Fuel-Cell Electric Vehicles: Plotting a Scientific and Technological Knowledge Map - MDPI
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sustainability Article Fuel-Cell Electric Vehicles: Plotting a Scientific and Technological Knowledge Map Izaskun Alvarez-Meaza * , Enara Zarrabeitia-Bilbao , Rosa Maria Rio-Belver and Gaizka Garechana-Anacabe Foresight, Technology and Management (FTM) Group, Department of Industrial Organization and Management Engineering, University of the Basque Country, Pl. Ingeniero Torres Quevedo, 48013 Bilbao, Spain; firstname.lastname@example.org (E.Z.-B.); email@example.com (R.M.R.-B.); firstname.lastname@example.org (G.G.-A.) * Correspondence: email@example.com; Tel.: +34-946-014-245 Received: 23 February 2020; Accepted: 13 March 2020; Published: 17 March 2020 Abstract: The fuel-cell electric vehicle (FCEV) has been defined as a promising way to avoid road transport greenhouse emissions, but nowadays, they are not commercially available. However, few studies have attempted to monitor the global scientific research and technological profile of FCEVs. For this reason, scientific research and technological development in the field of FCEV from 1999 to 2019 have been researched using bibliometric and patent data analysis, including network analysis. Based on reports, the current status indicates that FCEV research topics have reached maturity. In addition, the analysis reveals other important findings: (1) The USA is the most productive in science and patent jurisdiction; (2) both Chinese universities and their authors are the most productive in science; however, technological development is led by Japanese car manufacturers; (3) in scientific research, collaboration is located within the tri-polar world (North America–Europe–Asia-Pacific); nonetheless, technological development is isolated to collaborations between companies of the same automotive group; (4) science is currently directing its efforts towards hydrogen production and storage, energy management systems related to battery and hydrogen energy, Life Cycle Assessment, and greenhouse gas (GHG) emissions. The technological development focuses on technologies related to electrically propelled vehicles; (5) the International Journal of Hydrogen Energy and SAE Technical Papers are the two most important sources of knowledge diffusion. This study concludes by outlining the knowledge map and directions for further research. Keywords: fuel cell electric vehicle; bibliometric analysis; patent analysis 1. Introduction The increase in energy use and related emissions was generated by a higher demand for heat from the residential and commercial sectors and road transport demand; consequently, road transport greenhouse gas (GHG) emissions increased for the second subsequent year, continuing the upward trend in emissions that started in 2014 . The electrification of mobility is an essential element in a wider strategy for achieving reduced greenhouse gas emissions . During the previous century, the automotive industry transformed society, bringing new technologies to the market that enhanced their internal combustion engine vehicles, such as global electric vehicles, which are known as one of the most hopeful alternatives for lowering transport-sector carbon dioxide emissions [3,4]. An Electric Vehicle (EV) is a road vehicle that includes electric propulsion. With this definition in mind, EVs may include battery electric vehicles (BEV), hybrid electric vehicles (HEV), and fuel-cell electric vehicles (FCEV) . As sustainable products, FCEVs bring hope for solving several mobility-related problems, as they have no local emissions . One of the most promising ways to achieve an ideal zero-emissions replacement is to use cleanly produced electricity from non-fossil fuels, such as hydrogen, using Sustainability 2020, 12, 2334; doi:10.3390/su12062334 www.mdpi.com/journal/sustainability
Sustainability 2020, 12, 2334 2 of 25 fuel-cell technology . Although FCEVs are promising ways to avoid emissions, both technologies are far from being profitable for car manufacturers . In addition, the European Commission  set a target for 40% of new cars and vans to be zero- or low-emission vehicles by 2030. Furthermore, in the European Strategic Energy Technology Plan, hydrogen and fuel-cell technologies are identified as the key technologies for achieving GHG reduction targets by 2050 [9,10], and in the European Community Research Program, electromobility is a priority. Here, electric vehicle policy focuses mainly on technology optimization and market development, setting future challenges concerning battery and supercapacitor durability, and charging infrastructure, among others . In turn, the collaborative research and development (R&D) technological projects in Europe are funded by the European Commission , and one of the main priorities for transport research and innovation in Horizon 2020 (H2020) is making transport more sustainable ; for this reason, the European Commission is promoting clean transport, both for electric vehicles by investing in electromobility initiatives and for FCEVs or hydrogen FCEVs, enabling their commercial development by 2020 . In addition, Edwards et al.  performed a roadmap review of deployment status and targets for fuel-cell applications, such as fuel-cell vehicles, and the annual sales forecast was between 0.4–1.87 million during 2020–2025. In order to help all actors involved in clean transport, it is useful to understand how scientific research is evolving and whether it is having an impact on its technological development. Bibliometric techniques open the door to a fuller understanding of the scientific research carried out on FCEVs, differing from a conventional literature review: The bibliometric method supplies an innovative, objective perspective through reliable, quantitative processes, and has been broadly used in scientific research as an analytical tool to provide assistance to scholars with a general comprehension of typical research topics . According to Garousi , bibliometric analysis is a well-established method used to measure publications in a scientific research area, and assessing trends and the value of research is becoming increasingly important [17,18]. According to different authors, bibliometrics is approached in various ways and is defined as a research method, or research technique, that allows scientific literature representing extensive global data sets and reliable data to be analyzed and quantitatively measured [19–21]. We can take this a little further and introduce the term “scientometrics”, defined by Nowak : “Scientometrics focuses on the processes occurring in science” . Scientometrics is the quantitative study of research transfer, and its analysis makes it possible to capture and map scientific knowledge [21–23]. Hence, its main objective is to aid the analysis of emerging trends in the knowledge domain ; in addition, knowledge mapping and visualization are meaningful fields of scientometrics . In the main databases, such as Web of Science and Scopus, there is no bibliometric analysis of the “FCEV” research field. However, other bibliometric analyses have been carried out in research fields related to fuel-cell technology. Kang et al.  define a diffusion model based on bibliometric analysis applied to fuel-cell technologies. Cindrella et al.  present a bibliometric analysis about the field of fuel cells in general from 1992 to 2011, offering a comprehensive overview of trending publications, journals, and countries, and identifying research hotspots through keywords. A similar overview was conducted by Yonoff et al. , identifying research trends in Proton Exchange Membrane Fuel Cells (PEMFCs). Related to energy and fuel research in China, Chen et al.  conducted a bibliometric analysis and, as a result, hydrogen and fuel cells are among the energy research priorities. Bibliometric studies on energy materials related to hydrogen are also relevant, such as the analysis of sodium borohydride (NaBH4) done by Santos and Sequeira , as well as on a lithium mineral developed by Agusdinata et al. . Considering that FCEVs are a particular field of EV application, Egbue and Long  and Ramirez et al.  carried out bibliometric analyses in order to detect the most relevant research points. In turn, Zhao et al.  depict a bibliometric analysis for EV charging system reliability to analyze the emerging trends of this active research point, such as in EV batteries. Patents provide an exclusively detailed source of information of inventive activity  and increase the use and commercialization of technologies though market transactions , promoting the diffusion of knowledge and innovation. According to Griliches , patents are one of the most
