Graphene Composite Catalysts for Electrochemical Energy Conversion

Graphene with high surface area, high chemical stability, excellent conductivity, unique graphitic basal plane structure, and easiness of functionalization has emerged as an important and fascinating two-dimensional material in various research fields. Upon proper doping with heteroatoms (e.g., N, S, P) and/or transition metals (e.g., Fe, Co, Ni), graphene materials have become one of the most promising catalysts in electrochemical energy storage and conversion systems, especially for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). This chapter firstly introduces the graphene catalysis and its applications in energy conversion and storage systems. The synthetic strategy of highly active graphene-based catalysts has been systematically reviewed, including heteroatom doping, transition metal doping, and integration with transition metal oxides, sulfides, and so on. Abundant examples have been provided in order to comprehensively demonstrate the research process in the related field, regarding their applications in fuel cells and metal-air batteries. The catalytic nature of doped graphene materials remains in debate, and thus graphitic and pyridinic nitrogen, most active nitrogen configurations in the graphene catalysts, have been discussed both in theory and experiment. However, elucidation of the nature of active sites in graphene materials is still very challenging, even though it is directly responsible for catalytic activity. A better understanding of the catalytic nature of active sites will benefit for the designing and synthesizing more effective graphene materials with sufficient catalytic activity and durability for practical applications in advanced energy devices. It can be expected that highly efficient electrocatalysts based on graphene materials, with improved activity, selectivity, durability, and multifunctionality, will still be the “hot spot” in electrochemical devices in the future.