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Article

Bibliometric Analysis of Hydrogen-Powered Vehicle Safety and Reliability Research: Trends, Impact, and Future Directions

by
Rajkumar Bhimgonda Patil
1,
Anindita Roy
2,
Sameer Al-Dahidi
3,*,
Sandip Mane
1,
Dhaval Birajdar
1,
Rohitkumar Chaurasia
1 and
Shashikant Auti
1
1
Department of Mechanical Engineering, Dwarkadas J. Sanghvi Engineering College, Mumbai 400056, India
2
Symbiosis Institute of Technology, Symbiosis International (Deemed) University, Pune 412115, India
3
Department of Mechanical and Maintenance Engineering, School of Applied Technical Sciences, German Jordanian University, Amman 11180, Jordan
*
Author to whom correspondence should be addressed.
Hydrogen 2025, 6(2), 42; https://doi.org/10.3390/hydrogen6020042
Submission received: 29 April 2025 / Revised: 6 June 2025 / Accepted: 9 June 2025 / Published: 19 June 2025
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Abstract

:
Research on and the demand for hydrogen-powered vehicles have grown significantly over the past two decades as a solution for sustainable transportation. Bibliometric analysis helps to assess research trends, key contributions, and the impact of studies focused on the safety and reliability of hydrogen-powered vehicles. This study provides a novel methodology for bibliometric analysis that systematically evaluates the global research landscape on hydrogen-powered vehicle reliability using Scopus-indexed publication data (1965 to 2024). Eighteen key parameters were identified for this study that are often used by researchers for the bibliometric analysis of hydrogen-related studies. Data analytics, VOSviewer-based visualization, and research impact indicators were integrated to comprehensively assess publication trends, key contributors, and citation networks. The analysis revealed that hydrogen-powered vehicle reliability research has experienced significant growth over the past two decades, with leading contributions from high-impact journals, renowned institutions, and influential authors. The present study emphasizes the significance of greater funding as well as open-access distribution. Furthermore, while major worldwide institutions have significant institutional relationships, there are gaps in real-world hydrogen infrastructure evaluations, large-scale experimental validation, and policy-driven research.

1. Introduction

The most critical factors in the widespread adoption and commercialization of hydrogen-powered vehicles are safety and reliability concerns [1]. Hydrogen fuel cell technology extends beyond cars to include bicycles, buses, trucks [2], railways, aviation [3], and passenger ships, relying on breakthroughs in vehicle technology and safe hydrogen fueling infrastructure for success [4,5,6]. As the global automotive industry increasingly adopts sustainable energy solutions [7], advancements in fuel cell technology [8], hydrogen storage methods [9], and system integration are driving the evolution of hydrogen-powered vehicles [10]. The primary focus was initially on addressing fuel cells’ durability issues, such as membrane degradation [11], catalyst poisoning [12], and efficiency losses over time [13,14]. The 2000s saw a shift towards comprehensive system reliability assessments, integrating power electronics [15,16], hydrogen storage [17], and safety considerations [18,19]. With the growing interest in sustainable transportation, research in the 2010s incorporated machine learning [20] and predictive maintenance techniques to enhance the reliability of hydrogen-powered vehicles [21,22]. The focus of the research shifted to fault detection, failure mode analysis, and system optimization for an extended operational life [23,24]. Since 2020, advancements have included AI-driven diagnostics [25], real-time reliability monitoring, and hybrid hydrogen–electric powertrains [26]. These developments have improved vehicle efficiency, ensured safety, and supported commercial viability.
The earliest bibliometric analyses of hydrogen energy research began in the late 1990s and early 2000s, primarily focusing on general hydrogen fuel technologies [27,28,29], storage methods [30,31], and policy implications [32,33]. However, the reliability aspect of hydrogen-powered vehicles remained underexplored. By the 2010s, researchers started integrating bibliometric methods to assess publication trends related to fuel cell degradation [34], hydrogen-powered vehicle reliability [35], and fault detection in hydrogen-powered vehicles [36,37]. Using citation networks, co-authorship mapping, and keyword analysis became common, enabling a systematic understanding of key contributors and the evolution of this research [34]. In the 2020s, bibliometric studies have progressed significantly by applying advanced visualization tools such as VOSviewer and CiteSpace [38,39,40]. The integration of machine learning techniques for citation trend prediction and future research forecasting marked a new phase of bibliometric analysis [41,42], further refining insights into hydrogen-powered vehicle reliability research [43]. Table 1 summarizes the key milestones in bibliometric studies on the reliability analysis of hydrogen-powered vehicles.
A bibliometric analysis provides a systematic and quantitative assessment of scholarly publications [44], allowing researchers to identify key trends, influential authors, leading institutions, and high-impact journals [45,46]. Bibliometric analysis helps to identify the knowledge gaps, emerging technologies, and dominant research directions regarding hydrogen-powered vehicle reliability through citation networks and research collaboration studies [47,48]. It also plays a crucial role in evaluating the quality and impact of published work [49,50,51]. Citations, the publication volume, and impact metrics such as the CiteScore, h-index, and SNIP provide a reliable means to assess research’s influence and scholarly contributions [52,53]. Identifying top journals, organizations, and research trends ensures that future investigations are built on high-quality sources [54,55]. Furthermore, the systematic assessment of the global research output enables scholars and policymakers to make informed decisions regarding funding allocation, innovation strategies, and technology adoption regarding hydrogen-powered vehicles [56,57].
Table 2 and Table 3 provide the qualitative and quantitative parameters selected for the bibliometric analysis and prioritize them based on their use (frequency) by various researchers in the context of hydrogen-powered vehicle research. There were 21 bibliometric parameters used to assess research trends and collaborations. Researchers commonly used year-wise publication trends, keyword analysis, the top journals and countries, and network analyses to track hydrogen fuel research’s growth, highlight emerging topics, map collaborations, and identify influential contributors and regional or institutional research impacts. Citation trends received less attention than publication growth, while document types and publication metrics received a moderate focus. Funding sources, open-access distribution, and sponsorship remained largely overlooked, indicating a limited emphasis on research accessibility and funding influences in bibliometric studies.
The findings from recent studies provided key bibliometric indicators and parameters to be considered to evaluate the safety and reliability of hydrogen-powered vehicles. The emphasis on publication trends, keyword analysis, and collaboration networks provides a direction to conduct future studies in unexplored areas such as failure prediction, system optimization, and sustainability. Furthermore, recognizing gaps in the consideration of funding sources, open-access research, and citation trends offers potential directions for future bibliometric studies. Early studies emphasized material durability and fuel cell degradation, while recent research has explored predictive maintenance, AI-driven diagnostics, and life cycle assessments. Bibliometric analyses have revealed many publications in this research area, particularly on hybrid hydrogen–electric systems. Key research themes include fuel cell performance analysis, reliability assessment using statistical and machine learning models, sustainability evaluations, and global research collaborations. Increasing partnerships between academia and industry have accelerated hydrogen storage and fuel efficiency innovation.
This study aimed to answer the following research question: “What are the key research trends, influential contributors, and knowledge gaps in the hydrogen-powered vehicle safety and reliability field based on bibliometric analysis?” By addressing this question, the study sought to map the evolution of research, leading institutions, and the impact of scholarly contributions in this critical area. The following objectives were developed to address the research questions:
  • To develop a novel methodology for the bibliometric analysis of the “safety and reliability of hydrogen-powered vehicles”.
  • To identify qualitative metrics for assessing published work, the top journals, organizations, and researchers contributing to hydrogen-powered vehicle reliability research.
  • To analyze citation networks, co-authorship patterns, research collaborations, and trending keywords.
  • To evaluate the research trends, knowledge gaps, and emerging themes and provide a systematic research assessment that will guide future studies and policy recommendations.
This study used a well-defined dataset to conduct a bibliometric analysis of hydrogen-powered vehicle safety and reliability research. The analysis covered publications from 1965 to 2024, retrieved from Scopus databases. Only peer-reviewed journal articles, conference papers, books, and book chapters were considered to ensure the inclusion of high-quality research. The study utilized VOSviewer, Python, Publish or Perish, and MS Excel to analyze and visualize the results, patterns, and trends for data processing and analysis. This study provides valuable insights for researchers, policymakers, and industry professionals by highlighting influential contributors and emerging hydrogen-powered vehicle safety and reliability themes. It enables strategic decision-making regarding research funding, technology development, and industry collaborations. However, the study has limitations, such as database restrictions (Scopus), potential citation bias, and the exclusion of non-English publications, which may have affected the comprehensiveness of the analysis.
The Methodology (Section 2) details the data collection process, the publication selection criteria, and the bibliometric tools employed. The Results and Discussion (Section 3) presents key findings, patterns, emerging trends, and an in-depth interpretation of the analyzed data. Finally, the Conclusion (Section 4) summarizes the study’s significant insights, contributions to the field, existing limitations, and potential directions for future research.