Sustainability 2020, 12, x FOR PEER REVIEW 3 of 27 Sustainability 2020, 12, 2334 3 of 25 the diffusion of knowledge and innovation. According to Griliches , patents are one of the most influential proxies for assessing the performance of industry research and development (R&D). For influential proxies these reasons, for assessing the patent the performance is an important of industry research tool for investigating and development a technological development (R&D). fromForan these reasons, the patent is an important tool for investigating a technological economic perspective . According to Borgstedt et al. , in the automotive industry, patents are development from an economic perspective the most common way. According to protect to Borgstedt intellectual property, et al. so, in the it can automotive be used industry, as innovative patents output. are Patent the most common way to protect intellectual property, so it can be used as data analysis allows us to ascertain the technological state of the studied technology, defining who, innovative output. Patent data when, analysis where,allows and what us to ascertain is being the technological developed by mining staterelevantof the datastudied technology, from patent defining documents who, in terms when, where, and of technology what is being development developed . by mining In addition, in thisrelevant case, indatathefrom mainpatent documents databases, such in as terms Web of of technology development . In addition, in this case, in the main databases, Science and Scopus, there is no patent data analysis of “FCEV” research articles; nevertheless, other such as Web of Science and Scopus, research there related papers is no patent data analysis to patents of “FCEV” in fuel-cell research articles; technologies have beennevertheless, developed. other research Related to papers related to patents in fuel-cell technologies have been developed. Related biohydrogen, Leu et al.  carried out a patent data and citation analysis. With regard to fuel cells, to biohydrogen, Leu et al.  Chang et carried out a patent al.  studied data and between the coactivity citation analysis. science and With regard to by technology fuelanalyzing cells, Chang et al.  patent–paper studied the coactivity pairs. Related between to technology science and forecasting, Chen technology by analyzing et al.  defined a modelpatent–paper for a patentpairs. Related strategy to for fuel- technology forecasting, Chen et cell technologies using the S-curve method.al.  defined a model for a patent strategy for fuel-cell technologies usingInthe S-curve method. demonstrating the evolution of the scientific–technological research of the FCEV domain, this paper Inoffers demonstrating the evolution a comprehensive assessment of theofscientific–technological the FCEV research practices research of the which wereFCEV domain, published in this paper offers a comprehensive assessment of the FCEV research the Scopus database from 1999–2019, in order to identify the key actors in the generation and practices which were published in the Scopusofdatabase transmission knowledge from 1999–2019, related in order to FCEVs. As fartoasidentify the keydevelopment technological actors in theisgeneration concerned, andthis transmission paper presents the technological trends of industrial developments, mainly led in this case bythis of knowledge related to FCEVs. As far as technological development is concerned, the paper presents automotive the technological industry, trends of among in order to establish, industrial developments, others, who leads the mainly led in research andthis case by the development. automotive industry, All this is done in order in order to draw to establish, the FCEV among others,knowledge technology who leads the map,research and it to discuss development. All with the results this is done in order to draw the FCEV technology knowledge map, to discuss of other scientific–technological research studies, and, therefore, to be able to predict the future paths it with the results of other scientific–technological of research trends and foreseeable research studies, and, therefore, to be able to predict the future paths of scenarios. research trends and foreseeable scenarios. 2. Materials and Methods 2. Materials and Methods The research process, adapted from Bildosola et al.  with some changes, is based on three The research process, adapted from Bildosola et al.  with some changes, is based on three steps steps that are intended to define the scientific research activity profile and the technological profile that are intended to define the scientific research activity profile and the technological profile of FCEVs. of FCEVs. These steps are developed to answer the questions related to who, where, and what is These steps are developed to answer the questions related to who, where, and what is being or has being or has been researched or developed related to scientific literature and patents. Figure 1 shows been researched or developed related to scientific literature and patents. Figure 1 shows the research the research approach, revealing that each step has its input and output, creating a flow of approach, revealing that each step has its input and output, creating a flow of information that allows information that allows the set objectives to be achieved. In each step, the specific technique used is the set objectives to be achieved. In each step, the specific technique used is identified. The stages are identified. The stages are developed consecutively, until the scientific and technological profiles are developed consecutively, until the scientific and technological profiles are determined. However, the determined. However, the objective of this research process is to be able to cover any type of emerging objective of this research process is to be able to cover any type of emerging technology or application. technology or application. Figure 1. Figure 1. Research Research process process step step by by step. step. Profile generation Profile generationisiscarried carriedout outthrough throughthe the first first three three steps, steps, andand thethe main main tasks tasks tocarried to be be carried out out explained are are explained below. below. Step 1. Retrieving data and refining the search. The first assignment is to generate two specific databases concerning databases concerningscientific scientific publications publications and and patentspatents relatedrelated to the emerging to the emerging technology technology analyzed.
