Development of a robust photocathode using low-cost and high-performing materials, e.g., p-Si, to produce clean fuel hydrogen has remained challenging since the semiconductor substrate is easily susceptible to (photo)corrosion under photoelectrochemical (PEC) operational conditions. A protective layer over the substrate to simultaneously provide corrosion resistance and maintain efficient charge transfer across the device is therefore needed. To this end, in the present work, we utilized pulsed laser deposition (PLD) to prepare a high-quality SrTiO3 (STO) layer to passivate the p-Si substrate using a buffer layer of reduced graphene oxide (rGO). Specifically, a very thin (3.9 nm ∼10 unit cells) STO layer epitaxially overgrown on rGO-buffered Si showed the highest onset potential (0.326 V vs RHE) in comparison to the counterparts with thicker and/or nonepitaxial STO. The photovoltage, flat-band potential, and electrochemical impedance spectroscopy measurements revealed that the epitaxial photocathode was more beneficial for charge separation, charge transfer, and targeted redox reaction than the nonepitaxial one. The STO/rGO/Si with a smooth and highly epitaxial STO layer outperforming the directly contacted STO/Si with a textured and polycrystalline STO layer showed the importance of having a well-defined passivation layer. In addition, the numerous pinholes formed in the directly contacted STO/Si led to the rapid degradation of the photocathode during the PEC measurements. The stability tests demonstrated the soundness of the epitaxial STO layer in passivating Si against corrosion. This study provided a facile approach for preparing a robust protection layer over a photoelectrode substrate in realizing an efficient and, at the same time, durable PEC device.

Advanced Materials Department Jožef Stefan Institute 1000 Ljubljana Slovenia

Department of Dielectrics Institute of Physics of the Czech Academy of Sciences 182 00 Prague Czech Republic

Department of Materials Chemistry National Institute of Chemistry 1000 Ljubljana Slovenia

Department of Surface Engineering Jožef Stefan Institute 1000 Ljubljana Slovenia

Department of Thin Films and Surfaces Jožef Stefan Institute 1000 Ljubljana Slovenia

Laboratory of Physics Vinča Institute of Nuclear Sciences─National Institute of the Republic of Serbia University of Belgrade 11351 Belgrade Serbia

MESA Institute for Nanotechnology University of Twente Enschede 7522 NB The Netherlands

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ACS Appl Mater Interfaces. 2025 Jul 2;17(26):38811. doi: 10.1021/acsami.5c10225. PubMed

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