Nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

The oxygen reduction/evolution reactions (ORR/OER) are a key electrode process in the development of electrochemical energy conversion and storage devices, such as metal-air batteries and reversible fuel cells. The search for low-cost high-performance nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER alternatives to the widely-used noble metal-based catalysts is a research focus. This review aims to outline the opportunities and available options for these nanocarbon-based bifunctional electrocatalysts. Through discussion of some current scientific issues, we summarize the development and breakthroughs of these electrocatalysts. Then we provide our perspectives on these issues and suggestions for some areas in the further work. We hope that this review can improve the interest in nanocarbon-based metal-free and non-precious metal bifunctional electrocatalysts for ORR/OER.