Sustainability 2020, 12, 2334 4 of 25 Regarding the selection of the scientific database, different studies show that better results are obtained [43,44] by using all of the databases (Scopus, Web of Science (WoS), and Google Scholar (GS)). Nevertheless, a very high percentage of WoS and Scopus citations are normally found in GS; those that are not, called unique citations, present a lower scientific impact than WoS and Scopus citations . Furthermore, the two databases complement each other ; however, in this case, Scopus returns more citations than WoS. For this reason, in the case of FCEVs, the specific databases were generated from Scopus as the scientific database and Lens as the patent database. Scopus is one of largest abstract and citation databases of peer-reviewed literature (75 million documents indexed) , and it was selected to provide scientific publications. Because blooming technologies meet different approaches, the definition of the search query is very important. In bibliometric search strategies, the balance between recall and precision is very important . However, information scientists usually detect an inverse association between recall and precision . Therefore, the query was built using “fuel-cell vehicle/car/automobile” as author keywords, obtaining a highly precise query. In addition, to achieve greater recall, the search for the same terms based on the index terms is added to the query (see Table 1). Index terms are derived from thesauri that Elsevier owns and are added to improve search recall . The data collection time span was established between 1999 and 2019. In addition, according to Hawkins , gatekeeping publications, such as Abstracting and Indexing (A&I) publications, are the main way to identify advances of a technology. Therefore, the query is in line with the document type: Journal Article and Conference Proceeding. The main query used in the Scopus database retrieved a total of 2514 articles and conference papers for the defined time span. The patent analysis was carried out using Lens, a complete open-source global patent database and research platform containing the world’s most comprehensive full-text patent collection. The search for patents relating to FCEVs was carried out on the basis of Cooperative Patent Classification (CPC), also explained as the patent’s field of technological application. Specifically, the search is directed by the classification Y02T90/34—fuel-cell-powered electric vehicles—which makes the results of localized patents far more accurate. The Y CPC was created in order to give a technological application coverage to new technologies that are not included in the International Patent Classification (IPC); Y: General tagging of new technological developments. Y02T90: Technologies for climate-change mitigation or adaptation related to transportation—enabling technologies with a potential or indirect contribution to GHG emission mitigation. In addition, the search was limited to the patent priority year (or the year in which the patent was invented) in the period from 1999 to 2019. Table 1. Search query for fuel-cell electric vehicles adapted to the Scopus database. Query AUTHKEY(“fuel cell*” W/2 vehicle*) OR AUTHKEY(“fuel cell*” W/2 car) OR AUTHKEY(“fuel cell*” W/2 cars) OR AUTHKEY (“fuel cell*” W/2 automobile*) OR INDEXTERMS (“fuel cell*” W/2 vehicle*) OR INDEXTERMS (“fuel cell*” W/2 car) OR INDEXTERMS(“fuel cell*” W/2 cars) OR INDEXTERMS (“fuel cell*” W/2 automobile*) AND (LIMIT-TO (DOCTYPE, “cp”) OR LIMIT-TO (DOCTYPE, ”ar”)) Source: Own work. Step 2: Cleaning up the refined database. This second task includes the use of text mining tools. The scientific database and the patent database were imported into the Vantage Point (VP) software . VP works with search results from text databases. VP’s capabilities can be broad after importing raw data from scientific databases. VP includes powerful data cleaning tools based on a thesaurus or fuzzy matching techniques. Furthermore, VP integrates powerful techniques for analyzed data, such as natural language programming, a co-occurrence matrix, Principal Component Analysis (PCA), Social Network Analysis (SNA), clusters, and other capabilities for visualizing data. Scientific publications obtained from the previous step were integrated into the database, and in specific fields, such as authors, affiliations, journals, and authors’ keywords, a fuzzy matching was applied in order to group
Sustainability 2020, 12, 2334 5 of 25 the variations of a word (plurals, acronyms, and similar expressions, among others) that convey the same meaning. Step 3: Generating the profile. The profile is divided into two parts: The scientific research profile Sustainability and the 2020, 12, x FOR technological PEER REVIEW profile. The scientific profile is based on the literature profile and5 of 27 research community profile, and these describe the research activity in terms of publication trends, academic Step 3: Generating the profile. The profile is divided into two parts: The scientific research profile performance, research topics, and sources of knowledge. The technological profile deals with issues and the technological profile. The scientific profile is based on the literature profile and research related to patentprofile, community trends, the and main these countries describe of jurisdiction, the research activity ininventors and applicants, terms of publication and the main trends, academic technological performance, fields. To facilitate research the analysis topics, and sources ofofknowledge. scientific–technological The technologicaltrends, an deals profile analysis withofissues networks was carried related to out, visualizing patent trends, thethemain collaborative countries ofnetworks between jurisdiction, inventorscountries, co-authorship and applicants, and the networks, main keyword co-occurrences, technological fields. To and collaboration facilitate networks the analysis of applicants and inventors. of scientific–technological trends, anFor this, starting analysis of networks was carried out, visualizing the collaborative networks between from the matrices of co-occurrences, created both statically and dynamically in the VP software countries, co-authorship networks, (Search Technololy keyword Inc. co-occurrences, Atlanta, USA),and thecollaboration networks were networks of applicants generated and inventors. and visualized through Forthe this,Gephi starting software . from the matrices of co-occurrences, created both statically and dynamically in the VP software (Search Technololy Inc. Atlanta, USA), the networks were generated and visualized through the Gephi software . 