title: Solar energy conversion based on multi-components nanomaterials
Creators: name: Yin, Hang
Publisher: name: The Australian National University
Year: 2024

description: The production of clean energy is one of the most important challenges in modern society. Since the Industrial Revolution in 1760, the combustion of fossil fuels has caused serious environmental problems including the greenhouse effect, air pollution, and water pollution, to name a few. Therefore, several solutions were raised to solve these issues. Including nuclear energy, wind energy, tide energy, etc. However, chemical fuels cannot be easily replaced, as they are easily stored and transported. Whereas traditional thermal catalysis costs lots of energy, which is against the willingness to use clean energy. Thus, clean strategies including electrocatalysis, photo(electro)catalysis, and photocatalysis have emerged and been developed in the past few decades. Among these, photocatalysis, due to the reaction can spontaneously start with light as the sole input, has become one of the most important strategies. To obtain better photocatalytic efficiency, multicomponent photocatalysts, such as semiconductor-semiconductor and semiconductor-metal, were designed to facilitate different reactions including H2 production, CO2 reduction. In Chapter 1, we introduced the background of the challenges of energy and environmental problems, and the current solution to face these problems. Especially, the importance of photocatalysis was discussed. Subsequently, strategies of the design of different types of multicomponent photocatalysts were discussed, followed by the reactions that can solve both energy and environmental problems. In Chapter 2, we have introduced a plasmonic effect-based semiconductor-metal photocatalyst of g-C3N4-Ag. Herein, Ag nanoparticles act as plasmonic sources and were grown on the g-C3N4 via photodeposition method. After an annealing process, new N defects can be introduced and co-localized with Ag nanoparticles. As the N defects are the active sites for the CO2 photoreduction to CO, the increased number of N defects can enhance the catalytic efficiency. In addition, since the new N defects are close to Ag nanoparticles, they can efficiently use the plasmonic hot electrons from Ag nanoparticles to further enhance CO production rate. In Chapter 3, we have prepared a 2D TiO2-CuO heterojunction for H2 production from isopropanol (IPA) photoreforming. An interesting asymmetric evolution at the Ti-O-Cu interface after the annealing process was observed, where the Ti4+ was overoxidated to Ti-O while Cu2+ was reduced to Cu+. The DFT results have shown that the special interface can significantly reduce the energy barrier of cleavage of the alpha-C-H bond of IPA, which is the rate determining step of the H2 production from IPA. In addition, the heterojunction of TiO2-CuO forms a Z-scheme band structure, which can enhance the charge separation ability. All the benefits of this TiO2-CuO heterojunction promote the H2 production efficiency from IPA photoreforming. In Chapter 4, we have synthesized a series heterojunction of Co3O4-CdS for the photocatalytic syngas production from formate under alkali conditions. To pursue the high syngas production rates, noble metal based photosensitisers and sacrificial agents were used during the CO2 reduction reaction, or acidic conditions with a high concentration of formic acid during the formic acid degradation reaction. This will cost lots of money or induce inevitable CO2 emission. Our Co3O4-CdS realized photocatalytic syngas production under alkali conditions based on the dual functions of dehydration of formate to produce CO and dehydrogenation of formate to produce H2, where the CO2 can be absorbed by NaOH. In Chapter 5, the last part of this thesis, the current status and the demand of the development of photocatalysis has been summarized, along with the summary of the achievements during my PhD program. In the end, the future perspective of multicomponent nanomaterials for photocatalysis has been offered, aiming to promote the advancement of this research area.