BiVO 4 Photoanode with NiV 2 O 6 Back Contact Interfacial Layer for Improved Hole-Diffusion Length and Photoelectrochemical Water Oxidation Activity.

The short hole diffusion length (HDL) and high interfacial recombination are among the main drawbacks of semiconductor-based solar energy systems. Surface passivation and introducing an interfacial layer are recognized for enhancing HDL and charge carrier separation. Herein, we introduced a facile recipe to design a pinholes-free BiVO 4 photoanode with a NiV 2 O 6 back contact interfacial (BCI) layer, marking a significant advancement in the HDL and photoelectrochemical activity. The fabricated BiVO 4 photoanode with NiV 2 O 6 BCI layer exhibits a 2-fold increase in the HDL compared to pristine BiVO 4 . Despite this improvement, we found that the front surface recombination still hinders the water oxidation process, as revealed by photoelectrochemical (PEC) studies employing Na 2 SO 3 electron donors and by intensity-modulated photocurrent spectroscopy measurements. To address this limitation, the surface of the NiV 2 O 6 /BiVO 4 photoanode was passivated with a cobalt phosphate electrocatalyst, resulting in a dramatic enhancement in the PEC performance. The optimized photoanode achieved a stable photocurrent density of 4.8 mA cm -2 at 1.23 V RHE , which is 12-fold higher than that of the pristine BiVO 4 photoanode. Density Functional Theory (DFT) simulations revealed an abrupt electrostatic potential transition at the NiV 2 O 6 /BiVO 4 interface with BiVO 4 being more negative than NiV 2 O 6 . A strong built-in electric field is thus generated at the interface and drifts photogenerated electrons toward the NiV 2 O 6 BCI layer and photogenerated holes toward the BiVO 4 top layer. As a result, the back-surface recombination is minimized, and ultimately, the HDL is extended in agreement with the experimental findings.