Boosting Proton Conduction and Oxygen Reduction Kinetics via In Situ Reverse Atom Capture for Protonic Ceramic Fuel Cell Cathodes

Although triple‐conducting (H + /O 2− /e − ) cathodes have significantly advanced protonic ceramic fuel cells (PCFCs), limited proton transport and surface cation segregation remain major challenges to commercialization. Here we present a novel atomic layer deposition (ALD)‐enabled reverse atom capture strategy to achieve the in‐situ construction of a protonic conductor on the perovskite cathode. Sn species are first deposited onto PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) via ALD, followed by high‐temperature calcination. Through a reverse atom capture mechanism, Sn selectively captures Ba/Sr from the PBSCF lattice to in‐situ form a (Ba/Sr)SnO 3‐δ (BSS)@PBSCF heterostructure. This design synergistically increases oxygen vacancy concentration in PBSCF and harnesses the high protonic conductivity of BSS, thereby enhancing proton‐involved oxygen reduction reaction kinetics and suppressing cation segregation. The cells with the optimized Sn10‐PBSCF cathode deliver a peak power density of 1.90 W cm −2 at 650°C and demonstrate stable operation over 210 h. Density functional theory calculations further reveal a reduced proton migration barrier in BSS. This work introduces an efficient ALD‐enabled reverse atom capture strategy to advance the commercial viability of PCFCs.