Yao, Yuting; (2022) Development of self-supported transition-metal-based electrocatalyst via aerosol-assisted chemical vapour deposition towards efficient and stable bifunctional water electrolysis. Doctoral thesis (Ph.D), UCL (University College London).

Text Yuting Yao_PhD Thesis_Final version.pdf - Accepted Version Access restricted to UCL open access staff until 1 December 2024. Download (16MB)

Abstract

Hydrogen production though overall water splitting as clean and sustainable energy has gained prominent attention due to the increasing global energy and climate crisis. However, the design and development of cost-effective materials that can simultaneously catalyse hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in a highly efficient, stable, and scalable manner remain challenging. This thesis will focus on addressing this challenge by developing non-noble transition-metal-based derivatives (e.g., Mo, Ni, Co) on electroconductive substrates (i.e., graphene and carbon paper). In particular, a series of transition-metal sulphide heterostructures were in-situ synthesised on carbon paper with the aid of aerosol-assisted chemical vapour deposition (AACVD) and used as self-supported electrocatalysts with improved electrochemical performance. The main achievements include: (1) Firstly, a nanocomposite that integrates the HER active-site-rich [Mo₃S₁₃]²¯ cluster with electroconductive carbon-based substrates, including reduced graphene oxide (rGO) and exfoliated graphene oxide (exGO), was developed to enhance the electroconductivity and the dispersity for improving the HER catalytic performance. (2) Secondly, an AACVD-based method capable of in-situ growing low-cost electrocatalyst material, such as Ni-based compounds, on a free-standing carbon paper was established. Further modification, such as electrodeposition of Mo₃S₁₃ film or sulphurisation, was explored and the corresponding HER and OER activity was investigated. (3) Based on this method, the possibility of fabricating a bimetallic nanocomposite, nickel molybdenum sulphide, directly on carbon paper (NiMoS@CP) using AACVD was demonstrated. The NiMoS@CP synthesised by this method showed a strong interaction between Ni-Mo-S interfaces and defect-rich nature. This ternary NiMoS@CP material showed superior and stable HER and OER activity in acidic and alkaline electrolytes, respectively. (4) Further, the AACVD-based synthetic method was further used for the in-situ growth of cobalt molybdenum sulphide nanocomposites on carbon paper (CoMoS@CP) as a bifunctional electrocatalyst for HER and OER. This self-supported electrocatalyst exhibits outstanding HER activity in either acidic or alkaline conditions and excellent OER activity in alkaline electrolyte due to the strong interaction of Co-Mo-S atoms and rich interfacial defects. This CoMoS@CP electrode also showed exceptional bifunctionality for overall water electrocatalysis with a low cell voltage of 1.70 V at 10 mA cm¯² current density and superior stability of 50-hour continuous operation. In addition, this thesis also reviewed the emerging progress on this subject and provided a brief outlook on future directions.

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