Sun, Xin, Tiwari, Devendra, Li, Meicheng and Fermin, David J. (2022) Decoupling the impact of bulk and surface point defects on the photoelectrochemical properties of LaFeO3 thin films. Chemical Science, 13 (37). pp. 11252-11259. ISSN 2041-6520
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Abstract
Point defects (PDs) play a key role in the properties of semiconductor photoelectrodes, from doping density to carrier mobility and lifetime. Although this issue has been extensively investigated in the context of photovoltaic absorbers, the role of PDs in photoelectrodes for solar fuels remains poorly understood. In perovskite oxides such as LaFeO3 (LFO), PDs can be tuned by changing the cation ratio, cation substitution and oxygen content. In this paper, we report the first study on the impact of bulk and surface PDs on the photoelectrochemical properties of LFO thin films. We independently varied the La : Fe ratio, within 10% of the stoichiometric value, in the bulk and at the surface by tuning the precursor composition as well as selective acid etching. The structure and composition of thin films deposited by sol–gel methods were investigated by SEM-EDX, ICP-OES, XPS and XRD. Our analysis shows a correlation between the binding energies of Fe 2p3/2 and O 1s, establishing a link between the oxidation state of Fe and the covalency of the Fe–O bond. Electrochemical studies reveal the emergence of electronic states close to the valence band edge with decreasing bulk Fe content. DFT calculations confirm that Fe vacancies generate states located near the valence band, which act as hole-traps and recombination sites under illumination. Dynamic photocurrent responses associated with oxygen reduction and hydrogen evolution show that the stoichiometric La : Fe ratio provides the most photoactive oxide; however, this can only be achieved by independently tuning the bulk and surface compositions of the oxide.
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| Additional Information: | Funding information: X. S. and M. L. acknowledge the support from the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources (LAPS21004), National Natural Science Foundation of China (Grant nos. 51972110, 52102245, and 52072121), Beijing Science and Technology Project (Z211100004621010), Beijing Natural Science Foundation (2222076), Huaneng Group Headquarters Science and Technology (Project HNKJ20-H88), the FundamentalResearchFunds for the Central Universities (2022MS030, 2020MS023, and 2020MS028) and the NCEPU ‘Double First-Class’ Program. D. T. and D. J. F. thank the Advanced Computing Research Centre, University of Bristol (http://www.bris.ac.uk/acrc/) for the access to the high-performance computational facilities. D. T. and D. J. F. acknowledge the support from the UKRI-EPSRC (grants EP/ V008692/1 and EP/V008676/1). D. T. is also grateful for the support from the Royal Society of Chemistry (grant E20-9404). |
| Subjects: | F100 Chemistry F200 Materials Science |
| Department: | Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering |
| Depositing User: | Rachel Branson |
| Date Deposited: | 27 Sep 2022 08:55 |
| Last Modified: | 28 Sep 2022 12:45 |
| URI: | https://nrl.northumbria.ac.uk/id/eprint/50231 |
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