2. Methodology

Figure 1 presents the proposed novel methodology for systematic bibliometric analysis to evaluate the research landscape concerning hydrogen-powered vehicles’ safety and reliability. It systematically outlines the research process, from topic identification to data assessment and the scope for future research. This research focused on hydrogen energy, specifically addressing hydrogen-powered vehicles’ safety and reliability. The first step defined the research question, which set the foundation for data collection and analysis. The Scopus database was chosen due to its comprehensive coverage of research articles, reviews, conference papers, books, and book chapters. Scopus provides reliable citation and indexing information essential for bibliometric analysis. A detailed search strategy was formulated using keywords related to hydrogen fuel and vehicle safety, as given in Step 3. The keywords included “Hydrogen fuel,” “Hydrogen cell,” “Hydrogen storage,” “Hydrogen economy,” “Hydrogen energy,” “Vehicle safety,” and “Reliability.” Boolean operators (AND, OR) helped refine the search for relevant research articles. The retrieved articles underwent filtering based on their language (English) and publication year (1965–2024). Various parameters like the document type (articles, reviews, conference papers, books) and publisher details (Elsevier, Springer, IEEE, Wiley, Taylor & Francis) were considered. Data sources were validated to ensure high research quality.
In Step 5, pre-processing, the collected data underwent a cleaning process to ensure accuracy and consistency. This step involved handling missing values by addressing incomplete records, ensuring uniformity in publication details to eliminate inconsistencies, and treating outliers by removing extreme or irrelevant data points that could distort the analysis. The assessment focused on conducting bibliometric, statistical, and analytical evaluations to derive meaningful insights from the collected data in Step 6. This included analyzing publication and citation trends, performing co-authorship and co-citation analyses, and assessing the journal quality using impact factor metrics. VOSviewer, Microsoft Excel, Python Version R2024a, Publish or Perish, MATLAB, and the Scopus database were used to conduct the analyses. The methodology integrated descriptive, diagnostic, predictive, and prescriptive analytics to evaluate the data comprehensively and systematically.
The key research findings were summarized and a discussion of the results, along with key conclusions and future directions, was presented in Step 7. In Step 8, the outcome evaluation incorporated a feedback loop to ensure continuous research process assessment and improvement. The process could be concluded if the results met the requirements/desired outcomes and provided the required insights. A new dataset could be selected and the analysis restarted if the outcomes were not satisfactory.

