# Loading-Controlled Photoactivity in TiO2@BiVO4 Heterostructures

## TL;DR

This paper explores how adding BiVO4 nanoparticles to TiO2 affects the performance of photoanodes under UV and visible light.

## Contribution

The study introduces a loading-controlled approach to optimize the photoactivity of TiO2@BiVO4 heterostructures.

## Key findings

- Annealing BiVO4 increases visible light absorption due to a phase transition.
- The photocurrent response depends on the morphology of BiVO4 on TiO2.
- Thicker BiVO4 layers reduce absolute photocurrent due to transport losses.

## Abstract

In this study, we have investigated heterostructural TiO2/BiVO4 anodes to determine the effect of the amount and form of BiVO4 nanoparticles on TiO2 on the response of photoanodes under UV and visible illumination. BiVO4 nanopowders were prepared and annealed at temperatures ranging from 200 to 500 °C. Structural and optical characterization indicates that as the annealing temperature is increased, a phase transition from a weakly ordered to a dominant monoclinic BiVO4 phase is observed, which is accompanied by an increase in visible light absorption. Subsequently, the most crystalline powder was utilized to deposit BiVO4 on nanostructured TiO2 either as a compact overlayer (drop-casting) or as a progressively grown nanoparticle (TiO2@S series) in the successive ionic layer adsorption and reaction process (SILAR). Photoelectrochemical measurements were performed, revealing a morphology-dependent photocurrent response under UV and visible illumination. A further increase in the number of cycles systematically increases the photocurrent in the visible light range while limiting the response to UV radiation. The TiO2@d photoanode demonstrates the highest relative activity within the visible range; however, it also generates the lowest absolute photocurrent, indicating the presence of significant transport and recombination losses within the thick BiVO4 layer. The results demonstrate that the presence of BiVO4 nanoparticles on TiO2 exerts a substantial influence on the separation of charge between semiconductors and the synergistic utilization of photons from the UV and visible ranges. This research yielded a proposed scheme of mutual band arrangement and charge carrier transfer mechanism in TiO2@BiVO4 heterostructures.