Solar-Driven Photocatalytic CO2 Reduction in Water Utilizing a Ruthenium Complex Catalyst on p-Type Fe2O3 with a Multiheterojunction

A hybrid photocathode that consists of a ruthenium complex catalyst and a p-type semiconductor composed of earth-abundant elements, N,Zn-codoped Fe2O3, with a multiheterojunction structure (TiO2/N,Zn-Fe2O3/Cr2O3) was developed for the reduction of CO2 in aqueous solution with application of an electrical bias under simulated solar light irradiation. The TiO2 layer prevents contact between N,Zn-Fe2O3 and the electrolyte, so that dissolution of N,Zn-Fe2O3 by photoelectrochemical (PEC) self-reduction cannot occur. Both TiO2 and Cr2O3 significantly enhanced the cathodic photocurrent by tuning the band bending in N,Zn-Fe2O3. The use of a Ru complex with an electronic network provided by polypyrrole improved the performance and resulted in a stable photocurrent of 150 μA cm–2 for the production of HCOOH, CO, and a small amount of H2 under 1 sun irradiation with application of 0.1 V vs the reversible hydrogen electrode (RHE). The total amount of generated HCOOH, CO, and H2, two-electron-reduction products, was e...