Fuel cells have been attracting significant attention recently as highly efficient and eco-friendly energy generators. Here, we have comprehensively reviewed all types of fuel cells using computational analysis based on a citation network that detects emerging technologies objectively and provides interdisciplinary data to compare trends. This comparison shows that the technologies of solid oxide fuel cells (SOFCs) and electrolytes in polymer electrolyte fuel cells (PEFCs) are at the mature stage, whereas those of biofuel cells (BFCs) and catalysts in PEFCs are currently garnering attention. It does not mean, however, that the challenges of SOFCs and PEFC electrolytes have been overcome. SOFCs need to be operated at lower temperatures, approximately 500 • C. Electrolytes in PEFCs still suffer from a severe decrease in proton conductivity at low relative humidity and from their high cost. Catalysts in PEFCs are becoming attractive as means to reduce the platinum catalyst cost. The emerging technologies in PEFC catalysts are mainly heteroatom-doped graphene/carbon nanotubes for metal-free catalysts and supports for iron-or cobalt-based catalysts. BFCs have also received attention for wastewater treatment and as miniaturized energy sources. Of particular interest in BFCs are membrane reactors in microbial fuel cells and membrane-less enzymatic biofuel cells.

Abstract:Water electrolysis for hydrogen production has received increasing attention, especially for accumulating renewable energy. Here, we comprehensively reviewed all water electrolysis research areas through computational analysis, using a citation network to objectively detect emerging technologies and provide interdisciplinary data for forecasting trends. The results show that all research areas increase their publication counts per year, and the following two areas are particularly increasing in terms of number of publications: "microbial electrolysis" and "catalysts in an alkaline water electrolyzer (AWE) and in a polymer electrolyte membrane water electrolyzer (PEME).". Other research areas, such as AWE and PEME systems, solid oxide electrolysis, and the whole renewable energy system, have recently received several review papers, although papers that focus on specific technologies and are cited frequently have not been published within the citation network. This indicates that these areas receive attention, but there are no novel technologies that are the center of the citation network. Emerging technologies detected within these research areas are presented in this review. Furthermore, a comparison with fuel cell research is conducted because water electrolysis is the reverse reaction to fuel cells, and similar technologies are employed in both areas. Technologies that are not transferred between fuel cells and water electrolysis are introduced, and future water electrolysis trends are discussed.

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One-to-one inclusion compounds were obtained in high yields by the treatment of β- and γ-cyclodextrins(CD) with di-μ-chloro-bis(η3-allyl)dipalladium complex and its analogues. The formation of inclusion compounds is selective.

Hydrogen technologies are promising candidates of new energy technologies for electric power load smoothing. However, regardless of long-term public investment, hydrogen economy has not been realized. In Japan, the National Research and Development Institute of New Energy and Industrial Technology Development Organization (NEDO), a public research-funding agency, has invested more than 200 billion yen in the technical development of hydrogen-related technologies. However, hydrogen technologies such as fuel cell vehicles (FCVs) have not been disseminated yet. Continuous and strategic research and development (R&D) are needed, but there is a lack of expertise in this field. In this study, the transition of the budgetary allocations by NEDO were analyzed by classifying NEDO projects along the hydrogen supply chain and research stage. We found a different R&D focus in different periods. From 2004 to 2007, empirical research on fuel cells increased with the majority of research focusing on standardization. From 2008 to 2011, investment in basic research of fuel cells increased again, the research for verification of fuel cells continued, and no allocation for research on hydrogen production was confirmed. Thereafter, the investment trend did not change until around 2013, when practical application of household fuel cells (ENE-FARM) started selling in 2009, in terms of hydrogen supply chain. Hydrogen economy requires a different hydrogen supply infrastructure, that is, an existing infrastructure of city gas for ENE-FARM and a dedicated infrastructure for FCVs (e.g., hydrogen stations). We discussed the possibility that structural inertia could prevent the transition to investing more in hydrogen infrastructure from hydrogen utilization technology. This work has significant implications for designing national research projects to realize hydrogen economy.