In3+-Induced In–O–Sn Superexchange and Oxygen Vacancies Synergistically Boosting Acidic CO2-to-HCOOH Electrolysis at Ampere-Current Levels over Sn-Based Perovskite Oxides

Sn-based catalysts feature significant potential for acidic CO2 electroreduction (CO2RR) to HCOOH, but encounter unsatisfactory selectivity and poor stability, especially at high current densities. Here, we report In3+-induced In–O–Sn superexchange and oxygen vacancies synergistically enabling ampere-level, selective, and stable CO2-to-HCOOH electroreduction over Sn-based perovskite oxides in a strong acid. For the proof-of-concept catalysts of SrSn1–xInxO3−δ (x = 0.05, 0.1, and 0.2), In3+ introduction not only generates additional oxygen vacancies but also engenders marked In–O–Sn superexchange. This superexchange modulates electronic structures, including the upward-shifted band center (e.g., Sn 5p) and the strengthened Sn–O bond covalency. In HCOOH production, relative to the parent SrSnO3, the SrSn1–xInxO3−δ series demonstrate enhancements in activity and selectivity (more pronounced with In3+ content) while also featuring significantly boosted stability. In strong acid (pH = 1), SrSn0.8In0.2O3−δ achieves high HCOOH selectivity of 91.2% at 1 A cm–2 and a single-pass carbon efficiency of up to 81.0%, together with a steady operation over 80 h, outperforming previously reported Sn-based catalysts. Our experiments and theoretical calculations attribute these performance improvements to the following factors: the superexchange-shifted band centers and the additional oxygen vacancies synergistically facilitating *CO2 protonation to *OCHO; the superexchange-strengthened Sn–O bond covalency stabilizing the Sn–O lattice.