ANALYSIS OF THE SCIENTIFIC PRODUCTION ON THE GREEN HYDROGEN THEME PUBLISHED IN SCIENTIFIC JOURNALS INDEXED BY EBSCO

Purpose: to investigate the behavior and tendency of the formation of social networks of the scientific production on the Green Hydrogen theme published in scientific journals indexed in EBSCO. Theoretical framework: the theme of green hydrogen has been gaining attention and strength in the current context of global energy transition, as it is a clean alternative for generating energy for electricity, industry, heating, and transport sectors, and, in replacing fuels to carbon base, influencing sustainable development. Method: bibliometric analysis techniques were used, and predominantly social network analysis (SAR) through one-mode and two-mode network analysis. Results and conclusion: evolution of the theme in academia; weak ties in co-authorship and institutional networks; relevance of China and its originating institutions in the scientific production of the subject investigated; the most central keywords were: hydrogen, green hydrogen, renewable energy, production and hydrogen production; and the most fruitful themes were: production, sustainability, energy and carbon emissions. It concludes with a macro and contemporary view of the theme of green hydrogen in the international literary academic field. Research implications: the present study contributed to a better understanding and understanding of the formation of collaboration networks of the actors involved in the process of building international scientific knowledge, and, by verifying that green hydrogen presents opportunities for economic growth and job creation, this research also contributes to creating an entrepreneurial and social research agenda.


INTRODUCTION
Given the increase in population and energy demand worldwide, alternative methods have been adopted for the production of hydrogen as a source of clean energy (Andrade, Andrade, Alegre & Bezerra, 2022).This energy offers an alternative energy source due to its high energy content and no emissions to the environment (Dawood, anda & Shafiullah, 2020;Du, Shen, Chai, Nie, Shan & Zhou, 2022;Camargo, Comas, Escorcia, Alviz-Meza, Caballero & Portnoy, 2023).And hydrogen energy is a new source of clean, efficient, safe and sustainable energy.With high energy density and reproducibility, it is considered one of the most promising energy sources.Countries have incorporated the development and use of hydrogen energy into the national strategic energy layout.Hydrogen production technology is one of the key technologies for developing and using hydrogen energy (Zheng, 2021).
Thus, hydrogen can be produced from many renewable and non-renewable raw materials and technological paths, with widely varying greenhouse gas emissions.For hydrogen to play a role in future low-carbon energy systems, it must be demonstrated that it has sufficiently low carbon emissions (Abad & Dodds, 2020;Ali, Bennui, Chowdhury & Techato, 2022).Given the above, it is emphasized that fuel cells and other hydrogen-based technologies are increasingly seen as a key pillar of global decarbonization efforts (Lindner, 2022).
At present, most of the hydrogen is produced by the steam reforming of methane into natural gas (gray hydrogen), with high carbon dioxide emissions.Increasingly, many propose the use of carbon capture and storage to reduce these emissions, producing so-called "blue hydrogen", often promoted as low-emission.Hydrogen can also be generated by electrolysis of water.When that electricity is produced by a clean, renewable source such as hydroelectric, wind or solar, hydrogen is called "green hydrogen" (Howarth & Jacobson, 2021), that is, green hydrogen is interchangeably referred to as renewable hydrogen (Sgarbossa, Arena, Tang & Peron, 2023).
That said, the global shift is towards decarbonization, i.e. shifting to decarbonized fuels (mainly green hydrogen, decarbonized electricity and bioenergy) as the three pillars of the decarbonization strategy.Of these three pillars, it is highlighted, and at the same time a substantial boost is triggered in the hydrogen industry (Vats & Mathur, 2022).Hydrogen has been considered a clean energy carrier (Yan, He & Fan, 2023), while generating electricity through fuel cells without carbon dioxide emissions; however, at the current stage, most of the hydrogen is produced by a steam reforming of methane, emitting carbon dioxide as a byproduct, together (Harichandan, Kar, Bansal, Mishra, Balathanigaimani & Dash, 2022).
In response to the global challenge of climate change, 136 countries, accounting for 90 percent of global GDP and 85 percent of the population, have already set zero-carbon emission targets, requiring decarbonization of all sectors of the economy.Thus, it is noted that green hydrogen produced from renewable energy sources (Thapa, Neupane, Yang & Lee, 2021), poses little or no threat to the environment and increasing its production will support decarbonization targets (Raman, Nair, Prakash, Patwardhan & Nedungadi, 2022).In other words, a green hydrogen production system consisting of water electrolysis and a renewable energy plant must be expanded to prepare for the future hydrogen society (Lee, Choe, Lee, Gu, Cho, Won & Lim, 2022).
