Fully solution-processable Cu2O–BiVO4 photoelectrochemical cells for bias-free solar water splitting

We report a fully solution processable bias-free photoelectrochemical (PEC) cell for overall solar water splitting using a Cu2O photocathode and a BiVO4 photoanode. They were modified with catalytic multilayers (CMs) for hydrogen and oxygen evolution reactions (HER and OER), respectively, using simple and versatile layer-by-layer (LBL) assembly. The deposition of the respective CMs composed of cationic polyelectrolyte and anionic molecular polyoxometalate (POM) electrocatalysts resulted in remarkably improved performance in terms of both photocatalytic activity and stability. Detailed PEC analysis revealed that the CMs not only facilitated (1) charge transport to and (2) catalytic charge transfer at the photoelectrode/electrolyte interface, but also suppressed the deactivation of photoelectrodes, especially a labile Cu2O photocathode, by the formation of a protective coating layer. As a result, we could successfully fabricate an efficient and stable PEC cell for unassisted solar water splitting without the use of toxic/hazardous chemicals and energetic processes, which have been inevitably employed. We believe that this study provides a simple and versatile platform for the design and fabrication of various forms of electrochemical PEC devices in an environmentally friendly manner.