Nanoparticle Silver Catalysts That Show Enhanced Activity for Carbon Dioxide Electrolysis

Electrochemical conversion of CO₂ has been proposed both as a way to reduce CO₂ emissions and as a source of renewable fuels and chemicals, but conversion rates need improvement before the process will be practical. In this article, we show that the rate of CO₂ conversion per unit surface area is about 10 times higher on 5 nm silver nanoparticles than on bulk silver even though measurements on single crystal catalysts show much smaller variations in rate. The enhancement disappears on 1 nm particles. We attribute this effect to a volcano effect associated with changes of the binding energy of key intermediates as the particle size decreases. These results demonstrate that nanoparticle catalysts have unique properties for CO₂ conversion

In Situ Spectroscopic Examination of a Low Overpotential Pathway for Carbon Dioxide Conversion to Carbon Monoxide

Lowering the overpotential for the electrochemical conversion of CO₂ to useful products is one of the grand challenges in the Department Of Energy report, “Catalysis for Energy”. In a previous paper, we showed that CO₂ conversion occurs at low overpotential on a 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF₄)-coated silver catalyst in an aqueous solution of EMIM-BF4. One of the surprises in the previous paper was that the selectivity to CO was better than 96% on silver, compared with ∼80% in the absence of ionic liquid. In this article, we use sum frequency generation (SFG) to explore the mechanism of the enhancement of selectivity. The study used platinum rather than silver because previous workers had found that platinum is almost inactive for CO production from CO₂. The results show that EMIM-BF₄ has two effects: it suppresses hydrogen formation and enhances CO₂ conversion. SFG shows that there is a layer of EMIM on the platinum surface that inhibits hydrogen formation. CO₂, however, can react with the EMIM layer to form a complex such as CO₂-EMIM at potentials more negative than −0.1 V with respect to a standard hydrogen electrode (SHE). That complex is converted to adsorbed CO at cathodic potentials of −0.25 V with respect to SHE. These results demonstrate that adsorbed monolayers can substantially lower the barrier for CO₂ conversion on platinum and inhibit hydrogen formation, opening the possibility of a new series of metal/organic catalysts for this reaction