Preparation Of G-C₃N₄ Modified Semiconductor Nanoarrays And Their Photoelectrochemical Water Splitting Performance

In recent years, photoelectrochemical water splitting using solar energy has been considered to be one of the most promsing technologies for hydrogen production. To design and synthesize semiconductor photoelectrodes with high photoelectrochemical performance and excellent stability are essential to realize photoelectrochemical water splitting. CdS and WO₃ semiconductor nanoarrays were fabricated in the thesis and modified by graphitic carbon nitride?g-C₃N₄?. The morphology and structure of semiconductors were controlled, then modified to develop semiconductor photoanodes with excellent performance for photoelectrochemical water splitting. The research serve as an inspiration for designing and developing of semiconductor photoanodes with high photoelectrochemical performance and good stability and provide a base for achieving photoelectrochemical water?seawater? splitting with high efficiency. The main innovative results are as follows:?1? CdS@g-C₃N₄ core-shell nanorod arrays?CdS@g-C₃N₄ CSNRs? were prepared through simple hydrothermal growth and a thermal polycondensation process. The semiconductor nanorod arrays were systematically characterized and investigated by X-ray diffraction?XRD?, X-ray photoelectron spectroscopy?XPS?, Fourier transform infrared?FTIR?, Field emission scanning electron microscopy?FESEM?, Energy dispersive spectrometer?EDS?, Transmission electron microscopy?TEM?, UV-Vis diffuse reflectance spectra?UV-Vis DRS?, Incident photon to current efficiency?IPCE? and photoelecrochemical?PEC? measurements, respectively. The results indicated that the photocurrent density of CdS@g-C₃N₄ CSNRs as photoanode reaches up to 1.16 mA/cm2, which is 2.5-fold that of CdS nanorod arrays?CdS NRs??0.46 mA/cm2? at bias potentials 1.0 V vs. RHE. The photocurrent density of CdS@g-C₃N₄ CSNRs were quite stable and more than 85% of the initial photocurrent density was still sustained after continuous 3600 s illumination at bias potentials 1.0 V vs. RHE. while the photocurrent density of CdS NRs decay to 20% of the initial value at the same conditions. The origin of performance enhancement for photoelectrochemical water splitting was also analyzed by Electrochemical impedance spectroscopy?EIS? and Open circuit potential?OCP? decay measurements. The reaction mechanism of photoelectrochemical water splitting was proposed.?2? WO₃/g-C₃N₄ NSAs were prepared via facile hydrothermal growth and a deposition-annealing process. The semiconductor nanosheet arrays were systematically characterized and investigated by XRD, XPS, FTIR, FESEM, EDS, TEM, UV-Vis DRS, IPCE and PEC measurements, respectively. The results indicated that WO₃/g-C₃N₄ NSAs exhibited excellent photoelectrochemical performance and stability. The photocurrent density of WO₃/g-C₃N₄ NSAs as photoanode reaches up to 0.73 mA/cm2, which is 2-fold that of(WO₃ NSAs?0.36 mA/cm2? at bias potentials 1.23 V vs. RHE. The photocurrent density of WO₃/g-C₃N₄ NSAs were quite stable and no obvious decay was observed after continuous 3600 s illumination at bias potentials 1.23 V vs. RHE. However, the photocurrent density of WO₃ NSAs decay to 30% of the initial value at the same conditions. The origin of performance enhancement for photoelectrochemical seawater splitting was also analyzed by EIS and OCP decay measurements. The reaction mechanism of photoelectrochemical seawater splitting was proposed.