Efficient solar-driven water splitting by nanocone BiVO(4)-perovskite tandem cells

Bismuth vanadate (BiVO(4)) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO(4) photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO(4) film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO(4) (Mo:BiVO(4)) on an engineered cone-shaped nanostructure, in which the Mo:BiVO(4) layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO(4)/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm(−2) at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%.