The role of cation exchange membrane characteristics in CO2 electrolysis to CO using acid anolyte

Author(s)

Sakita, Alan M. P. ; Ticianelli, Edson A.

• Document type: Journal article
• Source: Electrochimica Acta; v. 509, p. 9-pg., 2025-01-01.

Abstract

Cation exchange membranes are considered a suitable option for zero-gap CO2 electrolysis due to their potential to avoid carbonation and improve carbon efficiency. However, the use of acidic anolytes remains an issue due to high hydrogen production. This study investigates Nafion (R) membranes (111, 112, 115, 211, and 212) with different thicknesses produced by extrusion or solution-cast processes in a zero-gap cell with an acidic anolyte containing K2SO4. Faradaic efficiencies for CO production (FECO) are higher with thinner membranes, regardless of the manufacturing process, reaching FECO around 75 % at 50 mA cm(-)(2). Additionally, membranes with similar thicknesses (similar to 50.8 mu m) but produced in different ways displayed flow field carbonation after 3 h of electrolysis at 30 degrees C and 50 mA cm(-)(2). Linear sweep voltammetry (LSV) in full and half-cell configurations shows limiting diffusion current (i(L)) relative to proton transport for all the employed membranes, no matter the thickness. In contrast, the i(L) for Nafion (R) 115, the thicker membrane, is suppressed, indicating that proton depletion is fast and the electrode surface alkalinization primarily results from water reduction in this case. A mechanistic analysis was performed to explain the behavior of the limiting currents in the cell with Ar- and CO2-feed, indicating that CO2 reduction aids in the consumption of H+ provided by the membrane, increasing the local pH at less negative potentials. Overall, thinner membranes exhibited higher values of FECO and energy efficiency for CO (EECO%). However, solution-cast membranes are more prone to provide K+, leading to better performance than those prepared by extrusion. (AU)

• FAPESP's process: 23/17801-8 - Electrocatalysts impregnated with ionic liquids for electroreduction of carbon dioxide
• Grantee: Alan Massayuki Perdizio Sakita
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 19/22183-6 - Electrocatalysis VI: fundamental and applied aspects of emerging and classical problems in electrochemical energy conversion
• Grantee: Edson Antonio Ticianelli
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 21/14163-5 - Electrocatalysts impregnated with ionic liquids for the electro-reduction of carbon dioxide
• Grantee: Alan Massayuki Perdizio Sakita
• Support Opportunities: Scholarships in Brazil - Post-Doctoral