 and impact on product selectivity: Nafion  is known for its ion exchange properties, allowing selective and restrictive transport of counterions and co-ions respectively. This impacts transport and concentration of H + and OH -ions in the local microenvironment of catalytic sites due to the residing negative charges, and favours formation of some products over others. The components of the catalyst ink that use Nafion  ionomer also affect product selectivity of the reaction. However, while this is very important, we do not account for these observed effects in our model due to lack of data in the literature on these effects on Cu electrodes. There is still limited understanding on the impact of Nafion  on product selectivity with regards to reaction mechanistic pathways that are accessible or inaccessible due to their energy barriers.