Trends and Evolution of Hydrogen Storage Technology Research: A Multidimensional Analysis Using Bibliometrics and LDA Model
Abstract
Accelerating the research and demonstration of safe, economical, and efficient hydrogen storage technologies is essential for the development of the hydrogen energy industry. This study examines the development and evolution patterns of hydrogen storage technologies through bibliometric analysis and the latent Dirichlet allocation (LDA) topic model, utilizing different dimensions of literature and patent data. The main conclusions are as follows: (1) Research in hydrogen storage exhibits a three-phase pattern. China accounts for over one-third of the publications, yet the average number of citations per paper is relatively low. Research in the United States shows fluctuations, while Japanese studies, though initiated early, display a gradual growth rate. Conversely, India has experienced rapid development in recent years. In Asian countries such as China, Japan, and South Korea, universities are the primary institutions driving influential research publications. In contrast, government-affiliated research agencies and scientific organizations play a more dominant role in the United States, Germany, and other European countries. (2) There is a growing interest in emerging materials technologies such as metal hydrides, hydrogen storage alloys, metal–organic frameworks (MOFs), and hydrogen storage metal oxides. Carbon capture and storage (CCS) enhance the application potential of hydrogen storage technologies. Interest in fundamental equipment and system integration research is declining, although interest in carbon-based materials, air filtration, and catalytic reactors shows fluctuating growth. (3) Research on hydrogen storage materials has shifted from basic studies to performance optimization and diversification, with system integration increasingly incorporating intelligent technologies. Catalytic technology is moving from precious metals to efficient nonprecious metal catalysts, with two-dimensional materials like graphene showing potential applications. Advancements in green recycling technologies have improved resource utilization efficiency, promoting environmentally friendly hydrogen energy applications.
1. Introduction
Amid the escalating global energy crisis and environmental challenges, nations worldwide are actively seeking low-carbon, clean, and renewable energy solutions [1, 2]. According to the Hydrogen Council’s report on future hydrogen trends, current hydrogen demand constitutes approximately one-tenth of the projected demand by 2050. Hydrogen is expected to be extensively utilized in sectors such as transportation, industry, electronics, and construction. It may also serve as an energy reserve to address energy shortages [3]. As one of the most abundant elements in the universe, hydrogen, with its versatile applications, high energy content, zero carbon emissions, and renewability, is recognized as one of the most promising energy sources of the 21st century. It plays a crucial role in ensuring national energy security, improving air quality, advancing energy industry upgrades, and achieving carbon peaking and carbon neutrality [4]. Efficient and safe hydrogen storage technologies are pivotal for the widespread adoption of hydrogen energy. These technologies not only help balance energy supply and demand and enhance energy efficiency but also enable diversified energy use and optimize resource allocation [5]. However, due to hydrogen’s characteristics—such as low weight, low density, low liquefaction temperature, small atomic radius, and high reactivity—its storage faces several technical challenges, including safety, storage density, energy loss, and cost control [6]. Consequently, reviewing the current research and future trends in hydrogen storage technologies can provide valuable insights for advancing basic research in hydrogen energy storage and facilitating the orderly and high-quality development of the global hydrogen energy industry.
The challenge of large-scale hydrogen storage is a critical barrier to the broad adoption of hydrogen energy, prompting extensive scholarly investigation into hydrogen storage materials and their properties. Currently, the proposed hydrogen storage methods include gaseous [7], liquid [8], and solid-state storage [9]. Gaseous hydrogen storage, which involves compressing hydrogen at high pressure, is characterized by low cost, low energy consumption, ease of dehydrogenation, and broad applicability. It is the most mature and commonly used hydrogen storage technology. Research primarily focuses on four types of hydrogen storage cylinders (Types I, II, III, and IV) made from different materials as gaseous hydrogen containers. Among these, Type III and Type IV cylinders are predominantly used for onboard hydrogen storage [10, 11]. Liquid hydrogen storage involves storing cryogenically liquefied hydrogen in thermally insulated containers for transportation. Given liquid hydrogen’s extremely low boiling point and the substantial temperature difference with ambient conditions, its storage containers require exceptionally high thermal insulation performance. Consequently, research in this area focuses on insulation technology [12] and storage containers [13]. While this method has achieved large-scale commercial application in the United States and Japan, it is limited to special fields like military and aerospace applications in China.
Solid-state hydrogen storage relies on the adsorption of hydrogen through chemical or physical means. This method offers several advantages, including high volumetric hydrogen storage density, moderate hydrogen absorption/desorption conditions, excellent reversibility and cycle life, superior safety, and high hydrogen supply purity [14]. Research in solid-state hydrogen storage is concentrated on controlling material systems [15], improving material performance, and optimizing hydrogen storage system designs [16]. Materials such as carbon nanotubes [17], metal–organic frameworks (MOFs) [18], and covalent organic frameworks (COFs) [19] are typical representations of physical hydrogen storage materials and have garnered significant academic interest, although they remain in the research phase. Comparatively, metal hydrides based on magnesium, rare earths, titanium, and zirconium, which are used for chemical hydrogen storage, are closer to commercial viability. However, the large-scale application of solid-state hydrogen storage still faces technical and economic challenges.
In the increasingly pivotal field of hydrogen energy, bibliometric and patent analyses have been widely applied as core tools for evaluating scientific research and technological innovation. These methods provide invaluable data support to researchers, enhancing their understanding of the evolution of hydrogen technologies, research trends, collaborative networks, and future directions. Bibliometrics employs quantitative and qualitative methods to analyze and evaluate research literature in critical areas such as green hydrogen [20], hydrogen storage materials [21], hydrogen safety [22], and underground hydrogen storage site selection [23]. This analysis reveals the scale, growth rate, disciplinary distribution, author contributions, and international collaboration within the field. Patent analysis, meanwhile, focuses on uncovering innovation dynamics [24], technological pathways [25], competitive landscapes [26], and market trends [27] within hydrogen technologies. In the domain of hydrogen storage, scholars utilize bibliometric and patent analyses to study the diffusion and convergence trajectories of storage materials and technologies. For instance, Huang et al. [23] analyzed the literature on underground salt cavern hydrogen storage to establish preliminary site selection standards, while Gao et al. [28] used patent data to analyze global diffusion and convergence networks of hydrogen storage technologies, revealing their evolutionary trajectories and innovation trends.
