Cobalt Hexacyanoferrate on BiVO₄ Photoanodes for Robust Water Splitting

The efficient integration of photoactive and catalytic materials is key to promoting photoelectrochemical water splitting as a sustainable energy technology built on solar power. Here, we report highly stable water splitting photoanodes from BiVO₄ photoactive cores decorated with CoFe Prussian blue-type electrocatalysts (CoFe-PB). This combination decreases the onset potential of BiVO₄ by ∼0.8 V (down to 0.3 V vs reversible hydrogen electrode (RHE)) and increases the photovoltage by 0.45 V. The presence of the catalyst also leads to a remarkable 6-fold enhancement of the photocurrent at 1.23 V versus RHE, while keeping the light-harvesting ability of BiVO₄. Structural and mechanistic studies indicate that CoFe-PB effectively acts as a true catalyst on BiVO₄. This mechanism, stemming from the adequate alignment of the energy levels, as showed by density functional theory calculations, allows CoFe-PB to outperform all previous catalyst/BiVO₄ junctions and, in addition, leads to noteworthy long-term stability. A bare 10-15% decrease in photocurrent was observed after more than 50 h of operation under light irradiation.