It is noted that, clean hydrogen (Huang & Liu, 2020), is classified as "green" when it is produced using water electrolysis powered by low-carbon renewable electricity (Pimm, Cockerill & Gale, 2021).That said, the theme of green hydrogen emerges, which has been gaining attention and strength in the current global energy transition framework, for being a clean alternative for energy generation for electricity, industry, heating, and transport sectors (Guarieiro et al., 2022), and, in the replacement of carbon-based fuels, influencing sustainable development (Genovese, Blekhman, Dray & Fragiacomo, 2020).
It can thus be understood that green hydrogen is an emerging area of study (Raman et al., 2022), as a result of being observed as a global trend of research around hydrogen as an essential component for achieving clean energy (Camargo et al., 2023).However, no studies have been found that investigate research trends and the potential of green hydrogen, bringing by way of a new perspective and analysis as is the case of Social Network Analysis (ARS), although a literature review reveals that previous authors had conducted bibliometric studies on green hydrogen (Zheng, 2021;Gevaert & Pause, 2022;Raman et al., 2022;Vallejos-Romero et al., 2023).It complements itself by stating that the theme of green hydrogen is still embryonic as far as studies on the subject of hydrogen and clean energy in global terms are concerned (Camargo et al., 2023).
Therefore, this study emphasizes the research question that will guide this research: What is the behavior and trend of the formation of social networks of the scientific production of the Green Hydrogen theme disclosed in the indexed scientific journals at EBSCO?Therefore, the objective of the aforementioned study is: to investigate the behavior and the tendency of the formation of social networks in the scientific production of the Green Hydrogen theme disclosed in the scientific periodicals indexed by the EBSCO.
The justification for the use of the EBSCO international database is that it is important and legitimized in academia (Campanario & Santos, 2011;Popadiuk & Silva, 2018).That is, it is focused that EBSCO is a database that has been in existence for 70 years (Job, 2018), and that indexes around 8,000 full-text journals, including almost 7,000 peer-reviewed scientific journals, as well as being consolidated by the global scientific community (Soykan & Uzunboylu, 2015;Bauer, Sohn, Oliveira & Vogel, 2020).It should also be noted that the international EBSCO platform has free access for consultations (Batista, Reis Neto, Pardini & Goulart, 2021), influencing its prominence in studies related to bibliometry and ARS (Ribeiro & Corrêa, 2022).
This study contributes to the scientific literature by investigating the scientific production of research on green hydrogen, from the perspective of ARS, evidencing the social networks one-mode and two-mode of the actors responsible for the diffusion and development of said theme in academia, thus contributing to its widening and strengthening and to its greater maturation of its information and scientific knowledge.It is also hoped that the aforementioned research, besides contributing to the growth of the aforementioned theme in the academic world, will provide opportunities for the emergence of new paths for future studies, in this matter.
In short, this research expands and contributes to the promotion of the current understanding and understanding on the theme of green hydrogen for academics and professionals in the field of Administration and related, focusing especially its scientific production in light of the formation of the social networks one-mode and two-mode of the actors responsible for the creation of knowledge, dissemination, dissemination and socialization of the said theme in academia, thus providing an agenda of studies for future research.

GREEN HYDROGEN
Hydrogen production is mainly divided into three color codes according to cleanliness: gray, blue and green.Gray hydrogen is produced mainly by reforming fossil fuels, which will generate a large number of industrial waste gases and cause severe environmental pollution.The process of producing blue hydrogen is an improvement in the production of gray hydrogen, which incorporates carbon capture and storage technology, but still has certain carbon emissions.However, green hydrogen is considered a form of clean energy with a low-carbon production method, which is carried out mainly by the electrolysis of water using renewable energy.In short, green hydrogen basically does not generate any environmental pollution in the whole production process.The transition from gray or blue hydrogen to green hydrogen is becoming the current idea for the development of hydrogen production, which is often seen as an important carrier of energy in a decarbonized future (Howarth & Jacobson, 2021;Dong, Yang, Yu, Daiyan & Amal, 2022;Guarieiro et al., 2022;Panah, Bornapour, Cui & Guerrero, 2022;Li, Zhang, Ou & Ma, 2022).
