclear EnergyElectricity for ElectrolysisPink Hydrogen
Aluminium (Metals)Chemical ReactionGrey Hydrogen
CoalGasificationGrey or Black Hydrogen
Natural GasElectricity for Electrolysis (Indirect)Grey Hydrogen
Steam ReformationGrey Hydrogen
Petroleum/OilSteam Reformation + Carbon SequestrationBlue Hydrogen
Electricity for Electrolysis (Indirect)Grey Hydrogen
CrackingGrey Hydrogen
Cracking + Carbon SequestrationBlue Hydrogen
Source: Author’s construct (based on [6,7]).
Table 2. Most relevant sources.
Table 2. Most relevant sources.
SourcesArticles
International Journal of Hydrogen Energy1107
Fuel405
Energy312
Energy and Fuels241
Energy Conversion and Management237
Fuel Processing Technology144
Energies133
Biomass and Bioenergy130
Applied Energy128
Renewable Energy124
Table 3. Main sources of the literature that obey Bradford’s Law.
Table 3. Main sources of the literature that obey Bradford’s Law.
SourceRankFrequencyCumulative FrequencyZone
International Journal of Hydrogen Energy111071107Zone 1
Fuel24051512Zone 1
Energy33121824Zone 1
Energy And Fuels42412065Zone 1
Energy Conversion and Management52372302Zone 1
Fuel Processing Technology61442446Zone 1
Energies71332579Zone 1
Biomass and Bioenergy81302709Zone 1
Applied Energy91282837Zone 1
Renewable Energy101242961Zone 2
Industrial and Engineering Chemistry Research111123073Zone 2
Chemical Engineering Journal121063179Zone 2
Journal of Cleaner Production13993278Zone 2
Chemical Engineering Transactions14833361Zone 2
Energy Procedia15833444Zone 2
Journal of The Energy Institute16833527Zone 2
Biomass Conversion and Biorefinery17753602Zone 2
European Biomass Conference and Exhibition Proceedings18713673Zone 2
Acs National Meeting Book of Abstracts19703743Zone 2
Renewable and Sustainable Energy Reviews20683811Zone 2
Journal of Supercritical Fluids21673878Zone 2
Energy Sources, Part A: Recovery, Utilisation And Environmental Effects22623940Zone 2
Proceedings of The ASME Turbo Expo23624002Zone 2
AIChE Annual Meeting, Conference Proceedings24584060Zone 2
Process Safety and Environmental Protection25584118Zone 2
Table 4. Co-occurrence of keywords.
Table 4. Co-occurrence of keywords.
ClusterKeywords
1Gasification, hydrogen production, biomass, biomass gasification, pyrolysis, steam, carbon, steam reforming, fluidized beds, steam gasification, tar, syn gas, chemical reactors, water gas shift, temperature.
2Hydrogen, carbon dioxide, synthesis gas, carbon monoxide, methane, gasification process, gas generators, gases, oxygen, syn-gas, gasifiers.
3Catalysts, supercritical water gasification, reaction kinetics, supercritical water, catalyst activity, nickel, catalysis, + catalyst.
4Coal, coal gasification, energy efficiency, fossil fuels, exergy, greenhouse gases, hydrogen fuels, economic analysis, gas emissions, fuels, coal combustion, fuel cells, natural gas.
Table 5. Most relevant affiliations.
Table 5. Most relevant affiliations.
AffiliationArticles
Xi’an Jiaotong University322
Huazhong University of Science and Technology106
King Fahd University of Petroleum and Minerals103
Universiti Teknologi Petronas98
Chulalongkorn University94
National Energy Technology Laboratory89
University of Tehran85
Southeast University83
Tsinghua University80
Zhejiang University79
Table 6. Funding sponsors for African research.
Table 6. Funding sponsors for African research.
Funding SponsorNumber of Documents
National Natural Science Foundation of China14
National Research Foundation11
European Commission10
Ministry of Science and Technology of the People’s Republic of China9
Ministerstvo Školství, Mládeže a Tělovýchovy8
Grantová Agentura České Republiky7
King Saud University7
Natural Science Foundation of Sichuan Province7
Chengdu University of Information Technology6
Deanship of Scientific Research, King Faisal University5
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Narra, S.; Ali, E. Tracing the Research Pulse: A Bibliometric Analysis and Systematic Review of Hydrogen Production Through Gasification. Processes 2025, 13, 1847. https://doi.org/10.3390/pr13061847

AMA Style

Narra S, Ali E. Tracing the Research Pulse: A Bibliometric Analysis and Systematic Review of Hydrogen Production Through Gasification. Processes. 2025; 13(6):1847. https://doi.org/10.3390/pr13061847

Chicago/Turabian Style

Narra, Satyanarayana, and Eliasu Ali. 2025. "Tracing the Research Pulse: A Bibliometric Analysis and Systematic Review of Hydrogen Production Through Gasification" Processes 13, no. 6: 1847. https://doi.org/10.3390/pr13061847

APA Style

Narra, S., & Ali, E. (2025). Tracing the Research Pulse: A Bibliometric Analysis and Systematic Review of Hydrogen Production Through Gasification. Processes, 13(6), 1847. https://doi.org/10.3390/pr13061847

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