3. Results 3. ResultsResearch Profile in FCEVs 3.1. Scientific 220.127.116.11.1. Scientific General Research Trends Profile in FCEVs of Publications and Citations The 3.1.1.evolution of publications General Trends andand of Publications citations Citationsin the last 20 years is represented in Figure 2 (on a logarithmic basis). Both of them increased sharply, The evolution of publications and citations in the indicating growing last 20 years academic is represented in interest Figure 2 in (onFCEVs. a Whereas in 1999, logarithmic thereBoth basis). were of only them 13 scientific increased articles, sharply, this number indicating growinggrew to 171 academic in 2018, interest an increase in FCEVs. of 1215%. WhereasBetween in 1999,the years there were 2005 onlyand 2006, thearticles, 13 scientific number thisofnumber publications grew tojumped markedly 171 in 2018, and then an increase of 1215%. stabilized withBetween the years a constant 2005 and 2009 production, 2006, being the number of publications the most productive jumped year markedly with 203 and then publications. stabilized However, the with number a constant production, of citations 2009rapidly per year being the most productive increased yearand from 2005, withwas 203 over publications. twenty-two However, the number of citations per year rapidly increased from 2005, times higher in 2018 (5081) than in 2005 (227). Hence, the scientific research community and was over twenty-two is paying moretimes higher in 2018 (5081) than in 2005 (227). Hence, the scientific research community is paying attention to topics related to cleaner transport. In addition, Figure 2 shows the results of a less more attention to topics related to cleaner transport. In addition, Figure 2 shows the results of a less precise search of the two terms, displayed independently (query: Fuel cell* and query: Vehicle*/car precise search of the two terms, displayed independently (query: Fuel cell* and query: Vehicle*/car or cars/automobile*), resulting in a very high number of publications, with a similar growth and or cars/automobile*), resulting in a very high number of publications, with a similar growth and continuous increase continuous of both increase searches. of both searches. 100000 14974 16834 12201 10000 9134 10056 9725 10880 7728 7911 8510 6318 6605 6437 7041 8499 7292 6333 6677 6489 7401 7117 5062 5663 4643 4504 4443 5081 4454 3964 4386 3968 3517 3592 3823 2912 2795 3437 2779 2763 1776 1749 1959 2081 1293 1393 1265 1562 1000 1209 786 904 698 669 608 566 555 484 311 227 203 193 179 174 154 123 133 171 171 145 100 108 131 143 129 120 74 79 91 54 46 51 35 30 18 10 13 2 1 nº of publications citations per year publications related to fuel cell publications related to vehicle/car/automobile Figure 2. General trends of publications and citations from 1999 to 2019. Figure 2. General trends of publications and citations from 1999 to 2019. 3.1.2. Academic Performance: Countries, Organizations, and Authors
Sustainability 2020, 12, 2334 6 of 25 Sustainability 2020, 12, x FOR PEER REVIEW 6 of 27 3.1.2. Academic Performance: Countries, Organizations, and Authors In total, authors In total, from authors 61 61 from countries published countries publishedpapers paperson onFCEVs. FCEVs.The Theaffiliations affiliationsofofauthors authors are a goodareindicator of the specific a good indicator patterns of the specific of research patterns concentration of research concentrationandand excellence excellence followed followedbybythese countries and organizations. these countries The most and organizations. Theadvantageous countries most advantageous in terms countries of publishing in terms of publishing about FCEVs about (seeFCEVs Figure(see Figure 3) are not 3) are not geographically geographically concentrated, concentrated, but arebut are rather rather located located in tri-polar in the the tri-polar world world (North (North Asia-Pacific, America, America, Asia-Pacific, and Europe). and Europe). The The two two principalcountries principal countries with withthethehighest highestnumber of number of publications are the USA (618) and China (451). Almost half of the publications are from publications are the USA (618) and China (451). Almost half of the publications are from USA, China USA, China and Japan (364). and Japan (364). Figure 3. Evolution of the number of articles by country according to publication year, from 1999 to 2019. Figure 3. Evolution of the number of articles by country according to publication year, from 1999 to 2019. In addition, the USA, UK, and Canada stand out as pioneers in scientific research (with regards to the 1999 start date), and they also grew progressively over time. Production in China, despite being In addition, the USA, UK, and Canada stand out as pioneers in scientific research (with regards the country with the second-most publications, began to be relevant in 2002–2003. to the 1999 start date), In order and they to identify also grew collaboration progressively activities betweenover time.countries, different Production an in China,method effective despiteisbeing the country a network with the second-most analysis. Using Gephipublications, began tothe for network analysis, be main relevant in 2002–2003. countries (countries that have at In order least three to identify collaboration collaborative publications)activities betweencollaborations with international different countries, an effective were identified method is a and plotted network analysis. (see Figure Using 4). The Gephi size of forrepresents the node network the analysis, numberthe main countries of connections; (countries consequently, that have a country withata least threelarger node, such as collaborative the USA, is more publications) withactive in academiccollaborations international collaborations inwere the field of FCEVs. identified Theplotted and width (see of the connecting line represents the cooperative frequency. Academic collaborations Figure 4). The size of the node represents the number of connections; consequently, a country with a between China, Germany, larger Japan,as node, such and theUSA, the USA are the most is more frequent. active In the main in academic cluster led by the collaborations USA, in the bothof field European FCEVs. The and North American countries, as well as Asian-Pacific countries, are collaborating. The identified width of the connecting line represents the cooperative frequency. Academic collaborations between collaborations between countries follow the same pattern of collaboration convergence clubs as those China, Germany, Japan, and the USA are the most frequent. In the main cluster led by the USA, both related to applied science, as defined by Barrios et al. . In addition, international collaborations are European and North American countries, as well as Asian-Pacific countries, are collaborating. The located in a tri-polar world (Europe, North America, and Asia-Pacific); the science powerhouses are identified countriescollaborations between placed in the central countries positions of thefollow thesurrounded networks, same pattern of collaboration by emerging convergence scientific countries. clubs as those Possible related reasons for to applied science, collaborations as defined may include by language English Barrios et al. . skills, In addition, post-colonial links,international science collaborations are economic skill proximity, located inproximity, a tri-polar world and (Europe, international North America, students, among othersand. Asia-Pacific); the science powerhouses are countries placed in the central positions of the networks, surrounded by emerging scientific countries. Possible reasons for collaborations may include English language skills, post- colonial links, science skill proximity, economic proximity, and international students, among others .
