Improving cathode electrocatalysis via Co-substitution-driven interstitial transport for proton-conducting solid oxide fuel cells

• Co substitution in La 1.2 Sr 0.8 NiO 4+δ causes structural reorganization. • Co incorporation induces the accommodation of interstitial oxygen species. • The oxygen and proton transport kinetics are concurrently optimized. • The resultant La 1.2 Sr 0.8 Ni 0.5 Co 0.5 O 4+δ cathode generates 1.7 W cm −2 at 700 °C. Strategic engineering of B-site coordination environment in K 2 NiF 4 -type oxides presents a rational pathway to optimize electrocatalytic functionality. Herein, Co substitution in La 1.2 Sr 0.8 NiO 4+δ (LSNO) induces structural reorganization that accommodates excess interstitial oxygen species, enabling dual enhancement of ionic transport with 30-fold enhanced oxygen diffusion and 3.5–11.1-fold improved proton migration. The NiO-BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ |BaZr 0.1 Ce 0.7 Y 0.2 O 3-δ |La 1.2 Sr 0.8 Ni 0.5 Co 0.5 O 4+δ (LSNCO) cell demonstrates exceptional electrochemical performance with the power density of 1698 mW cm −2 and polarization resistance of 0.056 Ω cm 2 at 700 °C, outperforming both LSNO counterpart and reported Ln 2 NiO 4 -based cathodes. The synergistic integration of exceptional power generation, optimized interfacial polarization, and excellent operational stability establishes LSNCO as a benchmark cathode material for proton conducting solid oxide fuel cells. This study systematically validates a Co-mediated B-site coordination engineering strategy in K 2 NiF 4 -type lattices, providing a generalized framework for designing high electrocatalytically active electrodes with coupled ionic transport channels.