Year

2020

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

With a rising global population and increasing energy consumption, major concerns have been raised over energy security in the future. Developing eco-friendly and sustainable pathways to produce energy sources is urgently needed and remains a huge scientific challenge. At the same time, developing low-cost and efficient electrochemical energy storage and conversion systems is also of critical significance to achieve the highly efficient utilization of renewable energy and beyond. Electrochemical water splitting has been considered to be one of the most promising approaches to achieve scalable and sustainable hydrogen production, and has been substantially studied over the past years. Electrocatalysts for both oxygen evolution reaction and hydrogen evolution reaction play a decisive role in delivering fast water splitting kinetics, and therefore the rational design of high-performing electrocatalysts with enhanced catalytic performance is of paramount significance. Electronic structure engineering strategy has been successfully developed to modify the physicochemical properties of electrocatalysts to enhance their catalytic activity and accelerate the reaction kinetics. Based on this, as a proof-of-concept application, electrocatalyst design strategies derived from electronic structure engineering, including defect engineering, heterostructure engineering, and coordination modulation, and 2D morphology engineering are successfully developed for tuning the catalytic performance of layered cobalt oxide (LiCoO2) towards accelerated water splitting kinetics. Importantly, the structure-property correlations are well established, and the effects of the electronic structure modulation on the catalytic activity are also unraveled in detail.

In the first case, a coupled heteroatom doping approach with 2D engineering is deployed to regulate the electronic structure to accelerate the oxygen electrocatalysis kinetics of LiCoO2. A new LiCoO2-based electrocatalyst with nanosheet morphology is designed and developed by a combination of Mg doping and shear-force-assisted exfoliation strategies. The modified LiCoO2 exhibited enhanced oxygen reduction and evolution reaction kinetics. It is demonstrated that the coupling effect of Mg doping and the exfoliation can effectively modulate the electronic structure of LiCoO2, in which Co3+ can be partially oxidized to Co4+ and the Co-O covalency can be enhanced, which is closely associated with the improvement of intrinsic activity. Meanwhile, the unique nanosheet morphology also helps to expose more active Co species. This work offers new insights into deploying the electronic structure engineering strategy for the development of efficient and durable catalysts for energy applications.

In the second case, a heterostructure engineering strategy is applied to develop LiCoO2-based hybrid electrocatalyst with tailored interface electronic structure. To achieve this aim, a novel multifunctional heterostructured electrocatalyst, platinum/lithium cobalt oxide (Pt/LiCoO2) composite with Pt nanoparticles (Pt NPs) well-anchored on ultrathin LiCoO2 nanosheets, is designed towards highly efficient overall water splitting. In this electrocatalyst system, the active center can be alternatively switched between Pt and LiCoO2 for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. Specifically, Pt is the active center and LiCoO2 acts as the co-catalyst for the HER, whereas the active center transfers to LiCoO2 and Pt turns into the co-catalyst for the OER. The unique architecture of the Pt/LiCoO2 heterostructure not only ensures the maximal exposure of active sites, but also endows it with a favorable electronic structure and coordination environment to optimize the adsorption/desorption behavior of reaction intermediates. This study will diversify the design strategies for the development of efficient electrocatalysts via interface engineering towards water electrolysis and other relevant electrocatalysis applications.

This thesis is unavailable until Wednesday, November 30, 2022

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.