Probing 2D materials for sustainable electrocatalysis using X-ray spectroscopies

2-dimensional (2D) materials are fundamentally intriguing as their physical properties can vary considerably by not just their composition, but also their dimensionality i.e. the number of layers. This tunability makes them promising candidates for a range of advanced technologies and devices such as transistors, gas sensors and fuel cells. A potentially transformative application for 2D materials is in electrocatalysis, for the sustainable synthesis of chemicals from renewable energy sources. Platinum is the most commonly employed heterogeneous electrocatalyst for hydrogen evolution, however its scarcity and cost has triggered intense interest in alternative materials. Molybdenum disulphide (MoS2) is a transition metal dichalcogenide (TMD), which theoretically displays a similar energy for H adsorption as Pt, and experimentally the same order of magnitude turnover frequency. Understanding how lower-cost catalysts such as MoS2 can be tuned to achieve performance similar to platinum group metals would have a significant impact in making electrochemical synthesis more commercially viable.

For simple metal catalysts, models based on d-electrons exist have been extremely powerful in describing how catalytic behaviour is intimately linked with electron structure. The aim of this project is to extend this understanding further to TMD electrocatalysts by combining experimental and theoretical approaches. This will involve the development of growth recipes to produce TMDs on a variety of substrates using chemical vapour deposition. These materials will then be characterised by photoemission spectroscopy (UPS/XPS) and X-ray absorption spectroscopy (NEXAFS), allowing both the valence and conduction band electronic structures to be experimentally probed. Advanced operando capabilities based on creating electron transparent windows from 2D materials, will then be used to probe changes to the electronic structure when in the electrochemical reaction environment. The applicability of the d-electron model will be tested on these systems using quantum mechanical simulations (density functional theory), to determine how the band structure changes with different support substrates and with the introduction of adatoms to the TMD surface. These results of these simulations will be compared with experimental measurements of band structure and catalytic performance, and then used to inform the design of supported 2D material catalysts.

This project falls within the EPSRC research areas of Energy Storage and Physical Sciences, involving the development of controlled 2D material deposition processes, the use novel operando characterisation methods, and the application of with state-of-the-art simulation methods. This will include the use of X-ray techniques available at Diamond light source, as well as other international facilities. Together these approaches will help reveal the origins of the catalytic performance achieved with 2D materials, and provide a rationale for designing and tuning 2D material electrocatalysts.