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.

工业领域的绿氢产能正持续提升，针对水电解槽的学术研究也显著增长。为实现绿氢的高效逆向电能转化，聚合物电解质燃料电池（Polymer Electrolyte Fuel Cells, PEFC）是当前最先进的技术方案。然而，当前主流的PEFC仍存在诸多局限：如水管理能力欠佳、铂族金属电催化剂成本高昂，且工作温度仅能限制在80℃以内。以聚苯并咪唑和磷酸替代Nafion®与水的高温型PEFC（工作温度160℃）虽已展现出应用潜力，但其耐久性往往会因组分浸出与催化剂中毒而受限。本研究聚焦于开发120℃的中温型PEFC，通过探究质子型离子液体（Protic Ionic Liquids, PIL）的液相结构——这类离子液体在质子传导率以及对氢氧化反应、氧还原反应相关过电位的调控作用两方面均已展现出应用前景。通过对质子化、部分氘代及全氘代PIL开展中子散射实验，可揭示温度、化学计量比以及阴离子侧链疏水性对这类液体内部纳米域结构的影响机制。通过深化对PIL纳米结构及整体氢键网络的认知，可为高温器件用离子液体基电解质的优化选型与设计提供理论支撑。