Despite extensive research on specific hydrogen storage technologies, significant breakthroughs remain necessary in material development and commercial application due to hydrogen’s unique properties. Current studies predominantly focus on technical details, lacking a systematic overview from multiple perspectives and dimensions of the status and evolution of hydrogen storage technologies. This limitation hinders comprehensive understanding and fails to provide policymakers and industry with sufficient information and references, thus affecting strategic decision-making and the advancement of large-scale applications.
This paper employs thorough analysis utilizing Web of Science (WOS) literature data and Derwent patent data to conduct a multidimensional review of the current research status of hydrogen storage technologies. It also identifies hot technologies in hydrogen storage across different years and provides a comprehensive analysis of their technical evolution. The aim is to offer academia, industry, and policymakers a more comprehensive and systematic reference to facilitate breakthroughs and the broader adoption of hydrogen storage technologies.
- •
A new multidimensional analysis method: This study, for the first time, combines bibliometrics and the latent Dirichlet allocation (LDA) topic model to systematically sort out the research status and evolution pattern of hydrogen storage technology from both literature and patent dimensions. This multidimensional analysis method not only enriches the research perspective but also provides a new methodological framework, which is conducive to a more comprehensive understanding of the development trend of hydrogen storage technology.
- •
Global research landscape and influence assessment: In the existing reviews on hydrogen storage technology, detailed analyses are mostly conducted on specific technologies in a particular field. This study not only analyzes the evolution of related technologies in the field of hydrogen storage but also conducts a detailed analysis of the research outputs and influences of major countries and regions in the field of hydrogen storage. It reveals the research characteristics and development trends of various countries in this field. Especially through the comparative analysis of China, the United States, Japan, South Korea, and India, the influence of policies and markets on the speed and direction of research development was discovered. Meanwhile, the deficiencies and improvement directions of the current research were pointed out.
- •
Identification of hot technologies and future development directions: This study employs the LDA model to systematically analyze the evolving research hotspots in hydrogen storage technology. Breaking through the limitations of traditional static reviews, this approach reveals the intrinsic logic and phased characteristics of technological evolution. Through quantitative analysis, this study clarifies the current status and future potential of five key technological priorities: material innovation, system integration optimization, thermal management enhancement, catalytic efficiency improvement, and green circular technologies. This approach not only encompasses the core aspects of hydrogen storage technology but also innovatively incorporates green circular technologies into the research framework, thereby addressing the existing research gap in synergistic life-cycle technology integration for hydrogen storage. The above research not only provides a direction for further study in the academic circle but also offers important references for policymakers and the industrial sector in terms of technological path selection and strategic planning.
2. Research Framework and Data Collection
2.1. Research Framework
Bibliometrics is an interdisciplinary field that combines mathematics, statistics, and linguistics to rapidly capture the latest research findings, theoretical breakthroughs, and emerging issues across various domains. It facilitates the discovery of intersections and innovations between different disciplines, thereby playing a crucial role in promoting interdisciplinary research and fostering knowledge innovation [29]. Mainstream software for bibliometric visualization, such as VOSviewer, CiteSpace, and HistCite [30], has been widely applied in fields like energy and environment, medicine, and information science. In this study, we utilized VOSviewer to analyze research frontiers and hotspots in the field of hydrogen storage using bibliometric data. Compared with other knowledge graph analysis methods, VOSviewer can provide three visualization methods in terms of visualization: network view, overlay view, and density view. This method can avoid the mutual overwriting of important nodes and labels as much as possible and focus on displaying the main information. The generated graph is easy to interpret.
Patent data, focusing primarily on the invention, improvement, and application of technologies, aligns closely with real-world production and technological innovation. Patent analysis provides in-depth insights into a field’s technological development trajectory, emerging hotspots, and key technical challenges, thereby supporting technological innovation and product development. Compared with other text analysis tools, the LDA topic model is more mature, and its advantage lies in the feature of unsupervised learning. It not only captures latent topics within documents but also effectively identifies and clusters related terms. By better revealing the underlying structure of textual data, it significantly reduces noise interference. Currently, LDA has been widely applied across multiple domains including text classification, information retrieval, and automated text summarization [31]. This study adopts the LDA approach for theme extraction and evolution analysis, as outlined by Huang et al. [25], to examine the technological evolution in hydrogen storage.
Figure 1 illustrates the research framework for hydrogen storage technology based on bibliometrics and the LDA model.
2.2. Data Acquisition and Processing
The data sample comprises journal articles from the WOS Core Collection and patents from the Derwent database. The WOS Core Collection search query was structured as TI = (“Hydrogen storage”) OR AK = (“Hydrogen storage”), while the Derwent patent search utilized TS = (“Hydrogen storage”) OR TI = (“Hydrogen storage”). The retrieval time frame spans from January 1, 2000, to December 31, 2023. After excluding irrelevant subject categories and duplicate entries, we obtained 16,422 journal articles and 16,174 patents. The exclusion criteria are as follows: (1) Eliminate duplicate literature: We use the Zotero literature management tool to remove duplicates from the collected literature to ensure that each article in the dataset appears only once. Manual verification: Manual verification was conducted on the data of papers and patents, excluding unpeer-reviewed conference papers, technical reports, informal patents, etc. (2) Exclude irrelevant literature: All documents must demonstrate substantial relevance to hydrogen storage research. We excluded documents that were completely unrelated or only marginally mentioned “hydrogen storage” in their abstracts or keywords without substantive technical content.
