(Invited) Developing Electrodes for Efficient Electroreduction of CO2 to Fuels or Chemicals
Authors: Kenis Paul J.A. 
Published: May 2020

Using CO2 as a feedstock for the production of intermediates for fuels/chemicals such as formic acid, CO, ethylene, and ethanol via electroreduction is one of several approaches being explored to help reduce anthropogenic CO2 emissions. In addition to reducing CO2 by using some of it as feedstock, an additional amount of CO2 emissions potentially can be avoided by replacing today’s energy-intense thermo-catalytic processes with (close to) carbon neutral CO2 electrolysis technology. Over the past decade a variety of promising electrocatalysts have been identified for the selective conversion of CO2 to products such as CO, formic acid, ethylene, and ethanol under different operating conditions (see for example [1,2,3]). Various techno-economic analyses indicate that several of these catalyst exhibit sufficient activity and selectivity, provided they are stable over thousands of hours of operation (see for example [4]).

This presentation will focus on structure-performance relationships of gas diffusion electrodes (GDEs), the type of electrodes often used in CO2 electrolysis cells. GDEs typically are comprised of three layers, a carbon fiber substrate (CFS) that provides lateral conductivity and structural stability, a micro-porous layer (MPL) that provides a barrier for the liquid electrolyte, and a catalyst layer (CL) that contains the catalyst. A variety of so-called gas diffusion layers comprised of a CFS covered by a MPL can be obtained commercially, and the catalyst layer can be applied to the MPL via painting or spray coating [5]. The electrochemical performance of a catalyst embedded onto a GDE depends on many factors including the exact composition and structure of each of the layers of the GDE, especially the catalyst layer (see for example [6]) and the micro-porous layer, MPL (see for example [7]). Also, structure-performance relationships of GDEs have been studied through computational models (see for example [8]). After an overview of key GDE structure and composition aspects as summarized above, the presentation will focus on studying the performance stability / durability of GDEs under electrolysis operation conditions (hundreds of mA/cm2). We have developed protocols for (accelerated) durability testing that include characterization of structure and composition before, during, and after hours of operation. These experiments revealed a number of degradation mechanisms, some of which are directly related to a drop in electrochemical performance. Understanding gained from studies such as these will allow for more stable / durable electrodes for CO2 electrolysis to be developed, thereby achieving the thousands of hours of performance needed to achieve economic feasibility.

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