Advanced Air Electrodes for Reversible Protonic Ceramic Electrochemical Cells: A Comprehensive Review

Reversible protonic ceramic electrochemical cells (R-PCECs) have great potential for efficient and clean power generation, energy storage, and sustainable synthesis of high-value chemicals. However, the sluggish and unstable kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in the air electrode hinder the R-PCEC development. Durable H⁺/e^-/O^2- triple-conducting air electrode materials are promising for enhancing reaction kinetics and improving catalytical stability. This review synthesizes the recent progress in triple-conducting air electrodes, focusing on their working mechanisms, including electrode kinetics, lattice and its defect structure in oxides, and the generation and transport processes of H⁺, O^2-, and e^-. It also examines the required physicochemical properties and their influencing factors. By synthesizing and critically analyzing the latest theoretical frameworks, advanced materials, and regulation strategies, this review outlines the challenges and prospects shaping the future of R-PCEC technology and air electrode development. Based on these theories and multiple strategies about the bulk triple conducting properties and surface chemical states, this review provides practical guidance for the rational design and development of efficient and stable air electrode materials for R-PCECs and related electrocatalytic materials.