In this panorama, decarbonization is highlighted, which is considered as a priority that needs to be supported by inclusive and democratic processes (Campos, Brito, Souza, Santino, Luz & Pera, 2022).In this scenario, it is noted that the global context suggests the need to move towards decarbonization as part of international climate change commitments, promoting clean energy and social welfare actions, and the green hydrogen market is a global trend because it responds to the needs for the reach of this mentioned clean energy (Rodríguez, Flores, Vera & Quiñones, 2022).
Thus, it can be seen that green hydrogen is the first molecule of fundamental importance in post-covid, for a renewable economy of the 21st century (Satinover et al., 2021).Thus, green hydrogen is seen as a precursor to different synthetic types of fuels and green chemicals such as liquid fuels: kerosene, gasoline, diesel, methanol; energy for gasoline such as methane; or energy for chemicals such as ammonia, thus offering synthetic green energy with significant impacts on sustainability compared to current fossil fuels (Hamukoshi, Mama, Shimanda & Shafudah, 2022).
Thus, green hydrogen can be conceptualized as a fuel, and consequently a source of renewable energy (Guarieiro et al., 2022), thus providing hydrogen demands in an economically and environmentally sound manner (Oskouei & Mehrjerdi, 2022), thus enabling the promotion of sustainable energy improvement (Guarieiro et al., 2022).However, unless alternatives for the supply of green hydrogen through infrastructure and imports are available at a lower cost, electrolyzed hydrogen may require long-term subsidies (George, Müller, Winkler & Ragwitz, 2022).
Anticipating a future market for green hydrogen, international standards are beginning to be discussed by national and international standardization organizations and policymakers.Several approaches have been adopted to define green hydrogen and guarantees of origin.They range on whether green hydrogen should be produced from renewable energy, on the limits of the carbon accounting system, on the emission limits in which hydrogen is considered green, and on what raw materials and production technologies are included in the scheme.Decisions on these factors are often influenced by other national and international standards and the legal structure in which the green hydrogen supply chain operates (Abad & Dodds, 2020).
Here an addendum is made, to glimpse that Japan, USA and China are the leaders in the development of green hydrogen technologies in the world (Marocco, Gandiglio, Audisio & Santarelli, 2023).It should be noted that China is the main research country in the field of green hydrogen production technology, but its wide-ranging influence is not as great as that of the United States.In addition to China, the United States and Japan, Germany and South Korea are also seen as nations involved in green hydrogen production, from basic research to product application (Zheng, 2021).
However, most existing green hydrogen initiatives are in Europe (Abad & Dodds, 2020).As a result, policy-making outcomes in the US, Europe and China will have a profound impact on green hydrogen production and storage over the next five years.If these policies are implemented, these countries will be responsible for two-thirds of this growth, and Asia will account for the most significant part and become the second largest producer in the world, with the collaboration of China and also India (Raman et al., 2022).It can be understood that Asia and Europe lead research on green hydrogen in the world (Vallejos-Romero et al., 2023).
Therefore, it is focused that the European Union recently presented to the European Green Deal an ambitious goal of making Europe climate neutral in 2050, reducing its carbon emissions by 80% to 90%, meaning the almost complete decarbonization of energy generation through high levels of renewable energy (Zuben et al., 2022).From this document, the Hydrogen Strategy was launched as a path to a climate-neutral Europe (Díaz-Abad, Fernández-Mancebo, Rodrigo & Lobato, 2022).
In the context of Brazil, this country has a great chance of becoming a market leader in green hydrogen, because the diversity of the Brazilian renewable energy matrix (wind, solar energy, hydroelectric and biofuels) creates opportunities for several short and medium term projects, including production through mature technologies, such as water electrolysis and renewable electricity use, as well as, storage and distribution of green hydrogen context, influencing in a greater sustainable development (Guarieiro et al., 2022).
Still with regard to Brazil, it is said that recently there was a green hydrogen agreement signed between the governments of Germany and Brazil.This agreement was made present because the government and companies in Germany are investing resources in promoting the generation and storage of Brazilian green hydrogen.These investments include knowledge and technology transfer, improvement of scientific research, economic analysis, regulatory decision-making, and technological support.As a result, the State of Minas Gerais launched the Hydrogen Mines program, and the State of Ceará received about US$8 million to build the first green hydrogen plant in Brazil (Almada, Borges & Ferreira, 2022).Here it complements itself by contemplating that Brazil has committed to reduce greenhouse gas emissions by 37% by 2025, and consequently a reduction of 43% by 2030 (Asencios, 2022).
