In situ Sn-doped WO3 films with enhanced photoelectrochemical performance for reducing CO2 into formic acid

We report exploiting effective Sn incorporation to enhance the photoelectrochemical activity of WO3 plate films, applied as photoanodes for photoelectrocatalytic (PEC) CO2 reduction into formic acid (HCOOH). The in situ Sn-doped WO3 films were prepared on a fluorine-doped tin oxide (FTO) substrates by a hydrothermal method with adding Na2SnO3 as the Sn precursor. Sn dopants were confirmed with an X-ray photoelectron spectroscopy (XPS), which enlarged the growth density and crystallinity of WO3 plate films. Comparing the PEC properties, Sn-doped WO3 anode exhibits a photocurrent density of 1.11 mA/cm(2) at 1.2 V vs. Ag/AgCl, which is approximately 1.4 times higher than that of the undoped films. The highest IPCE value increased from 28.3% to 45.1% after Sn doping, which is approximately 1.6 times higher than that of the undoped ones. After 3 h for PEC reduction of CO2, the maximum formic acid yield of Sn-doped WO3 film is 485 nmol/cm(2), while that of undoped WO3 film is 206 nmol/cm(2). Based on the electrochemical and photoelectrochemical analysis, the enhanced PEC performance in Sn-doped WO3 films owes to its improved carriers density, electrical conductivity, and electrons lifetime. This is the first report to investigate the effect of Sn doping on the photoelectrochemical properties of WO3 nanostructures.