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

Photoelectrocatalytic (PEC) reduction of carbonyl-containing compounds provides a sustainable approach to upgrading biomass-derived feedstocks with reduced energy requirements. However, PEC reduction has primarily focused on hydrogen evolution and carbon dioxide reduction reactions, limited by the availability of stable photocathode materials. In this study, we demonstrate the extended PEC performance of defect-engineered CuFe2O4 films, achieving over 18 hours of stable benzaldehyde reduction to benzyl alcohol. Modulating CuFe2O4 conductivity from n-type to p-type through controlled annealing conditions enhanced its hole concentration, achieving a cathodic photocurrent density of 1.5 mA/cm2 at 0.5 V vs. RHE. Using 1,4-benzoquinone as a redox mediator in a mixed acetonitrile/water electrolyte, the PEC system produced benzyl alcohol at a rate of 2.57 μmol/h with a Faradaic efficiency of 51.3% at 0.50 V vs. Ag/AgNO₃. Photoelectrochemical impedance spectroscopy (PEIS) revealed that oxygen-rich annealing conditions improved charge transport and surface catalytic activity, resulting in a threefold increase in benzyl alcohol production rate. This PEC approach lowered the required applied potential by ~1 V compared to traditional electrocatalysis methods, offering a more energy-efficient route for carbonyl reduction. These findings underscore the potential of CuFe₂O₄ as a viable photocathode material for sustainable organic transformations under mild reaction conditions.