(390h) What Is the Role of Nafion in the Electroreduction of CO2 into Ethylene?

The electroreduction of CO₂ into added-value products has been studied extensively in the past few years. Gas difussion electrodes (GDE) are prepared using several components; carbon is used to enhance electron transport across the GDE, copper is generally used as an active metal for the electroreduction of CO₂, PTFE is used to avoid flooding and Nafion® is found in all GDE formulations to enhance the concentration of protons in the vicinity of the catalytic center. In the paper, we deep-dive in the role of each component and optimise the formulation of the GDE. We found that the presence of Nafion® decreases the performance of CO₂ reduction into ethylene and that those materials formulated without Nafion® yield the highest Faraday efficiency to ethylene. The best result we have obtained with Cu as single-metal active component is 37% Faraday efficiency to ethylene. We have also observed that those electrocatalysts formulated without Nafion® increase the production of liquid products, and that the presence of Nafion® just utilises this excedent of current density that is captured in the formation of liquid products to dramatically enhance the evolution of hydrogen at the electrocatalyst.

From a more fundamental point of view, we also found that the evolution of ethylene at the electrode is not correlated with that of carbon monoxide, which questions the accepted mechanistic path in which ethylene is formed by coupling of two CO molecules. Of course, the macroscopic analysis of the performance of the electrocatalyst does not necessarily exclude such elementary step at microscopic level.

Figure. Hydrogen Faraday efficiency versus the total sum of Faraday efficiencies of gas products classified by content of Nafion® in the formulation of the GDE.