Sustainability 2020, 12, 2334 7 of 25 Sustainability 2020, 12, x FOR PEER REVIEW 7 of 27 Figure 4. Academic collaborations among the main countries. Figure 4. Academic collaborations among the main countries. According to organizations, Table 2 describes the 10 most active organizations, including the numberAccording to organizations, of publications, Table 2countries, their affiliated describesand the their 10 most activecitations average organizations, includingThe per publication. the number most of publications, productive organization theirby affiliated countries, far is Tongji and their University average with 134 citationsHowever, publications. per publication. The the average most productive organization by far is Tongji University with 134 publications. However, citations per publication for the Tsinghua University (ranked #2) is four times greater, and for General the average citations(ranked Motors per publication #9), it is for seventhetimes Tsinghua University greater than for(ranked #2) is four times Tongji University. greater, Therefore, and this for General organization Motors Univ.) (Tongji (ranked #9), ittoisimprove needs seven times greaterofthan the quality for Tongji University. its publications Therefore, to ensure that this organization its publications become (Tongji Univ.) needs to improve the quality of its publications to ensure that sources of knowledge for other scientific publications. In general, Chinese organizations have its publications become fewer sources of knowledge for other scientific publications. In general, Chinese organizations average citations per publication, and their publications are concentrated within a few organizations. have fewer average With thecitations perofpublication, exception and theirthe Tongji University, publications are concentrated National Renewable Energywithin a few organizations. Laboratory, and the US With the exception of Tongji University, the National Renewable Department of Energy, the publications from the most active organizations do impact Energy Laboratory, and the US academic Department research. of Energy,the Highlighting thepresence publications from the most of non-academic active organizations organizations among the do topimpact academic 10 organizations research. Highlighting the presence of non-academic organizations among the (General Motors, Ford Motors, and Toyota Motors), the research results have an important impact on top 10 organizations (General the Motors, Ford science-driven Motors, and Toyota Motors), the research results have an important impact on domain. the science-driven domain. Table 2. The most active organizations. Table 2. The most active organizations. Organization Publications Country Average Citations Per Publication Organization Tongji University Publications 134 Country China Average Citations 3.98per Publication Tsinghua TongjiUniversity University 76 134 China China 16.72 3.98 Toyota Motor Corporation Tsinghua University 56 76 Japan China 23.34 16.72 University of California, Davis 50 USA 15.00 Toyota Motor Corporation Argonne National Laboratory 44 56 Japan USA 23.34 17.95 University of California, Davis National Renewable Energy Laboratory 44 50 USA USA 15.00 5.48 Argonne National Seoul National Laboratory University 43 44 USA South Korea 17.95 22.42 NationalFord Motor Company Renewable Energy Laboratory 41 44 USA USA 11.02 5.48 General Seoul Motors National University 35 43 USA South Korea 28.91 22.42 US Department of Energy 35 USA 9.09 Ford Motor Company 41 USA 11.02 General Motors 35 USA 28.91 The US Department analysis of theofmost Energy 35 productive authors USA3) reveals Minggao9.09 (see Table Ouyang (Tsinghua University, China), Joeri Van Mierlo (Vrije Universiteit, Brussel), and Jianqiu Li (Tsinghua, China) as theThe analysis three of the publishing researchers most productive the mostauthors in the(see Table field. All 3) of reveals the top Minggao Ouyang authors have (Tsinghua at least fifteen University, China), Joeri Van Mierlo (Vrije Universiteit, Brussel), and Jianqiu Li (Tsinghua, publications; however, if we evaluate their citation average per publication, important differences China) as the threeauthors between researchers publishing appear. the the For instance, most in the sixth field. author, AllS.ofwith Zuo, the 16 top authors have publications, hasata low leastaverage fifteen publications; number however, of citations per ifpublication we evaluate theirmeaning (2.19), citation that average theirper publication, academic work important differences has little influence on between authors appear. For instance, the sixth author, Zuo, S. with 16 publications, other scientific research. In general, the top 10 most productive authors have a high average number of has a low average number of citations per publication (2.19), meaning that their academic work has little influence on other scientific research. In general, the top 10 most productive authors have a high
Sustainability 2020, 12, 2334 8 of 25 citations per publication, highlighting the authors from Tsinghua University, whose research work has an important influence on other scientific developments. Table 3. Top 10 most productive authors. Average Authors Institution Country Counts Citations per Subject Area a Publication Ouyang, Energy and Tsinghua University China 25 33,20 Minggao Engineering Van Mierlo, Energy and Vrije Universiteit Brussel Belgium 23 25,91 Joeri Engineering Energy and Li, Jianqiu Tsinghua University China 21 36,90 Engineering Energy and Xu, Liangfei Tsinghua University China 18 42,28 Engineering Université de Ravey, Energy and Technologie France 16 15,44 Alexandre Engineering Belfort-Montbéliard Zuo, Shuguang Tongji University China 16 2,19 Engineering Seoul National South Cha, Sukwon 15 17,60 Engineering University Korea Djerdir, Université Bourgogne Energy and France 15 6,67 Abdesslem Franche-Comté Engineering Rathore, Concordia University Canada 15 26,93 Engineering Akshay Kumar National Renewable Wipke, Keith B. USA 15 8,53 Engineering Energy Laboratory a Subject areas are summarized from the selected publications in the established dataset (Scopus), taking into account the most frequent subject areas. A co-authorship network was generated and plotted by using Gephi, as shown in Figure 5, identifying a collaboration network of the top authors (authors with over three publications as