BiVO4/Bi:NiO/Co–Ci photoanode and BiVO4–Cu3BiS3 tandem cell for unbiased solar hydrogen evolution and simultaneous urea oxidation

Abstract

Photoelectrochemical urea oxidation enabled by BiVO₄ photoanodes offers an attractive and sustainable pathway for concurrently achieving efficient hydrogen production and efficient remediation of urea-rich wastewater. However, the intrinsically sluggish kinetics of the urea oxidation reaction, coupled with inefficient interfacial charge transfer at the electrode/electrolyte interface, remain critical challenges that hinder the further enhancement of photoelectrochemical urea oxidation performance of BiVO₄ photoanodes. Herein, we report a rational surface engineering strategy to enhance both the efficiency and stability of BiVO₄ photoanodes via the construction of a NiO hole transport layer and Co–Ci cocatalyst. Furthermore, a Bi ion doping strategy was adopted to further optimize the hole-extraction capability of NiO, thereby promoting charge separation and transport. Ultimately, the champion BiVO₄/2.5%Bi:NiO/Co–Ci photoanode delivered a photocurrent density of 5.8 mA cm⁻² at 1.23 V_RHE, a Faradaic efficiency of 88.6%, and excellent operational stability exceeding 8 hours. Notably, integration with a Cu₃BiS₃ photocathode enables a BiVO₄–Cu₃BiS₃ tandem cell for unbiased, solar-driven, coupled urea oxidation and hydrogen evolution, delivering a photocurrent density of 2.0 mA cm⁻² and stable operation exceeding 20 hours. This work presents a viable approach to overcoming the inherent challenges of BiVO₄ photoanodes for photoelectrochemical urea oxidation, underscoring their potential for integrated solar energy conversion and wastewater remediation.