A review of nitrogen-doped graphene catalysts for proton exchange membrane fuel cells-synthesis, characterization, and improvement

Platinum group metals (PGM), such as platinum (Pt) or ruthenium (Ru), are the most common catalyst materials for the oxygen reduction reaction (ORR) because of their excellent catalytic performance. However, the high raw material cost of PGM catalysts has become a significant issue. Currently, the nitrogen-doped graphene (N-G) catalyst emerges as one of the promising non-PGM catalysts with the advantages of low cost and high ORR catalytic performance to replace expensive PGM catalysts in electrochemical systems. This paper reviews the investigation of N-G catalysts through the synthesis, characterization, and improvement methodologies. And comparisons between various chemical and mechanochemical synthesis methods and the properties of final N-G catalysts are discussed as well. The paper also reviewed a nanoscale high energy wet ball milling (NHEW) method which was investigated recently for the synthesis of N-G catalysts. Recent research results show that the performance of the N-G catalyst is already comparable to the commercialized Pt/C catalyst. It is also possible to enhance the electrochemical performance of N-G catalysts by the modification of metal organic framework (MOF) materials. The new MOF-modified N-G catalyst shows higher current density than Pt/C catalyst.