co-authorships). The layout of the networks was developed using Force Atlas 2. Each node represents each author, while each link represents the pattern of collaboration. Among the top 10 authors, only the authors affiliated with Tsinghua University (Minggao Ouyang, Jianqiu Li, and Liangfei Xu) have a strong co-authorship between them; the rest of the authors have less intense relationships with other authors who are not in the top 10. The main academic groups can be identified, highlighting that there is no collaboration between them. Five research groups can be identified, whose main authors work in the research field (subject area) of energy and engineering related to FCEVs. Therefore, as far as the research field is concerned, they present few differences, but their locations do: Each group is from a different country or continent (USA, Japan, and Belgium), except for research group 1, in which the authors located in the tri-polar world (France, Canada, USA, China, and South Korea) collaborate, and research group 4, in which authors from China and South Korea collaborate. 3.1.3. Sources and Subject Area Classification Sources with more documents published about FCEVs were identified. The search was limited to journals and conference proceedings, with 60% of the publications published in journals and 40% as conference proceedings. The most productive journal is closely related to hydrogen; however, most of the top journals are related to the automobile industry, electrochemical science, and energy applications. The most notable of the 10 most productive sources was the International Battery, Hybrid, and Fuel-Cell Electric Vehicle Symposium (EVS) organized by the World Electric Vehicle Association (WEVA). The 2514 publications were published in 721 different sources; therefore, the works are not centered around a few journals, but more than 20% were published in two sources. Specially, the International Journal of Hydrogen Energy (271 articles, 10.7%), SAE Technical Papers (257 articles, 10.15%), and Journal of
Sustainability 2020, 12, 2334 9 of 25 Power Sources (104 articles, 4.1%) are the top journals (see Figure 6). Moreover, the top journals are indexed in2020, Sustainability the 12, Clarivate Analytics x FOR PEER REVIEWJournal Citation Report with upper quartile rankings. 9 of 27 Figure 5. Co-authorship network. 3.1.3. Sources and Subject Area Classification Sources with more documents published about FCEVs were identified. The search was limited to journals and conference proceedings, with 60% of the publications published in journals and 40% as conference proceedings. The most productive journal is closely related to hydrogen; however, most of the top journals are related to the automobile industry, electrochemical science, and energy applications. The most notable of the 10 most productive sources was the International Battery, Hybrid, and Fuel-Cell Electric Vehicle Symposium (EVS) organized by the World Electric Vehicle Association (WEVA). The 2514 publications were published in 721 different sources; therefore, the works are not centered around a few journals, but more than 20% were published in two sources. Specially, the International Journal of Hydrogen Energy (271 articles, 10.7%), SAE Technical Papers (257 articles, 10.15%), and Journal of Power Sources (104 articles, 4.1%) are the top journals (see Figure 6). Moreover, the top journals are indexed in the Clarivate Analytics Journal Citation Report with upper quartile rankings. Co-authorshipnetwork. Figure5.5.Co-authorship Figure network. 3.1.3. 25th International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium… Sources and Subject Area Classification 25 24th International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium… 25 Sources with more documents published about FCEVs Energy Policy 26 were identified. The search was limited Applied Energy 27 to journals and conference proceedings, with 60% of the publications published in journals and 40% 22nd International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium… as conference proceedings. The most productive journal is 35 closely related to hydrogen; however, most ECS Transactions 42 of the top journals are related to the automobile industry, electrochemical science, and energy World Electric Vehicle Journal 50 applications. The most notable of the 10 most productive sources Journal of Power Sources 104 was the International Battery, Hybrid, and Fuel-Cell Electric Vehicle Symposium SAE Technical Papers (EVS) organized by the World Electric257Vehicle Association (WEVA). The 2514 Journal International publications were published in 721 different sources; therefore, of Hydrogen Energy 271 the works are not centered around a few journals, but more than 20% were published in two sources. Specially, the International Figure 6. Journal A summary of Hydrogen Energy of publications (271 articles, according 10.7%), to the top SAE Technical Papers journals. Figure 6. A summary of publications according to the top journals. (257 articles, 10.15%), and Journal of Power Sources (104 articles, 4.1%) are the top journals (see Figure According 6). Moreover, thetotop Scopus, journals theare publications indexed incan thebe categorized Clarivate into four Analytics general Journal areas, Citation which Report are with furtherAccording divided to Scopus, the publications can be categorized into four into 27 major subject areas . With regard to the research fields for the identifiedgeneral areas, which are upper quartile rankings. further divided into 27 major subject areas . With regard to the publications, they are categorized into a total of 21 specific areas, and these are primarily the areas ofresearch fields for the identified Engineering 25th International(67.3%), Energy Battery, Hybrid (40.6%), and Fuel Cell Environmental Electric Vehicle Symposium… Science (16.3%), Physics and Astronomy (14.7%), 25 and24th Computer Science International Battery, (7.8%). Hybrid and Fuel Cell Electric Vehicle Symposium… 25 Energy Policy 26 3.1.4. Research Topic Applied Energy 27 22nd International Battery, Hybrid and Fuel Cell Electric Vehicle Symposium… 35 Keywords represent the knowledge hubs of academic studies; therefore, the analysis of keywords ECS Transactions 42 can help to identify the leading Worldand Electricdeveloping Vehicle Journal topics in50the research field of FCEVs. A total of 3263 keywords (author keywords) were extracted Journal of Power Sources from 2514 publications104 by using Vantage Point. The maturity level of those data can be SAE determined Technical Papersby analyzing the first year in which a term in the 257 analysis International Journal of Hydrogen Energy data set appears. In the case of the analysis of the authors’ keywords, two growth phases are identified 271 Figure 6. A summary of publications according to the top journals. According to Scopus, the publications can be categorized into four general areas, which are further divided into 27 major subject areas . With regard to the research fields for the identified
