Improving Catalytic Activity in the Electrochemical Separation of CO₂ Using Membrane Electrode Assemblies

Abstract

The direct electrochemically driven separation of CO2 from a humidified N2, O2, and CO2 gas mixture was conducted using an asymmetric membrane electrode assembly (MEA). The MEA was fabricated using a screen-printed ionomer bound Pt cathode, an anion exchange membrane (AEM), and ionomer bound IrO2 anode. Electrocatalyst materials were physically and chemically characterized prior to inclusion within the electrode. Electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements using a rotating disk electrode (RDE) were used to quantify the catalytic activity and determine the effects of the catalyst-to-ionomer ratio. Catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface analysis, and (dynamic light scattering) DLS to evaluate catalyst structure, active surface area, and determine the particle size and bulk particle size distribution (PSD). The electrocatalyst layer of the electrodes were fabricated by screen printing a uniformly dispersed mixture of catalyst, dissolved anionic ionomer, and a solvent system onto an electrode supporting gas diffusion layer (GDL). Pt IrO2 MEAs were fabricated and current-voltage relationships were determined using constant-current measurements over a range of applied current densities and flow rates. Baseline reaction kinetics for CO2 separation were established with a standard set of Pt-IrO2 MEAs.

Effects of Electrode Support Structure on Electrode Microstructure, Transport Properties, and Gas Diffusion within the Gas Diffusion Layer

“…Although they can also have a possible effect on the gas permeability for this study, the catalyst particle size and ionomer level were fixed at 75:25 black catalyst to FAA-3 ionomer (deposited by screen printing), which was found to be the optimal formulation in a previous study of the MEA fabrication parameters. 27 Within an MEA, gaseous reactants and products must diffuse from the flow channels, where it is convectively well mixed in the cell through the GDL to the catalyst layer deposited on the MPL of the GDL. Gas permeability measurements at 25 °C with 100% relative humidity with catalyst loading varying from 0.4 up to 2.7 mg/cm 2 are shown in Figure 4 .…”

“…Pt and IrO 2 electrodes were made using the previously developed catalyst inks to screen-print each ink onto 216 cm 2 of the SGL Sigracet 10BB, 10BC, 29BC, 34BC, and 39BC GDL materials. 27 Electrodes were dried to remove organic solvents from the catalyst ink before undergoing an ion exchange treatment by soaking in 1 M NaOH solution for 2 h to exchange the as-received bromide (Br – ) ion in the ionomer (Fuma-Tech, FAA-3) with hydroxide ions (OH – ). Next, the electrodes were rinsed to remove any excess hydroxide or contaminants and dried.…”

“…Pt and IrO 2 electrodes were cut into 54 cm 2 electrodes (6 cm × 9 cm) and constructed into an MEA with a 30 μm membrane (Fuma-Tech FAA-3-PE-30); the MEA was tested in a two-electrode configuration, as described in a previous paper. 27 Initially, the 29BC-based IrO 2 anode was used as the constant, controlled electrode and evaluated with Pt electrodes composed of the SGL Sigracet 10BB, 10BC, 29BC, 34BC, and 39BC GDL materials. Then, a 29BC-based Pt cathode served as the control electrode to evaluate 10BB, 10BC, 29BC, 34BC, and 39BC GDL-based electrodes.…”

“…Physical and electrical properties of the GDL materials are listed in Table for the SGL Sigracet 10BB, 10BC, 29BC, 34BC, and 39BC GDL materials. , The 29BC GDL material has been demonstrated as a suitable electrode support material for fuel cells, electrolysis, and gas separation under high-humidity environments. ,, SEM images were analyzed to determine the average carbon fiber layer, MPL, and overall thickness with a measure of the thickness layer variability. The manufacturer-specified thicknesses have a reported tolerance range from ±20 to ±30 μm from the average overall GDL thickness, which is in line with the measurements presented here.…”

“…Next, the electrodes were rinsed to remove any excess hydroxide or contaminants and dried. Pt and IrO 2 electrodes were cut into 54 cm 2 electrodes (6 cm × 9 cm) and constructed into an MEA with a 30 μm membrane (Fuma-Tech FAA-3-PE-30); the MEA was tested in a two-electrode configuration, as described in a previous paper . Initially, the 29BC-based IrO 2 anode was used as the constant, controlled electrode and evaluated with Pt electrodes composed of the SGL Sigracet 10BB, 10BC, 29BC, 34BC, and 39BC GDL materials.…”