Proceedings of MATSUS Fall 2023 Conference (MATSUSFall23)
DOI: https://doi.org/10.29363/nanoge.matsus.2023.281
Publication date: 18th July 2023
Harnessing solar energy through photoelectrochemical (PEC) water splitting approach offers a promising and sustainable pathway to produce green hydrogen (H2). However, to ensure the viability, cost-effectiveness, and long-term stability of this approach, fabricating an abundant and durable photoelectrode is crucial. Barium stannate (BaSnO3) has not been considered promising material for PEC water splitting applications due to its wide band gap (˃3 eV) and limited solar absorption characteristics.[1] In this study, we optimized a spray pyrolysis method to fabricate phase pure BaSnO3 photoanodes with a smaller optical gap of ∼2.2 eV. By annealing these photoanodes in a mild H2 gas environment, we observed a significant decrease in the optical gap to ~1.5 eV. This led to an enhanced photoelectrochemical performance, with a 5-fold increase in the photocurrent density reaching ~0.5 mAcm-2 at 1.23 V vs. RHE and an improved onset potential of ~0 V vs. RHE. To understand the reason behind this enhancement, we have used a combination of spectroscopy techniques, including photoluminescence (PL), time-resolved surface photovoltage analysis (TR-SPV), and time-resolved microwave photoconductivity (TRMC) measurements. We find that mild H2 annealing of BaSnO3 generates a set of mid-gap defect states associated with oxygen vacancies and Sn2+ centres.[2] Increasing the population of these mid-gap states, shifts the optical onset of photocurrent collection and mobile charge carrier generation to photon energies as low as ~1.5 eV. Furthermore, the transient signals of charge carriers show the extended lifetime after H2 treatment and provides the evidence that carriers are transported via tunnelling through delocalized defect states. We show here that BaSnO3 is a promising material with tunable optical properties and electronic structure.
Authors would like to thank DAAD (Deutscher Akademischer Austauschdienst) for financial support and Helmholtz Association for financial support and scientific facilities.
SG is thankful to CEST and FFG for providing funding to present this work.
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