In the past few decades, atmospheric CO2 levels increased significantly, which has been associated with the climate change. Renewable energy sources such as solar and wind need to be pursued to replace the energy currently produced from fossil fuels. However, these renewable sources are often intermittent. Electroreduction of CO2 to various value-added chemicals provides an approach to reduce atmospheric CO2 emissions and utilize otherwise wasted intermittent renewable energy (when supply exceeds demand) to provide a source of chemical building blocks not derived from fossil fuels.[1, 2]
For this process to become economically feasible, more active and stable catalysts as well as better electrodes that allow for high conversion rate (current density >250 mA/cm2), reasonable energetic efficiency (>60%), and sufficient product selectivity (Faradaic efficiency >90%) are necessary. Currently, most work report 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 cathode catalysts for efficient conversion of CO2 to products such as CO, ethylene, and ethanol: (i) Ag nanoparticles supported on TiO2 (for CO production); (ii) Au nanoparticles supported on polymer wrapped multiwall nanotubes (for CO production); (iii) organometallic Ag complexes (for CO production); (iv) Ag nanoparticles with different sizes (for CO production); (v) metal-free N-doped carbons, and most interestingly, (vi) active Cu nanoparticles for efficient production of ethylene and ethanol. This paper also covers the use of automated airbrushing electrode preparation method to decrease catalyst loadings to 0.75 mg/cm2 for Ag and 0.17 mg/cm2 for Au. We will also present the optimization of anode catalyst and electrolyte in a continuous flow electrolyzer to make the catalysts perform under optimum conditions. As a result, these above catalysts have achieved current densities between 100 and 450 mA/cm2 as well as energy efficiencies of up to 70% with the use of IrO2 as the anode catalyst in the flow electrolyzer.
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