# Photoswitchable Activity of Mixed Bismuth Oxide (BiO x ) for Water Splitting in Neutral Media

## TL;DR

Researchers found that bismuth oxide can be used for water splitting with improved efficiency when exposed to light.

## Contribution

The study reveals the photoswitchable properties of bismuth oxide for enhanced water splitting in neutral media.

## Key findings

- Illumination reduced electrodeposition time from 90 to 10 minutes without changing the amperometric profile.
- BiOx achieved a higher current density under light (2.5 mA cm–2) compared to dark conditions.
- Light exposure decreased depletion layer resistance and improved intrinsic conductivity.

## Abstract

Unary bismuth oxide (BiO
x
), containing
both Bi3+ and Bi5+ species, exhibits a photoswitchable
response that, to the best of our knowledge, has not yet been reported.
The material has attracted increasing attention as an anode for the
oxygen evolution reaction (OER), often in combination with additional
elements to enhance electrochemical performance. This study investigates
the electrodeposition of BiO
x
and its
unexplored photoswitchable properties as an anode for solar-driven
enhanced water splitting. Illumination with a xenon lamp equipped
with solar simulation filters reduced the deposition time from 90
to 10 min without altering the amperometric profile, offering significant
energy savings and potential for scale-up. Structural and morphological
characterization were performed using scanning electron microscopy
with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction
(XRD). Chopped light voltammetry revealed that the photocurrent in
neutral media has a mixed photo- and electrocatalytic contribution.
Under illumination, the BiO
x
electrode
achieved a total current density of 2.5 mA cm–2,
140 mV lower than in dark conditions. Electrochemical impedance spectroscopy
(EIS) revealed a decrease in depletion layer resistance with illumination,
and an electrolyte-free impedance measurement indicated that changes
in intrinsic conductivity also contribute to the PEC response. Overall,
illumination enhances BiO
x
electrocatalytic
water splitting, with a particularly pronounced effect on thin-layer
films.