Gradient-Doped BiVO₄ Dual Photoanodes for Highly Efficient Photoelectrochemical Water Splitting

Bismuth vanadate (BiVO₄) is regarded as a promising photoanode candidate for photoelectrochemical (PEC) water splitting, but is limited by low efficiency of charge carrier transport and short carrier diffusion length. In this work, we report a strategy comprised of the gradient doping of W and back-to-back stacking of transparent photoelectrodes, where the 3-2 wt.% W gradient doping enhances charge carrier transport by optimizing the band bending degree and back-to-back stack configuration shortens carrier diffusion length without much sacrifice of photons. As a result, the photocurrent density of 3-2 % W:BiVO₄ photoanode reaches 2.20 mA cm^-2 at 1.23 V vs. hydrogen electrode (RHE) with a charge transport efficiency of 76.1 % under AM 1.5 G illumination, and the back-to-back stacked 3-2 % W:BiVO₄ photoanodes achieves a photocurrent of 4.63 mA cm^-2 after loading Co-Pi catalyst and anti-reflective coating under AM 1.5 G illumination, with long-term stability of 10 hours.