Structure And Performance Manipulation Study On Two Dimensional Nanocomposites Photoelectrocatalytic Materials

In the 21st century, energy and environmental problems are the biggest challenges faced by humanity for their sustainable development. Inspired by nature photosynthesis, to capture solar energy and to store it as hydrogen energy through artificial photosynthesis are seemed as the "Holy Grail" to effectively solve the energy problems. It is the key point to develop stable and high-efficiency photoelectrocatalytic/ electrocatalytic materials. For a long time, the low carrier transfer rate and the high overpotential of the surface reaction severely restrict the improvement of the water splitting efficiency. The super thin atomically structure characteristics of two dimensional semiconductor materials promote the carrier transfer rate, and the large surface area of 2D nanosheets provides abundant active sites for water splitting reaction, so they are seemed as excellent catalyst materials. However, there remain surface reaction kinetic bottleneck unsolved in many materials. Surface modification of cocatalyst quantum dots or fabricating multifunctional 2D nanocomposites is beneficial for promoting carrier separation and transfer, and decreasing surface reaction energy barrier. As a result, the hydrogen evolution rate of the two dimensional semiconductor materials is obviously enhanced. This dissertation achieved an enhancement of the photocatalytic performance of the carbon nitrides through deposition of the Co-Pi catalyst. And this dissertation achieved a notable enhancement of the electrocatalytic oxygen evolution performance of δ-FeOOH through combining graphene with it. The detail contents of this dissertation are as follows:1. Investigating the photocatalytic water splitting performance of Co-Pi deposited carbon nitrides nanosheetsGraphitic carbon nitride is a novel solar water splitting catalyst. The combination of photo-generated carriers and the sluggish kinetic of oxygen evolution reaction end up with a low energy conversion efficiency. The combination of cocatalyst with photocatalyst is an effective way to enhance the stability of photocatalyst and inhibit the combination of the photo-induced carriers. We successfully exfoliated carbon nitride nanosheets and deposited Co-Pi catalyst on it by photo-deposition method. Photocatalytic water splitting testing system determined the photocatalytic hydrogen evolution rate of the composites which is 4 times higher than the carbon nitrides nanosheets’, and is 26 fold of that of the carbon nitrides bulk. The photoluminescence spectrum result demonstrated that the combination rate of the photocarriers in the composites is obviously inhibited by the deposition of Co-Pi catalyst.2. Investigating electrocatalytical oxygen evolution performance of graphene-based δ-FeOOH nanosheetsThe large specific surface area of graphene is a good substrate for the deposition of nanosheets, and its good conductivity may promote charge transportation. Therefore, we manufactured graphene based δ-FeOOH nanosheets. Using TEM morphology characterization we can see that the homogeneously deposited δ-FeOOH nanosheets on the graphene surface. Utilizing XRD, Raman and XPS structure characterization technologies, it is disclosed that the precursor graphene oxide is reduced during the in situ growth process, and the deposited nanosheets are the same phase of the pure δ-FeOOH. XAFS results further give the local structure information of the composites. Electrocatalytic performance test indicated that the electrocatalytical oxygen evolution overpotential of the FeOOH/rGO composites is dramatically decreased. EIS results demonstrated that the carrier transfer rate of the composites electrode is obviously enhanced.