Phosphoric acid clustering in porous composite membranes for high temperature fuel cell

High-temperature PEM fuel cells (HT-PEMFCs) are crucial for achieving net-zero emissions by efficiently converting hydrogen and oxygen into electricity, with only water as a byproduct. Operating at 120-200°C, these fuel cells rely on phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes to deliver high power density and durability. Unlike low-temperature fuel cells where water conducts protons, PA is the proton conductor in HT-PEMFCs. However, PA leaching from PBI membranes reduces performance, accelerates catalyst migration, and shortens the cell’s lifespan.
Our research addresses this by developing composite membranes made from cardo polymers of intrinsic microporosity (cPIM-1) and polyvinylpyrrolidone (PVP). These membranes show improved electrochemical performance over commercial alternatives due to their microporous structure, which retains PA through capillary forces and hydrogen bonds, reducing acid loss. Small-angle and wide-angle X-ray scattering (SAXS and WAXS) experiments show that PA clusters in these composite membranes are smaller and more uniformly distributed, enhancing stability and efficiency.
To deepen our understanding of the PA interactions within the membranes, we plan to use neutron scattering techniques. This will offer insights into hydrogen bonding and microstructural behavior, aiding in the design of more efficient, durable fuel cells.

高温质子交换膜燃料电池（High-temperature PEM fuel cells, HT-PEMFCs）是实现净零排放的核心技术，可将氢气与氧气高效转化为电能，副产物仅为纯水。该类电池工作温度区间为120~200℃，依靠磷酸（phosphoric acid, PA）掺杂的聚苯并咪唑（polybenzimidazole, PBI）膜实现高功率密度与耐用性。与以水作为质子传导介质的低温燃料电池不同，高温质子交换膜燃料电池的质子传导依赖磷酸。但聚苯并咪唑膜中溶出的磷酸会降低电池性能、加速催化剂迁移并缩短电池使用寿命。
本研究针对该问题，开发了由本征微孔螺环聚合物（cardo polymers of intrinsic microporosity, cPIM-1）与聚乙烯吡咯烷酮（polyvinylpyrrolidone, PVP）制备的复合膜。相较于商用膜材，该复合膜凭借微孔结构通过毛细作用与氢键截留磷酸，减少酸损耗，因此电化学性能更优。小角与广角X射线散射（small-angle and wide-angle X-ray scattering, SAXS and WAXS）实验显示，该复合膜内的磷酸团簇尺寸更小且分布更均匀，可提升稳定性与能效。
为进一步厘清膜内磷酸的相互作用机制，本研究计划采用中子散射技术，该技术可揭示氢键作用与微观结构行为，助力开发更高性能、更耐用的燃料电池。