Enhanced photoelectrochemical water splitting by effect of a Ni-Fe oxide surface promoter

,,Green" hydrogen production by photoelectrochemical water splitting has been widely investigated, but no commercialisation of this technology has emerged. The main issues to marketing are: low solar-to-hydrogen efficiency, expensive electrode materials, fast degradation of prototypes, and energy losses in separating hydrogen from oxygen and water vapour in the output stream. In this work, a tandem cell [1], composed by cheap hematite and cupric oxide semiconductors [2], as photoanode and photocathode, respectively, and anionic membrane is investigated. First of all, the performance of different co-catalysts (LSFCO, IrRuOx and NiFeOx), deposited onto the TCO/Fe2O3 photoanode of a photoelectrochemical cell, was carried out both under light (1.5 AM) and in the dark. PEC cells based on LSFCO and IrRuOx showed a similar performance; this was lower than the cell based on the NiFeOx promoter. Successively, we studied the effect of the surface promoter mass loading (0, 6, 12, 60 µg/cm2) by varying the precursor concentration. A volcano shaped relationship for conversion vs efficiency with the promoter concentration was observed. This resulted from a compromise between the catalytic activity and absorption properties of the surface promoter affecting the photoresponse of the tandem cell. Nichel Iron Oxide appears to promote suitably the oxygen evolution reaction at hematite photo-electrodes thus enhancing the conversion efficiency of photo-electrolysis cells.