Solar-Driven Reduction of 1 atm CO2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO2-Protected III-V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C Cathode Electrocatalyst

A solar-driven CO2-reduction (CO2R) cell, consisting of a tandem GaAs/InGaP/TiO2/Ni photoanode in 1.0 M KOH(aq) (pH=13.7) to facilitate the oxygen- evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8 M KHCO3(aq) (pH=8.0) to perform the CO2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values, was constructed. At the operational current density of 8.5 mA cm(-2), in 2.8 M KHCO3(aq), the cathode exhibited <100 mV overpotential and >94% Faradaic efficiency for the reduction of 1 atm of CO2(g) to formate. The anode exhibited 320 +/- 7 mV overpotential for the OER in 1.0 M KOH(aq), and the bipolar membrane exhibited similar to 480 mV voltage loss with minimal product crossover as well as >90% and >95% selectivity for protons and hydroxide ions, respectively. The solardriven CO2R cell converted sunlight to fuels at an energy-conversion efficiency of similar to 10%.