A tandem electrode concept for CO2-to-C2+ products conversion proposed.
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Spatial management of CO transport to enhance C2+ products yield.
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CO utilization efficiency as the key to increase the C2+ products yield discussed.
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A high yield of C2+ products demonstrated in Cu/ZnO tandem electrodes.
Abstract
The electrochemical reduction of CO2 into C2+ products is a promising route to store renewable electricity in the form of chemical energy. The current barrier to this technique is the low efficiency of C-C coupling through dimerization of adsorbed *CO or coupling of *CO with its hydrogenated derivatives over the Cu catalyst. Tandem catalysts, which integrate Cu with another CO-generation catalyst (e.g., ZnO), can enhance the C-C coupling kinetics by increasing the local concentration of the key intermediate of CO. However, the degree of enhancement is strongly dependent on the spatial manipulation of supplementary CO transport. Herein, inspired by the reactant species concentration profile in a plug flow reactor, Cu/ZnO tandem electrodes are designed by spatially adding a ZnO catalyst layer on top of the Cu catalyst layer, in which the ZnO catalyst layer fed CO concentration progressively decreases over the Cu catalyst layer. Such a spatial management of CO transport dramatically increases the CO utilization efficiency, leading to an enhancement of Faradaic efficiency and partial current density of C2+ products by 1.2 and 3.4 times, respectively, compared to the bare Cu electrode, while by 1.3 and 1.8 times, respectively, compared to the Cu&ZnO mixed electrode.
