Boosting the Performance of Cu₂O/<i>p</i>-Si Hybrid Photocathodes for Solar-Driven H₂ Generation: from Charge Dynamics to Thermodynamic Factors

Solar fuels are a promising approach for providing sustainable fuels by harnessing sunlight. Hydrogen evolution using photoelectrochemical (PEC) cells is a promising solution. Herein, a hybrid photocathode of a <i>p</i>-type Si array coupled with a Cu₂O heterostructure and a SnS_x cocatalyst (<i><b>p</b></i><b>-Si/PANI/Cu</b>_<b>2</b><b>O/SnS</b>_<b>x</b>) was synthesized for the PEC H₂ evolution reaction (HER). The optimized <i>p</i>-Si/PANI/Cu₂O/SnS_x array delivered 1.76 mmol/cm² H₂ with a current density of 21.5 mA/cm² at 0 V_RHE (reversible hydrogen electrode), achieving an applied bias photon-to-current efficiency of 2.52% in a harsh alkaline electrolyte under one-sun condition. Regarding the thermodynamic factor, the characterization of the device has enabled a comprehensive understanding of the anodic shift in the onset potential due to SnS_x deposition. For charge dynamics, the charge transfer kinetics and surface energetics in this hybrid photoelectrode were improved to ensure the collection of photogenerated carriers. In addition, an integrated device of the optimal Si photocathode for the HER with the BiVO₄ photoanode for the oxidation of triethanolamine (<b>Si/PANI/Cu</b>_<b>2</b><b>O/SnS</b>_<b>x</b><b>||BVO-TEOA</b>) could be successfully constructed to achieve an unassisted PEC system with an approximate photocurrent density of 1.2 mA/cm². This work paves the way for the rational design and fabrication of artificial photosynthetic cells to produce hydrogen.