Perceptions of metal-nitrogen-carbon catalysts for oxygen reduction reaction

Abstract

Non-noble metal-nitrogen-carbon (M-N-C) catalysts are promising alternatives to precious platinum (Pt) group metals-based catalysts for oxygen reduction reactions (ORR). However, their practical applications toward proton exchange membrane fuel cells and metal-air batteries remain challenging because of the insufficient electrocatalytic activity and stability. In this review, a comprehensive perception of M-N-C catalysts has been summarized in terms of the electrocatalytic fundamentals (ORR mechanisms and degradation mechanisms), identification of active sites (metal-nanoparticle, metal-atom, and non-metal), design of regulation strategies (improving intrinsic activity of active sites, increasing site density, and enhancing fundamental properties of carbon-based materials), and advanced characterization techniques (in-situ and operando) for understanding of the structure-performance relationship. Particularly, this review highlights the innovative strategies for the improvement of intrinsic activity through optimizing the catalysts’ coordination numbers, coordination shell, and peripheral environment. Also, for obtaining in-depth insight into M-N-C catalysts, the potential challenges and possible perspectives are presented. This review aims to providing a valuable guideline for efficient and stable non-noble metal carbon catalysts.