DIMENSIONALLY STABLE ELECTRODES FOR SUPERCRITICAL WATER ELECTROLYSIS (SuperH2)

The development of cost-effective green hydrogen-generation systems is one of the most pressing challenges towards the development of a vibrant low-carbon economy. The impact of hydrogen on the UK's roadmap to Net Zero is extensively described in the government's 2021 Hydrogen Strategy and the Ten-Point Plan for a Green Industrial Revolution. The UK aims to develop a 5 GW low-carbon production by 2030. Towards this target, hydrogen production by water electrolysis, green hydrogen, play a central role.

Matured water electrolysis technologies such as alkaline (AEC) and polymer electrolyte membrane (PEM) electrolysers are currently being scaled up as energy-storage systems coupled to renewable-energy generation. However, aspects such as hydrogen compression and availability of key raw materials (e.g. Pt and Ir) pose important challenges towards operations at the GW scale. Operating electrolysers at high temperature and pressure, such as in the case of solid oxide electrolysers (SOE), offers substantial advantages with regards to the overall energy balance and hydrogen generation efficiency. However, SOE is an emerging technology which also faces challenges in scalability associated with manufacturing high-quality ceramic membrane systems.

SuperH2 is a collaboration between University of Bristol and Supercritical Solutions Ltd, a SME based in London, aiming at the development of dimensionally stable materials for water electrolysis under supercritical conditions. These materials will be key active elements in a highly novel electrolyser design working under flow of supercritical water, leading to the separation of H2 and O2 driven by buoyancy, without the presence of a membrane. This unique technology can utilise waste heat from industrial sites, while generating H2 at pressures above 220 bar.

SuperH2 will examine the electrocatalytic activity of Ni based materials, modified with Pt, Fe and Co, towards the hydrogen evolution reaction (HER) in alkaline solutions from standard to supercritical conditions. We will utilise boron-doped diamond (BDD) electrodes as dimensionally stable supports for the metallic active sites. The project will deliver a composition-activity correlation towards HER in alkaline electrolytes at standard and supercritical conditions. At the fundamental level, these studies will uncover how water dissociation dynamics at metallic sites, the key limiting step in HER under alkaline conditions, can be affected by temperature and pressure. These studies will also establish correlations between stability and activity, which is key for formulating electrode material in supercritical water electrolysers.