Synergistic Effect of Grain Boundaries and Oxygen Vacancies on Enhanced Selectivity for Electrocatalytic CO Reduction.

Dual-engineering involved of grain boundaries (GBs) and oxygen vacancies (V) efficiently engineers the material's catalytic performance by simultaneously introducing favorable electronic and chemical properties. Herein, a novel SnO nanoplate is reported with simultaneous oxygen vacancies and abundant grain boundaries (V,G-SnO/C) for promoting the highly selective conversion of CO to value-added formic acid. Attributing to the synergistic effect of employed dual-engineering, the V,G-SnO/C displays highly catalytic selectivity with a maximum Faradaic efficiency (FE) of 87% for HCOOH production at -1.2 V versus RHE and FEs > 95% for all C products (CO and HCOOH) within all applied potential range, outperforming current state-of-the-art electrodes and the amorphous SnO/C. Theoretical calculations combined with advanced characterizations revealed that GB induces the formation of electron-enriched Sn site, which strengthens the adsorption of *HCOO intermediate. While GBs and V synergistically lower the reaction energy barrier, thus dramatically enhancing the intrinsic activity and selectivity toward HCOOH.