Metal-Free Electrocatalysts for Oxygen Reduction

Polymer electrolyte membrane (PEM) fuel cells are attracting much attention as promising clean alternative power sources to conventional power sources, including internal combustion engines and secondary batteries. Electrocatalysts for the oxygen reduction reaction (ORR) are a key component of PEM fuel cells, which convert chemical energy directly into electricity by coupling the ORR with the oxidation of fuel molecules at the other electrode via the diffusion of ions through the membrane. Although Pt-based ORR catalysts are given high priority in formulating electrodes for PEM fuel cells, they still suffer from multiple competitive disadvantages, including their high cost, susceptibility to CO gas poisoning, and fuel crossover effect. Due to their unique electrical and thermal properties, wide availability, environmental acceptability, corrosion resistance, and large surface area, certain carbon nanomaterials have recently been studied as metal-free ORR electrocatalysts to circumvent those issues associated with the Pt catalyst. Much effort has been devoted to developing metal-free ORR catalysts for fuel cells, which led to great advances in both fundamental and applied research. In this chapter, we present an overview on recent progresses in the development of metal-free ORR electrocatalysts for fuel cells.