WO3/BiVO4 composite photoelectrode prepared by improved auto-combustion method for highly efficient water splitting

We report on the improvement in the water splitting efficiency of a WO₃/BiVO₄ composite photoelectrode by the application of an improved auto-combustion method to the preparation of porous BiVO₄ thin films. The unique feature of this preparation method is the addition of both NH₄NO₃, as a strong oxidizing agent, and an organic additive into BiVO₄ precursor solution. The local decomposition heat of the organic additive and oxidizing agent created a porous film with small, highly crystalline BiVO₄ particles. The photoelectrode has many advantages over existing ones, such as the high light-harvesting efficiency (LHE), a single BiVO₄ phase, the facile access of the holes to the photoelectrode/electrolyte interface, and the ease of water and oxygen diffusion. The maximum incident photon-to-current efficiency (IPCE) was estimated to be 64% (at 440 nm, 1.23 V vs. RHE) and the applied bias photon-tocurrent efficiency (ABPE) reached as high as 1.28%. This ABPE value is highest among all oxide semiconductor photoelectrodes reported previously, except for the case of a stacking photoelectrode system.