PhotoElectroChemical applicCation of Uranium oxides for enhanced LIght AbsoRption (PECULIAR)

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Uranium oxides with band-gap energies in the range of 2.0 - 2.6 eV coupled with their good electrical and catalytic properties mostly driven by facile valence dynamics of the uranium cations are promising electrode materials in photoelectrochemical water splitting reactions. Although being considered a scarce element, huge amounts of depleted uranium sources (e.g.,alone 700,000 Tons UF6 in the USA) originally produced as waste streams in the enrichment process of nuclear fuels, is currently stored without any prospect for further applications that poses a perpetual environmental hazard, due to accidental release of volatile, corrosive and toxic compounds. In view of their interesting electronic and structural properties (depleted) uranium oxides are potentially useful materials for energy applications, however alternative concepts have been not probed so far due to the limited accessibility. For the first time uranium metal-organic precursors for the gas phase deposition (thermal and plasma-assisted chemical vapor deposition) of uranium oxide coatings have been achieved and the resulting thin-films have been investigated as potential photoelectrodes in water-splitting setups. Preliminary studies by the applicants illustrate the enormous and mostly unexplored potential of UOx in (photo)chemical energy conversion cycles. Uranium oxides are suitable semiconductor materials for PEC applications due to their band gap energies that imply high photon absorption in the visible part of the solar spectrum, and more importantly the fact that their band edge positions straddle with the hydrogen and oxygen potentials. The proposed - PECULIAR - will explore the suitability of different uranium oxide phases and polymorphs in photoelectrochemical experiments. Compared to well-known semiconductor metal oxides such as TiO2, Fe2O3 and ZnO, the chemistry and materials aspects of uranium oxides is scantily explored and therefore this effort will be accompanied by ab-initio DFT calculationsto understand the underlying processes with respect to water-splitting reactions . In addition, influence of U:O ratio on the band gap energies as well thermodynamical stability of UOx with other potential photoanode materials will be investigated by theoretical studies followed by their experimental validation. Further, the effect of impurities (dopants) and combination with already existing potent absorbers in heterostructures will be elaborated for a detailed understanding of the photoelectrocatalytical performance and the assessment of the beneficial use of uranium oxide to produce hydrogen from water.