To enhance text mining capabilities, we employed Python for preprocessing the patent texts. This included extracting key terms, removing common patent phrases and stop words, and performing lemmatization. Additionally, taking into account the cyclical nature of technological evolution, we divided the thematic content evolution into three phases: the first phase from 2000 to 2007, the second from 2008 to 2016, and the third from 2017 to 2023. The number of patent terms before and after preprocessing for each phase is outlined in Table 1.
| Stage | Number of patents | Number of words before data cleaning | Number of words after data cleaning |
|---|---|---|---|
| Stage 1 (2000–2007) | 2530 | 713,469 | 84,634 |
| Stage 2 (2008–2016) | 4192 | 1,338,717 | 83,528 |
| Stage 3 (2017–2023) | 9452 | 3,064,802 | 214,176 |
| Total text sets | 16,174 | 5,116,988 | 382,338 |
3. Overview of Hydrogen Storage Technology Development Based on Bibliometrics
3.1. Temporal Analysis
Figure 2 illustrates the phased and fluctuating growth of literature in the hydrogen storage research domain. The global scholarly output on hydrogen storage can be categorized into three distinct phases:
- 1.
Emergence phase (2000–2007): During this period, the number of published papers increased annually. This growth can be attributed to the rising global energy demand around 2000 and the environmental pollution issues associated with exploiting and using traditional fossil fuels. Hydrogen energy, as a clean, efficient, and renewable energy source, gained significant international attention. Notably, the first Type IV hydrogen tank for storing compressed hydrogen at 700 bar (10,000 PSI) was introduced in 2001, and the first hydrogen fuel cell-powered locomotive appeared in Quebec, Canada, in 2002 [32].
- 2.
Exploration phase (2008–2016): This stage witnessed fluctuating growth in the publication of global hydrogen storage papers, influenced by technological development cycles and uncertainties in the policy environment.
- 3.
Development phase (2017–2023): Research on hydrogen storage has expanded significantly, especially after 2020. Amidst the vigorous emergence of a new wave of technological revolution and industrial transformation globally, emerging energy technologies like hydrogen energy are accelerating their iteration at an unprecedented pace [33]. Currently, over 130 countries and regions worldwide have announced carbon neutrality targets [34]. Nations such as Japan, South Korea, Germany, the United States, and China have formulated national strategies for hydrogen energy development, emphasizing policy support, funding, and talent cultivation for advancing hydrogen and fuel cell technologies. In this period, significant technological advancements were achieved in developing new hydrogen storage materials, optimizing efficient storage techniques, and integrating storage systems, thereby providing robust technical support for the industrialization of hydrogen energy.
3.2. National/Regional Analysis
Figure 3 displays the number and proportion of hydrogen storage-related publications from the top six countries between 2000 and 2023.
China has published far more papers in the field of hydrogen storage than any other country. From 2000 to 2019, the number of papers published generally showed a fluctuating upward trend, with the proportion remaining at around 30%. After 2020, the number of papers published increased rapidly, accounting for more than 35%. China promotes the synergy between technological breakthroughs and industrialization through systematic policy planning. In 2020, the “Energy Law of the People’s Republic of China (Draft for Comment)” included hydrogen energy in the energy system for the first time. In 2022, the “Medium and Long-Term Plan for the Development of the Hydrogen Energy Industry (2021–2035)” further clarified the hydrogen storage technology route [35]. It directly leads to a sharp increase in the number of published papers after 2020 and the continuous iteration of solid-state hydrogen storage material technology. The cycle life exceeds 3000 times, and the theoretical hydrogen storage density is as high as 7.6 wt.%. Policy-driven innovation in application scenarios has enabled China to achieve large-scale applications in equipment fields such as 70 MPa hydrogen storage cylinders. For instance, in the 2022 Beijing Winter Olympics, hydrogen served as the sole fuel for the Olympic torch, and hydrogen fuel cell vehicles became the main force in transportation, accelerating the process of technology verification and commercialization.
The number of papers published by the United States in the field of hydrogen storage shows a peak distribution trend. The number of related papers in the field of hydrogen storage in the United States continued to rise from 2000 to 2009, sharply declined from 2010 to 2020, and rebounded somewhat from 2021 to 2023. In 2003, the U.S. Department of Energy formulated a national template for hydrogen regulations and standards to meet the requirements of hydrogen technology infrastructure, which greatly enhanced the enthusiasm of researchers related to hydrogen storage [36]. The decline after 2010 might be related to the possible technological maturity as well as the beginning of the production and commercialization of the relevant technologies [37]. Although the “Hydrogen Energy Development Plan” of 2020 respectively proposed short-term, medium-term, and long-term technical development options for hydrogen storage, the industrialization process was restricted due to inter-state policy differences [38].
Around 2000, the number of papers published by Japan in the field of hydrogen storage was basically the same as that of China. However, the growth rate has been slow since then, resulting in a continuous decline in the proportion of papers. In recent years, it has only remained at around 6%. The conservatism of policies has led to slow technological iteration in Japan. Although the “Basic Strategy for Hydrogen Energy” in 2002 promoted the early layout of hydrogen storage technology, due to the high cost of hydrogen energy and the incomplete infrastructure, it has not shown a significant advantage in competition with other clean energy sources. This has led to doubts within Japan about the underlying logic and technical route of the “Basic Strategy for Hydrogen Energy” [39]. In June 2023, Japan revised its “Basic Hydrogen Energy Strategy”, which had been implemented for over 5 years. It was clearly stated that in the storage and transportation sector, the focus would be on the development of technologies such as efficient hydrogen liquefaction devices, hydrogen storage alloys, low-cost hydrogen carriers, and ammonia cracking.
