Carbon-encapsulated electrocatalysts for oxygen electrocatalysis

Abstract

Oxygen electrocatalysis, which underpins key energy conversion technologies through the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), is plagued by inherently sluggish kinetics arising from its four-electron-proton coupled mechanism. This bottleneck necessitates the development of high-performance electrocatalysts to surmount energy barriers and advance practical device efficiency. Encapsulated electrocatalysts (EECs), a class of materials comprising carbon-based outer layers (OCLs) and metal-based inner components (IMCs), have emerged as a transformative solution, leveraging synergistic OCL-IMC interfaces to simultaneously enhance activity, stability, and electrical conductivity. This review synthesizes recent progress in EEC design for oxygen electrocatalysis, focusing on three interconnected pillars: (1) Mechanistic insights into active sites, where debates over the dominant role of OCLs versus IMCs are addressed through advanced in situ characterization and density functional theory (DFT) simulations, unraveling critical phenomena such as interfacial charge redistribution and d-p orbital hybridization; (2) Quantitative structure-performance relationships, which reveal how OCL and IMC modulate electron transfer and mass transport; (3) Scalable synthesis strategies with a focus on parameter control to tailor OCL-IMC architecture. Despite these advances, unresolved challenges persist, including ambiguous active-site localization and poorly understood dynamic interfacial behavior under operating conditions. Addressing these requires next-generation operando characterization tools and machine-learning-guided modeling frameworks. Future directions must prioritize scalable synthesis of defect-engineered EECs, integration of in situ techniques to decode reaction mechanisms, and establishment of robust quantitative structure-performance relationships. By bridging molecular-level insights with macroscopic performance, this review provides a blueprint for rational EEC design, accelerating their deployment in next-generation energy devices with unprecedented efficiency and durability.