Study on nanoporous CuBi2O4 photocathode coated with TiO2 overlayer for photoelectrochemical CO2 reduction

Investigation on the electrode/electrolyte interface of nanotextured electrodes is very challenging but critical to understand the CO2 reduction reactions. Here we present that the nanoporous CuBi2O4 photocathodes coated by a TiO2 overlayer with gradient thickness show improved CO2 reduction performance compared to pristine CuBi2O4. Different activity and selectivity for photoelectrochemical CO2 reduction are observed when the thickness of TiO2 coating layer is set at two extreme values, i.e., less and longer than its Debye length. The CuBi2O4 with a thin TiO2 layer shows higher CO/H2 yield ratio, and the one with a thick layer exhibits lower CO/H2 ratio but higher yield for both CO and H2. All these are elucidated based on the results of Mott-Schottky plots, photocurrent response and SEM/TEM images. Results indicate that the TiO2 overlayer on CuBi2O4 is in favor of the generation and separation of electron/hole pairs, and thus facilitate CO and H2 production, while the nanoporous structure and the nonuniform TiO2 overlayer on CuBi2O4 have a great impact on mass transport, local pH, and exposed active sites and, thereby, on the CO production selectivity.