3. Results and Discussion

3.1. Quality Metrics

The bibliometric analysis of research on hydrogen-powered vehicles’ safety and reliability revealed a substantial body of work spanning 1965 to 2024, with 2545 papers contributing to the field. These publications had collectively amassed 58,383 citations, averaging 973.05 per year and 22.94 citations per paper, indicating a significant academic impact. The research community in this domain was highly collaborative, with an average of 4.28 authors per paper. A h-index of 103 and g-index of 153 suggest that many papers have received high citation counts, underlining their influence. The hI, norm (48), and hA-index (24) also reflected individual researchers’ consistency and sustained contributions. The distribution of papers with citations (ACC ≥ 1, 2, 5, 10, 20) further highlighted that 1528 papers had received at least one citation, while 47 papers had over 20 citations, demonstrating the field’s growing impact and recognition within the scientific community.

3.2. Assessment Based on Document Type

The classification of publications, as shown in Figure 2, clearly highlighted that journal papers dominated with a total count of 1869, followed by conference papers (566). The contributions of review articles, book chapters, and other publications were minimal, with only one book recorded. The preference for journals ensures research credibility, while low review and book publications indicate a lack of consolidated knowledge. The citation analysis, shown in Table 4, demonstrated that journal papers dominated with 86.84% of citations, averaging 27.11 citations per paper. Review articles, though only 2.4% of the total, had the highest citation rate (72.95). Conference papers contributed 22.24% but received fewer citations (5.43 per paper), whereas the books, though scarce, had a high citation impact (34.50 per book). Researchers should focus on producing systematic reviews, research papers, and book publications through interdisciplinary studies to improve and maintain high-impact research and help to boost the citation impact and knowledge dissemination.

3.3. Publication Trend Analysis

Figure 3 illustrates the trend of research article publications from 2005 to 2024, showing a gradual increase from 2005 to 2017, followed by significant growth from 2020 onwards, peaking at 339 publications in 2024. An exponential growth model with an R2 value of 0.8646 indicated a strong correlation. Figure 4 illustrates the journal paper publication trend from 2005 to 2024, showing an exponential growth pattern with a strong correlation (R2 = 0.9205). The number of publications increased from 27 in 2005 to 293 in 2024, with a more rapid rise post-2020. Figure 5 illustrates the publication trend for conference papers, books, and book chapters from 2005 to 2024, showing fluctuations until 2021, followed by a sharp rise from 2022. The overall trend shows that there has been a significant improvement in research participation, institutional support for infrastructure and funding, and global collaboration for high-impact publications.

3.4. Assessment of Publications by Publishers, Journals, and Conferences

Table 5 presents the top 10 journals with the maximum number of publications selected for publication based on various quality metrics. The “International Journal of Hydrogen Energy” led with 311 publications and 11,888 citations, followed by the “Journal of Power Sources” with 226 publications and 10,820 citations. The highest number of citations per document was 67.58 for the “Journal of the Electrochemical Society”, indicating a high impact. “Applied Energy” had the highest CiteScore (21.2) and impact factor (10.1). All the journals belonged to Quartile 1 (Q1), indicating high-quality publications. These metrics highlight leading hydrogen and energy research platforms with strong academic influence.
Table 6 highlights the top 10 conference proceedings for publications, listing the number of papers, citations, and citations per paper. “ECS Transactions” led in terms of its number of publications (59) but had a moderate citation rate (5.78 per paper), while the “International Journal of Hydrogen Energy” had fewer papers (12) but the highest citation impact (41.00 per paper). “Energy Procedia” also had a strong citation rate (12.50). Some venues, like the AIChE Annual Meeting publication and Advanced Materials Research, had low citation efficiency.
Table 7 presents the publishers’ publication and quality metrics, listing the number of journal papers, total citations, and citations per paper. Elsevier led with 853 publications and 27,473 citations (32.21 per paper), indicating its dominance in academic publishing. The Electrochemical Society Inc. had the highest citation impact (56.74 per paper), despite only having 31 publications. MDPI and the Royal Society of Chemistry also showed strong citation performance. Publishers like the Italian Association of Chemical Engineering (4.07 per paper) and Science Press (3.29 per paper) had lower citation impacts.

3.5. Publications in Various Subject Areas

Table 8 presents the number of publications across different subject areas, highlighting these areas’ contributions. Energy (58.39%) and engineering (48.57%) dominated the research output, followed by chemistry (21.85%) and physics and astronomy (19.25%). The “Other” category, covering diverse disciplines, contributed 11.04%. The focus on energy and engineering aligns with industry demands, but the amount of interdisciplinary research could be enhanced.

3.6. Sponsored and Non-Sponsored Research

Figure 6 and Table 9 illustrate the distribution of sponsored and non-sponsored research, where 72% (2969 studies) was non-sponsored and 28% (1132 studies) received funding support. The dominance of non-sponsored research suggests a reliance on institutional or personal resources, limiting the number of large-scale, high-impact studies. Increasing the amount of sponsored research could enhance the research quality, infrastructure, and collaboration opportunities. Institutions should actively seek funding from government agencies, industry collaborations, and international grants. Encouraging faculty to apply for grants, forming interdisciplinary teams, and aligning research with funding priorities can improve sponsorship rates, leading to greater innovation, better facilities, and a stronger research ecosystem.
Table 9 and Figure 7 compare research published in open-access vs. subscription-based publications. Subscription-based papers (1990 papers, 78%) dominated, receiving the highest number of citations (47,810, 24.03 per paper). Sponsored research (1132 papers) had the highest impact, with 28.67 citations per paper. Open-access papers (555 papers, 22%) received moderate citations (19.22 per paper), indicating their accessibility advantage. The majority of research relied on subscription-based models, while open-access papers were categorized into different types, with Gold Open Access being the most common (174 papers). The relatively low proportion of open-access publications suggests limited accessibility to research. Institutions should encourage open-access publishing to enhance research visibility and citations. Funding bodies should provide support with open-access fees. Researchers should consider using hybrid models and repositories to balance their visibility and impact, ensuring their work reaches a broader audience while maintaining quality.

