Recent work toward development of efficient, selective, and active copper electrocatalysts for reduction of CO2 to ethylene is presented. Copper is well known as a unique CO2 reduction electrocatalyst, capable of forming alcohol (e.g., ethanol) and hydrocarbon (e.g., methane, ethylene) products in addition to aldehydes, carboxylic acids, carbon monoxide and hydrogen [,]. Ethylene is of specific interest, as its role as a platform feedstock for the chemicals and plastics industries affords it an appreciably higher market value than many other potential products []. However, the catalytic activity and selectivity achieved to date with Cu catalysts and CO2-saturated aqueous carbonate solutions have not been sufficient to enable development of an industrially viable process. Faraday and MIT are currently investigating pulse/pulse-reverse electrodeposition methods as a means to fabricate copper catalysts with greater activity and ethylene selectivity in order to enable large-scale electrocatalytic conversion of CO2.
The microstructure of metallic catalysts is known to influence various properties including selectivity and activity; for copper in particular, a strong effect on the selectivity for ethylene versus methane as a function of crystallographic orientation has been reported [,]. Given that pulsed electrodeposition is known to have a significant effect on the microstructure of the resulting metal films [,], the technology is a natural candidate for fabrication of novel, high-performance copper CO2 reduction catalysts. In this work, catalyst activity and selectivity were further enhanced through the use of a modified literature activation protocol involving aerobic thermal oxidation followed by electrochemical reduction []. Photographs of a representative catalyst coupon at each stage of fabrication are presented in Figure 1. This talk will present data confirming that catalytic properties can be enhanced by tuning both the pulsed waveform used for deposition as well as the conditions used in the oxidation/reduction activation protocol.
We are focusing development toward the use of aqueous solutions containing CO2-solubilizing additives such as room-temperature ionic liquids and cyclic amines. These materials have been extensively studied as a liquid-phase capture media for removing CO2 from post-combustion exhaust streams (e.g., power plants) [,], and have the potential to increase the effective CO2 concentration at catalyst active sites and thus enhance the faradaic efficiency of the CO2 reduction reaction relative to H2 formation from water electrolysis. There are advantages to developing an advanced technology for electrocatalytic conversion of CO2 using capture media already in large-scale industrial use, since it would dramatically reduce the logistical and economic costs of integration into existing facilities. The data gathered to date provide encouraging evidence that enhanced catalytic performance can be realized through the use of such CO2-solubilizing additives in tandem with pulse-deposited copper electrocatalysts.
The authors acknowledge the financial support of NASA Contract NNX14CC53P and US DOE Contract DE-SC0015812.
[] K.W. Frese, Jr. “Electrochemical Reduction of CO2 at Solid Electrodes.” Electrochemical and Electrocatalytic Reactions of Carbon Dioxide, B.P. Sullivan et al., eds. Amsterdam: Elsevier, pp. 145 (1993).