Reduced SnO 2 Porous Nanowires with a High Density of Grain Boundaries as Catalysts for Efficient Electrochemical CO 2 ‐into‐HCOOH Conversion

Electrochemical conversion of CO 2 into energy‐dense liquids, such as formic acid, is desirable as a hydrogen carrier and a chemical feedstock. SnO x is one of the few catalysts that reduce CO 2 into formic acid with high selectivity but at high overpotential and low current density. We show that an electrochemically reduced SnO 2 porous nanowire catalyst (Sn‐pNWs) with a high density of grain boundaries (GBs) exhibits an energy conversion efficiency of CO 2 ‐into‐HCOOH higher than analogous catalysts. HCOOH formation begins at lower overpotential (350 mV) and reaches a steady Faradaic efficiency of ca. 80 % at only −0.8 V vs. RHE. A comparison with commercial SnO 2 nanoparticles confirms that the improved CO 2 reduction performance of Sn‐pNWs is due to the density of GBs within the porous structure, which introduce new catalytically active sites. Produced with a scalable plasma synthesis technology, the catalysts have potential for application in the CO 2 conversion industry.