Sustainion® XA-9 ionomer reduces parasitic ORR to generate C2 Products from Fuel Gas

Parasitic ORR is of particular concern since the thermodynamic voltage of ORR is more than 1 V more positive than CO2RR, and thus could displace CO2RR activity. Researchers at University of Toronto published a journal article titled ‘Oxygen-tolerant electroproduction of C2 products from simulated flue gas’ which featured in the themed collection of Energy and Environmental Science HOT Articles.

To slow O2 transport selectively and enhance the stability of copper (Cu) catalysts, they develop a catalyst comprised of a Sustainion XA-9 ionomer with hydrophilic nanopores and titanium dioxide (TiO2) nanoparticles. Operating this electrode structure at 10 bar, they converted O2-containing flue gas concentrations of CO2 to C2 products with 68% selectivity and 26% energetic efficiency, competitive with reactors that convert pure CO2. All other tried commercial ionomers (Fumion, Nafion, Aquivion)could not yield the same level of performance. To investigate the stability of the new catalyst during prolonged operation, the TiO2 nanoparticle layer was hence bound with Sustainion XA-9 ionomer was coated on the Cu-GDE and operated at 10 bar. The current density and selectivity toward C2 products were stable for 10 hours of operation at a cell potential of -3.00V in 1 M KOH.

Stability performance test of CO2 reduction to C2 products for Cu-PTFE GDE coated with DMXA-9 ionomer/TiO2 support particles at 10 bar absolute pressure in 1 M KOH electrolyte, utilizing 15% CO2 (v/v) and 4% O2 (v/v) mixture gas feed stocks.

Scanning electron microscopy (SEM) images of the GDE before and after operation also show minimal changes in surface morphology:

Top row: Cu-PTFE GDE coated with DM XA-9/TiO2 support particles before prolonged operation.
Bottom row: Cu-PTFE GDE coated with DM XA-9/TiO2 support particles after prolonged operation.

This report illustrates the potential for the direct electrocatalytic conversion of flue gas CO2 streams by utilizing O2-tolerant hydrated ionomer catalyst support layer which selectively slows the ingress ofO2, thereby enabling the selective and stable generation of C2 products.