Abstract
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.
Highlights
Fuel cells are efficient energy devices that convert chemical energy sources, typically hydrogen, directly to electricity [1,2]
As emerging technologies in topics related to polymer electrolyte fuel cells (PEFCs) catalysts, we introduce clusters whose average publication year is two years younger than that of the main cluster of PEFC electrolytes (Table 10)
As an overall trend of fuel cell research, technologies regarding solid oxide fuel cells (SOFCs) and PEFC electrolytes are in the mature phase and technologies about PEFC catalysts and biofuel cells (BFCs) are receiving increased attention
Summary
Fuel cells are efficient energy devices that convert chemical energy sources (fuels), typically hydrogen, directly to electricity [1,2]. Fuel reacts with oxygen from the air. When the fuel is hydrogen, water is the resultant product and the reaction is non-harmful. The main components are a catalyst and an electrolyte (see Figure 1). A catalyst, which facilitates reactions, is deposited on an electrode, or a catalyst itself is used as an electrode. There are two types of electrodes: anode (extracting electrons) and cathode (receiving electrons). The extracted electrons that separate from the fuel pass through an electronic device and the ions are conducted through an electrolyte to form an electric circuit
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