3.7. Country-Wise Assessment of Publications

Table 10 shows a list of the top 20 countries based on the number of publications and citations, whereas Figure 8 and Figure 9 illustrate the co-authorship network among 48 countries with at least 05 publications. China led in terms of the number of research publications (733 documents with 12,412 citations), while the US demonstrated the strongest collaborative influence and research impact with 32.71 citations per paper. India exhibited a substantial number of research publications and secured the third rank in terms of the number of publications. Canada, Germany, and Spain published around 265 papers altogether; however, these articles received 44.30, 37.74, and 36.13 citations per paper, highlighting their strong regional and global collaboration and quality research output. The United Kingdom, France, Denmark, Australia, and Singapore were some of the other countries that were expanding their research output with a significant impact. Strengthening global collaborations, funding cross-regional research, encouraging open-access publishing, and fostering partnerships can enhance research’s visibility and impact.

3.8. Co-Occurrence of Indexed Keywords

Figure 10 represents a co-occurrence analysis of indexed keywords in research on the safety and reliability of hydrogen-powered vehicles. Out of 12,760 total keywords, 1413 met the threshold of having at least five occurrences, and 1000 were plotted. Larger and centrally placed keywords, such as “proton exchange membrane fuel (943),” “fuel cells (903),” “solid oxide fuel cells (470),” “performance (403),” “cathode (246),” “hydrogen (245),” “degradation (228),” and “polyelectrolytes (209)” indicate emerging topics with frequent occurrences and a strong research focus.

3.9. Citation Analysis

Table 11 ranks the top 10 most highly cited articles in research on the safety and reliability of hydrogen-powered vehicles based on their citation count. Among 2545 articles, 690 met the minimum citation threshold of 25. The most cited article, published in the “International Journal of Hydrogen Energy” (2019), had 912 citations, underscoring its impact. The “Journal of the Electrochemical Society” dominated the list, reflecting its influence in the field. Key topics included hydrogen storage, proton exchange membrane fuel cells, solid oxide fuel cells, and catalytic reforming, highlighting their importance in advancing fuel cell technology and sustainability. Figure 11 represents the co-citation network as a heatmap and highlights highly cited authors, with yellow regions indicating a higher citation density. Figure 12 presents a co-citation network of 130 authors who met the thresholds of having at least five publications and 25 citations out of a total of 8230 authors. The network consisted of clusters of authors, with highly cited researchers like Zhang Houcheng, Qin Jiang, and Ni Meng appearing centrally, indicating their strong influence in the field. Notable contributors such as [144,145] were highly cited, revealing their influence. Clustering analysis showed interconnected research themes, with older foundational work continuing to shape recent studies, emphasizing the evolution of fuel cell research and emerging trends.
Moradi and Groth [144] provided a comprehensive review of hydrogen storage technologies and included a risk and reliability assessment framework. The methodology combined technical performance benchmarks with probabilistic risk modeling and highlighted its importance in laying the foundation for safety considerations in hydrogen infrastructure. A 1995 study on the empirical modeling of proton exchange membrane (PEM) fuel cells’ performance was analyzed by Kim. This study helped in increasing the understanding of operational characteristics under varying load conditions, offering one of the earliest performance prediction models, still cited in contemporary research. The 2003 review by Fleig on polarization mechanisms in solid oxide fuel cells (SOFCs) was discussed in detail. This work has been influential due to its analytical treatment of cathode behavior and degradation patterns, which are essential to understand for long-term reliability assessments.

3.10. Journal Citation Network Analysis

Figure 13 presents a citation network of sources (journals, conferences, books) created using 69 sources out of 748 that met the threshold of having at least five publications and five citations. The “International Journal of Hydrogen Energy (329 publications)” was the most influential, followed by the “Journal of Power Sources (231 publications),” and “Energy Conversion and Management (83 publications).” The color gradient represents publication years, indicating recent growth in hydrogen energy research. Strong interconnections highlight interdisciplinary research trends. The dominance of energy-focused journals underscores the significance of hydrogen and fuel cell technologies in the global transition toward sustainable energy solutions.

3.11. Highly Cited Organizations

Figure 14 illustrates the publication and citation network of organizations (institutions) contributing to hydrogen and energy research. Among 4783 organizations, 4103 met the threshold of having at least one publication and one citation, with the top 1000 organizations displayed. The heatmap indicates the existence of highly active institutions such as Tongji University, Shanghai; Ningbo University; and the Shanghai University of Science and Technology. The clustering highlights strong research contributions from China, Iran, India, and Europe. The dense regions suggest institutional collaborations and research hotspots, emphasizing the growing global focus on hydrogen and sustainable energy technologies.
This study fills critical gaps by offering a comprehensive bibliometric analysis of research on hydrogen-powered vehicles’ reliability, an area with limited prior systematic reviews. It identifies leading journals, key researchers, and institutional collaborations, providing a structured roadmap for scholars entering this field. Moreover, by highlighting publication trends and keyword clusters, the study reveals emerging research themes and areas that require further exploration. Importantly, this work bridges the gap between engineering reliability studies and scientometric approaches, establishing a methodological foundation for future bibliometric research in energy and sustainability. High-impact papers were often published in non-specialized energy journals, indicating that hydrogen-powered vehicle reliability research is dispersed across disciplines rather than centralized within core automotive or mechanical engineering outlets. Additionally, some highly cited authors had relatively low publication counts, suggesting that a few seminal contributions disproportionately influence the field. Furthermore, some highly ranked institutions did not have a proportionate citation impact, highlighting disparities between the publication quantity and influence. A key strength of this study is its systematic and data-driven approach, utilizing robust bibliometric techniques to analyze publication trends and research impacts. Using VoSviewer for network visualization enhanced the clarity of the findings, making complex citation and co-authorship relationships accessible.