Research in the field of hydrogen storage in India started relatively late, but it has developed rapidly [40]. In 2023, the number of papers published in India exceeded that of the United States. India has focused on low-cost hydrogen storage paths (such as steel hydrogen storage cylinders) through its policy latecomer advantage (National Hydrogen Mission 2021), achieving cost reduction at the expense of hydrogen storage density.
The research levels in the field of hydrogen storage in Germany and South Korea have tended to be consistent in recent years, both increasing from less than 10 papers in 2000 to over 100 papers in 2023. The reason for this is that Germany, starting from the goals of energy transition and carbon neutrality, regards the development of hydrogen energy as an important part of energy transition and a solution to the decarbonization problems in some sectors. However, due to the conservative nature of policies restricting scene innovation, the focus of the research mainly lies in the field of underground salt cavern hydrogen storage. South Korea, similar to Japan, imports 97% of its energy and has also chosen to shift from fossil fuels to hydrogen in its energy strategy. In the new hydrogen energy economic policy direction of South Korea in 2022, it is required to develop technologies such as ammonia cracking, hydrogen liquefaction, and liquid hydrogen storage for long-distance hydrogen transportation, which has driven the continuous deepening of research in related fields.
Overall, policy differences have led to significant disparities among countries in terms of resource allocation, technological paths, and industrialization rhythms. China’s scale effect and technological advantages formed through the dual-wheel drive of policy and market are reshaping the global hydrogen storage competition landscape. In contrast, the United States, Japan, and other countries are facing technological lags and industrialization bottlenecks due to policy focus shifts, resource dispersion, or conservatism. In the future, the competition in hydrogen storage technology will focus more on the contest of policy innovation and implementation efficiency.
3.3. Research Institutions Analysis
To assess the contributions of research institutions in hydrogen storage across six economies, we used VOSviewer software to analyze their impact, identifying key players in the field. Table 2 presents the top 10 institutions in terms of publication volume from 2000 to 2023. The number of publications ranges from 198 to 766, with total citations between 2671 and 25,012 and total link strength ranging from 24 to 346. Notably, seven of these top institutions are based in China, highlighting the country’s significant research investment in hydrogen storage. The Chinese Academy of Sciences tops the list in publication count (766), total citations (25,012), and total link strength (346). However, its average citations per paper rank only 24th globally, indicating a typical “large but not strong” characteristic in China’s research, which suggests room for improvement in international influence. The reasons for this are as follows: First, the scientific research evaluation system in China pays too much attention to the number of published papers and the impact factor of journals. This may lead to researchers pursuing short-term achievements while neglecting the quality, originality, and practical application value of scientific research results. Second, the depth of basic research is insufficient, and some studies lack disruptive innovation, making it difficult to attract widespread attention in the international academic community. Finally, in some international hydrogen energy research cooperation organizations and projects, China has difficulty playing a significant role in formulating international research rules and guiding research directions, which has affected the recognition and influence of China’s research achievements in the international community. To enhance the international influence of China’s scientific research achievements in the field of hydrogen energy, the following measures are suggested: First, increase investment in basic research and encourage innovative research. The second is to reform the scientific research evaluation system and guide scientific researchers to carry out research that is forward-looking and challenging. Third, deepen international cooperation and exchanges to enhance China’s say in the international hydrogen energy research field.
| Rank | Institution | Country | Publications | Total citations | Average citations | Total link strength |
|---|---|---|---|---|---|---|
| 1 | Chinese Academy of Sciences | China | 766 | 25,012 | 32.65 | 346 |
| 2 | Zhejiang University | China | 677 | 18,057 | 26.67 | 203 |
| 3 | Inner Mongolia University of Science | China | 328 | 3440 | 10.49 | 278 |
| 4 | Central Iron and Steel Research Institute | China | 288 | 3655 | 12.69 | 271 |
| 5 | AIST | Japan | 238 | 12,310 | 51.72 | 45 |
| 6 | Tohoku University | Japan | 226 | 10,125 | 44.80 | 54 |
| 7 | Indian Institute of Technology | India | 206 | 5551 | 26.95 | 31 |
| 8 | Nankai University | China | 203 | 6843 | 33.71 | 70 |
| 9 | Yanshan University | China | 202 | 3715 | 18.39 | 24 |
| 10 | Sichuan University | China | 198 | 2671 | 13.49 | 54 |
Conversely, Japan’s AIST and Tohoku University, despite fewer publications, have high average citations per paper, at 51.72 and 44.80, respectively, indicating high research quality and academic impact. Furthermore, an analysis of the types of research institutions reveals that in Asian countries like China, Japan, and South Korea, universities dominate the field, whereas in the United States and European countries like Germany and the UK, government research institutions and research groups play a leading role.
Figure 4 illustrates the collaboration network among the top 100 institutions by publication volume in hydrogen storage. Node size reflects publication volume, line thickness indicates collaboration strength, and node/line color denotes the publication year, with darker colors indicating earlier collaborations. Japanese institutions, such as Tokai University, Toyota Central R&D Labs, and Tohoku University, were early collaborators in hydrogen storage research, driven by Japan’s focus on national energy security due to its limited resources and high fossil fuel imports. In 2017, Japan released the first national hydrogen energy strategy [41].
Following Japan, the U.S. institutions like Caltech, Pacific Northwest National Laboratory, and the University of Michigan are prominent contributors. Although China has a high volume of publications, widespread institutional collaboration didn’t begin until after 2013. Recently, new Chinese institutions such as Jilin University, North China Electric Power University, and South China University of Technology have emerged, adding dynamism to the field.
New research institutions have also emerged in Australia, including Edith Cowan University, the University of New South Wales, and Curtin University, indicating Australia’s strategic positioning in the hydrogen market, leveraging its resource, industrial, and geographic advantages for economic growth.
