TiO2/BiVO4 dual photoanodes: Extending light harvesting and addressing band edge misalignment for photoelectrochemical water splitting

Combining two photocatalysts to form heterojunctions is a common strategy to enhance the photoelectrochemical (PEC) performance in water splitting. However, this approach requires suitable band alignment between the two photocatalysts, which limits its effectiveness or even deteriorate the performance, as seen with mismatched type I heterojunctions. In this work, we design a dual photoanode configuration overcoming the unfavorable type I band alignment commonly formed in TiO₂/BiVO₄ heterojunctions. Using pulsed laser deposition (PLD), we optimized the deposition parameters to independently maximize photocurrent generation in transparent TiO₂ and BiVO₄ films, deposited separately on FTO substrates. The two photoanodes were then connected and positioned back-to-back, with the TiO₂ photoanode facing the light source and the BiVO₄ photoanode illuminated by light passing through the TiO₂ layer. The TiO₂/BiVO₄ dual photoanode generates a photocurrent of 1.72 mA/cm² at 1.3 V vs. RHE, 2.3 times higher than that of TiO₂/BiVO₄ heterojunction. Similarly, PEC hydrogen production increased to 14.2 μmol cm⁻² h⁻¹, which is 2.25 times higher than BiVO₄ alone and 2.9 times greater than TiO₂/BiVO₄ heterojunction. This improvement is attributed to the extended light absorption and larger active surface area provided by the dual photoanode, while avoiding the charge carrier recombination typically associated with type I heterojunction interfaces.