Advanced and sustainable thin-film nanocomposites for photoelectrochemical solar energy conversion and hydrogen generation

Solar energy conversion has gained popularity in recent years due to evolving industrialisation. Hydrogen energy generation coupled with solar-driven biomass valorisation is an attractive way to lower the energy demand. In addition, photoelectrochemical energy conversion stands out because of low-cost hydrogen production, along with the production of value-added chemicals through biomass reforming. However, there is an urgent need to look for cost-effective, non-critical, durable functional materials to complement hydrogen production and organic oxidation reactions This Ph.D. thesis aims to explicitly detail the role of Transition Metal Oxide (TMO) photoanodes in harnessing solar energy to drive biomass reforming. The role of structural, morphological, and functional properties of the TMO, significantly impacting glycerol and water oxidation are highlighted. The synergy between the metal oxyhydroxide co-catalyst and the TMO photoanode in catalysing glycerol oxidation is investigated. Transition metal oxysulphide electrocatalysts were fabricated to interpret their role as a co-catalyst for photocathodes. The TMO photoanodes were fabricated using Physical Vapour Deposition (PVD) and hydrothermal techniques to correlate their structural properties with the morphological change. Transition metal oxysulphides were synthesised through simple electrodeposition techniques. The morphological and structural characterisation was carried out through Scanning Electron Microscopy (SEM) and Grazing Incidence X-Ray Diffraction (GIXRD). The chemical composition and structural studies were undertaken through X-Ray Photoelectron Spectroscopy (XPS), X-ray Absorption Spectroscopy (XAS) and Raman Spectroscopy. The operando Raman and XAS gave a distinct picture of the metal oxysulphide electrocatalyst undergoing in-phase during operating conditions. High Performance Liquid Chromatography (HPLC) provided quantification of value-added glycerol oxidation products on solar biomass reforming. This work explains the strategic design of two (photo)electrochemical systems to put forward an attempt to solve the global energy crisis. (i) PVD grown planar and nanostructured hematite photoanodes and (iii) molybdenum oxysulphide electrocatalyst. The role of NiOOH cocatalyst on the PVD-grown hematite photoanode in harnessing glycerol oxidation products having economic value, such as glyceraldehyde (GLAD) and dihydroxyacetone (DHA) is explained thoroughly. In particular, the coordinated effect of the electrolyte on the photoanode composite is determined. In a similar context, the influence of the morphology on the structural and photoelectrochemical performance of the nanostructured hematite photoanode is explored. Enhanced effective surface area significantly increases the production rates of these molecules by several folds. To the best of our knowledge, promising production rates and selectivity towards GLAD and DHA are reported for glycerol oxidation in mild alkaline pH. Finally, the operando XAS and Raman spectroscopy on molybdenum oxysulphide investigated an in situ phase change around the Mo centres. The evolution of amorphous to quasi-crystalline phase induced within the electrocatalyst under hydrogen evolution is understood. In conclusion, the advanced nanocomposites fabricated in this study promote the development of techno-economic strategies to lower carbon footprint and harness green energy.