Electrocatalytic Reduction of CO2 for the Production of Fuels: a Comparison between Liquid and Gas Phase Conditions

In this contribution we report on the electrocatalytic reduction of CO2 for the production of liquid fuels by using two different approaches under i) liquid and ii) gas phase conditions. The main aim of the work is the comparison of these two experimental setups, in terms of productivity, kinds of liquid compounds produced and efficiencies, due to the differences in the mechanism which underlay the reactions occurring. Particularly, gas phase CO2 reduction has some advantages such as ease in recovery of products, no CO2 solubility issues and it allows the formation of oxygenates and hydrocarbons with higher chains (C2-C9). On the other hand, liquid phase CO2 reduction yielded in higher productivity, giving formic acid and acetic acid as the major products and trace amounts of methanol. The experiments were performed in homemade electrochemical cells, designed on purpose to maximize the electrocatalytic area and reduce the volume of the cathodic hemicell. Initially, experiments were conducted using Cu thin film electrodes. Then, metal based nanostructured catalysts (using Fe and Cu, deposited on carbon-based substrates) were synthesized in order to improve the productivity and fine tune the selectivity in achieving longer chain hydrocarbon fuels. The final perspectives of this study regard the integration of this electrocatalytic device with a photo-anode to obtain a sort of artificial leaf, which collects energy in the same way as the nature does, by capturing directly CO2 and converting it back to fuels.