Date of Award

2021

Document Type

Thesis - ECU Access Only

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Engineering

First Supervisor

Professor Hongqi Sun

Second Supervisor

Professor Lai-Chang Zhang

Abstract

Hydrogen energy is an ideal energy resource owing to its clean and efficient utilization. As an energy carrier without natural abundance, the limited reserve makes the high consumption a big challenge. In the meantime, fossil fuels, e.g., coal, oil and gas, have been important carbon carriers in the long-term carbon cycle, but their upgrading is restricted to conventional thermocatalysis. Solar energy with the advantages of large abundance, widespread distribution, and high flux appeals extensive attention, but unfortunately is underutilized at the moment. Photocatalysis initiated with semiconductors is a promising pathway towards the conversion and storage of solar energy into chemical stocks, and has been studied for several decades. However, due to the low photoresponse capacity and solar energy conversion efficiency of the existing photocatalysts, the prospect of their industrialization is still unclear. Photothermal catalysis integrating photocatalysis and thermocatalysis into one unit has been proposed in the past several years. Although its quantum efficiency and reaction turnover frequency were significantly improved, the reaction mechanisms have not yet been well illustrated. This PhD study is to develop photo assisted catalysis to obtain high performances for energy preparation and fossil fuels upgrading, and to have a deep insight into their reaction mechanisms. First, in-plane heterostructured graphene/carbon nitride photocatalyst was prepared via a hydrogeninitiated chemical epitaxial growth strategy. With the insert of nano-graphene into the porous carbon nitride, the quantum efficiency of the water splitting reaction for hydrogen generation was significantly enhanced (Chapter 3). Considering the unsatisfied incident light to electron efficiency, the study unveiled the potential difference as the internal electrical field affecting the separation, transfer and output of photoinduced charge carriers. Meanwhile, the quantum efficiency and utilization of solar light were both improved via the optimization of potential differences in photocatalytic systems (Chapter 4). In addition, the active sites (Chapter 5) and relationships between photocatalysis and thermocatalysis (Chapter 6) in photothermal catalytic systems were both in-depth studied. With the available reaction mechanism and optimization of reaction conditions, the photothermal catalytic performances in the upgrading of fossil fuels are increased to a industrialization level. This PhD project contributes to the improvements of quantum efficiency via catalyst modification, reaction optimization and mechanism investigation and then expects to provide both technological and scientific knowledge for the full storage and conversion of solar energy into fuels.

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