EXPERIMENTAL AND FIRST PRINCIPLES THEORETICAL STUDIES ON METAL OXIDE NANOSTRUCTURES IN PHOTOELECTROCHEMICAL SPLITTING OF WATER

Abstract

In order to successfully split water with solar irradiation, suitable semiconductor electrodes are needed. Following the discovery of the photocatalytic splitting of water on rutile TiO2 electrodes by Honda and Fujishima in 1972, a lot of effort was devoted to the development of low-cost transition metal oxides. newlineAmong the various candidates for the photoanode, semiconductor metal oxides are relatively inexpensive and have better photoelectrochemical stability. newlineEarlier PEC studies used dopants by hit and trial experimentation to strike the optimal amount and the novelty of present work lies in theoretical screening of materials by calculating optimal doping, and then performing its experimental verification. newlineIn the present work, materials chosen are BaTiO3 and Cu2O with right kind of dopants e.g. Ag, Fe, Ru, Ni etc. (not well studied earlier). newline newlineIMPORTANT RESULTS newlineIron (Fe) doped BaTiO3 photoelectrodes newline newlineOn studying the PEC response of various samples prepared at different sintering temperatures and varying doping concentrations of Fe, it was found that sample doped with 2.0 at.% Fe sintered at 900°C exhibited the highest photocurrent density. The Photocurrent density obtained with undoped BaTiO3 sample sintered at 900°C was 0.07 mAcm-2 at 0.5 V/SCE, whereas maximum photocurrent density recorded in the sample doped with 2.0 at. % Fe was 2.55 mAcm-2 at 0.5 V/SCE. Doping of iron into the BaTiO3 structure caused a decrease in resistivity, resulting in decrease in the numbers of recombination centres. It is supposed that decrease in the number of recombination centres results into an increase in the photocarriers lifetime, leading to the increase in photoconductivity. Moreover, the red shift caused due to Fe doping resulted into more absorption in the visible region causing an increase in photocurrent. newline newlineRuthenium (Ru) doped BaTiO3 photoelectrodes newline newlineWe have also carried Photoelectrochemical study using Ruthenium (Ru) as dopant in BaTiO3 and the results found were not much encouraging as compared to Fe-doped BaTiO3. The Photocurrent density obtained with undoped BaTiO3 sample sintered at 900°C was 0.07 mAcm-2 at 0.5 V/SCE. On doping these samples with different concentration of Ru, a remarkable increase in the photocurrent density was observed for the samples sintered at 700ºC. Maximum photocurrent density was recorded in the sample doped with 0.5 at. % Ru with value of 0.70 mAcm-2 at 0.5 V/SCE. newline newlineSilver (Ag) doped Cu2O photoelectrodes newlineThe current-voltage characteristic curves were obtained for all the samples with varying doping concentration of Ag in the visible light source of irradiance 150 mW/cm2. The increase in photocurrent density with an increase of cathodic bias confirms the p-type nature Cu2O films. The open-circuit photovoltage (Voc), Resistivity and Conductivity were also measured using current-voltage characteristics under dark conditions for all the samples. It was observed that photocurrent density increases up to 1 at. % Ag-doping and then started decline when dopant concentration was further increases. The highest current density of 2.34 mA/cm-2 under visible light illumination for the 1 at.% Cu2O sample at 0.8 V/SCE was obtained. Thus, 1at % Ag-doping is the optimum doping level in Cu2O to exhibit best PEC response. newline newlineIron (Fe) doped Cu2O photoelectrodes newline newline We have also carried Photoelectrochemical study using Iron (Fe) as dopant in Cu2O. Detailed data, results and discussions would be presented in the thesis. newline newline