Effects of Gas Diffusion Layers on a CO2 electrolysis Cell with an Anion Exchange Membrane for Ethylene Production

Abstract

The concept of an electrolysis system, where CO2 is converted into hydrocarbons using renewable electricity, has been attracting much attention because it is expected to be one solution to achieve a decarbonized society. In order to realize an economical electrolysis system, it is important to produce high-value products such as ethylene with high reaction rate (i.e. the operating current density of CO2 electrolysis), and high efficiency (low operation voltage).The anion exchange membrane (AEM) CO2 electrolysis cells using gas diffusion electrodes (GDEs) are more advantageous than the traditional flow cell using a solution purged with CO2, both in terms of higher current density and lower voltage operation. This is because of the efficient CO2 reduction occurring at the three-phase interface of a GDE (i.e. CO2 is directly fed to the vicinity of the electrocatalysts though a gas diffusion layer (GDL)), increasing the current density, and of the cell electrodes being closely spaced, lowering the voltage. However, there are only several studies of the AEM CO2 electrolysis cells for high rate of ethylene production [1].Here, we investigate ethylene production performance of an AEM CO2 electrolysis cell consisting of copper and copper oxide nanoparticles coated on GDL as a cathode, iridium oxide-coated titanium support as an anode, and an AEM. Among these components, the GDL can play a crucial role in the efficient transport of CO2 and water management, therefore we focus on understanding the effects of GDL properties such as thickness, porosity and density on ethylene production. We evaluated the electroreduction characteristics of the cells under ambient condition by a constant current method in which a constant current is supplied for a period of time. The faradaic efficiency (FE) and partial current density (PCD) of gas products such as ethylene, carbon monoxide, methane and hydrogen are examined as a function of the total current densities (TCD). We found that the FEs and PCDs depended on the density and the thickness of the GDLs. The low density and thick GDL showed high FE and PCD of ethylene due to high gas diffusibility. The FE and the PCD of ethylene at the TCD of 600 mA/cm2 reached a maximum of 50 % and 300 mA/cm2, respectively.