4. Evolutionary Analysis of Hydrogen Storage Technology Based on LDA Model
4.1. Topic Extraction Results
An in-depth analysis of the text data, using integrated meanings and intrinsic connections of feature terms within each topic, yielded the detailed topic extraction results shown in Table 3. In the first phase (2000–2007), 13 technical topics were identified. The second phase (2008–2016) revealed 14 technical topics, while the third phase (2017–2023) identified 16 technical topics. Overall, the text corpus identified a total of 22 distinct technical topics.
| Stage | Topic mining results |
|---|---|
| Stage 1 | Topic 0: Nanoengineered solid solutions, Topic 1: Carbon nanotubes, Topic 2: Air filtration, Topic 3: Metal hydride stores hydrogen, Topic 4: Curing agent, Topic 5: Waste disposal, Topic 6: Connection technology for internal combustion engines, Topic 7: Liquid hydrogen delivery unit, Topic 8: Carbon fiber composites, Topic 9: Temperature control, Topic 10: Hydrogen storage cylinder base fixed protection device, Topic 11: Load the data storage program, Topic 12: High-pressure hydrogen storage injection device |
| Stage 2 | Topic 0: Carbon-based materials, Topic 1: Electrode material, Topic 2: Catalytic reactors, Topic 3: Elemental doping of solid solutions, Topic 4: Carbon capture and storage, Topic 5: Carbon fiber reinforced composites, Topic 6: Liquid hydrogen flow and heat transfer, Topic 7: Air filter, Topic 8: Connection technology for internal combustion engines, Topic 9: Modular design, Topic 10: Carbon fiber wound hydrogen storage cylinder, Topic 11: Sensor components, Topic 12: Hydrogen storage alloy material, Topic 13: Hydrogen storage cylinder base fixed protection device |
| Stage 3 | Topic 0: Composite hydrogen storage tank, Topic 1: Waste gas recovery unit, Topic 2: Carbon capture and storage, Topic 3: Heat exchanger, Topic 4: Air filter, Topic 5: Activated hydrogen charging and discharging water bath device, Topic 6: Organometallic frame material, Topic 7: Hydrogen storage metal oxide, Topic 8: Hydrogen storage bottle base fixed protection device, Topic 9: Pressure regulation monitoring system, Topic 10: Recovery of waste hydrogen storage alloy powder, Topic 11: Reactor, Topic 12: Preparation of composite hydrogen storage materials, Topic 13: Electrode material, Topic 14: Data transmission and capacity optimization methods, Topic 15: Air control valve |
| Total text sets | Topic 0: Carbon-based material, Topic 1: Air filter, Topic 2: Metal hydrides store hydrogen, Topic 3: Internal combustion engine connection technology, Topic 4: Carbon fiber composite, Topic 5: Temperature control device, Topic 6: Hydrogen storage bottle base fixed protection device, Topic 7: Electrode material, Topic 8: Catalytic reactor, Topic 9: Element doped solid solution, Topic 10: Carbon capture and storage, Topic 11: Hydrogen storage device sensor assembly, Topic 12: Hydrogen storage alloy material, Topic 13: Waste gas recovery unit, Topic 14: Heat exchanger, Topic 15: Organometallic frame material, Topic 16: Hydrogen storage metal oxide, Topic 17: Pressure regulation monitoring system, Topic 18: Recovery of waste hydrogen storage alloy powder, Topic 19: Composite hydrogen storage material, Topic 20: Data transmission and capacity optimization methods, Topic 21: Air control valve |
4.2. Analysis of Topic Popularity Evolution
Using the topic popularity evolution stream graph (Figure 5), we analyze the significance of various technological fields represented by key terms and their importance in current society and future trends.
First, in terms of growing popularity, topics related to emerging hydrogen storage materials, such as Topic 2: Metal hydrides, Topic 4: Carbon fiber composites, Topic 12: Hydrogen storage alloys, Topic 15: MOFs, Topic 16: Hydrogen storage metal oxides, and Topic 19: Composite hydrogen storage materials, have shown sustained increases in interest. Metal hydrides are particularly noted for their high hydrogen storage density and stability, making them a research hotspot. Hydrogen storage alloys, known for their rapid hydrogen absorption and release capabilities and excellent cyclability, are widely applied in hydrogen energy systems. MOFs, with their high surface area and tunable pore structures, demonstrate significant potential in gas storage. Hydrogen storage metal oxides enhance reversible hydrogen storage and release by optimizing composition and structure, advancing technology in fuel cells and similar fields.
The expanding applications of hydrogen energy, such as in fuel cell vehicles and distributed energy systems, are driving the demand for efficient hydrogen storage technologies. This burgeoning market provides ample opportunities for Topic 7: Electrode materials, primarily focusing on two fronts. One involves the exploration of new materials with superior catalytic activity and stability, such as transition metal nitrides, sulfides, and phosphides, to replace traditional precious metal electrodes, thereby reducing costs and enhancing performance. The other focuses on optimizing the hydrogen storage and electrochemical performance of electrode materials by altering their microstructure, crystal form, or surface properties.
With growing global attention to climate change, integrating Topic 10: Carbon capture and storage (CCS) with renewable energy forms complementary energy systems that boost energy efficiency and reduce greenhouse gas emissions. Topic 18, which deals with the recycling of scrap hydrogen storage alloy powders, addresses technical challenges like oxidation and high impurity content. Breakthroughs in vacuum induction melting and hydrometallurgical processes have improved recycling efficiency and product quality, thus increasing the topic’s appeal.
Progress in hydrogen storage technology imposes higher demands on heat exchanger performance, driving innovation in materials, structure, and processes for Topic 14: Heat exchangers. This innovation enhances their application value in hydrogen storage, drawing more attention and study. The rise in interest for Topic 20: Data transmission and capacity optimization methods and Topic 11: Sensor components in hydrogen storage devices reflects technological innovation and collaborative development across industry sectors.
