Single‐Atom Enables Reverse Hydrogen Spillover for High‐Performance Protonic Ceramic Fuel Cells

Abstract Protonic ceramic fuel cells (PCFCs) offer a promising avenue for sustainable energy conversion, however, their commercial potential is hindered by sluggish proton‐involved oxygen reduction reaction (P‐ORR) kinetics and inadequate durability of cathode materials. Here, a novel single‐atom Ru anchor on BaCe 0.125 Fe 0.875 O 3−δ (BCF) perovskite, synthesized by a facile and scalable solid‐state approach, as a potential cathode for PCFCs is reported. Theoretical and experimental analyses demonstrate that the single‐atom Ru on BCF, characterized by a unique 4‐coordinate Ru‐O‐Fe configuration, not only induces reverse hydrogen spillover but also acts as an active site for P‐ORR. The application of the optimized 2Ru‐BCF (2 wt.% Ru) cathode in a single cell delivers an exceptional peak power density of 1.78 W cm −2 at 700 °C, along with excellent operational stability over 200 h. These findings provide new insights into single‐atom engineering, advancing the commercial viability of PCFCs.