390325 Catalysts for Electroreduction of CO2 to CO
The study of electrochemical reduction of CO2 to various value-added chemicals has intensified over the last several years because this approach may help reduce atmospheric CO2 levels. Multiple approaches need to be implemented to curb the atmospheric CO2 levels, including switching to renewable energy sources, increasing the energy efficiency of buildings, increasing the fuel efficiency of vehicles, and underground carbon sequestration.[1,2] Electrochemical reduction of CO2 into useful chemicals such as carbon monoxide (CO), formic acid, methane, and ethylene is another approach to address this challenge, as we recently summarized in a review . Coupled to renewable energy sources such as wind and solar, this process can produce carbon-neutral fuels or commodity chemicals by using CO2 as the starting material, while this approach may also provide a method for storage of otherwise wasted excess energy from intermittent renewable sources.
For this process to become economically feasible, more active and stable catalysts as well as better electrodes are necessary such that CO2 electrolyzers can be operated at sufficient conversion (current density >250 mA/cm2), reasonable energetic efficiency (>60%), and sufficient product selectivity (Faradaic efficiency >90%).
For CO production, a key reactant in the Fischer-Tropsch process, the best performance reported to date is current densities on the order of 90 mA/cm2 and energy efficiencies up to 45%, when operating at ambient conditions . This presentation will focus on new catalysts systems for efficient conversion of CO2 to CO: (i) Ag nanoparticles supported on TiO2 ; (ii) Au nanoparticles supported on multiwall nanotubes; and most interestingly (iii) metal-free N-doped carbons. These catalysts have been characterized in a 3-electrode cell and in an electrolyzer. Current densities of between 100 and 250 mA/cm2 as well as energy efficiencies of up to 70% were obtained. The electrodes in all these cases are prepared using automated airbrushing , which reduced catalyst loadings to 0.75 mg/cm2 for Ag and 0.17 mg/cm2 for Au. These performance levels, together with the lower cost due to low precious metal loading (due to the use of catalyst supports), or even the elimination of precious metals altogether (N-doped carbons), brings electrochemical reduction of CO2 to CO closer to economic feasibility.
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