**2. E-mobility and significance of patent research**

accumulating more than 16,000 international publications over the past 10 years. Conversely, patent study on e-mobility failed to go up by the same proportion even though it plays a tremendous role in promoting the development of technological innovation while being the focal point of a thoroughly international academic discourse. Referring to vehicles that rely on plug-in electricity for their primary energy [5], e-mobility is currently supported as a favorable approach to transform road transport by reducing carbon emissions and discussing drivers of change in the automotive industry [6, 7]. For accelerating technological progress, e-mobility has been extensively explored from commercial, political, and social network perspectives [8–10], indicating that this field represents a significant technical challenge and requires complex social changes. Even some deficiencies inherent in patent research are not to be neglected, for instance, not every technical invention is patented [11, 12]. Patent data as a special type of literature still has the advantage of being more retrievable and well organized in research for supporting scientific and technological decision, creating preferential development domains and protecting enterprise rights. Amid the rising concern and limited publication counts, new questions arise: How are patents integrated into e-mobility studies? How do e-mobility studies in turn shape them? And how, if at all, might scholars intervene

In retrospect, patent documents have been assessed in conjunction with data extracted from scientific publications and industry products to examine recent developments and research progress on cold startup of automotive proton exchange membrane fuel cells (PEMFC), complete oxidation of methane at low temperature over noble metal, powertrain architectures, adsorbed natural gas technologies, and robust battery pack for electric vehicles (EVs) [13–17]. To trace the commercial pathway for ultra-capacitor technology, patents, especially the assignment information, are analyzed combined with investment figures [18]. However, the reason for applying patents to those studies has not been pointedly outlined and reviewed. Recent articles focus on patent-based indicators as to counts, families, portfolios, and citations in evaluating the effectiveness of e-mobility technology forcing policies and identifying technological changes, particularly around EVs [19–22], while the existing literature lacks details in conclusion on specific approaches and findings. The methods and design practices of e-mobility patent studies deserving of greater attention are the ones that place references at the forefront of the discussion about technol-

The present study, with a data set of 48 journal papers, is developed to review the patent research in the field of e-mobility by integrating a bibliometric overview on keywords and citations for insights into relevant research topics and knowledge base, then to trace back to the texts for an in-depth understanding of patent-use in practice and its contexts for answering the question: Does a lower share of international publications correspond to a less useful or more difficult intersection of patent analysis, especially into a field like e-mobility involving both traditional and emerging technologies? This special issue is a bridging effort to bring together patent study and bibliometric analysis by putting a spotlight on research progress,

limitations, and potential topics in a period of industry transformation.

in these processes?

138 Scientometrics

ogy-driven innovation.

The invention of automobiles has been perceived as the promotion of global economic development and improvement of living standards by enabling mobile freedom. However, the growing concern for energy, environment, traffic safety, industrial competitiveness, and technology improvements raises the question of whether this freedom of mobility would be sustainable in the new era [7, 23]. The current and renewed interest in e-mobility can be explained in accordance with drivers of change earlier in the automotive industry. This term is not entirely new, and its central idea is urban electric cars which can be traced back to 50 years earlier than the first petrol-powered internal combustion engine vehicle (ICEV) [24, 25]. For stimulating technological progress, EVs in principle should now have a bright future; however, a lighter, cleaner, and smarter automobile era with adoption of wireless connections is in the movement [8, 9]. There is still considerable concern that efforts to date on making conventional powertrains more fuel efficient and less-polluting are insufficient [26]. This study thus is more inclined to adopt an expanded scope of e-mobility technologies other than the single category of EV-based technologies. Academics in this field are traditionally identified as having strong connections to governments and industries, as it is associated with the shift to a broader network of actors and stakeholders, ranging from automotive giants to battery-charging services providers [10, 27]. Thus, research on e-mobility not only seeks to answer the question of technology updating but is designed to give a sharp focus on changes caused by automotive industry transformation.

A wealth of technological, geographical, and industry information provided by patent has generated it to be a frequently used measure for studying basic research and anticipating emerging trends in automobile innovation [19, 21]. Bibliographic data extracted from patent documents is largely publicly available and quantitatively measurable [28, 29], which offers clear benefits in comparison with other indicators, for example, the one built upon R&D, to identify and measure patterns concerning innovative activities in uncertain technological fields [21]. Despite the controversial debate on the use of patent statistics to evaluate technological progress, the advantages prevail and empirical studies, particularly in researchintensive areas like e-mobility, support the application in obtaining an adequate output with a minimized input [11, 30]. The current publication counts contrast starkly with the significance of delving into patent issues of e-mobility. Hence, to drive further adoption of patent analysis as for e-mobility, scrutinizing related articles for progress, limitations, and potential topics is causally necessary.
