Sujat Sen 1
, Brian Skinn 2
, Tim Hall 2
, E.J. Taylor 2
, Fikile Brushett 1 1
, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2
, Faraday Technology, Englewood , Ohio, United States
Utilizing carbon dioxide (CO2) as a chemical feedstock has been identified as a means of reducing greenhouse gas emissions and moving towards a carbon neutral energy cycle . A promising approach for CO2 conversion is electrocatalytic reduction to selectively generate hydrocarbons such as ethylene and propylene that are the primary building blocks of the petrochemical industry . The production of these precursors by conventional means from petroleum feedstocks is energy intensive, requiring high temperatures and pressures. Hence, electrochemical methods, which can operate at conditions much closer to ambient, represent a potentially less costly and more sustainable alternative.
Prior reports have demonstrated electroreduction of CO2 to hydrocarbons on copper (Cu)-loaded gas diffusion layers (GDLs) to obtain ethylene, with the best performance to date at a potential of -0.8 V RHE, yielding a current density of 200 mA/cm2, and a current efficiency of 46% . These studies have typically used Cu nanoparticles, mixed with an ionomer and spray coated onto a microporous carbon layer (MPL) supported by a carbon fiber substrate (CFS), to form a gas diffusion electrode (GDE). This approach limits the electroreduction process due to 1) low catalyst specific surface area due to the relatively large Cu particle size (40-100 nm), and 2) poor utilization of a fraction of the Cu catalyst particles, which are surrounded by ionomer and thus not in electrical contact with the MPL. Previous work directed towards platinum (Pt) catalyst utilization in polymer electrolyte fuel cell GDEs demonstrated a novel “electrocatalyzation” approach to obtain highly dispersed ~5 nm Pt catalyst particles using pulse-reverse electrodeposition . Additionally, since the Pt was electrodeposited through an ionomer pre-coated on the MPL surface, the catalyst was inherently in electronic and ionic contact within the GDE and catalyst utilization was enhanced. Such an electrocatalyzation approach has also been successfully demonstrated for tin-based GDEs for the conversion of CO2 to formate .
Herein we investigate the electrocatalytic performance of novel Cu-coated GDEs prepared by direct electrodeposition onto GDL substrates using pulse-reverse waveforms. We demonstrate the potential for significant enhancements in catalytic activity due to 1) increased control of particle size, nucleation site density, and surface texture, as well as 2) improved Cu catalyst utilization via enhanced electronic and ionic contact with the MPL. Electrolysis experiments were conducted in a lab-scale reactor with gas-phase CO2 delivered across a GDE to determine the catalyst activity and stability as a function of deposition parameters and cell operating conditions.
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