Structure and hydrogen bonding in protic ionic liquid fuel cell electrolytes

Green hydrogen production is ramping up industrially, and academic research into water electrolysers is increasingly markedly. To provide the most efficient means of converting green hydrogen back to electricity, polymer electrolyte fuel cells (PEFC) represent the state-of-the-art technology. However, the current form of PEFC faces a range of issues, such as poor water management, high costs of platinum group metal electrocatalysts and limited operation to 80 oC. High-temperature variants (160 °C), which replace Nafion® and water with polybenzimidazole and phosphoric acid have shown promise, but often their durability is limited by leaching and catalyst poisoning. This work focuses on unlocking an intermediate-temperature PEFC (120 °C), by exploring the liquid structure of protic ionic liquids (PIL) that have shown promise, both in terms of their proton conductivity and their influence of the overpotentials associated with the hydrogen oxidation reaction and the oxygen reduction reaction. By neutron scattering experiments on protiated, and partially and fully deuterated PILs, insight into the impact of temperature, stoichiometry, and anion side chain hydrophobicity on the nano-domains within these liquids can be realised. By improving our understanding of PIL nanostructure and the hydrogen-bonding networks throughout, a better selection and design of ionic-liquid-based electrolytes for elevated temperature devices can be achieved.