Functional coupling hole transport and extraction units over BiVO4 for efficient solar-to-hydrogen conversion

Photoelectrochemical (PEC) water splitting based on BiVO₄ nanostructures is largely limited by the fast recombination of charge carriers and the low oxygen evolution reaction (OER) kinetics. To enhance PEC performance of BiVO₄, combining hole transport units and hole extraction units is a simple and effective methods. In this work, Co₃O₄ and NiFe layered double hydroxide (NiFe-LDH) were coupled to promote bulk-phase charge separation and solid–liquid interface transfer, which accelerated OER kinetics on surface of target photoanodes. Moreover, p-n heterojunction between BiVO₄ and Co₃O₄ suppressed charge recombination and promoted charge transfer, resulting in an effectively enhanced photocurrent density and applied bias photon to current efficiency (ABPE). To facilitate involvement of photogenerated holes in OER, BiVO₄/Co₃O₄ electrodes are coated with NiFe-LDH as a hole extraction layer using a straightforward chemical bath deposition (CBD) technique. Successful fabrication of NiFe-LDH with rich oxygen vacancies significantly improves transport of charge carriers and provides many activity sites on the electrode surface. The optimized BiVO₄/Co₃O₄/NiFe-LDH photoanode displayed a photocurrent density of 5.41 mA cm⁻² at 1.23 V_RHE with an ABPE of 1.08 % at 0.86 V_RHE under light. These values are approximately 4.66 and 8.30 times higher than those of BiVO₄ photoanodes. This study presents a powerful approach to enhance charge separation and transport in BiVO₄-based photoanodes by functionally coupling hole transport and extraction units, thereby enabling efficient solar-to-hydrogen conversion.