Development of Nanostructured Semiconductors and Electrocatalysts for Water Splitting and CO2 Reduction
This thesis focuses on the development of nanostructured semiconductors and electrocatalysts for artificial photosynthesis, which mainly includes the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) and carbon dioxide reduction reaction (CO2RR) at the cathode. The first study was synthesizing nanostructured CuWO4 photoanodes and integrating cobalt phosphate as the electrocatalysts for photoelectrochemical water oxidation. The triclinic CuWO4 nanoparticles had an indirect band gap of 2.2 eV. The photocurrent of the cobalt phosphate complex-catalyzed CuWO4 electrodes exhibited an 86% higher photocurrent response than that of the unmodified CuWO4 nanoparticles under the irradiation of one simulated sun. The second study employed scanning photoelectrochemical microscopy and developed a new methodology to optimize a photocatalyst surface with an electrocatalyst layer in a matrix fashion and monitored its localized activity toward the OER. The FeOOH electrocatalyst was photodeposited onto a BiVO4 thin film using various deposition times on a single photoanode electrode. The loading of the electrocatalyst on the photocatalysts affected the local photoelectrochemical reaction rate. The morphology of this photocatalyst/electrocatalyst hybrid and its localized activity toward the water oxidation reaction could be simultaneously probed. A photoanode surface comprised of CuWO4/BiVO4/FeOOH was prepared and investigated. The third study examined intermediate species formation and mechanism of the CO2RR on gold nanoparticles by using the in-situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Both H2O and D2O were used as the solvents to assign the IR peaks and to identify the formed intermediates and products. The experimental results have provided direct evidence of the formation of COO- species on the Au nanoparticles, confirming that COO- is one of the main intermediates during CO2 activation. Product HCOO- was also detected during the CO2 reduction on gold nanoparticles. The fourth study was designing and synthesizing nanocomposite TiO2@Cu for CO2RR by chemical reduction method. The catalytic activity of the TiO2@Cu nanocomposite was optimized with various compositions of copper precursors. The material with a Cu:TiO2 molar ratio of 4.8% exhibited the highest catalytic activity for the electrochemical CO2RR. Syngas was produced with tunable ratios of CO/H2 ranging from 2:1 to 2:3 by applying various potentials.