Novel semiconductor nano-structures for photocatalytic applications

The rapid decrease in fossil energy sources and the increase in carbon emissions in the world has led to the search for renewable, cheap, and environmentally friendly energy sources. Solar energy is the most researched energy source because it is clean, abundant, and sustainable. Photoelectrochemical (PEC) water splitting studies, which convert solar energy directly into electrical energy using semiconductor photocatalysts have been continuously researched since 1972. Recently, zinc oxide (ZnO) has emerged as one of the most promising semiconductors for photocatalytic applications among various metal oxides. In this study, two zinc-based photoanodes were fabricated in a star shape, and the PEC water splitting performance was investigated. Initially, PDA bridged ZnO@PDA/CeO2 Z-scheme ternary heterojunction were rationally synthesized. PDA was utilized as an electron transfer mediator, and its PEC performance was investigated under LED illumination. A low photocurrent density for ZnO@PDA/CeO2 heterostructures was obtained due to the low separation of electron-hole pairs under dark conditions (24 µA/cm2). However, thanks to the novel Z-scheme system, this rate has been increased by approximately ten times (251 µA cm2) under LED (30 mW/cm2) irradiation. In the second study, carbon-incorporated ZnO@MOF-5-C Z-scheme ternary heterostructures were fabricated. These novel synthesized nanoparticles PEC water splitting efficiency was investigated under Xenon (300mW/cm2) irradiation. The photocurrent density for the ZnO@MOF-5-C nanoparticle was measured under dark (0.27 mA/cm2) and light conditions (3.49 mA/cm2) at 2.50 V vs. RHE respectively. Moreover, the Z-scheme charge transfer mechanism within ZnO@PDA/CeO2 and ZnO@MOF-5-C ternary heterojunctions was verified using radical scavengers and trapping experiments as well as X-ray photoelectron spectroscopy methods. According to this thesis, the PDA and an N-doped carbon layer facilitated the separation and also pumping of photogenerated charge carriers for enhanced PEC H2 generation. Keywords: Z-scheme heterojunction, Electron transfer layer, PDA, ZnO/CeO2, N-doped carbon layer, ZnO@MOF-5, Water splitting, H2 generation