Conversely, foundational technologies like Topic 3: Internal combustion engine linkage techniques, Topic 5: Temperature control devices, Topic 6: Hydrogen cylinder base protection devices, Topic 9: Element-doped solid solutions, Topic 13: Exhaust recovery devices, Topic 17: Pressure regulation monitoring systems, and Topic 21: Air control valves, though vital for early hydrogen storage development, are witnessing a gradual decline in interest. These establish a robust foundation for hydrogen storage technology, supporting the sustainable development of the hydrogen energy industry by ensuring safety, efficiency, and cost-effectiveness. As these technologies mature and enter commercialization, the focus shifts toward application dissemination and innovation, resulting in reduced emphasis on earlier foundational technologies. Meanwhile, research resources are redirected toward addressing challenges and bottlenecks in emerging technologies like efficient hydrogen storage materials and system integration.
Topics such as Topic 0: Carbon-based materials, Topic 1: Air filtration devices, and Topic 8: Catalytic reactors demonstrate cyclical growth patterns. Advances in material science have driven significant breakthroughs in developing new carbon-based hydrogen storage materials, such as graphene and carbon nanotubes, known for higher hydrogen storage density and faster adsorption/desorption rates, propelling carbon-based hydrogen storage technology. However, the development and application of new technologies require time and financial investment and face challenges around maturity and cost control, leading to fluctuations in topic interest.
4.3. Analysis of Topic Content Evolution
Figure 6 outlines the emerging trends in hydrogen storage technology based on thematic content evolution across different phases.
4.3.1. Development and Application of Hydrogen Storage Materials
- •
2000–2007: This foundational phase in hydrogen storage material research focused on metal hydrides, which store hydrogen by forming stable hydrides, offering high storage density, safety, reversibility, and cyclic stability [42]. Carbon nanotubes also emerged as a promising hydrogen storage material due to their unique pore structure and high surface area, capturing global research interest [43]. Carbon fiber composites were explored for hydrogen storage containers, with their superior mechanical properties and lightweight characteristics enabling new applications.
- •
2008–2016: This phase emphasized optimizing hydrogen storage materials. Carbon-based materials remained a critical focus, with significant advancements in carbon fiber-reinforced composites optimizing their composition and structure for improved container lightness and strength. Research on hydrogen storage alloys also progressed, with various alkaline, titanium, and magnesium alloy systems exhibiting distinct advantages in storage capacity, kinetic properties, and stability [44].
- •
2017–2023: A period marked by diversification and enhanced performance, solid-state technology progressed by integrating hydrogen storage powder materials into high-pressure composite storage tanks, enabling gas-solid hybrid storage [45]. This innovation improved container design in terms of weight and strength, enhancing performance and safety. New materials like MOFs and hydrogen-storage metal oxides emerged, offering unique storage mechanisms and advanced capabilities [46, 47].
- •
Overall, hydrogen storage generally shows a development trend from “gaseous state to multiphase state,” and the hydrogen storage methods suitable for different application scenarios also vary. Increasing the storage density of hydrogen and reducing the storage cost are the common development goals. From 2000 to 2007, the research on hydrogen storage materials was in the foundational stage. The research on basic materials such as metal hydrides, carbon nanotubes, and carbon fiber composites laid the foundation for subsequent development. From 2008 to 2016, focusing on performance optimization, significant progress was made in the research of carbon-based materials and hydrogen storage alloy materials, promoting the practical application of hydrogen storage technology. From 2017 to 2023, hydrogen storage technology has entered a stage of diversification and performance improvement. Solid-state hydrogen storage technology has driven the development of high-pressure composite hydrogen storage containers. New materials such as organic metal frame materials and hydrogen storage metal oxides have emerged, bringing new vitality and broad prospects to hydrogen storage technology.
4.3.2. System Integration and Protection Devices
- •
2000–2007: The focus was on integrating connection technologies for internal combustion engines [48] and methods for mounting hydrogen tanks [49] to ensure stability and efficiency. Standalone hydrogen concentration monitoring was limited by technology, unable to meet increasing safety and efficiency demands.
- •
2008–2016: The adoption of modular design in hydrogen systems improved maintainability and upgrade potential, incorporating sensors for better monitoring of concentration, temperature, and pressure parameters. This modularity facilitated cost-effective and timely system updates [50].
- •
2017–2023: The period saw advancements in smart and precise systems, with big data and AI technologies enhancing system data analysis capabilities for predicting and preventing performance bottlenecks [51]. Innovations in pressure regulation and emergency response systems improved safety and reliability while predictive maintenance techniques began shifting from reactive to proactive stances.
- •
Over time, the research focus on hydrogen storage system integration and protection devices has changed significantly: In the early stage (2000–2007), it mainly focused on basic connection and fixation technologies as well as simple hydrogen concentration monitoring to meet basic functional and safety requirements; between 2008 and 2016, the emphasis shifted toward modular design and the application of various active protection devices, aiming to enhance system maintainability, scalability, and the precision and real-time capability of safety monitoring. Recently (2017–2023), it has moved toward an intelligent and refined stage. By leveraging big data analysis and artificial intelligence technologies, it has achieved in-depth mining of system operation data and prediction of potential problems.
4.3.3. Thermal Management Technologies
- •
2000–2007: Focused on leveraging the high energy density of liquid hydrogen by controlling temperature below its boiling point to prevent vaporization.
- •
2008–2016: Emphasized improvements in thermal management strategies—such as developing new insulation materials, refining insulation structures, and enhancing cold and warm fluid integration—to boost efficiency. Ensuring the low-temperature adaptability of pumps and valves became crucial for stable liquid hydrogen flow [52].