In short, green hydrogen is a field of scientific research in growth, with the major part of the studies aligned with clean energy and climate action.With more than 200 hydrogen projects in the value chain, the focus in the future is on a green hydrogen economy at a competitive target price with a cost to adopt en masse, however, green hydrogen is still not close to being cost competitive for electricity or mobility purposes.Finally, it is found that green hydrogen plays a role in achieving a highly electrified net zero economy and, the potential use of green hydrogen will depend on more to foster its compatibility with the environment (Oliveira, Beswick & Yan, 2021;Raman et al., 2022).

METHODOLOGICAL PROCEDURES
The aim of this study was to investigate the behavior and tendency of the formation of social networks in the scientific production of the Green Hydrogen theme, as reported in the scientific journals indexed by the EBSCO.To this end, the techniques of Social Network Analysis were used from the one-mode and two-mode perspectives.It is stressed that, to be able to enter ARS (Favaretto & Francisco, 2017), and concomitantly create their social networks matrices one-mode and two-mode (Pineda-Ospina, 2019;Ribeiro, 2021), it was necessary to use bibliometrics in the first stage of this research (Guimarães, Motta, Farias, Kimura, Quintella & Carneiro, 2018;Santos & Reis, 2021), and, such a choice has made this method popular and rigorous to explore and investigate scientific data, thus allowing to unveil the evolutionary nuances (Donthu, Kumar, Mukherjee, Pandey & Lim, 2021).
ARS has important elements to better understand it, that is, ways to verify the structure and interactions of a cooperation network, among which are highlighted the following: the nodes that are the positions that define the relative locations of the actors in the network structure.The bonds that are placed by the actors in a given panorama, thus defining patterns of relationship and interaction dynamics.The degree of network density that is understood as the set of actors' connections.And the centralities, which are properties of the most used networks, which make the characteristics relevant to the relevance or visibility of a given actor emerge in a collaboration network (Williams dos Santos & Farias Filho, 2016;Allegretti, Moysés, Werneck, Quandt & Moysés, 2018;Farias & Carmo, 2021;Severiano Junior, Cunha, Zouain & Gonçalves, 2021;Ribeiro, 2022).
Among these centralities, one distinguishes the degree centrality that is the property that glimpses the relational activity of an actor (Balestrin, Verschoore & Reyes Junior, 2010), by measuring the number of interactions of each of these actors in a graph (Alves, Pavanelli & Oliveira, 2014), that is, the number of partnerships in the creation and publication of the scientific study (Pessoa Araújo, Mendes, Gomes, Coelho, Vinícius & Brito 2017).And the centrality of intermediation that is the property that emphasizes the potential of intermediation of the actors, by measuring how much a given actor acts as north, thus collaborating to widen the links of the multiple actors of the social network (Bataglin, Smemorbon, Carvalho & Porsse, 2021).Here it is worth noting that in this study, it was chosen to highlight the centrality of degree, and such a choice is presented by this structural connection being the most common and most direct measure of centrality (Cunha & Piccoli, 2017).
In general, ARS can be: one-mode (1 mode) and or two-mode (2 modes).The network of 1 mode is characterized when actors of a social network have connections with other actors of the same division, as, for example: a social network composed only of authors.And the network of 2 modes is individualized when its members have interactions with actors of other categories, such as, for example: authors and their respective Higher Education Institutions (HEIs) of origin.Having said that, in Brazil, it is infrequent to discover scientific studies that analyzed networks in 2 ways.To put it simply, the research of social networks in one way far outweighs, in quantity, the studies of social networks in two ways worldwide.In short, in the scientific literature, the number of scientific works evidenced about social networks in 2 ways is about 80% lower than in 1 mode (Tomaél & Marteleto, 2013).
The research community has highlighted all the articles of the scientific journals available in the international EBSCO database.In the scientific literature, research using fully the EBSCO database was published (Ribeiro, 2019;Ribeiro, 2020;Bauer et al., 2020), corroborating, ratifying and legitimizing that the said international database is feasible for bibliometric-focused research (first stage of this study), and at the same time for research that puts ARS in prominence.
