Rational engineering of metal oxide nanomaterials for solar-driven water splitting

• Main Author: Zhang, Yanyan
• Other Authors: School of Materials Science & Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Materials::Energy materials
• Online Access: http://hdl.handle.net/10356/51112
• Institution: Nanyang Technological University

Solar water splitting, converting solar energy into chemical fuel by using semiconductors as the mediator, is one of the most promising approaches for sustainable development. However, its commercial applications are still limited, largely due to its high cost and low photocatalytic efficiency. Hence, this dissertation aims at the challenges in terms of cost-effective and photocatalytic performance. For one thing, a novel and cheap photocatalyst was rationally designed and synthesized through electronic structure engineering. On the other hand, the structure of metal oxide nanoparticles was rationally designed to enhance the charge separation and to achieve overall water splitting. Firstly, a novel photocatalyst (C-doped Al2O3) converted from the well-known insulator, Al2O3, was successfully developed. It was for the first time used in the solar water splitting system and showed good photocatalytic performance. In order to reveal the intrinsic mechanism of this new earth-abundant photocatalyst, many advanced techniques were conducted such as TEM, AES, STXM, XPS and UPS. Finally, we figured out that the bandgap narrowing is resulting from the mid-gap state formed by the C 2p orbital in the forbidden band. The photocatalytic H2 generation performance indicated the successful transition from insulator to semiconductor. However, the efficiency of the C-doped Al2O3 is expected to be further increased with visible-light irradiation. As we know the solar energy is mostly composed of visible light, therefore, it is very essential to design visible-light active photocatalytic systems. CdS nanomaterials, with a small bandgap (ca. 2.4 eV), is a very well-known and promising photocatalytic materials for visible-light water splitting. However, CdS nanoparticles notoriously tend to aggregate, leading to the increment of the charge recombination rate. Herein, 3D echinus-like titanate nanomaterials with the anti-aggregation structure was designed and successfully synthesized, in which CdS nanoparticles are spatially distributed. And we found that the 3D CdS-titanate composite showed excellent photocatalytic performance than that of the pure CdS under visible light. This is owing to the quick electron injection from the CdS to titanate (~ 0.33 ns), supported by the transient absorption (TA) measurement, which greatly enhance the separation of the photoinduced electron/hole pairs on CdS.