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 TiO 2 /BiVO 4 heterojunctions. Using pulsed laser deposition (PLD), we optimized the deposition parameters to independently maximize photocurrent generation in transparent TiO 2 and BiVO 4 films, deposited separately on FTO substrates. The two photoanodes were then connected and positioned back-to-back, with the TiO 2 photoanode facing the light source and the BiVO 4 photoanode illuminated by light passing through the TiO 2 layer. The TiO 2 /BiVO 4 dual photoanode generates a photocurrent of 1.72 mA/cm 2 at 1.3 V vs. RHE, 2.3 times higher than that of TiO 2 /BiVO 4 heterojunction. Similarly, PEC hydrogen production increased to 14.2 μmol cm −2 h −1 , which is 2.25 times higher than BiVO 4 alone and 2.9 times greater than TiO 2 /BiVO 4 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. • TiO 2 and BiVO 4 photoanodes were optimized by PLD. • TiO 2 /BiVO 4 Dual photoanode was fabricated. • TiO 2 /BiVO 4 Dual photoanode addresses the limitations of TiO 2 /BiVO 4 heterojunction. • The TiO 2 /BiVO 4 Dual generates 2.3 times more photocurrent than the heterojunction. • The dual photoanode delivers an amount of 14.2 μmol cm −2 h −1 of hydrogen.