4. Conclusions and Future Directions

This bibliometric study provides a comprehensive overview of the research environment regarding hydrogen-powered vehicles’ safety and reliability, indicating enormous development over the last two decades. Papers from Scopus-indexed databases published in the last twenty years were used as a basis to develop this study. Keyword search analysis revealed that 2545 publications have collectively reported 58,383 citations, with an average of 973 annual citations and 22.94 citations per publication. The publishing rate increased after 2020, peaking at 339 publications in 2024, showing the rising worldwide interest in sustainable hydrogen-powered mobility. The key findings from this paper are summarized as follows:
  • The top contributors in terms of the publication count were China (733 papers, 28.8%), the United States (337 papers, 13.2%), and India (230 papers, 9.0%), while the highest research impact was reported for Canada (44.30 citations/paper) and Germany (37.74 citations/paper).
  • A total of 72% of research was non-sponsored, showing a reliance on institutional or personal resources, but funded research (28%) had a larger effect, averaging 28.67 citations per publication versus 8.76 for non-sponsored studies.
  • The “International Journal of Hydrogen Energy” (311 papers, 11,888 citations) and the “Journal of Power Sources” (226 papers, 10,820 citations) were the most significant publishing platforms.
  • According to the keyword analysis, the most common study subjects were “proton exchange membrane fuel” (943 occurrences), “fuel cells” (903), and “solid oxide fuel cells” (470), with machine learning and AI-driven predictive maintenance gaining popularity as new trends.
  • Only 22% of articles were open-access, which limited the research’s accessibility and necessitates additional efforts to encourage open-access research.
  • Strong institutional connections were evident, with Tongji University, Ningbo University, and the Shanghai University of Science & Technology spearheading worldwide research initiatives.
  • The most referenced publications addressed hydrogen storage, fuel cell degradation, and system optimization, emphasizing major issues in hydrogen-powered vehicle development.
  • The findings from the keyword and co-occurrence analysis highlighted the growing interest in terms such as hydrogen leakage, explosion risk, hazard assessment, and safety monitoring, particularly since 2020.
  • Hydrogen research is extending beyond transportation, with more studies looking at its potential uses in aviation, maritime transport, and microgrid energy systems.

4.1. The Limitations of the Study

This study relied solely on the Scopus database, potentially overlooking relevant research indexed in the Web of Science, IEEE Xplore, or Google Scholar. This may have led to incomplete citation networks and an underrepresentation of the key contributions. The exclusion of non-English publications may have introduced regional bias, limiting the global applicability of the findings. Furthermore, self-citations and institutional collaborations may have inflated certain impact metrics, necessitating the further scrutiny of network relationships. Theoretical limitations exist, particularly in the reliance on quantitative bibliometric indicators without qualitative validation. Citation counts alone do not capture the practical impact or technological advancements resulting from research. Additionally, the study did not account for latent variables such as policy shifts, industry demands, or interdisciplinary collaborations that may have influenced publication trends in this domain.

4.2. Future Directions

While this analysis demonstrates a significant global research focus on hydrogen-powered vehicles’ durability, some crucial gaps remain. The prevalence of non-sponsored research indicates a pressing need for more financing, particularly for large-scale experimental investigations that can verify theoretical models and predictive maintenance procedures. Despite an increase in multidisciplinary cooperation, the integration of policy research, industrial partnerships, and real-world hydrogen infrastructure concerns is still underexplored. Furthermore, a more qualitative assessment of research impacts, such as through patent analysis and using industry adoption rates, would provide a more complete picture of hydrogen technology advancements. In addition to mobility, other potential applications of hydrogen, including energy storage at the grid level or decentralized power generation, should be explored. Addressing all of these challenges is significant to the practical use of hydrogen-powered vehicles, moving from the realm of scientific investigation towards widespread commercial viability. There was a noted gap in experimental safety validation, with relatively few high-impact papers addressing real-world crash simulations, leak detection systems, or safety protocol standardization for hydrogen refueling stations and vehicle applications. There was the lack of a bibliometric emphasis on safety-focused policy research, regulatory frameworks, and risk communication strategies, which are critical for public acceptance and industrial adoption.

