Engineering In/In2O3 Heterointerfaces for Highly Efficient Acidic CO2-to-HCOOH Electroreduction at Ampere-Level Current Density

Efficient acidic CO2 electroreduction to formic acid (HCOOH) offers a promising pathway for chemical manufacturing, yet catalyst stability remains a major obstacle. For example, while In2O3 catalysts exhibit high selectivity toward HCOOH, the cationic In3+ species are prone to reduction to metallic In under harsh acidic conditions. Herein, we demonstrate that high-valent In3+ species are dynamically regenerated by integrating In/In2O3 heterointerfaces with periodic anodic pulses, preventing the irreversible deactivation observed under conventional steady-state conditions. Combined in situ characterizations and theoretical calculations reveal that the heterointerface enhances *OCHO intermediate formation and accelerates interfacial water dissociation to supply abundant *H, enabling highly efficient and stable HCOOH production. As a result, the In/In2O3 catalyst achieves a HCOOH Faradaic efficiency of 95.5% at –1.0 A cm–2 and maintains stability for 133 h under pulsed electrolysis in pH 2 electrolyte, significantly outperforming the neat In catalyst. Moreover, concentrated HCOOH (1.43 M) is directly produced at –0.4 A cm–2 in a solid-state electrolyte reactor. This work demonstrates that metastable high-valent active sites can be sustained under industrially relevant acidic CO2 electrolysis through synergistic interfacial stabilization and dynamic electrochemical regeneration, providing a universal strategy for catalyst-state management in electrochemical systems.