Activating SnOx-coated Cu2O photocathodes for efficient photoelectrochemical CO2 reduction and unassisted tandem device integration

Abstract

Efficient and selective photoelectrochemical CO₂ reduction remains a significant challenge for solar fuel production. Here, we fabricated a heterostructured Cu₂O/Ga₂O₃/ZnGeO_x/TiO₂/SnO₂ photocathode featuring a pristine SnO₂ layer deposited via atomic layer deposition. Upon photoelectrochemical activation, the SnO₂ layer transformed into uniformly distributed SnO_x nanoparticles across the photocathode surface. Systematic characterization revealed the SnO₂ layer's structural evolution. The Cu₂O/Ga₂O₃/ZnGeO_x/TiO₂/SnO_x (activated) photocathode significantly enhanced the charge transfer characteristics and PEC CO₂ reduction performance, delivering a current density of −2.5 mA cm⁻² at −0.2 V vs. RHE and a formate faradaic efficiency of 75.4% at −0.1 V vs. RHE. Coupling with a semitransparent BiVO₄/NiCo LDH photoanode enables unassisted, solar-driven CO₂ reduction and ethylene glycol (EG) oxidation, achieving a current density of 0.11 mA cm⁻² and producing 0.13 µmol cm⁻² formate yield in the first 0.5 hour. This work presents a scalable and earth-abundant material-based strategy for efficient PEC CO₂ reduction and underscores the potential of tandem architectures for sustainable solar fuel generation.