Next-generation sulphide perovskite photocatalysts for sustainable production of energy-dense fuels and chemicals

A fully funded 3-year PhD studentship is now available in our group for national and international students to join us from October 2023. Be at the forefront of developing next-generation sulphide perovskite photocatalyst materials with atomic layer deposition (ALD) that will help drive green chemistry for a sustainable future. Our group website is in construction and soon online but for now, please see details on the PhD supervisor, Prof. Ludmilla Steier, here https://www.chem.ox.ac.uk/people/ludmilla-steier and the project description below.

You will work in an interdisciplinary and multicultural team (currently 6 nationalities) with several opportunities to engage in collaborations with top researchers and research institutions worldwide. We have a modern new lab and a bright spacious office in the Department of Chemistry (in the PTCL building) and are certain you will enjoy a stimulating and friendly environment in our group, the Department and broader at the University of Oxford and its Colleges.

Entry requirements for a DPhil in Inorganic Chemistry are given here: https://www.ox.ac.uk/admissions/graduate/courses/dphil-inorganic-chemistry

Project background and description:

Going beyond electricity generation in solar cells, we aim at driving key chemical reactions with suitable semiconducting photocatalysts converting sunlight, abundant chemical feedstocks and/or waste products into valuable energy-dense fuels and chemicals. Such semiconducting photocatalysts need to absorb sunlight efficiently and also excel in catalysing challenging multi-electron transfer reactions, such as the reduction of atmospheric CO₂ to e.g. methanol, ethylene or ethanol. However, such multi-electron transfer reactions are typically rather slow and hence compete with several (often faster) energy-loss pathways (i.e. charge recombination back to the ground state). This recombination is especially critical in commonly used oxide photocatalysts. Due to their strong ionic character, oxides tend to localise photogenerated charge carriers as they move through the lattice which drastically limits carrier mobilities and makes them susceptible to recombination.^{1, 2} In stark contrast, common semiconductors used in high-efficiency photovoltaics have orders of magnitude higher mobilities and carrier lifetimes but their instability under chemical environments (especially humidity) limits their use in photocatalytic systems.^3-5

Sulphide perovskites (ABS₃) are an emerging relatively unexplored class of materials with a highly promising trajectory. Many compositions in this material class show desirable optoelectronic properties such as suitable (direct) bandgaps in the visible, strong band edge absorption and high absorption coefficients,⁶ easily tuneable bandgaps (via A, B and X-site engineering),⁷ and high mobilities.⁸ In addition, sulphide perovskites have been shown to be robust in humid conditions.⁹ Most of the suitable sulphide perovskite materials are also entirely made up of non-toxic and earth-abundant elements. However, thus far, their synthesis requires temperatures well beyond 700 °C under harsh sulfurisation conditions and hence severely limits their development.

Atomic layer deposition (ALD) is a low-temperature growth technique that gives you the ultimate control in material synthesis due to its layer-by-layer growth mechanism formed by alternating surface reactions in the gas phase. The ALD setup is fully automated and allows setting the number of cycles (and hence the number of atomic layers) to be deposited making it particularly suitable for ultrathin and thin film growth.¹⁰ Furthermore, materials can be easily doped with a precise concentration of the dopants and similarly, ternary materials can be developed systematically. More to this versatile modern technique can be found in several comprehensive review articles.^{11, 12}

Hence the main project goals will be:

1. the development of the first low-temperature (~200-400 °C), reproducible and highly controlled ALD process for crystalline perovskite sulphide films starting with the prototype BaZrS₃. These films will be epitaxially grown on single crystal supports of various orientations ((001, (110), (111)), ideal for the development of in-situ calibrated growth rate monitoring for the highest precision and reproducibility. You will have the opportunity to be trained in ALD and a series of material characterisation methods (electron microscopy, optical characterisation, synchrotron experiments, etc.) that will help us understand the composition and material properties of these thin films.
2. the development of the first efficient and stable sulphide perovskite photocatalyst for CO₂ hydrogenation in the gas phase as well as in electrolyte solutions. Studies will strongly focus on the assessment of the stability of sulphide perovskites in harsh chemical environments and the effects of the surface composition in catalysis.

If this sounds like your dream project, please send your application (including CV, transcript of records, name and contact details of 2 referees and a statement of purpose (max. 1000 words) directly to [Email Address Removed] by 30^th June*. Suitable candidates will be invited for interviews shortly after receiving the application package. We are looking forward to hearing from you!

*Please note that submission of a formal DPhil application will be required at a later stage.