Comparing Commercially Available Gas Diffusion Layers in the Electrochemical CO2 Reduction Reaction

Abstract

One of the most urgent challenges of our society is the continuously rising level of CO2 in the atmosphere, caused by anthropogenic emission, including different point sources (e.g., cement factories, automobiles, airplanes). The electrochemical CO2 reduction reaction (CO2RR) can be an alternative route for the chemical- and energy industries to convert CO2 into useful products (e.g., carbon monoxide, methane, ethylene), hence providing a value-added approach for CO2 neutralization1.In our work we employed a zero gap electrolyzer cell (active area = 8 cm2), where the catalyst coated electrodes are separated by only a Grade-T Sustainion® X37-50 anion exchange membrane (AEM). As the cathode we used Ag nanoparticle coated gas diffusion layers and as the anode we used Iridium Black coated Ti frit. During the experiments, an anolyte was recirculated continuously through the anode side and humidified CO2 was fed to the cathode side. Beyond the cell structure and membrane, the applied catalyst coated gas diffusion layer (GDL) is one of the most critical elements, determining the efficiency of CO2RR. In this work we compared commercially available GDLs in the CO2RR. All GDLs are used in identical electrochemical cells, under the same experimental conditions2.Our goal was to provide a comprehensive conclusion of the most frequently used commercially available GDLs in CO2RR. We studied the effect of the microporous layer (MPL), the PTFE content, the thickness, and the structure of the selected GDLs. One-hour long chronoamperometric measurement revealed some trends and important differences - in case of five of the tested GDLs (Sigracet 28BC, Sigracet 39BB, Freudenberg H23C6, Toray H60 MPL and Elat LT 1400W), the CO partial current density exceeded 500 mA cm−2 already at 3.0 V cell voltage. To unravel which structural parameters affect the electrolyzer performance the most, the results were compared along a few selected properties (Figure 1.): (A) whether they contained MPL or not, (B) the PTFE content, (C) the overall thickness, and (D) the structure of the GDL.<Figure 1.> Figure 1. Comparing commercially available gas diffusion layers in the CO2RR. Partial current densities for CO and H2 production during one-hour long chronoamperometric CO2RR measurements at ΔU = 3.0 V, applying different GDL based cathode GDEs with Ag catalyst. The electrolyte solution was 0.1 M CsOH, humidified CO2 was fed to the cathode at a flow rate of 12.5 cm3 cm−2 min−1 and the temperature of the electrolyzer cell was 60 °C. The error bars represent the deviations of two consecutive analyses during the same measurements.Long-term electrolysis experiments (100 hours) were performed with two GDLs, the Sigracet 39BB and the Toray H60 MPL. Throughout the long-term electrolysis, a stable total current density and CO formation selectivity was measured in both cases. Throughout our study, to understand the differences among their electrochemical behavior, of the various GDLs, we characterized their wetting properties and microstructure before the electrochemical measurements. The structure and morphology of the GDLs were characterized with SEM, micro-CT and contact angle measurements. References (1) Samu, A. A.; Kormányos, A.; Kecsenovity, E.; Szilágyi, N.; Endrödi, B.; Janáky, C. Intermittent Operation of CO2 Electrolyzers at Industrially Relevant Current Densities. ACS Energy Lett. 2022, 1859–1861(2) Samu, A. A.; Szenti, I.; Kukovecz, Á.; Endrődi, B.; Janáky, C. Systematic Screening of Gas Diffusion Layers for High Performance CO2 Electrolysis. Commun. Chem. 2023, 6 (1), 1–9 Supported by the KDP-2021 program of the Ministry for Innovation and Technology from the source of the National Research, Development and Innovation fund. Figure 1