Photoelectrochemical and Impedance Spectroscopic Analysis of Amorphous Si for Light-Guided Electrodeposition and Hydrogen Evolution Reaction

For more efficient photoelectrochemical water splitting, there is a dilemma that a photoelectrode needs both light absorption and electrocatalytic faradaic reaction. One of the promising strategies is to deposit a pattern of electrocatalysts onto a semiconductor surface, leaving sufficient bare surface for light absorption while minimizing concentration overpotential as well as resistive loss at the ultramicroelectrodes for faradaic reaction. This scheme can be successfully realized by “maskless” direct photoelectrochemical patterning of electrocatalyst onto an SiO_<i>x</i>/amorphous Si (a-Si) surface by the light-guided electrodeposition technique. Electrochemical impedance spectroscopy at various pHs tells us much about how it works. The surface states at the SiO_<i>x</i>/a-Si interface can mediate the photogenerated electrons for hydrogen evolution, whereas electroactive species in the solution undergo outer-sphere electron transfer, taking electrons tunneling across the SiO_<i>x</i> layer from the conduction band. In addition to previously reported long-distance lateral electron transport behavior at a patterned catalyst/SiO_<i>x</i>/a-Si interface, the charging process of the surface states plays a crucial role in proton reduction, leading to deeper understanding of the operation mechanisms for photoelectrochemical water splitting

Efficient and Stable Pt/TiO₂/CdS/Cu₂BaSn(S,Se)₄ Photocathode for Water Electrolysis Applications

The Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> (CBTSSe) system has attracted remarkable attention as an emerging chalcogenide semiconductor with desirable electronic and optical properties for solar energy conversion applications. The current study combines sputtered band gap-tailored CBTSSe films with TiO₂/CdS protective overlayers to significantly improve photoelectrochemical (PEC) properties as well as device stability in aqueous solutions under AM 1.5G simulated sunlight. The Pt/TiO₂/CdS/CBTSSe­(<i>x</i> ≈ 3) photocathode exhibits relatively high photocurrent (∼12.08 mA/cm² at 0 V/RHE, i.e., the highest value reported for CBTSSe-based PEC devices) and stable hydrogen evolution for more than 10 h. The applied TiO₂/CdS layers protect the underlying CBTSSe and create desirable band alignment for efficient charge extraction at the heterointerfaces. The present results highlight the opportunities that CBTSSe materials provide as efficient and stable photocathodes for water electrolysis