title: Novel inorganic material for hydrogen evolution reaction in electrochemical water splitting
Creators: name: Moca, Roberta
Publisher: name: University of Glasgow
Year: 2019
Subjects: subject: electrocatalysts, water splitting, hydrogen evolution reaction.

description: Sunlight is the most abundant renewable source of energy available on earth, providing an amount more than several hundred times sufficient to satisfy human’s need. However, it is diffusive and inconsistent over time, leading to problems related to its harvesting and storage. Devices able to perform splitting of water by the use of sunlight can be used to overcome these problems by producing hydrogen, which is an excellent fuel. Nevertheless, those devices need to be cheap to produce, and therefore an investment in research of earth abundant electrocatalysts for water splitting is necessary to make them available in a larger scale. This thesis focussed on the development of new inorganic catalysts for the half-reaction responsible for hydrogen production known as hydrogen evolution reaction. The prepared catalysts were morphologically characterized by the use of various techniques and their performances were then probed electrochemically. The first synthesis carried out was the preparation of Co-doped molybdenum sulphide materials by hydrothermal synthesis. This catalyst exhibited a disordered structure, however it could be probed by Raman spectroscopy. The second project was to investigate the role of replacing nickel with molybdenum within the Ni2P structure. A MoxNi2-xP series were prepared using the solid-state method, where nickel was selectively substituted. Optimisation of the method allowed the synthesis of phase pure materials by time programmed reduction. Finally, the potential of the nitride class as hydrogen evolution reaction catalysts was investigated with the synthesis of a ternary nitride using a modified Pechini method. In general, all the prepared materials exhibited good electrochemical performances in acidic media, while the overall performance in basic media was lower. It was possible to deposit the Co-doped molybdenum sulphide in a semi-transparent film on a Fluorine-doped SnO2 substrate without the use of any binder. The material exhibited good electrochemical performance in acid media in line with what was already reported in the literature. The compounds belonging to the MoxNi2-xP series were successfully synthesised and showed enhanced catalytic performance proportional to the number of molybdenum within the formula. All the prepared compounds showed a high stability of the performance over time in acidic media. Moreover, the used synthesis strategy had the advantage of being easy to perform, opening up to the possibility of being scaled up for industrial purposes. The obtained ternary nitride exhibited great performance in acidic media if compared to most of the nitrides already reported in the literature. The high activity was tentatively attributed to the zero state of the nickel within the structure. Further theoretical studies, however, will be needed to fully understand the reason behind this enhanced activity. In conclusion, all the catalysts reported in this work showed good electrochemical performance in acidic media similar to what was already reported in the literature, with the additional synthetic advantage of being simple and cheap to produce.