Enhanced Electrochemical Methanation of Carbon Dioxide with a Dispersible Nanoscale Copper Catalyst

Abstract

Although the vast majority of hydrocarbon fuels and products are presently derived from petroleum, there is much interest in the development of routes for synthesizing these same products by hydrogenating CO 2 . The simplest hydrocarbon target is methane, which can utilize existing infrastructure for natural gas storage, distribution, and consumption. Electrochemical methods for methanizing CO 2 currently suffer from a combination of low activities and poor selectivities. We demonstrate that copper nanoparticles supported on glassy carbon (n-Cu/C) achieve up to 4 times greater methanation current densities compared to high-purity copper foil electrodes. The n-Cu/ C electrocatalyst also exhibits an average Faradaic efficiency for methanation of 80% during extended electrolysis, the highest Faradaic efficiency for room-temperature methanation reported to date. We find that the level of copper catalyst loading on the glassy carbon support has an enormous impact on the morphology of the copper under catalytic conditions and the resulting Faradaic efficiency for methane. The improved activity and Faradaic efficiency for methanation involves a mechanism that is distinct from what is generally thought to occur on copper foils. Electrochemical data indicate that the early steps of methanation on n-Cu/C involve a pre-equilibrium one-electron transfer to CO 2 to form an adsorbed radical, followed by a rate-limiting nonelectrochemical step in which the adsorbed CO 2 radical reacts with a second CO 2 molecule from solution. These nanoscale copper electrocatalysts represent a first step toward the preparation of practical methanation catalysts that can be incorporated into membrane-electrode assemblies in electrolyzers.

Face the Edges: Catalytic Active Sites of Nanomaterials

“…One advantage of NPs to serve as catalysts is that the amount of atoms on surface is enlarged, meanwhile the edge fraction is also increased. The 7.0 nm Cu NPs reach up to 4 times methanation current densities comparing with high purity copper foil electrodes 85. However, they are not stable under electric treatment.…”

CO2 Reduction: From the Electrochemical to Photochemical Approach

“…This experimental observation was rationalized by DFT calculations, which showed that smaller Cu NPs could provide more undercoordinated atoms as strong binding sites to key intermediates such as H and COOH, thus accelerating HER and the reduction of CO 2 to CO while decreasing further recombination reaction to hydrocarbons. However, conflicting results were also disclosed by Alivisatos and co‐workers showing that Cu NPs (≈7 nm, grew to ≈25 nm during electrochemical experiments) exhibited an enhanced methanation current density four times greater than that of Cu foil, and an average Faradaic efficiency of 80% during extended electrolysis 55. The marked difference in reaction selectivity might be caused by the different synthetic approaches and measurement conditions employed.…”

RETRACTED ARTICLE: An overview of CO2 electroreduction into hydrocarbons and liquid fuels on nanostructured copper catalysts

“…Nanostructured copper has been reported as an exclusive novel material for the electrochemical reduction of CO 2 into hydrocarbons with high Faraday efficiency and selectivity (33,34,42,(49)(50)(51)(52)(53). The onset potential for the reduction of CO 2 at porous copper foam was −1.0 V vs. Ag/AgCl with the formation of formic acid (HCOOH) initially ( Figure 1).…”

“…highly connected networks of fused NPs (Figure 2(d)), which resemble a polycrystalline foil, were produced by the polarization of thicker films (Figure 2(c)) and these electrodes exhibited low Faraday efficiencies for methanation (Figure 2(e)) (49). This suggests that more isolated NPs expose catalytic sites that are more effective for methanation, which were lost as they fused to form dense aggregates.…”