Generation of fuel from CO ₂ saturated liquids using a p-Si nanowire n-TiO ₂ nanotube array photoelectrochemical cell

Light-driven, electrically biased pn junction photoelectrochemical (PEC) cells immersed in an electrolyte of CO ₂ saturated 1.0 M NaHCO ₃ are investigated for use in generating hydrocarbon fuels. The PEC photocathode is comprised of p-type Si nanowire arrays, with and without copper sensitization, while the photoanode is comprised of n-type TiO ₂ nanotube array films. Under band gap illumination, the PEC cells convert CO ₂ into hydrocarbon fuels, such as methane, along with carbon monoxide and substantial rates of hydrogen generation due to water photoelectrolysis. In addition to traces of C3-C4 hydrocarbons, methane and ethylene were formed at the combined rate of 201.5 nM/cm ²-hr at an applied potential of -1.5 V vs. Ag/AgCl. The described technique provides a unique approach, utilizing earth abundant materials, for the photocatalytic reduction of CO ₂ with subsequent generation of higher order hydrocarbons and syngas constituents of carbon monoxide and hydrogen.