The process of selecting the sample of articles took place in the following way: a) choice of the keywords applied in the search filter of the databases; b) collection of the data in the EBSCO database; c) search for the keywords in the titles, abstracts and keywords of the articles; d) definition of the sample, by reading the titles and/or abstracts of each article.In the EBSCO database, a filter with the keywords 'green hydrogen' was placed.These keywords were searched in the title, abstract and keywords of each article, not simultaneously, thus allowing all articles on the subject subject matter of this research to be identified and related.
With this, the sample consisted of 53 articles, in a time cut from 2006 to 2023.The analyzes of these 53 academic works were carried out using the ARS indicators: (i) two-mode social network of the publication periods and articles; (ii) co-authoring networks; (iii) two-mode social network of academic journals and authors; (iv) collaboration network of institutions; (v) collaboration network of countries; (vi) social networks of keywords; and (vii) social network of authors and themes.
This data and information was taken from the respective articles, and, a posteriori, the procedures for measuring symmetric and asymmetric matrices were initiated, and then the graphical visualization of the actors' respective one-mode and two-mode collaborative networks.Table 1 glimpses the start and end dates of each initiative.Bibliometric data were measured using Bibexcel and Microsoft Excel 2007 software; and ARS indicators were measured using theUCINET andUCINET 2007 software.

ANALYSIS AND DISCUSSION OF RESULTS
This section will cover the analysis and discussion of the results of the 53 studies identified in this research.Figure 1 visualizes the two-mode social network of the six publication periods of the articles on green hydrogen and the 53 articles identified in this research on the aforementioned theme.Looking at Figure 1, it can be seen that the theme green hydrogen began to be disclosed in 2006, and since then, it only appears again in international publications in the period of 2015, however, from 2020 (with three studies evidenced), it begins to have a rise, that is, in 2021 it was found that there were 16 scientific researches published on the theme now investigated, and in 2022 it reached its peak with 30 studies published in the scientific periodicals indexed in EBSCO.Reference is made here to an article published in 2023.In general, there is a growing trend of publications on the theme green hydrogen, especially in the two most recent years finalized, namely 2021 and 2022, where the growth of the publication was multiple, making it emerging in the global scientific literature (Raman et al., 2022).
Figure 2 shows the coauthoring networks, which manifests 224 nodes and 1,090 loops.Figure 2 brings to the table the network co-authored by the 224 researchers, which gives rise to a density of 0.0225, equivalent to 2.25% of the interactions carried out between the authors, meaning that the aforementioned network of collaboration has low density, providing weak ties (Williams dos Santos & Farias Filho, 2016).Such a finding may be due to the theme of green hydrogen is in a phase of recent evolution (Zuben et al., 2022), in the global academic environment, thus enabling and impacting in its embryonic maturation and, consequently, its consolidation in a more macro way through other scholars who wish to embark on and better understand the dynamics and importance (Satinover et al., 2021), that the aforementioned theme has for the world scientific literature.
However, as noted in Figure 1, the subject has a growth trend (Rodríguez, Flores, Vera & Quiñones, 2022), and as a result, its maturation and legitimacy in the global academic environment tends to become broader and more robust, influencing a posteriori in a more prominent network of authors' cooperation and, concomitantly, with stronger ties.However, it is useful to inform the authors who have distinguished themselves in the proficiency of international studies on green hydrogen, although the aforementioned authors do not influence and thus do not stand out in the centralities of the co-authoring network, they are: Bai, Yueyang; Jia, Yuke; Hong, Jinglan; Huang, Jingsi; Li, Wei; Ren, Ke; Wu, Xiangyu; Zhai, Yijie; Zhang, Tianzuo, all with two publications, and natives of IES of China, which makes it ascertain the importance of these authors and their IES of China in the dissemination, dissemination and socialization of the theme of green hydrogen for the global scientific panorama (Zheng, 2021).
Figure 3 contemplates the two-mode social network of 13 scientific journals and 224 authors.The Journal of Cleaner Production was the most sought after by the authors to publish their respective studies on green hydrogen, that is, 159 researchers, which is equivalent to approximately 71% of the amount of the 224 scholars identified in this academic work.Next, the journal Energy Policy is published with 21 researchers who searched for this referred international periodical to highlight their findings and contributions on the theme now investigated in this research.Such international scientific journals are considered the most influential and relevant TOPs journals for the dissemination of academic articles on green hydrogen (Raman et al., 2022).The aforementioned academic journals are also among the most prominent in topics that have a strong intersection with hydrogen (Camargo et al., 2023), particularly with the "green", as is the case of the energy transition (Harichandan et al., 2022), which is also present and highlighted in Figures 6 and 7 of this study.