(14.7%), and Computer Science (7.8%). 3.1.4. Research Topic Keywords represent the knowledge hubs of academic studies; therefore, the analysis of keywords can help to identify the leading and developing topics in the research field of FCEVs. A Sustainability 2020, 12, 2334 10 of 25 total of 3263 keywords (author keywords) were extracted from 2514 publications by using Vantage Point. The maturity level of those data can be determined by analyzing the first year in which a term in the analysis (See Figure 7). The data first set appears. phase can be In called the casetheofgrowth the analysis phase of between the authors’ thekeywords, two growth years 1999–2010, and the second phase, maturity, between the years 2011–2019, can be considered as a stage ofthe phases are identified (See Figure 7). The first phase can be called the growth phase between years continuous 1999–2010, and the second phase, maturity, between the years 2011–2019, can be considered as a stage downturn and growth, in which the appearance of new study terms is very important. of continuous downturn and growth, in which the appearance of new study terms is very important. Records Terms 284 Maturity 2007-2019 254 249 236 222 223 212 205 191 200 Growth 1999-2006 155 203 180 160 193 165 179 174 171 171 154 145 143 100 133 131 129 120 123 76 63 91 41 79 31 46 51 5 11 35 30 13 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Figure Figure 7. Number 7. Number of new of new author’skeywords author’s keywords in in any any year yearvs. vs.the number the of records number of that of records year.year. of that In addition, In addition, the the co-occurrence co-occurrence networkof network ofauthors’ authors’ keywords keywordsthat thatco-occur at least co-occur five five at least timestimes was was plotted by using Gephi. The analysis was carried out using a dynamic matrix of co-occurrences, plotted by using Gephi. The analysis was carried out using a dynamic matrix of co-occurrences, which which made it possible to analyze the evolution of keywords in the period 1999–2019. In order to made it possible to analyze the evolution of keywords in the period 1999–2019. In order to analyze the analyze the current situation and to be able to deduce a future trend of the research topics, Figure 8 current situation and to be able to deduce a future trend of the research topics, Figure 8 shows the shows the keyword networks for the 2018–2019 period. In this network, the three most important keyword networks clusters for three define the the 2018–2019 period. areas of action In thisresearch in which network, the three science most important is currently clusters working: FCEVs as define a the three areas of development technological action in which research to improve thescience is currently environment working: or reduce FCEVs asbatteries GHG emissions, a technological and development to improve the energy management environment systems, or reduce and hydrogen GHG emissions, production batteries and storage, with and energy a loss management of interest in research related to the topic of powertrains. systems, and hydrogen production and storage, with a loss of interest in research related to the topic ofSustainability powertrains. 2020, 12, x FOR PEER REVIEW 11 of 27 Figure 8. Authors’ keyword co-occurrence networks: 2018–2019 period. Figure 8. Authors’ keyword co-occurrence networks: 2018–2019 period. The analysis of these dynamic networks based on the author keywords with the greatest number of co-occurrences allows us to focus on the path followed by research, and also to predict future trends. These research topics have been ongoing for the past twenty years. However, they have evolved until reaching their technological maturity, generating new fields of research related to the
Sustainability 2020, 12, 2334 11 of 25 The analysis of these dynamic networks based on the author keywords with the greatest number of co-occurrences allows us to focus on the path followed by research, and also to predict future trends. These research topics have been ongoing for the past twenty years. However, they have evolved until reaching their technological maturity, generating new fields of research related to the main topics. Mainly related to the cluster led by PEMFCs are FC hybrid vehicles, batteries, and energy management systems (EMSs), and to the cluster led by FCEVs: Hydrogen storage/production and Solid Oxide Fuel Cell (SOFC.) As a summary of the analysis in Figure 9, the keyword networks of the periods 1999–2010 (growth period) and 2011–2019 (maturity period) are shown. 3.1.5. Source of Knowledge In addition, analysis was carried out to identify the five most cited articles in order to be able to detect the origin of the knowledge (See Table 4). These articles were published between 2004–2011; these were years of growth of the scientific development of FCEV technology. However, the results show that China and the USA are the reference countries, and the authors of the most cited articles are affiliated with universities and research entities, such as Harbin Institute of Technology (Wuhan University), Institut National de la Recherche Scientifique, Énergie, Matériaux, and Télécommunications, and Los Alamos National Laboratory. Nevertheless, only one of the most cited articles was made in collaboration between different organizations from different countries (USA and Canada). As far as sources are concerned, the most cited articles were published in IEEE Proceedings, which covers technical developments in electronics, electrical and computer engineering, and computer science, and in Energy and Environmental Science, which is related to energy conversion and storage, alternative fuel technologies, and environmental science.
