# Surface hole polaron site tuning governs charge carrier separation in BiVO4 photoanodes

## TL;DR

This paper shows how modifying the surface of a material can improve its ability to split water using sunlight, boosting efficiency for clean energy production.

## Contribution

A surface-selective strategy using In3+ substitution to suppress hole polarons in BiVO4 is proposed and experimentally validated.

## Key findings

- In3+ substitution weakens electron-phonon coupling and suppresses hole polaron formation.
- The optimized photoanode achieves a 6.46 mA cm-2 photocurrent density and 2.19% photo-to-current efficiency.
- The unbiased tandem system reaches a 6% solar-to-hydrogen conversion efficiency.

## Abstract

The self-trapping of charge carriers, resulting in the formation of polarons, significantly restricts the separation and transport of charge carriers in photoelectrochemical systems. Herein, using bismuth vanadate as a model photoanode, we propose a surface-selective strategy to regulate hole polarons. Density functional theory calculations predict that substituting bismuth ions with indium ions suppresses hole polaron formation by weakening electron-phonon coupling. This substitution is achieved through a liquid-phase cation exchange method, enabling precise surface modification. The electron paramagnetic resonance, temperature-dependent photoluminescence spectroscopy, in situ irradiation X-ray photoelectron spectroscopy, and femtosecond time-resolved absorption spectroscopy all confirm the suppression of hole polaron formation. After loading co-catalyst, the optimized photoanode achieves a water-splitting photocurrent density of 6.46 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, with an applied bias photo-to-current efficiency of 2.19%. The unbiased tandem system exhibits a solar-to-hydrogen conversion efficiency of 6%. Here, we show that suppressing surface hole polaron formation facilitates hole carrier release, offering a pathway for enhancing photoelectrochemical performance.

Surface-selective In3+ substitution in BiVO4 suppresses hole polarons by weakening electron-phonon coupling. This strategy releases trapped carriers, significantly enhancing solar water splitting efficiency for sustainable fuel production.