Engineering of perovskite photocatalysts for sunlight-driven hydrogen evolution from water splitting (SunToChem)
The main aim of the SunToChem project was to design new efficient H2-evolution photocatalysts. The engineering of the photocatalysts was performed based on an in-depth understanding of nucleation-crystallization phenomena and supported by density functional theory (DFT) calculations. The research was focused on perovskite titanates, particularly on two-dimensional (2D) SrTiO3/Bi4Ti3O12 nanoheterostructures, 2D SrTiO3 nanoplatelets, SrTiO3 cube-like particles with different types of exposed facets and Al-doped SrTiO3 particles. We overcome the natural habit of SrTiO3 for growing in a cube-like shape and synthesized SrTiO3 in 2D shape by a new hydrothermal topochemical conversion (TC) approach, which also enables the formation of epitaxial SrTiO3/Bi4Ti3O12 heterostructural nanoplatelets at the intermediate stage of the TC. Atomic scale scanning transmission electron microscopy enabled us to obtain thorough insight into the TC mechanism and unravel the experimental conditions for tuning the nanoplatelets composition (SrTiO3:Bi4Ti3O12 ratio, bismuth remains) and surface roughness, which all determine the surface and functional characteristics of the platelets. Photocatalytic evaluation disclosed that without any addition of noble-metal co-catalyst, SrTiO3/Bi4Ti3O12 heterostructural nanoplatelets show (under AM 1.5G irradiation, from H2O/CH3OH (75/25) solutions) more than 35-times-higher photocatalytic H2 production (2950 mol g-1 h-1) than commercial SrTiO3 nanopowders (81 mol g-1 h-1). Through the development of a detailed understanding of this particular TC reaction, we provide ideas and guidelines for low-temperature engineering of other defined shaped epitaxial heterostructures, anisotropic nanostructures or nanostructures with pre-defined exposed facets, that otherwise cannot form. The other important theoretical and experimental results were obtained in the field of Al-doped SrTiO3 particles, grown in different molten salts (SrCl2, NaCl, KCl) at 900C-1000C. We showed that the highest improvement of the photocatalytic efficiency was achieved for Al-doped SrTiO3, prepared in molten KCl at 1000C. H2 production rates from pure water significantly enhanced to 784 and 431 μmol g-1h-1 under UV light and AM 1.5G irradiation, respectively. First-principles calculations imply that Al-doping most probably leads to photostimulated mobile hole trapping at local energy levels close to the valence band top, which likely prevents the electron-hole recombination and thus stimulates the H2 generation. The project results were published in 14 peer-reviewed articles (e.g. ACS Appl. Mater. & Interfaces 13 (2021) 370-381, Appl. Catal. B. 324 (2023) 122183, J. Catal. 416 (2022) 222-232, J. Mater Chem C 9 (2021) 1693-1700, J. Phys. Chem. C 127 (2023) 9981−9991) and at least 2 additional will be produced. Additionally, the partners disseminated the project results in 17 communications at Scientific Conferences, whereby some of them were also Invited lectures.
