Rational Design of Ion Exchange Membrane Material Properties Limits the Crossover of CO₂ Reduction Products in Artificial Photosynthesis Devices

Abstract

Efficient operation is crucial for the deployment of photoelectrochemical CO2 reduction devices for large-scale artificial photosynthesis. In these devices, undesired transport of CO2 reduction products from the reduction electrode to the oxidation electrode may occur through a liquid electrolyte and an ion exchange membrane, reducing device productivity and increasing the energy required for product purification. Our work investigated the CO2 reduction product crossover through ion exchange membranes separating the cathode and anode compartments in CO2 reduction cells. The concentrations of liquid products produced by CO2 reduction on copper foil were measured. A systematic approach for the investigation of product crossover was developed. The crossover of products was analyzed over a range of working electrode potentials (−1.08 V vs RHE to −0.88 V vs RHE) in cells employing a commercial Selemion AMV membrane and a new poly­(vinylimidazolium) family of ion exchange membranes with variable chemical and structural properties. We found that product loss due to electromigration of charged species in the device was more significant than product loss due to diffusion of uncharged species. To reduce the crossover of CO2 reduction products, the influence of membrane properties such as the ionic conductivity and water volume fraction was investigated for the Selemion AMV membrane and poly­(vinylimidazolium) membranes with variable material properties. We show that the water volume fraction and, by extension, ionic conductivity of the membrane may be controlled to reduce product crossover in CO2 reduction artificial photosynthesis devices.

Role of ion-selective membranes in the carbon balance for CO2 electroreduction via gas diffusion electrode reactor designs

“…In addition to the detected gas products, liquid-phase products in both catholyte and anolyte were all analyzed due to the potential crossover of liquid products from the catholyte to the anolyte via membranes. 39,40 As noted in Fig. 2a, substantial anionic CO 2 reduction products (such as formate and acetate) crossed over from the catholyte to the anolyte via the AEM by electromigration, with only minimal crossover for uncharged liquid products.…”

Transport and co‐transport of carboxylate ions and alcohols in cation exchange membranes

“…Major roles of the IEM in such devices are to provide a preferential ion transport (i.e., proton (H + )) for cation exchange membranes (CEMs) with membrane-bound charged functional groups (i.e., sulfonate for CEMs) and to minimize the permeation of these CO 2 reduction products to anode chamber, as they readily oxidize back to CO 2 and by-products. 5,6 Traditionally, IEM design for PEC-CRC has been focused on anion exchange membranes (AEM [9][10][11][12] ) as they show higher diffusibility for negatively-charged electrolytes, such as bicarbonates. However, CEMs [13][14][15][16] can be advantageous as they can minimize the permeation of negatively-charged CO 2 reduction products, such as OFm À and OAc À .…”

Fabrication and Characterization of Cross-Linked Phenyl-Acrylate-Based Ion Exchange Membranes and Performance in a Direct Urea Fuel Cell

“…Ion exchange membranes (IEMs) are hydrated, dense polymeric membranes with a charged functional group that have been applied in various applications, such as direct fuel cells (direct methanol fuel cells − and direct urea fuel cells (DUFCs) − ) and CO 2 reduction cells. − Major roles of IEMs in these devices are to provide ion-selective transport for device operation and to minimize the crossover of charge-neutral solutes (i.e., methanol (MeOH), ethanol (EtOH), and urea), which reduce performance. While many efforts have focused on enhancing the ion selective transport through higher ionic conductivity, − investigations on minimizing neutral solute crossover are relatively lacking. − Common strategies for mitigating this type of solute crossover are (1) to engineer the surface of the membrane with functional groups or chemistry that inhibit transport and (2) to incorporate solid additive materials (silica nanoparticles and carbon nanotubes , ) within the membrane to obstruct the transport of undesired molecules.…”