Integrative defect engineering and NiCo-layered double hydroxide decoration of W-doped BiVO₄: a high-performance...

Solar hydrogen production using photoelectrochemical (PEC) water splitting is an efficient method for mitigating energy issues and adverse environmental impacts. BiVO₄ is a highly promising photocatalytic material for PEC water oxidation because it features appropriate bandgap and advantageous band-edge locations. However, the restricted hole diffusion length and surface electron-hole recombination in BiVO₄ result in a sluggish water-splitting process. To address the existing shortcomings, a highly effective W-BiVO₄/H/NiCo-layered double hydroxide (LDH) photoanode is designed through W doping, hydrogen treatment, and NiCo-LDH modification of BiVO₄ in this study. W-BiVO₄/H/NiCo-LDH exhibited considerably higher photocurrents, 5.89 and 1.64 times higher than those of BiVO₄ and W-BiVO₄/H at 1.23 V vs. RHE, with negatively shifted onset potentials of 270 and 170 mV, respectively. The maximum applied bias photo-to-current conversion efficiency of W-BiVO₄/H/ NiCo-LDH is 6.5 and 2.5 times higher than those of BiVO₄ and H/W-BiVO₄, respectively. Furthermore, the photoanode exhibits high surface charge injection efficiency of ∼74% and exceptional stability holding ∼91% of its initial photocurrent density after 7200 s of continuous PEC reaction. This enhancement can be attributed to three factors: (i) W doping, which enhances PEC performance through n-type doping by substituting V⁵⁺ sites with higher-valence W⁶⁺ ions, increasing donor density and electrical conductivity; (ii) subsequent hydrogen treatment, which creates oxygen vacancies that facilitate charge separation, increase the carrier concentration, and reduce the bulk charge recombination; and (iii) the NiCo-LDH layer facilitating efficient hole extraction and accelerating interfacial charge injection for the oxygen evolution reaction.