Figure 4 glimpses the institutions' collaborative networks, contemplating 91 knots and 154 ties.4 represent the countries that have a scale, proficiency, initiative and relevance in terms of the scientific production of articles on the subject of green hydrogen, and, at the same time, are essential and prominent in actions to disseminate and disseminate green hydrogen technologies and procedures for the expansion, robustness and consolidation of clean energy in the world (Zheng, 2021;Almada, Borges & Ferreira, 2022;Raman et al., 2022;Marocco et al ., 2023;Vallejos-Romero et al., 2023) Figure 5 discloses the countries' cooperation networks, which are made up of 31 nodes and 68 links.The results show the prominence of China as the country with the highest number of publications (Camargo et al., 2023), that is, 13 studies released, and, concomitantly, being the most central nation in terms of scientific research cooperation with other countries, in particular with Canada, as can be verified by the strength bond between the two countries.The focus was also on nations: Germany (with nine studies published), the United Kingdom (with five articles published), the USA and Italy (both with four researches), Australia, Canada, South Korea and Spain, all with three publications each.These results are in line with the findings of research that highlighted green hydrogen (Abad & Dodds, 2020;Díaz-Abad, Fernández-Mancebo, Rodrigo & Lobato, 2022;Guarieiro et al., 2022;Zuben et al., 2022).
Here is a highlight to the scientific production studies of the theme green hydrogen (Zheng, 2021;Gevaert & Pause, 2022;Raman et al., 2022;Vallejos-Romero et al., 2023) that also addressed, and, concomitantly, emphasized in their respective results and contributions, the said countries as the largest and most important, not only in the scientific production of studies on the theme now investigated, but also, in actions regarding the proliferation and dissemination of procedures and technological processes of green hydrogen in the public and private policies of institutions in North America, Asia and Europe, especially those that were highlighted in Figure 5 of this research.
Figure 6 makes the social networks emerge from the keywords, and from right to left the aferi network 247 nodes and 1432 loops.And, from left to right, you have the social network that was in relief, and the aforementioned network brings 169 nodes and 1090 links.It should be noted that the nodes are the keywords and their sizes are proportional to their frequency in the dataset investigated, and, the bonds simulate the interactions between the keywords (Guimarães et al., 2018).It should also be noted that the 247 occurrences of keywords are unique, because the criterion of not distinguishing between upper and lower case letters was only supported, and the words in the singular and plural were kept different (Favaretto & Francisco, 2017;Ribeiro, 2022).Figure 6 (from right to left) includes a social network with 247 keywords, and highlights a social network of more integrated keywords, that is, a cluster formed with 169 keywords (from left to right), corresponding to approximately 68% of the total of 247 keywords.In the conglomerate that was highlighted in Figure 6, the investigation of keywords identified 13 important research points for future discussions (Camargo et al., 2023), were: hydrogen, green hydrogen, renewable energy, production, hydrogen production, economic analysis, life cycle assessment, energy transition, cascade hydropower stations, energy storage, electric vehicles, CO2 emissions, and carbon emissions.Therefore, these keywords that have been highlighted can be considered as those that occupy positions of central importance and prominence in the thematic and theoretical knowledge flow of the subject now under investigation in this research (Favaretto & Francisco, 2017;Ribeiro, 2022).These findings are similarly corroborated in the research of: Zheng ( 2021).
An addendum is made here stating that the keyword green hydrogen was focused on the aforementioned figure because this was the keyword used for the search and selection of articles on green hydrogen in this research, and, therefore, its relief was a condition sine qua non of the search action of these scientific studies.The visualization of the keywords in relief in Figure 6 is complemented by verifying their most selected connections, i.e., the keywords "partners" that most connected with them, are: green hydrogen with renewable energy; green hydrogen with CO2 emissions; hydrogen production with hydrogen; hydrogen production with hydrogen; and "partners" with life cycle assessment, in all cases with two connections between the keywords "partners".Meeting what was propagated and visualized through Figure 6, and, a posteriori, analyzing Figure 7, it was found that the subjects, which remained as the most central of this study, and concomitantly relate to the theme "umbrella" green hydrogen, and concomitantly call the attention of the authors to research and later publish are: production, and such emphasis by this theme is explained by understanding that the production of clean and sustainable hydrogen is the key to the establishment of zero carbon hydrogen, which is an energy system in response to the challenge of global warming (Huang & Liu, 2020 ), thus seeking to achieve greater sustainable development (Camargo et al., 2023).
