Advantages of CO over CO2 as reactant for electrochemical reduction to ethylene, ethanol and n-propanol on gas diffusion electrodes at high current densities

The electrochemical conversion of CO2 to value-added chemicals is a technology gaining broader interest as society moves towards a carbon-neutral circular economy. Nonetheless, there are still several challenges to overcome before this technology can be applied as an industrial process. In the reaction path of the electrochemical reduction of CO2 with Cu as an electrocatalyst, it is known that carbon monoxide is the key intermediate to chemicals such as ethylene, ethanol, and n-propanol. However, a better understanding of the electrochemical reduction of CO is still necessary to improve selectivity and efficiency at high current densities. In this work, the electrochemical reduction of CO2 and CO towards C2 and C3 products is investigated using gas diffusion electrodes in a flow cell. Thereby the electrochemical reaction is not limited by the solubility of the feed gas in the electrolyte, and current densities of industrial relevance can be achieved. The electrodes are prepared using commercial Cu-powders consisting either of nano- or microparticles that are deposited on gas diffusion layers. Potentiostatic experiments show that with CO as the reactant, higher current densities for C2 and C3 products can be achieved at lower working electrode potentials compared to CO2 as the reactant. Galvanostatic CO electrochemical reduction at -300 mA cm(-2 )with Cu-nanoparticles (40-60 nm) results in a cumulative Faradaic efficiency of 89% for C2 and C3 products. This represents a two-fold increase in selectivity to ethylene and a three-fold increase towards ethanol and n-propanol compared to the selectivity obtained with CO2 as the reactant. This enhancement of selectivity for C2 and C3 products at current densities of industrial relevance with CO as reactant provides a new perspective regarding a two-step electrochemical reduction of CO2. (C) 2019 Elsevier Ltd. All rights reserved.