Author Contributions

Conceptualization, R.B.P.; methodology, R.B.P.; software, R.B.P. and A.R.; validation, R.B.P., A.R., S.A.-D., S.M., D.B., R.C. and S.A.; formal analysis, R.B.P., A.R. and S.A.-D.; investigation, R.B.P., A.R., S.A.-D., S.M., D.B., R.C. and S.A.; resources, R.B.P.; data curation, R.B.P.; writing—original draft preparation, R.B.P., A.R., S.A.-D., S.M., D.B., R.C. and S.A.; writing—review and editing, R.B.P., A.R., S.A.-D., S.M., D.B., R.C. and S.A.; visualization, R.B.P., A.R. and S.A.-D.; supervision, R.B.P. and S.A.-D.; project administration, R.B.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data were derived from public-domain resources.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. The novel methodology proposed in this work.
Figure 1. The novel methodology proposed in this work.
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Figure 2. Classification of publications according to “document type”.
Figure 2. Classification of publications according to “document type”.
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Figure 3. Research article publication trend from 2005 to 2024.
Figure 3. Research article publication trend from 2005 to 2024.
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Figure 4. Journal paper publication trend from 2005 to 2024.
Figure 4. Journal paper publication trend from 2005 to 2024.
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Figure 5. Publication trend for conference papers, books, and book chapters from 2005 to 2024.
Figure 5. Publication trend for conference papers, books, and book chapters from 2005 to 2024.
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Figure 6. Sponsored and non-sponsored research.
Figure 6. Sponsored and non-sponsored research.
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Figure 7. Open-access and subscription-based papers.
Figure 7. Open-access and subscription-based papers.
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Figure 8. Co-authorship network of countries with research collaborations.
Figure 8. Co-authorship network of countries with research collaborations.
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Figure 9. Global citation network of the countries.
Figure 9. Global citation network of the countries.
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Figure 10. Indexed keyword co-occurrence analysis.
Figure 10. Indexed keyword co-occurrence analysis.
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Figure 11. Assessment of articles with greatest number of citations.
Figure 11. Assessment of articles with greatest number of citations.
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Figure 12. Author co-citation network.
Figure 12. Author co-citation network.
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Figure 13. Citation network of journals.
Figure 13. Citation network of journals.
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Figure 14. Publication and citation network of organizations engaged in hydrogen and energy research.
Figure 14. Publication and citation network of organizations engaged in hydrogen and energy research.
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Table 1. Key milestones in bibliometric studies on reliability analysis of hydrogen-powered vehicles.
Table 1. Key milestones in bibliometric studies on reliability analysis of hydrogen-powered vehicles.
YearsKey MilestoneImpact on Bibliometric Studies
1990sEarly bibliometric studies on hydrogen energy researchFocused on hydrogen production and storage rather than reliability
2000sInitial citation-based analyses of fuel cell technologyTracked growth of research on hydrogen-powered vehicles
2010sIntroduction of bibliometric tools like VOSviewer and CiteSpaceEnabled visualization of citation networks and co-authorship collaborations
2015–2020Growing interest in reliability-focused bibliometric studiesIdentified key research areas in hydrogen-powered vehicle reliability
2020sIntegration of AI and machine learning in bibliometric analysisEnhanced predictive modeling of future research trends
Table 2. Prioritization of the parameters selected for bibliometric analysis by various researchers in the context of “hydrogel fuel research”.
Table 2. Prioritization of the parameters selected for bibliometric analysis by various researchers in the context of “hydrogel fuel research”.
Sr. No.Variable/ParameterRef.Count
1Year-wise publication trend[44,45,47,48,49,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134]82
2Keyword analysis[45,47,48,49,58,59,61,62,63,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,85,89,90,91,92,94,96,97,98,100,104,105,106,109,110,111,113,115,116,117,118,119,120,125,127,128,130,133,134,135,136,137,138,139,140,141]64
3Top journals according to publications and citations [44,45,47,48,49,58,61,62,65,66,69,70,74,75,77,78,79,81,82,83,85,89,90,92,93,94,97,98,100,101,102,105,106,107,108,109,110,112,114,116,119,123,125,128,129,130,135,137,139,141]50
4Top countries according to publications and citations[44,45,48,67,68,73,74,75,77,78,79,80,82,84,85,89,91,92,93,94,96,97,98,99,100,101,102,103,105,106,107,108,109,110,114,115,117,121,123,124,125,130,133,134,135,139,141]47
5Network analysis of countries[44,48,49,58,61,62,63,64,66,68,69,70,71,72,74,78,79,80,84,85,86,88,90,94,97,100,102,105,107,109,114,115,116,118,123,125,128,130,135,136,137,141,142]43
6Article classification according to the number of publications and citations[44,45,49,60,62,65,66,67,68,69,70,72,73,74,75,77,80,82,85,86,89,92,93,94,99,100,105,106,107,114,117,118,119,124,125,128,129,130,136,141]40
7Keyword network and cluster analysis[76,78,79,80,82,84,85,86,88,89,91,93,94,97,98,100,101,103,104,106,107,108,109,110,111,112,114,116,118,120,123,125,128,129,130,134,137,138,141,142]40
8Top authors according to publications and citations [44,47,48,60,61,62,69,71,73,75,77,78,79,80,82,84,85,88,90,92,93,97,98,99,106,107,109,114,116,118,123,124,128,130,135,139]36
9Network analysis of organizations/institutions[44,48,49,58,61,66,68,69,70,71,74,78,81,82,83,85,88,89,90,92,94,97,99,100,102,105,106,107,110,117,120,124,135]33
10Network analysis of authors’ and co-authors’ citations and co-citations[44,45,47,48,49,58,61,65,66,68,70,74,77,78,79,80,81,84,85,90,97,106,107,115,116,128,130,137,139]31
11Research/subject areas[44,58,63,64,66,69,71,72,73,74,77,79,82,83,88,94,96,97,102,105,107,110,114,119,125,128,134,135,137,143]30
12Year-wise citation trend[44,47,49,67,69,70,72,73,76,77,78,79,85,116,118,123]16
13Classification by document type[49,58,66,83,88,89,91,93,94,103,125,137]12
