All-Bismuth-Based Oxide Tandem Cell for Solar Overall Water Splitting

Photoelectrochemical overall water splitting without an external bias is demonstrated using an all-bismuth-based oxide tandem cell with a CuBi2O4 photocathode and a BiVO4 photoanode. A solution-based nitrate salt decomposition method is developed for preparing a crystalline p-type CuBi2O4 film with a suitable band gap and Fermi level to serve as a photocathode for water splitting. The optimum CuBi2O4 photocathode is prepared by three-layer deposition and heat-treatment at 823 K, which yields the highest photocurrent density of −0.66 mA cm–2 at 0.4 VRHE and reduction onset potential of ≥1.0 VRHE under 1 sun in O2-purged KPi electrolyte. The all-bismuth based oxide tandem cell of Pt/CuBi2O4 photocathode and a cobalt-phosphate (Co-Pi) modified Mo-doped BiVO4 photoanode give a photocurrent density of ∼0.15 mA cm–2 without any applied bias.