- •
2017–2023: Research centered on heat exchangers for liquid hydrogen and coolant interactions, catering to diverse storage system scales [53]. Solid-state technologies emphasized stable bath-maintained conditions to mitigate material performance fluctuations [54].
- •
From the above analysis, it can be known that in the early stage (2000–2007), thermal management technology focused on the basic application of liquid hydrogen storage to ensure storage stability. From 2008 to 2016, the focus shifted to enhancing system performance, with an emphasis on flow and heat transfer technologies as well as the low-temperature operation of key components. Recently (2017–2023), emphasis has been placed on system integration and optimization. Research on heat exchangers and solid-state hydrogen storage water bath devices has become a hot topic, promoting diversified and integrated technological development.
4.3.4. Catalytic Reaction Technologies
- •
2000–2007: Initially focused on using titanium and vanadium transition metal catalysts in hydride systems to enhance hydrogen adsorption/desorption [55]. Precious metals like palladium and platinum were used to improve hydride reactions in chemical storage systems.
- •
2008–2016: Developed transition metal alloy catalysts (e.g., titanium–iron, vanadium–aluminum), resulting in optimized catalyst performance and improved cyclic stability while reducing costs through nanoprocessing techniques [56].
- •
2017–2023: Shifted toward efficient nonprecious metal catalysts like nickel, cobalt, and iron to maintain high activity while minimizing costs [57]. Two-dimensional materials like graphene and molybdenum disulfide showed great promise due to their unique electronic structures and high surface areas [58].
- •
The research focus of catalytic reaction technology in hydrogen storage applications has been continuously changing. In the early stage (2000–2007), traditional transition metal and precious metal catalysts were mainly used. Subsequently, efforts were made to develop multielement transition metal alloy catalysts and integrate nanotechnology to optimize their performance; recently (2017–2023), the focus has been on making breakthroughs in highly efficient nonprecious metal catalyst systems. Meanwhile, two-dimensional materials have become a new focal point due to their unique structural advantages.
4.3.5. Green Recycling Technologies
- •
2000–2007: Focused on exploring hydrogen storage materials, particularly metal hydrides, and regenerating storage alloys. Key objectives included enhancing material performance and addressing degradation issues [59] alongside the initial exploration of recycling and reuse technologies.
- •
2008–2016: Adoption of green recycling methods, with advancements in exhaust recovery devices and CCS technologies significantly reducing environmental impact. System optimization and catalyst recycling enhanced process efficiency [60].
- •
2017–2023: Advanced methods for recycling hydrogen storage alloy powders improved resource efficiency and reduced costs [61]. Optimized industrial exhaust recovery devices increased hydrogen extraction efficiency and purity, while CCS applications converted hydrogen and carbon dioxide into stored liquids, promoting recycling, reducing carbon emissions, and utilizing excess renewable energy.
- •
In conclusion, the relevant research on green circular technology from 2000 to 2007 focused on the improvement of basic material properties and the initial exploration of recycling. From 2008 to 2016, the focus shifted to the application of green circular technologies and the integration of technological optimization. From 2017 to 2023, the focus will be on advanced recovery technologies, optimization of industrial waste gas recovery, and large-scale application of CCS technology, promoting the green, efficient, and sustainable development of hydrogen storage technology.
5. Discussion
To understand the characteristics and underlying causes of the current status in the hydrogen storage field, the following analysis is based on the study’s findings.
5.1. Regional Perspectives
Variations exist between economies regarding hydrogen storage types and research stability. These differences are largely influenced by factors such as policy support, research infrastructures, and technological strategies [62]. The primary drivers for hydrogen energy development include reducing carbon emissions, ensuring energy security, and fostering economic growth [63]. Since the beginning of the 21st century, countries have actively pursued hydrogen storage research. However, as research deepens, issues such as the diversity of technological paths, economic considerations, safety assurance, and policy standards have sparked global debates, leading to fluctuations in hydrogen storage research at various stages. In terms of research stability, the differences among countries in terms of unique scientific research environments, strategic positioning, cultural values, and the degree of international cooperation have led to variations in the stability of hydrogen storage research among countries. Research institutions in the United States, Japan, and Europe may, due to long-term scientific research accumulation and policy support, be more inclined to conduct in-depth exploration in specific technical fields, thus forming stable research directions and profound research foundations. As a country with a rapidly developing scientific research system, China’s research may exhibit more extensive and diverse characteristics, aiming to respond quickly to national demands and promote innovation. This diversity may, to some extent, be interpreted as “lacking focus and shallow depth,” but in fact, it also reflects the flexibility and adaptability of China’s scientific research system. Overall, the differences demonstrated by various economies in the field of hydrogen storage research stem from the interweaving of complex and diverse factors. To promote the development of this field more effectively, scholars urgently need to deeply explore how to flexibly apply and integrate the most cutting-edge technological achievements based on the specific circumstances of each region so as to promote cross-economic cooperation and win–win results and jointly move toward a more sustainable future.
5.2. Technical Perspectives
Current hydrogen storage methods are categorized into high-pressure gaseous storage, liquid storage, and solid-state storage.
