Photoelectrochemical performance of a spin coated TiO 2 protected BiVO 4 -Cu 2 O thin film tandem cell for unassisted solar water splitting.

A tandem cell consisting of a Mo-BiVO 4 /TiO 2 /FeOOH photoanode-Cu 2 O/TiO 2 /MoS 2 photocathode was prepared for unassisted solar water splitting. The protective TiO 2 layer was prepared by a cost-effective spin coating technique. The individual Mo-BiVO 4 /TiO 2 /FeOOH photoanode and the Cu 2 O/TiO 2 /MoS 2 photocathode yielded a current density of ∼0.81 mA cm -2 at 1.23 V vs. RHE and ∼-1.88 mA cm -2 at 0 V vs. RHE, respectively under 100 mW cm -2 xenon lamp illumination. From the individual photoelectrochemical analysis, we identify the operating points of the tandem cell as 0.66 V vs. RHE and 0.124 mA cm -2 . The positive current density from the operating points proves the possibility of non-zero operation of the tandem cell. Finally, a two-electrode Mo-BiVO 4 /TiO 2 /FeOOH-Cu 2 O/TiO 2 /MoS 2 tandem cell was constructed and analysed for unassisted operation. The obtained unassisted current density of the tandem cell was ∼65.3 μA cm -2 with better stability compared to the bare BiVO 4 -Cu 2 O tandem cell. The results prove that the spin coated TiO 2 protective layer can be a viable approach to protect the photoelectrodes from photocorrosion with better stability and enhanced photoelectrochemical (PEC) performance.