14Network analysis of journals[47,71,77,97,106,130,135]07
15Publication count; citation count; impact factor (IF); CiteScore; quartile; h-index; SJR; SNIP [72,107,110,119,121,129]06
16Publication classification according to the language[44,69,94]03
17Funding agencies[78,99,130]03
18Top publishers[72,73]02
19Sponsored vs. non-sponsored research 0
20Subscription vs. open-access publications 0
21Top 10 conference proceedings 0
Table 3. Assessment and selection of bibliometric parameters in the context of the “safety and reliability of hydrogen-powered vehicles” [45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134].
Table 3. Assessment and selection of bibliometric parameters in the context of the “safety and reliability of hydrogen-powered vehicles” [45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134].
Sr. No.Variable/ParameterMeasure/IndicatorDescriptionScope of Work/SignificanceKey Findings/StrengthsLimitations
1Publication CountNumber of papers publishedMeasures research output in the domainIdentifies growth trendsHighlights increasing interest and publication trendsIt does not account for the quality or impact of publications
2Citation CountTotal citations receivedMeasures the influence of published researchDetermines key papers shaping the fieldHighlights most influential workHigh citations do not always indicate research quality
3Citations per PaperAverage citations per publicationEvaluates the impact of individual studiesIdentifies highly referenced studiesProvides insight into research significanceBiased towards older publications
4Impact Factor (IF)Journal IFMeasures the average citation impact of a journalHelps in selecting reputable journals for publishingIdentifies leading journals in the fieldVaries significantly across disciplines
5CiteScoreScopus CiteScoreAnother measure of journal quality based on citationsAlternative to IF, covering a wider citation windowIdentifies high-impact journalsDifferences in calculation methods across sources
6QuartileQ1, Q2, Q3, Q4Ranks journals based on impact metricsIdentifies top-tier journalsUseful for journal selectionQuartile ranking varies across databases
7h-IndexResearcher h-indexMeasures productivity and impact of a researcherEvaluate the researcher’s contributionHelps in author impact assessmentFavors senior researchers with long publication history
8SJRSCImago Journal RankWeighted citation metric considering journal prestigeIdentifies top-ranking journalsHelps in journal selectionInfluenced by self-citation
9SNIPSource-Normalized Impact per PaperAdjusts for field-specific citation behaviorEnsures fair comparison across disciplinesBalances citation variationsLess intuitive than IF or CiteScore
10Year-Wise Publication Trend Publications vs. timeTracks research growth over timeIdentifies periods of high research activityShows emerging trendsIt may not reflect impact of quality
11Top 10 JournalsList of most-published journalsHighlights primary publication sourcesAssists researchers in targeting journalsShows domain-specific publication hubsLimited to dataset scope
12Top 10 PublishersLeading publishers in the fieldIdentifies key publishing bodiesHelps in understanding research disseminationHighlights publication preferencesMay exclude emerging publishers
13Top 10 Conference ProceedingsMajor conferences publishing hydrogen vehicle researchRecognizes influential conferencesAssists researchers in conference selectionShows active research forumsLimited by indexing restrictions
14Top 10 Most Highly Cited Articles Most-referenced papersIdentifies seminal work in the fieldRecognizes highly influential researchGuides literature reviewOlder papers have a citation advantage
15Research AreasPublications by domainMaps contributions across disciplinesIdentifies multidisciplinary research impactHighlights domain overlapMay exclude niche research areas
16Keyword AnalysisKeyword co-occurrence networkIdentifies research trends and themesHelps in trend analysisShows emerging topicsThis may be influenced by indexing variations
17Collaboration DataCo-authorship and institutional tiesTracks research partnershipsMaps international and institutional collaborationsShows influential research networksData availability constraints
18Research CollaborationCountry-wise collaboration analysisHighlights global research effortsIdentifies leading research nationsShows cross-border partnershipsSkewed by regional research funding
19Network AnalysisCitation and co-authorship networksMaps influential connections in researchHighlights interconnected researchersVisualizes research impactLimited by dataset coverage
20Co-Citation and Co-Authorship AnalysisCitation linkagesReveals patterns in scholarly influenceIdentifies influential research clustersShows knowledge disseminationOlder papers may dominate
21Classification by Document TypeJournals, conference papers, books, book chapters, review articlesCategorizes research outputHighlights preferred publication typesShows academic dissemination preferencesMay be database-specific
22Sponsored vs. Non-Sponsored ResearchFunding acknowledgment in publicationsDistinguishes industry-funded vs. independent researchAssesses funding impact on research outputShows the role of funding agenciesData availability issues
23Subscription vs. Open-Access PublicationsOpen- vs. closed-access papersIdentifies accessibility trendsIt helps in understanding knowledge disseminationHighlights open-access distributionSome OA journals have a lower impact
24Co-Authorship Network of CountriesCountry collaboration networkMaps international research linkagesIdentifies global research leadersShows regional collaborationsData bias in indexing systems
25Network Analysis of Highly Cited CountriesCitation-based country rankingHighlights top-contributing nationsRecognizes leading research hubsMaps country-wise impactCitation disparity between regions
26Network Analysis of Highly Cited JournalsJournal impact networkIdentifies influential journalsAssists in journal selectionHighlights research dissemination patternsLimited by citation indexing scope
27Network Analysis of Highly Cited OrganizationsInstitutional citation impactRanks top institutions contributing to researchIdentifies research leaders in academia and industryHelps in institutional benchmarkingBias towards well-funded institutions
Table 4. Assessment based on citations.
Table 4. Assessment based on citations.
Sr. No.Source TypeNo. of Documents (% of Total)No. of CitationsCitations per Document
1Journal papers1870 (73.48%)50,697 (86.84%)27.11
2Conference papers566 (22.24%)3076 (5.27%)5.43
