Efficient pathways for photogenerated charge transfer induced by Co dopants in WO3/TiO2 nanorod arrays

Modifying the energy band structure in heterostructured photocatalysts enhances charge separation efficiency and improves photoelectrochemical (PEC) performance by decreasing the charge transfer barrier. In this study, cobalt doping into WO ₃/TiO ₂ core/shell heterojunction nanorod arrays introduces versatile valence states of cobalt altering the oxygen coordination environment around W atoms in WO ₃, resulting in an increase in W ⁵⁺ ions and oxygen vacancy defects in WO ₃ lattice, facilitating the water splitting reaction. Photogenerated electrons transfer easily from the WO ₃:Co shell to the TiO ₂ core due to the lower conduction band minimum (CBM) of WO ₃:Co shell. Moreover, photogenerated holes transfer from the TiO ₂ core to the WO ₃:Co shell efficiently due to the higher valence band maximum (VBM) of TiO ₂ core. The heterostructure has a high photogenerated carrier density (9.89 × 10 ¹⁸ cm ^-3), improving photoconversion efficiency (2.55 mA cm ^-2 at 1.23 V vs. RHE) and reducing charge recombination rates (6.51 × 10 ^–4 s ^-1). Co doping increases the -OH bond on WO ₃/TiO ₂ surface, improves its hydrophilicity, and is more conducive to the reaction in aqueous electrolyte. Additionally, the nanorod array structure facilitates PEC reaction kinetics by providing open spaces for mass exchange. This work proposes a feasible strategy for improving photogenerated charge transport and enhancing PEC by combining regulation of the band structure of WO ₃/TiO ₂ heterostructures with morphology design.