Carbons as low-platinum catalyst supports and non-noble catalysts for polymer electrolyte fuel cells

Polymer electrolyte fuel cells, including acidic proton exchange membrane fuel cells (PEMFCs) and alkaline anion exchange membrane fuel cells (AEMFCs), are the types of the most promising high-efficiency techniques for conversion hydrogen energy to electricity energy. However, the catalysts' insufficient activity and stability toward oxygen reduction reaction (ORR) at the cathodes of these devices are still the important constraints to their performance. So far, carbon black supported platinum (Pt/C) and its alloys are still the most practical and best-performing type of catalysts. However, the scarcity of Pt is highly challenging and the high price of commercial catalyst will continue to drive up the cost of both PEMFCs and AEMFCs. Moreover, the traditional carbon black support is susceptible to corrosion especially under electrochemical operation, itself inactive for ORR and weakly binding with Pt-based nanoparticles. In this review, the advanced carbons synthesized by various template methods, including hard-template, soft-template, self-template and combined-template, are systematically evaluated as low-Pt catalyst supports and non-noble catalysts. For the templates-induced carbon-based catalysts, this review presents a comprehensive overview on the carbon supported low-Pt catalysts from aspect of composition, size and shape control as well as the non-noble carbon catalysts such as transition metal-nitrogencarbons, metal-free carbons and defective carbons. Furthermore, this review also summarizes the applications of low/non-Pt carbon-based catalysts base on the template-induce advanced carbons at the cathodes of PEMFCs and AEMFCs. Overall, the templates-induced carbons can show some perfect attributes including ordered morphology, reasonable pore structure, high conductivity and surface area, good corrosion resistance and mechanical property, as well as strong metal-support interaction. All of these features are of particular importance for the construction of high-performance carbon-based ORR catalysts. However, some drawbacks mainly involve the removal of templates, maintenance of morphological structure, and demetalation. To address these issues, this review also summarizes some effective strategies, such as employing the easily removed hard/soft-templates, developing the advantageous self-templates, enhancing the metal-support interaction by formation of chemical binds, etc. In conclusion, this review provides an effective guide for the construction of template-induced advanced carbons and carbon-based low/non-Pt catalysts with analysis of technical challenges in the development of ORR electrocatalysts for both PEMFCs and AEMFCs, and also proposes several future research directions for overcoming the challenges towards practical applications.