3Reviews61 (2.40%)4450 (7.62%)72.95
4Book chapters25 (0.98%)29 (0.05%)1.16
5Books2 (0.08%)69 (0.12%)34.50
6Other21 (0.83%)62 (0.11%)2.95
Total254558,38322.94
Table 5. Top 10 journals for publications with quality metrics.
Table 5. Top 10 journals for publications with quality metrics.
Sr. No.Journal NameDocumentsCitationsCitations per DocumentCiteScoreImpact Factorh-IndexSJRQuartileSNIP
1International Journal of Hydrogen Energy31111,88838.2313.58.12631.51311.38
2Journal of Power Sources22610,82047.8816.48.13571.85711.399
3Energy Conversion and Management80273734.21199.92502.55312.124
4Energy65331350.9715.39.02512.11012.052
5Journal of the Electrochemical Society57385267.587.23.13100.86810.773
6Applied Energy52255049.0421.210.12922.82012.411
7Energies5073514.706.23.01520.65110.947
8Electrochimica Acta39176445.2311.35.52761.15910.943
9Renewable Energy3276023.7518.49.02501.92311.934
10International Journal of Energy Research2845316.189.14.31230.82610.915
Table 6. Assessment of the quality metrics of the conference proceedings.
Table 6. Assessment of the quality metrics of the conference proceedings.
Sr. No.Conference ProceedingsPapersCitationsCitations per Paper
1ECS Transactions593415.78
2SAE Technical Papers23431.87
3Proceedings of the ASME Turbo Expo13544.15
4International Journal of Hydrogen Energy1249241.00
5Lecture Notes in Electrical Engineering11181.64
6Energy Procedia1012512.50
7E3S Web of Conferences09242.67
8Advanced Materials Research08060.75
9AIChE Annual Meeting, Conference Proceedings08040.50
10Journal of Physics: Conference Series08121.50
Table 7. Publications by publishers and their quality metrics.
Table 7. Publications by publishers and their quality metrics.
Sr. No.Names of the PublishersNumber of Journal PapersNo. of CitationsCitations per Paper
1Elsevier85327,47332.21
2MDPI112149813.38
3John Wiley and Sons Ltd.575399.46
4Springer555429.85
5Electrochemical Society Inc.31175956.74
6Taylor and Francis Ltd.302026.73
7Royal Society of Chemistry1732519.12
8American Society of Mechanical Engineers (ASME)1415110.79
9Italian Association of Chemical Engineering—AIDIC14574.07
10Science Press14463.29
Table 8. Number of publications by the subject area.
Table 8. Number of publications by the subject area.
Sr.
No.		Subject AreaNo. of PublicationsPercentage Contributed (%)
1Energy148658.39
2Engineering123648.57
3Chemistry55621.85
4Physics and astronomy49019.25
5Chemical engineering33313.08
6Environmental science32312.69
7Materials science28611.24
8Mathematics1756.88
9Computer science1435.62
10Other: (1) social science; (2) biochemistry, genetics, and molecular biology; (3) multidisciplinary; (4) Earth and planetary sciences; (5) agricultural and biological sciences; (6) decision sciences; (7) business, management, and accounting; (8) medicine; (9) economics, econometrics, and finance; (10) immunology and microbiology; (11) pharmacology, toxicology, and pharmaceutics; (12) arts and humanities28111.04
Total publications2545
Table 9. Comparison of open-access vs. subscription-based publications and sponsored vs. non-sponsored publications.
Table 9. Comparison of open-access vs. subscription-based publications and sponsored vs. non-sponsored publications.
Sr. No.Article TypeNumber of PapersNumber of CitationsCitations per Paper
1Open access55510,66519.22
2Subscription199047,81024.03
3Sponsored research113232,45328.67
4Non-sponsored research296926,0228.76
Table 10. Contribution of top 20 countries based on publications and citation rate.
Table 10. Contribution of top 20 countries based on publications and citation rate.
Sr. No.CountryDocumentsCitationsCitations per Paper
1China73312,41216.93
2United States33711,02232.71
3India230376616.37
4South Korea175353320.19
5Italy159328420.65
6United Kingdom129442034.26
7Japan126316025.08
8Iran121352829.16
9Canada111491744.30
10Germany102384937.74
10Turkey80177322.16
11Taiwan80168821.10
12France76245032.24
13Spain52187936.13
14Denmark37112830.49
15Malaysia3544912.83
16Thailand3244914.03
17Australia3086628.87
18Saudi Arabia2753819.93
19Singapore2788232.67
20Russian Federation2629011.15
Table 11. Top 10 most highly cited articles.
Table 11. Top 10 most highly cited articles.
Sr. No.TitleYearSource TitlePublisherCited by
1Hydrogen storage and delivery: Review of the state of the art technologies and risk and reliability analysis [144]2019International Journal of Hydrogen EnergyElsevier, Amsterdam, Netherlands
Electrochemical Society, Pennington, NJ, USA		912
2Modeling of Proton Exchange Membrane Fuel Cell Performance with an Empirical Equation [145]1995Journal of the Electrochemical Society--614
3Performance modeling of the Ballard Mark IV solid polymer electrolyte fuel cell I. Mechanistic model development [146]1995Journal of the Electrochemical SocietyElectrochemical Soc Inc.548
4Performance Modeling of the Ballard Mark IV Solid Polymer Electrolyte Fuel Cell II. Empirical Model Development [147]1995Journal of the Electrochemical Society--452
5Solid Oxide Fuel Cell Cathodes: Polarization Mechanisms and Modeling of the Electrochemical Performance [148]2003Annual Review of Materials Research--432
6The effect of porous composite electrode structure on solid oxide fuel cell performance I. Theoretical analysis [149]1997Journal of the Electrochemical SocietyElectrochemical Society Inc.403
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Patil, R.B.; Roy, A.; Al-Dahidi, S.; Mane, S.; Birajdar, D.; Chaurasia, R.; Auti, S. Bibliometric Analysis of Hydrogen-Powered Vehicle Safety and Reliability Research: Trends, Impact, and Future Directions. Hydrogen 2025, 6, 42. https://doi.org/10.3390/hydrogen6020042

AMA Style

Patil RB, Roy A, Al-Dahidi S, Mane S, Birajdar D, Chaurasia R, Auti S. Bibliometric Analysis of Hydrogen-Powered Vehicle Safety and Reliability Research: Trends, Impact, and Future Directions. Hydrogen. 2025; 6(2):42. https://doi.org/10.3390/hydrogen6020042

Chicago/Turabian Style

Patil, Rajkumar Bhimgonda, Anindita Roy, Sameer Al-Dahidi, Sandip Mane, Dhaval Birajdar, Rohitkumar Chaurasia, and Shashikant Auti. 2025. "Bibliometric Analysis of Hydrogen-Powered Vehicle Safety and Reliability Research: Trends, Impact, and Future Directions" Hydrogen 6, no. 2: 42. https://doi.org/10.3390/hydrogen6020042

APA Style

Patil, R. B., Roy, A., Al-Dahidi, S., Mane, S., Birajdar, D., Chaurasia, R., & Auti, S. (2025). Bibliometric Analysis of Hydrogen-Powered Vehicle Safety and Reliability Research: Trends, Impact, and Future Directions. Hydrogen, 6(2), 42. https://doi.org/10.3390/hydrogen6020042

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