And sustainability was the second most widely disseminated theme by scholars in their respective research related to green hydrogen, being due to the said word is the main one in many scientific subjects (Panah et al., 2022), particularly nowadays in relation to green hydrogen, i.e. in the framework of the improvement of renewable sources, and in this case energy sustainability is strong (Ali et al., 2022), through the change of carbon-based fuels (Genovese,et al., 20200220), through the hydrogen which is progressively verified as a relevant foundation for achieving decarbonization (Lindner, 2022) for renewable energy generation (Zuben, et al., 2022).This is how the third topic most sought after by researchers to publish their respective findings and contributions in relation to green hydrogen, which is anergy, and its relevance is due, therefore, to the production of hydrogen from hydroelectric energy, which is a niche opportunity to lead countries towards sustainable energy solutions and a hydrogen-powered economy (Thapa et al., 2021), thus influencing the decarbonization goals in the world (Raman et al., 2022), and thus corroborating energy development to make it feasible sustainable development (Guarieiro et al., 2022), while simultaneously providing opportunities for expansion into a green hydrogen-based society (LeeTentet al., 2022).In short, hydrogen energy is a promising solution for storing renewable energy to achieve a 100% renewable and sustainable hydrogen economy (Dawood, Andre & Shafiullah, 2020).
It thus refers to the next theme that was highlighted, as the most central ones, in Figure 7 of this study that is carbon emission, which is recognized as a global issue, and, for this research, which focuses on green hydrogen, it is emphasized that, for each fuel with high carbon emission factor, if it can be replaced by hydrogen, then there will be a reduction of carbon emissions (Dong, Yang, Yu, Daiyan & Amal, 2022), which is an imperative challenge in this century (Du et al., 2022), corroborating the enlargement and the robustness of clean energy (Yan, He & Fan, 2023).In short, the demand for clean fuels is driven by hydrogen processes and technologies, and is predominant in order to be able to flow innovative aspects into a lowcarbon future, and consequently to achieve sustainable development based in particular on green hydrogen (Genovese et al., 2020;Oliveira, Beswick & Yan, 2021;Guarieiro et al., 2022;Camargo et al., 2023).
In addition to the themes highlighted and contextualized in this subsection, others were also highlighted in Figure 7, in terms of the authors' desire and search to understand them, better understand them: bio-hydrogen, supply chains, life cycle, fuel, cost, economy, efficiency, electrolysis, strategy, export, greenhouse gases, initiatives and characteristics, policy, circular processes, risk, hydroelectric system, technology and trend.Such observation becomes an opportunity to foster the scientific production of these subjects for the support, foundation and north of the "mother" theme of this research, which was, green hydrogen.This finding holds true, because, by optimizing research on themes that interact with green hydrogen in the global scientific literature, it will influence its greater proliferation, upwelling, dissemination, socialization of its scientific production, and, concomitantly, will corroborate its maturation, consolidation and legitimation in the academic world.

CONCLUSION
The aim of this study was to investigate the behavior and tendency of the formation of social networks in the scientific production of the Green Hydrogen theme, as reported in the scientific journals indexed by the EBSCO.Methodologically, the techniques of bibliometric analysis were used, and in a predominant way the analysis of social networks (ARS) by way of the analyzes of one-mode and two-mode networks in 53 identified articles.
There has been an increase in the theme of green hydrogen in academia, particularly over the last two years.Concerning the authors, the most prolific were: Bai, Yueyang; Jia, Yuke; Hong, Jinglan; Huang, Jingsi; Li, Wei; Ren, Ke; Wu, Xiangyu; Zhai, Yijie; Zhang, Tianzuo, all publishing two studies each.However, when one emphasizes co-authoring networks, one observes a low density, influenced by weak ties, and, not being observed authors that mediate scientific production between conglomerates of other research groups, and may by virtue of the theme now investigated be embryonic, although it is ascertained that the said subject is in a phase of growth and, consequently, emergence in academia.
