Spectroelectrochemical\nIdentification of CuO Impurities\nCatalyzing Water Reduction on CuBi₂O₄ Photocathodes

Abstract

We identify the function of CuO impurities in CuBi₂O₄ photocathodes significantly improving the photoelectrochemical\nwater reduction efficiency. Spectroelectrochemical photo/voltage-induced\nabsorption spectroscopies are employed to investigate the charge carrier\ndynamics of pure, CuO-impure, and CuO-covered CuBi₂O₄ photocathodes during photoelectrochemical water reduction,\nin comparison with the CuO/FTO for electrochemical water reduction.\nElectrons after photoexciation are found to accumulate at the surface\nCuO in both CuO-covered and impure CuBi₂O₄ photocathodes,\nrather than directly reducing water from the CuBi₂O₄ conduction band. A rate law analysis is employed to compare\nthe kinetics of water reduction in CuO/FTO electrochemically and CuBi₂O₄ photoelectrochemically, showing a faster water\nreduction rate constant in CuO than CuBi₂O₄.\nThe kinetic comparison demonstrates that the CuO impurity functions\nas a cocatalyst on the surface of CuBi₂O₄ during\nwater reduction due to the faster kinetics. Our results demonstrate\nthe importance of considering the catalytic function of surface impurities\nresponsible for the enhancement of water reduction efficiency.