Interface-engineered STO thin films on silicon photocathodes for photoelectrochemical hydrogen evolution reaction

Abstract

Epitaxial strontium titanate (STO) thin films were deposited by pulsed laser deposition onto bare and reduced graphene oxide (rGO)-buffered silicon (Si) substrates to explore their potential as protective and functional coatings for Si photocathodes in photoelectrochemical (PEC) hydrogen evolution reaction. Depositions were carried out at 515 ℃ and 700 ℃, and the resulting films were characterized using reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), and X-ray photoelectron spectroscopy (XPS). AFM and XRR analyses revealed that the STO films grown on rGO-buffered Si exhibited smoother surfaces and lower roughness compared to those grown directly on Si. XRD and RHEED methods revealed that the growth at 700 °C led to the formation of textured film, while deposition at 515 ℃ on rGO-buffered Si substrate produced highly crystalline STO film with a dominant (002) out-of-plane orientation. The sharp RHEED streaks further confirmed its high crystallinity and smoothness. Electrochemical measurments showed that epitaxial STO/rGO photocathodes achieved significantly improved PEC performance, featuring a reduced onset potential (0.24 V vs RHE), higher photocurrent density (−27.78 mA cm⁻²), and greater long-term stability. Conversely, non-epitaxial samples containing interfacial silicate or silicide layers, particularly those deposited at 700 °C, exhibited lower activity and reduced stability, as confirmed by electrochemical impendance spectroscopy (EIS). The results highlight the crucial role of interface engineering and deposition temperature in tailoring the structural and functional performance of oxide/Si heterostructures for efficient hydrogen evolution reaction.