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 into energy-dense liquids, such as formic acid, is desirable as a hydrogen carrier and a chemical feedstock. SnO is one of the few catalysts that reduce CO into formic acid with high selectivity but at high overpotential and low current density. We show that an electrochemically reduced SnO porous nanowire catalyst (Sn-pNWs) with a high density of grain boundaries (GBs) exhibits an energy conversion efficiency of CO -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 nanoparticles confirms that the improved CO 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 conversion industry.