# Unraveling Defect-Dependent Conductivity-Type Switching in CuFe2O4 for Enhanced Photoelectrocatalytic Reduction of Benzaldehyde

## TL;DR

A defect-engineered CuFe2O4 photocathode enables efficient and sustainable benzaldehyde reduction under mild conditions using photoelectrocatalysis.

## Contribution

A defect-tuned CuFe2O4 photocathode enables direct PEC reduction of benzaldehyde with high efficiency and low energy input.

## Key findings

- Oxygen-rich annealing stabilizes copper vacancies and enhances hole concentration in CuFe2O4.
- The optimized photocathode achieves a benzyl alcohol production rate of 2.57 μmol/h with 51.3% Faradaic efficiency.
- The PEC method reduces the required applied potential by ~1 V compared to traditional electrocatalytic methods.

## Abstract

Photoelectrocatalytic
(PEC) reduction provides a sustainable route
for upgrading biomass-derived feedstocks with reduced energy requirements,
yet remains largely unexplored beyond hydrogen evolution and CO2 reduction due to the scarcity of stable photocathodes. Here,
we report a defect-engineered CuFe2O4 photocathode
that enables directly quantified PEC reduction of benzaldehyde to
benzyl alcohol using a single-component, earth-abundant oxide. By
controlling annealing temperature and oxygen partial pressure, CuFe2O4 is systematically tuned from n-type to p-type
conductivity. Electrochemical measurements, X-ray and ultraviolet
photoelectron spectroscopy, and first-principles defect calculations
collectively show that oxygen-rich annealing conditions suppress deep
donor-type oxygen vacancies while stabilizing shallow acceptor-type
copper vacancies, resulting in enhanced hole concentration and improved
charge transport. In a mixed acetonitrile/water electrolyte employing
1,4-benzoquinone as a redox mediator, the optimized CuFe2O4 photocathode achieves stable photoelectrochemical operation
over 18 h under continuous illumination with a benzyl alcohol production
rate of 2.57 μmol/h at −0.50 V vs Ag/AgNO3, corresponding to a Faradaic efficiency of 51.3%. This PEC approach
lowers the required applied potential by ∼1 V compared to traditional
electrocatalytic methods, offering a more energy-efficient route for
carbonyl reduction. These findings establish CuFe2O4 as a viable photocathode platform for sustainable photoelectrocatalytic
organic transformations under mild reaction conditions.