(585ax) Pulse/Pulse-Reverse Electrodeposition of Copper Electrocatalysts for CO2 Reduction to Ethylene
AIChE Annual Meeting
Tuesday, October 31, 2017 - 3:36pm to 3:57pm
This talk presents recent work toward development of efficient, selective, and active copper electrocatalysts for reduction of carbon dioxide to ethylene. Copper is well known as a unique CO2 reduction electrocatalyst, capable of forming alcohol (e.g., ethanol) and hydrocarbon (e.g., methane and ethylene) products in addition to aldehydes, carboxylic acids, carbon monoxide and hydrogen [3-6]. 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 to our knowledge 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 [8,9]. Given that pulsed electrodeposition is known to have a significant effect on the microstructure of the resulting metal films [10-12], 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 . 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. In particular, the electrodeposition and activation parameters have been demonstrated to have significant effects on the total faradaic efficiency of carbon conversion and the selectivity of the CO2reduction reaction for ethylene over methane.
As an adjunct means of optimizing system performance, we are focusing development toward the use of aqueous solutions containing CO2-solubilizing additives such as room-temperature ionic liquids (RTILs) and saturated amines (monoethanolamine, diethanolamine, N-methyldiethanolamine, etc.). These materials have been extensively studied in academia and industry as a liquid-phase capture media for removing CO2 from post-combustion exhaust streams (e.g., bulk generation power plants) [14-17], 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 also advantages to developing an advanced technology for electrocatalytic conversion of CO2using capture media already in large-scale industrial use, since it would dramatically reduce the logistical and economic costs of integration into existing facilities.
Two primary conclusions can be drawn from the preliminary data gathered to date: (1) EMIM and BMIM ionic liquids and saturated primary amines (e.g., monoethanolamine) in aqueous carbonate solution participate significantly in anodic reactions at the potentials required for CO2 reduction to hydrocarbons, and are thus not suitable additives for enhancing electrocatalytic CO2 conversion; and (2) saturated secondary and tertiary amines, though stable under relevant electrocatalysis conditions, completely inhibit electrocatalytic conversion of CO2at ambient temperature and pressure, and are thus unsuitable additives at these conditions. We hypothesize that it may be possible to overcome this inhibitory behavior via operation at elevated temperatures (e.g., 40 to 70 °C), enabling further enhancement in the performance of the pulse-deposited copper electrocatalysts under development.
The authors acknowledge the financial support of NASA Contract No. NNX14CC53P and US DOE Contract No. DE-SC0015812.
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