ENHANCING LIGHT HARVESTING AND WATER OXIDATION AT Mo:BiVO4 PHOTOANODES BY COUPLING WITH TiO2 PHOTONIC CRYSTALS AND OXYGEN EVOLUTION CATALYSTS

Abstract

This MS thesis work aims to fabricate a Mo:BiVO4 photoanode with improved photoelectrochemical properties for solar water splitting by coupling with photonic crystals to enhance absorbance in the films and oxygen evolution catalysts to enhance the kinetics of water oxidation. The effect of coupling Mo-doped BiVO4 photoanode of different thicknesses to TiO2 photonic crystals of varying stop bands on light harvesting in a photoelectrochemical cell was studied in sulfate sulfite electrolyte in the presence of a hole scavenger. The TiO2 inverse opals stop band was varied by varying the sphere size in the opal template. The PEC behavior was compared to that of Mo: BiVO4 coupled to disordered and non-scattering nanocrystalline films. This photoanode aimed to create heterojunction that facilitates electron separation and transport and to enhance absorption by light trapping. Photocurrents were measured at Mo: BiVO4 coupled to inverse opals with different stop bands leading to a significant enhancement in %IPCE. The photoanodes that are coupled with inverse glass and non-scattering nanocrystalline showed smaller enhancement or even showed decreased light-harvesting efficiency. The second aim focuses on oxygen evolution reaction (OER) catalysts coupled with the photoanodes. In the second aim, the electrolyte was varied to potassium borate solution to study water oxidation in the absence of a hole scavenger. The bilayer photoanodes that were fabricated in the first aim were coupled to nickel borate (Ni-Bi), which was observed to produce enhanced %IPCE of ca. 2.21-fold. Ni-Bi is believed to have a dual role, a catalytic effect, and decreasing recombination.