In Situ Structural Study of MnPi-Modified BiVO4 Photoanodes by Soft X-ray Absorption Spectroscopy

In this study we demonstrate that the PEC performance of BiVO4 photoanodes can be improved by deposition of a MnPi catalyst layer. We investigated the electronic structure of the layer using in situ soft X-ray absorption spectroscopy (XAS) at the Mn L-edge upon varying the applied potentials and the illumination conditions. Using the linear combination method, information on different Mn species and Mn oxidation states was obtained. We found that the charge transfer at the MnPi/electrolyte interface is affected by band bending related to the applied and built-in potential. With increasing potential the electronic properties of the MnOx layer and its structure are changing, leading to a birnessite-type layer structure associated with an electron transfer from the MnPi film to the BiVO4 photoanode. The present work should benefit the potential applications of other oxygen evolution catalysts (OECs) on photoanodes.