Sustainability 2020, 12, 2334 12 of 25 Sustainability 2020, 12, x FOR PEER REVIEW 12 of 27 Figure 9. Authors’ keyword co-occurrence networks: Growth period (1999–2006) and Maturity period (2007–2019). Figure 9. Authors’ keyword co-occurrence networks: Growth period (1999–2006) and Maturity period (2007–2019). 0
Sustainability 2020, 12, 2334 13 of 25 Table 4. Most cited articles: Where knowledge comes from. Times Cited Title Publication Year Authors Organizations Country Source Author Keywords Fuel-cell electric vehicle (FCEV) International Research Electric machines The state of the art of electric, Centre for Electric Vehicles, Proceedings of the 1107 2007 Chan, C.C. China Electric vehicle (EV) hybrid, and fuel cell vehicles  University of Hong IEEE Modeling Kong/Wuhan University Hybrid electric vehicles (HEV) Jaouen, F. Fuel-cell performance * Proietti, E. Institut National de la Fuel-cell vehicles * Lefèvre, M. Recherche Scientifique, United States metal catalysis * Recent advances in non-precious Chenitz, R. Énergie, Matériaux and Energy and metal catalysis for 1021 2011 Dodelet, J.-P. Télécommunications/Materials Environmental oxygen-reduction reaction in Wu, G. Physics and Applications Science polymer electrolyte fuel cells  Cathodes * Chung, H.T. Division, Los Alamos National Laboratory Canada Johnston, C.M. Zelenay, P. Atmospheric science: Cleaning Jacobson, M.Z. Electrolysis * 591 the air and improving health with 2005 Colella, W.G. Stanford University United States Science Hydrogen Fuel-cell vehicles* hydrogen fuel-cell vehicles  Golden, D.M. Air quality * Peng, F.Z. University of Michigan Fuel-cell electric vehicle A new ZVS bidirectional DC–DC Li, H. Florida State University IEEE Transactions DC–DC converter 557 converter for fuel cell and battery 2004 Oak Ridge National United States on Power Su, G.-J. Power generation application  Laboratory Electronics ZVS Lawer, J.S. University of Tennessee Auxiliary power supply Wagner, F.T. Automotive applications * Electrochemistry and the future General Motors Research Journal of Physical 532 2010 Lakshmanan, B. United States Li-ion batteries * of the automobile  and Development Chemistry Letters Mathias, M.F. Hydrogen infrastructure * * These articles only have the Indexed Keywords registered. Times cited: Data according to the Scopus database.
Sustainability 2020, 12, x FOR PEER REVIEW 16 of 27 Sustainability 2020, 12, 2334 14 of 25 19 3.2. Technological Profile in FCEVs 3.2. Technological Profile in FCEVs 20 3.2.1. General Trends 3.2.1. General Trends 21 Technological trends were analyzed by using the patent data. For this, Lens.org was used, as it Technological trends were analyzed by using the patent data. For this, Lens.org was used, as 22 is a global patent database that includes European Patent Office (EPO), United States Patent and it is a global patent database that includes European Patent Office (EPO), United States Patent and 23 Trademark Office (USPTO), World Intellectual Property Organization (WIPO), and Australian patent Trademark Office (USPTO), World Intellectual Property Organization (WIPO), and Australian patent 24 data collections. The search was carried out based on patent families. A patent family (PF) is a data collections. The search was carried out based on patent families. A patent family (PF) is a 25 collection of patent applications covering the same or similar technical content. For the period from collection of patent applications covering the same or similar technical content. For the period from 26 1999 to 2019, a total of 1909 PFs were detected. 1999 to 2019, a total of 1909 PFs were detected. 27 First, it is interesting to answer the questions: When did the invention publication take place? First, it is interesting to answer the questions: When did the invention publication take place? 28 Who is inventing it? Who is its beneficiary? What is the framework for commercial foresight? What Who is inventing it? Who is its beneficiary? What is the framework for commercial foresight? What 29 other fields of technological application do these patents cover? The production of patents is low up other fields of technological application do these patents cover? The production of patents is low up 30 until 2000, but in the period from 2001 to 2016, technological development is in constant growth (see until 2000, but in the period from 2001 to 2016, technological development is in constant growth (see 31 Figure 10). It is to be expected that there are not many patents in the years 2018 and 2019 because the Figure 10). It is to be expected that there are not many patents in the years 2018 and 2019 because the 32 search was made by the earliest priority year, and the patent applications are normally published 18 search was made by the earliest priority year, and the patent applications are normally published 18 33 months after the date of filing or the earliest priority date, so patents filed in 2018 and 2019 may not months after the date of filing or the earliest priority date, so patents filed in 2018 and 2019 may not 34 have been published yet. have been published yet. 212 211 178 167 154 155 156 139 140 121 118 112 99 95 95 90 85 66 13 9 1 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 35 36 Figure Figure10. 10.The Thenumber numberofoffuel-cell fuel-cellelectric electricvehicle vehicle(FCEV) (FCEV)patent patentfamilies familiesby bypublication publicationyear. year. 37 3.2.2.Inventive 3.2.2. InventivePerformance: Performance:Inventors, Inventors,Applicants, Applicants,and andCountries Countries 38 InInorder ordertotoreflect reflectinventive inventiveperformance, performance,the thetop topinventors inventorsare arefrom fromSouth SouthKorea, Korea,Japan, Japan,and andthe the 39 USA,and USA, andtheir theirmain mainapplicants applicantsare areautomotive automotivecompanies companies(See (SeeTable Table5). 5). Table 5. Who is inventing? 40 Table 5. Who is inventing? Number Number of of Patent Patent Family Family (PFs) (PFs) Inventors Inventors Main MainApplicants Applicants 3737 KWONSANG KWON SANGUKUK Hyundai Hyundai Motor Motor CoCo LTDLTD 3535 TABATA TABATAATSUSHI ATSUSHI Toyota Motor Toyota Corp. Motor Corp. 3333 BORRONI-BIRD BORRONI-BIRDCHRISTOPHER CHRISTOPHEREE General Motors General Corp. Motors Corp. 3333 VITALE VITALEROBERT ROBERTLOUIS LOUIS General Motors General Corp. Motors Corp. 3333 HIBIKI HIBIKISAEKI SAEKI Honda HondaMotor CoCo Motor LTDLTD 3232 CHERNOFF CHERNOFFADRIAN ADRIANBB General Motors General Corp. Motors Corp. 32 SHABANA MOHSEN D General Motors Corp. 32 SHABANA MOHSEN D General Motors Corp. 27 KENJI UMAYAHARA Toyota Motor Corp. 27 KENJI UMAYAHARA Toyota Motor Corp. 25 KOTA MANABE Toyota Motor Corp. 2519 KOTA MANABE WALTER MARKUS Toyota Motor Daimler AG Corp. 1918 WALTER KERETLI MARKUS FAHRI Daimler Renault SAAG 18 KERETLI FAHRI Renault SA
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