Molecular-Level Control over Oxygen Transport and Catalyst–Ionomer Interaction by Designing Cis–Trans Isomeric Ionomers

We here demonstrate a monographic study to investigate the effects of cis–trans conformation on the properties of anion exchange ionomers for the first time. Twisted cis-conformation possessed of abundant subnanoscale free volume cavities facilitates oxygen permeability and water adsorption. Moreover, its nonplanar conformation can alleviate the undesirable absorption of ionomer on Pt and Pt–Ru surfaces, thus improving the electrochemical performance of the catalyst layers. Theoretical and electrochemical investigations are mutual corroborations, demonstrating our proof-of-concept. The catalyst layer equips cis-ionomer showing 51% and 54% increases in limiting current density and electrochemically active surface area. The H2/O2 single-cell peak power density of the cis-membrane electrode assembly (c-MEA) is increased by 56% (1.0 vs 0.64 W cm–2) compared with that of the t-MEA at 100% relative humidity (RH). Moreover, the performance of c-MEA is particularly prominent at low humidity (increased by 114% and 113% at 80% and 60% RH, respectively).