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 CuBi 2 O 4 photocathode and a BiVO 4 photoanode. A solution-based nitrate salt decomposition method is developed for preparing a crystalline p-type CuBi 2 O 4 film with a suitable band gap and Fermi level to serve as a photocathode for water splitting. The optimum CuBi 2 O 4 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 V RHE and reduction onset potential of ≥1.0 V RHE under 1 sun in O 2 -purged KPi electrolyte. The all-bismuth based oxide tandem cell of Pt/CuBi 2 O 4 photocathode and a cobalt-phosphate (Co-Pi) modified Mo-doped BiVO 4 photoanode give a photocurrent density of ∼0.15 mA cm –2 without any applied bias.