Influence of Headgroups in Ethylene-Tetrafluoroethylene-Based Radiation-Grafted Anion Exchange Membranes for CO2 Electrolysis

Carlos A. Giron Rodriguez, Bjørt Óladottir Joensen, Asger Barkholt Moss, Gastón O. Larrazábal, Daniel K. Whelligan, Brian Seger*, John R. Varcoe*, Terry R. Willson

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

The performance of zero-gap CO2 electrolysis (CO2E) is significantly influenced by the membrane’s chemical structure and physical properties due to its effects on the local reaction environment and water/ion transport. Radiation-grafted anion-exchange membranes (RG-AEM) have demonstrated high ionic conductivity and durability, making them a promising alternative for CO2E. These membranes were fabricated using two different thicknesses of ethylene-tetrafluoroethylene polymer substrates (25 and 50 μm) and three different headgroup chemistries: benzyl-trimethylammonium, benzyl-N-methylpyrrolidinium, and benzyl-N-methylpiperidinium (MPIP). Our membrane characterization and testing in zero-gap cells over Ag electrocatalysts under commercially relevant conditions showed correlations between the water uptake, ionic conductivity, hydration, and cationic-head groups with the CO2E efficiency. The thinner 25 μm-based AEM with the MPIP-headgroup (ion-exchange capacities of 2.1 ± 0.1 mmol g-1) provided balanced in situ test characteristics with lower cell potentials, high CO selectivity, reduced liquid product crossover, and enhanced water management while maintaining stable operation compared to the commercial AEMs. The CO2 electrolyzer with an MPIP-AEM operated for over 200 h at 150 mA cm-2 with CO selectivities up to 80% and low cell potentials (around 3.1 V) while also demonstrating high conductivities and chemical stability during performance at elevated temperatures (above 60 °C).

Original languageEnglish
JournalACS Sustainable Chemistry and Engineering
Volume11
Issue number4
Pages (from-to)1508-1517
ISSN2168-0485
DOIs
Publication statusPublished - 2023

Keywords

  • Anion exchange membrane (AEM)
  • Cationic functional group
  • Electrochemical CO reduction
  • Ion exchange capacity
  • Ion transport
  • Zero-gap approach

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