Photoelectrochemical reduction of CO2 to HCOOH on silicon photocathodes with reduced SnO2 porous nanowire catalysts

Abstract

Electrochemical reduction of CO₂ to liquid products offers a route for the energy-dense storage of intermittent renewable electricity while simultaneously helping to mitigate greenhouse gas emissions. In this work, high-quality Si photocathodes decorated with an earth-abundant Sn porous nanowire catalyst utilized the energy from visible light absorption to provide a photovoltage-assisted conversion of CO₂ to liquid HCOOH. The Sn porous nanowire catalysts were selected for their high density of grain boundaries which was previously shown to enhance activity for formic acid formation. A faradaic efficiency of ∼60% with a partial current density of 10 mA cm⁻² for HCOOH was achieved at −0.4 V vs. RHE under illumination, which reflected a positive potential shift of ∼400 mV compared to the dark electrocatalytic behavior. The photo-assisted electrolysis efficiency for formic acid was calculated to be 11.0%. The results represent a promising photocathode for a narrow bandgap subcell for a tandem photoelectrode system for unbiased light-driven CO₂ electroreduction.