Emerging Carbon-Based Catalysts for the Oxygen Reduction Reaction: Insights into Mechanisms and Applications

The oxygen reduction reaction (ORR), as a key electrode process in fuel cells and metal-air batteries, plays a pivotal role in advancing clean energy technologies. However, the slow kinetics and high overpotential of the ORR significantly limit the efficiency of these energy devices. Therefore, the development of efficient, stable, and cost-effective ORR catalysts has become a central focus of current research. Carbon-based catalysts, with their excellent conductivity, chemical stability, and tunable structural features, have emerged as promising alternatives to traditional precious metal catalysts. Nevertheless, challenges remain in the design of active sites, the tuning of electronic structures, and the large-scale synthesis of carbon-based catalysts. This review systematically introduces the fundamental mechanisms and key factors influencing the ORR, providing an analysis of the critical variables that affect catalyst performance. Furthermore, it summarizes several common methods for synthesizing carbon-based catalysts, including pyrolysis, deposition, and ball milling. Following this, the review categorizes and discusses the latest advancements in metal-free carbon-based catalysts, single-atom and dual-atom catalysts, as well as metal-based nanoparticle catalysts, with a particular focus on their mechanisms for enhancing the ORR performance. Finally, the current state of research on carbon-based ORR catalysts is summarized, and future development directions are proposed, emphasizing the optimization of active sites, improvements in catalyst stability, and potential strategies for large-scale applications.