A Review of Carbon-based Non-noble Catalysts for Oxygen Reduction Reaction

Proton exchange membrane fuel cells (PEMFCs) that directly convert chemical energy into electrical energy can be applied to portable power and fuel cell electric vehicles, due to their advantages such as environment-friendliness, high power density and high convert efficiency.However, the high loading of Pt-based catalysts on the cathode oxygen reduction reaction (ORR) hinder the commercial application of PEMFCs for the high price, resource shortage and easy poisoning of Pt.Thus, developing inexpensive, high performance and durability non-noble metal cathode catalysts will promote the large-scale commercialization of PEMFCs.As the most likely alternative to Pt, carbon-based non-noble ORR catalysts have been widely studied.In this review, firstly, the electrocatalytic mechanism for ORR is simply introduced.Secondly, the carbon-based non-noble ORR catalysts are divided into transition metal-nitrogen-carbon compounds (M-N-C) and non-metal heteroatom-doped carbon catalysts; the researches of material preparations and active sites are summarized and discussed.Thirdly, the applications of carbon-based non-noble ORR catalysts in PEMFC are reviewed.Although great progress has been achieved in this area of research and development, there are still some challenges for carbon-based non-noble ORR catalysts.Firstly, the ORR electrocatalytic mechanism isn't clear, especially carbon-based non-noble catalysts.Secondly, the ORR active sites of carbon-based non-noble catalysts remain controversial, which can be mainly divided into the transition metal coordination compounds, the doped heteroatom, the filled metal and the defect sites.Thirdly, the actual activity and stability of carbon-based non-noble catalysts are still below the PEMFC target.In summary, the future research directions on carbon-based non-noble catalysts for PEMFC applications would be proposed as follows: (1) fundamentally understanding the ORR mechanisms and their relationship with catalyst active site structures and composition using both theoretical calculations and experimental approaches; (2) improving catalyst activity and stability to satisfy the practical application of PEMFC.