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 H-2/O-2 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).

Automated summary

We have demonstrated for the first time the effects of cis-trans conformation on the properties of anion exchange ionomers. The twisted cis-conformation with abundant subnanoscale free volume cavities enhances oxygen permeability and water adsorption. Additionally, the nonplanar conformation of the cis-ionomer reduces undesired absorption on Pt and Pt-Ru surfaces, thus improving the electrochemical performance of catalyst layers. The theoretical and electrochemical investigations provide mutual support for our proof-of-concept. The catalyst layer incorporating cis-ionomer shows significant increases in limiting current density and electrochemically active surface area (51% and 54% respectively). The H-2/O-2 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 to the t-MEA at 100% relative humidity (RH). Furthermore, the performance of c-MEA is particularly outstanding at low humidity (increased by 114% and 113% at 80% and 60% RH respectively).