Photoelectrochemical and Photocatalytic Water Oxidation using Metal Oxides.

Abstract

Photoelectrochemical (PEC) water splitting is a sustainable and environmentally friendly method for the conversion of solar energy. However, in order to drive the paradigm shift toward these new sources of energy, this process needs to be cost competitive with current technologies. This thesis focuses on developing oxides capable of using visible light to drive water splitting. The major contribution of the work presented in this thesis focuses on the development of CuWO4 as a visible light absorbing oxide for PEC water splitting. Various synthetic methods were developed to evaluate the PEC properties of CuWO4 including a sol-gel spin casting and electrochemical deposition method. The experimental results show that CuWO4 is capable of converting visible light (lambda > 500 nm) into photocurrent, driving water oxidation at its surface. CuWO4 is chemically stable over extended periods of illumination, particularly in a borate buffer. CuWO4 electrodes are also selective to performing water oxidation in the presence of competing electron donors such as Cl–, a common ion in terrestrial water. In order to show water oxidation using only the sun’s input, a Z-scheme approach was targeted. On the oxygen evolution side, CuWO4 can photochemically drive water oxidation with the reduction of an electron acceptor in solution. New phases and composite oxides were synthesized and tested for performing photocatalytic water oxidation in the presence of IO3–, an electron acceptor. Bronze phase TiO2 chemically bonded to reduced graphene oxide is capable of oxidizing water with significantly enhanced rates compared to native TiO2-bronze. Hydrothermally synthesized PbCrO4 rods loaded with Pt and RuO2 co-catalysts were also discovered to be competent light absorbing oxides for performing photocatalytic water oxidation under simulated solar irradiation. Finally, a wolframite solid solution Zn1–xCuxWO4 (x = 0–1) was synthesized using a Pechini citric-acid assisted sol-gel method. The photocatalytic properties of this series were tested, and the solid-solution behavior of this series was confirmed using optical spectroscopy and magnetism.