Degradation of M-N-C Catalysts and Their Mitigation Strategies for Oxygen Reduction Reaction

Abstract

Fossil fuels come with significant disadvantages, primarily due to their contribution to greenhouse gas emissions, which drive climate change and environmental damage. This has led to an urgent need for cleaner, more sustainable energy sources. Electrochemical energy systems, such as fuel cells, metal-air batteries, and electrolyzes, offer promising alternatives for energy generation and storage. In these systems, the oxygen reduction reaction is a key process occurring at the cathode. ORR can follow two main pathways: the four-electron pathway, which directly reduces oxygen to water and is more efficient, and the two-electron pathway, which produces hydrogen peroxide as an intermediate and is less efficient. Traditionally, platinum group metals have been used as the primary catalysts for ORR due to their high activity and good stability. However, PGMs have significant drawbacks, including high cost and limited availability. These issues create challenges for the widespread adoption of sustainable energy technologies. As a result, there has been a growing interest in developing non-precious metal catalysts as alternatives. Among these, single-atom catalysts have gained attention due to their promising performance, lower cost, and greater abundance compared to PGMs. Despite these advantages, M-N-C catalysts face limitations, including low intrinsic activity and fast degradation, especially in acidic media. These weaknesses hinder their practical use and long-term stability in real-world applications. Understanding these challenges is crucial for improving the performance and durability of M-N-C catalysts for ORR. This thesis focuses on developing multiscale engineering strategies aimed at enhancing the intrinsic activity of MNCs and gaining deeper insights into their degradation mechanisms.