Activating SnOx-Coated Cu2O Photocathodes for Efficient Photoelectrochemical CO2 Reduction and Unassisted Tandem Device Integration

Efficient and selective photoelectrochemical CO2 reduction remains a significant challenge for solar fuel production. Here, we fabricated a heterostructured Cu2O photocathode featuring a pristine SnO2 layer deposited via atomic layer deposition. Upon photoelectrochemical activation, the SnO2 layer transformed into uniformly distributed Sn/SnOₓ nanoparticles across the photocathode surface. Systematic characterization revealed the SnO2 layer's structural evolution. The activated Cu2O 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 materials-based strategy for efficient PEC CO2 reduction and underscores the potential of tandem architectures for sustainable solar fuel generation.