High-pressure gaseous hydrogen storage technology is currently one of the more widely used hydrogen storage technologies. At present, most hydrogen storage containers are designed with carbon fiber wound steel or aluminum inner liners to ensure the mechanical strength of the containers [64]. However, it is unlikely to form a large-scale production technology with controllable costs in the short term. Liquid hydrogen storage technology has received extensive attention due to its large hydrogen storage capacity. It achieves hydrogen storage by liquefying hydrogen or using liquid hydrogen carriers. However, the liquid hydrogen storage system is expensive and has strict environmental requirements, and there is a risk of evaporation leakage. Solid-state hydrogen storage not only solves the problems of safety and hydrogen storage density but also can be applied on a large scale [65]. However, it has problems such as the expensive preparation of adsorption materials, high hydrogen absorption, and release temperatures, and slow hydrogen charging and releasing speeds. Solid-state hydrogen storage materials mainly include organic porous hydrogen storage materials, metal-based hydrogen storage materials, and coordination hydride hydrogen storage materials, etc. Each type of hydrogen storage material has its own characteristics. Among them, the MOFs have a very large specific surface area and can provide multiple adsorption sites for hydrogen. By regulating the pores, the hydrogen storage process can be precisely controlled. However, MOFs materials are prone to being affected by oxygen and water vapor in the environment, and the reaction temperature cannot be controlled at room temperature [66]. The resolution of these issues will facilitate the early entry of the MOFs material hydrogen storage system into the industrialization stage. Meanwhile, graphene, as a kind of two-dimensional structured carbon material with good performance, has the advantages of high adsorption capacity and recyclability and has great development potential in the field of hydrogen storage. However, physical adsorption for hydrogen storage by graphene has significant limitations. It can only store hydrogen in the form of molecular hydrogen on the surface of graphene at relatively low temperatures. Therefore, improving the adsorption capacity of graphene for hydrogen molecules by doping other elements (alkali metals, alkaline earth metals, nonmetals, etc.) is a future research direction. Metal-based hydrogen storage materials have a relatively high hydrogen storage density. After modification, they can adsorb and release hydrogen under relatively mild conditions. However, its further development is restricted by its own thermodynamic and kinetic properties, as well as its relatively high cost. Coordination hydride hydrogen storage materials have attracted the attention of scholars due to their high quality and high volume hydrogen storage density. However, the disadvantages, such as poor kinetic performance and irreversible hydrogen storage process, have greatly affected the application [67].
6. Conclusion and Outlook
6.1. Conclusion
- 1.
The evolution in the number of hydrogen storage-related papers reflects research progression and development speed, identifiable in three stages: the emergence phase (2000–2007), marked by increasing interest due to environmental imperatives and initial research investments; the exploration phase (2008–2016), characterized by fluctuating growth influenced by technological cycles and policy changes; and the development phase (2017–2023), seeing significant advancements driven by global carbon neutrality goals and national hydrogen strategies, leading to breakthroughs in materials, efficiency, and system integration.
- 2.
Research trends in leading countries highlight the competitive landscape and future directions for global hydrogen storage technologies. Between 2000 and 2023, China’s research output distinguished itself with over a third of the published papers, accelerating post-2020 due to policy and market drivers. The United States showed peaks in interest, indicating shifting research focuses. Though Japan began its efforts earlier, its growth has been steady, while India has shown rapid advancements later on. Germany and South Korea continue to enhance their research contributions to the field.
- 3.
From 2000 to 2023, analysis of research institution contributions revealed that Chinese institutions produce a high volume of papers but with lower average citations, suggesting large-scale research with room for greater impact. Japanese and Korean universities stand out for academic influence, while Europe and the United States lean on government and research organizations. Collaboration timelines show Japan leading early research partnerships, followed by the United States, with China rapidly expanding its collaborations recently. Australia, leveraging its resources, is joining the hydrogen research landscape, marking hydrogen as a strategic focus for many nations.
- 4.
In terms of topic popularity, new hydrogen storage materials such as metal hydrides, storage alloys, MOFs, and hydrogen metal oxides are gaining attention, underscoring their current and future relevance. The melding of CCS technologies enhances hydrogen storage application potential. As research progresses and commercialization grows, interest in foundational devices and system integration is waning, while carbon-based materials, air filtration, and catalytic reactors show fluctuating growth.
- 5.
Analyzing topic evolution reveals a shift in hydrogen storage materials from fundamental research to performance optimization and diversification. Research on system integration and protective devices has moved from basic setups to intelligent systems incorporating sensors and big data. Thermal management techniques are advancing, notably in liquid and solid-state hydrogen storage. Catalytic technology trends shift from noble metal to efficient nonprecious metal catalysts, with two-dimensional materials like graphene offering considerable application potential. Progress in green recycling significantly enhances resource efficiency, supporting eco-friendly hydrogen applications.
6.2. Research Deficiencies and Prospects
- 1.
Literature databases and patent databases depend on the inclusion criteria of the databases and the precision of keyword indexing. This may result in an insufficiently comprehensive aggregation of research findings, as well as potential imbalances in the coverage and representativeness of studies across different countries. Consequently, future research should transcend the reliance on a single database by integrating multisource data and incorporating qualitative assessments from domain experts to construct a more robust and comprehensive research framework.
- 2.
Although this study initially delineated the overall evolution of global hydrogen storage technologies, the constraints of research scope and data accessibility precluded a deeper analysis of the development disparities in hydrogen storage technologies across specific countries and regions. Future research could concentrate on leading nations or emerging markets within the global hydrogen energy domain, elucidating regional variations in technological trajectories through cross-national comparative analyses. Additionally, case studies targeting specific countries or regions could be conducted to thoroughly investigate the driving mechanisms of policy, economic, and social factors influencing the advancement of hydrogen storage technology.
- 3.
This study focuses on analyzing technological evolution at the macro level and lacks an in-depth exploration of different subfields of hydrogen storage technology. In the future, constructing technological evolution models could help reveal the life cycle stages and key influencing factors for different technological categories.
Conflicts of Interest
The authors declare no conflicts of interest.
Author Contributions
Huiyang Wang: data curation, visualization, writing–original draft. Jianhua Liu: conceptualization, supervision, writing–review and editing. Yubing Zhao: data curation, methodology. Tianle Shi: formal analysis, software, writing–review and editing. Liangchao Huang: investigation, writing–review and editing.
Funding
This work was funded by the Henan Center for Outstanding Overseas Scientists “Green Low-Carbon Technology and Energy Transition” (Grant GZS2024001) and the Soft Science Major Project of Henan Province (Grant 242400411004).
Open Research
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
