Recent Advances in M-N-C Electro-catalysts for O<sub>2</sub> Reduction Reaction in Fuel Cells

Transition metal–nitrogen–carbon (M-N-C) catalytic materials are widely considered the most promising non-Pt metal for oxygen reduction reaction (ORR), they are extensively studied as potential electrocatalysts in energy conversion and storage devices like fuel cells. The ORR is a critical reaction that significantly impacts the performance and efficiency of these devices. Recently, tremendous researches have been made to obtain high-performance M-N-C catalysts. This review article provides insights into the mechanism of the O<sub>2</sub> reduction reaction, offering insights that are crucial for designing effective catalysts. It also provides a detailed account of the recent progress in the synthetic methods, which are pivotal for tailoring the structure and properties of M-N-C materials. The article also examines different transition metal - nitrogen - carbon species, the choice of transition metal and its coordination environment significantly influence the electronic structure and catalytic activity. Furthermore, it highlights approaches to enhance the catalytic activity of M-N-C catalysts, these strategies aim to optimize the active sites and improve electron transfer, thereby boosting ORR performance. Finally, several key factors must be solved to create efficient and robust electrocatalysts are summarized briefly.