DESIGNING HETEROSTRUCTURED PHOTOCATALYST TO ENHANCE LIGHT HARVESTING AND CHARGE SEPARATION FOR WATER SPLITTING

Abstract

Kazakhstan is a mineral-rich country now heavily dependent on fossil fuels for energy. To eliminate this dependency and build a sustainable and green economy, the country needs to develop alternative energy production methods. Photoelectrochemical water splitting (PEC) is an attractive method of producing clean and high-energy-density hydrogen fuel using only solar light and water. However, despite many years of attempts by researchers worldwide to build an inexpensive PEC system using abundant materials, the efficiency of the state-of-the-art photoelectrodes is far from the requirements due to low light absorption and severe charge recombination in solar water splitting systems. This thesis work explores an emerging photoanode Bi2S3 material and methods for improving its light harvesting and charge separation properties through morphology control and heterostructure design. Three distinct bubble-templated dendrite, diffusion-controlled dendrite, and nanoneedle array morphologies of Bi2S3 were synthesized using electrochemically deposited Bi metal structures through sulfurization. The nanoneedle array and bubble-templated dendritic structures of Bi2S3 show the highest photocurrent density (3.1 mA·cm2 and 2.5 mA·cm2 at 0.7 V vs. Ag/AgCl, respectively) among all pristine Bi2S3 structures reported in the literature. Different Bi2S3-based heterostructures like semiconductor-based heterostructure of Bi2S3/CdS, plasmonic particle enhanced Bi2S3/Au, and co-catalyst enhanced Bi2S3/Co(OH)x and Bi2S3/Co3O4 were synthesized and tested for their PEC performance. Among them, Bi2S3/Co(OH)x and Bi2S3/Co3O4 were found to be viable options to improve the charge separation of the photoanode by decreasing the dark current tremendously. These results indicate that morphology control and heterostructure design are effective methods for enhancing the performance of PEC systems.