Photogenerated charge separation at BiVO4 photoanodes enhanced by a Ag-modified porphyrin polymer skeleton

Abstract

Bismuth vanadate (BiVO₄) has been considered a promising photoactive material in photoelectrochemical (PEC) water-splitting systems. However, the performance of BiVO₄-based photoanodes is currently unsatisfactory, indicating the need for new architectural designs to improve their efficiency. In this paper, a porphyrin-phosphazene polymer (THPP-HCCP) was synthesized with a sizeable conjugated structure, and Ag particles were deposited on its surface as an organic–inorganic composite interface improvement layer. The deposition of the composite polymer film on BiVO₄ resulted in a significant increase in photocurrent density, reaching up to 2.2 mA cm⁻² (1.23 V vs. RHE), almost three times higher than pristine BiVO₄, which benefits from the synergistic effect of Ag nanoparticles and porphyrin-phosphazene. Furthermore, photophysical and intensity-modulated photocurrent analysis demonstrated that the Ag–THPP-HCCP heterostructures could broaden the light-absorbing range and facilitate hole transfer to the semiconductor surface, resulting in an improved water oxidation process. The dynamic charge transport behavior of Ag–THPP-HCCP/BiVO₄ was investigated using scanning photoelectrochemical microscopy, which showed that the rate constant (K_eff) exhibits an almost 4-fold increase compared to pristine BiVO₄, indicating a significant improvement in the transport of photogenerated holes. This experiment presents a novel strategy for designing high-efficiency polymer-based photoanodes.