In relation to the collaborative networks of HEIs, the most prominent ones are native to China and Europe, however, as will occur in the co-authored networks, there is evidence of a low density in these networks.Thus, in reference to the cooperation networks of the nations, China and Germany stand out, however it is possible to also contemplate the United Kingdom, USA and Italy.Generally speaking, Asia, the USA and Europe are prominent in the academic production of scientific studies on green hydrogen in the world (Marocco et al., 2023;Vallejos-Romero et al., 2023).
The most widely viewed and, at the same time, the most central keywords were: hydrogen, green hydrogen, renewable energy, production, hydrogen production, economic analysis, life cycle assessment, energy transition, cascade hydropower stations, energy storage, electric vehicles, CO2 emissions and carbon emissions.These results are similarly confirmed in the study by: Zheng (2021).It should be noted that, the keywords that were highlighted in Figure 6, prospect a tendency of the authors of this area of knowledge for scientific works focused on themes that explore or interact with these keywords in evidence, emphasizing with this that the keywords depicted in the cluster in relief in Figure 6 of this research, and at the same time their respective frequencies, may reinforce the main lines of research and or studies published (Favaretto & Francisco, 2017;Ribeiro, 2022).
Four prominent clusters of thematic distributions of green hydrogen scientific research were found based on two-mode social networks of the themes and authors: production, sustainability, energy and carbon emission.It is then understood that, the said subjects show that the production of green hydrogen, evolves through the growth of studies related to the aforementioned themes, suggesting greater interest of the researchers for studies on green hydrogen through the aforementioned and emphasized four thematic groups.
However, the diffusion of knowledge about green hydrogen occurred not only through the most central themes in this study, but also through the occurrence of the other subjects seen through Figure 7, that is, through the less used themes as central subjects for the dissemination of studies on green hydrogen such as: bio-hydrogen, supply chains, cost, economy, efficiency, electrolysis, strategy, export, greenhouse gases, initiatives and characteristics, policy, circular processes, risk, hydroelectric system, technology and trend, and may show a trend of growth of these themes, opportunizing the enlargement and robustness, and, simultaneously the maturation, consolidation and legitimization of the theme of green hydrogen in the academic literature global level.
As a limitation, the aforementioned study referred to the survey of the articles in a database, the EBSCO.This being said, it is suggested for future research: (i) studies of the same nature, expanding the search for other databases such as: Web of Science, Scopus, direct science, among others; (ii) do a systematic review of literature on the topics covered in this research; and (iii) improve the ARS indicators, especially with regard to the intermediation and approximation centralities.

Figure 1 :
Figure 1: Social network two-mode of publication periods and articles Source: Survey data (2023)

Figure 3 :
Figure 3: Two-mode Social Network of Academic Journals and Authors Source: Survey data (2023)

Figure 7
Figure6(from right to left) includes a social network with 247 keywords, and highlights a social network of more integrated keywords, that is, a cluster formed with 169 keywords (from left to right), corresponding to approximately 68% of the total of 247 keywords.In the conglomerate that was highlighted in Figure6, the investigation of keywords identified 13 important research points for future discussions(Camargo et al., 2023), were: hydrogen, green hydrogen, renewable energy, production, hydrogen production, economic analysis, life cycle assessment, energy transition, cascade hydropower stations, energy storage, electric vehicles, CO2 emissions, and carbon emissions.Therefore, these keywords that have been highlighted can be considered as those that occupy positions of central importance and prominence in the thematic and theoretical knowledge flow of the subject now under investigation in this research(Favaretto & Francisco, 2017;Ribeiro, 2022).These findings are similarly corroborated in the research of: Zheng (2021).An addendum is made here stating that the keyword green hydrogen was focused on the aforementioned figure because this was the keyword used for the search and selection of articles on green hydrogen in this research, and, therefore, its relief was a condition sine qua non of the search action of these scientific studies.The visualization of the keywords in relief in Figure6is complemented by verifying their most selected connections, i.e., the keywords "partners" that most connected with them, are: green hydrogen with renewable energy; green hydrogen with CO2 emissions; hydrogen production with hydrogen; hydrogen production with hydrogen; and "partners" with life cycle assessment, in all cases with two connections between the keywords "partners".Figure7brings to the surface the two-mode social network of the 22 themes and of the 224 researchers. 13

Figure 7 :
Figure 7: Social network two-mode of themes and authors Source: Survey data (2023)