Silver-Doped Porous Copper Catalysts for Efficient Resource Utilization of CO-Containing Flue Gases

Abstract

CO is both a key intermediate in the electrocatalytic conversion of CO₂ and a valuable C₁ resource, with the potential to reduce carbon emissions and mitigate the energy crisis. However, industrially emitted CO remains underutilized due to inefficiencies and economic challenges. Electrocatalytic CO reduction offers a promising approach for the efficient and environmentally friendly utilization of CO-containing flue gases. Nevertheless, current technologies face limitations, such as low operating currents and difficulties in adaptation to complex reaction gas components. Here, we report a low-cost silver-doped porous copper oxide (Ag-pCuO) catalyst. The doping of a moderate amount of Ag (0.875% doping) endows porous CuO with highly selective Cu-Ag active sites, enhanced CO adsorption, and improved surface valence stability, allowing Ag_0.875%-pCuO to achieve remarkable catalytic performance in a carbon-doped titanium-based membrane electrode assembly electrolytic cell. It achieves a remarkable C₂₊ faradic efficiency of up to 94% at a high current density of -4 A under a simulated calcium carbide furnace gas atmosphere and demonstrates exceptional stability, with only a 6.08% decline in C₂₊ faradic efficiency after over 110 h of continuous operation. In summary, this research presents a novel approach for applying Ag-doped copper-based catalysts to industrially utilize CO-containing flue gases, especially from calcium carbide furnaces.

Keywords: CO reduction; electrocatalytic; electrolyzer; flue gas; resource utilization.

1

Preparation methods and characterization of Ag _x%-pCuO, pCuO, and Cu­(OH)₂ needles. (a) Schematic illustration of the preparation of Ag _x%-pCuO, (b) TEM images of Cu­(OH)₂ needles, (c) SEM images of Ag_0.875%-pCuO, (d, g) TEM images of Ag_0.875%-pCuO, (e) TEM images of pCuO, (f) high-resolution TEM (HR-TEM) images of Ag_0.875%-pCuO, and (h–k) element mapping analyses of Ag_0.875%-pCuO.

2

Structural characterizations of the Ag-pCuO series and pCuO. (a) XRD patterns of Ag-pCuO series and pCuO, (b) Cu 2p spectra of Ag_0.875%-pCuO, (c) Ag 3d spectra of Ag-pCuO series and pCuO, and (d) specific surface area measurement of Ag-pCuO series and pCuO.

3

Lab-scale measurement of Ag-pCuO series’ electrocatalytic CORR performances. Faradic efficiency of the reduction products for (a) Ag_0.875%-pCuO and (b) pCuO at different applied currents.

4

Pilot test of Ag-pCuO series’ electrocatalytic CORR performances. FE distribution of the CORR products for the (a) Ag_0.875%-pCuO and (b) pCuO catalyst at different currents in an MEA cell, (c) comparison of the electrocatalytic performances of Ag-pCuO series and pCuO at −4 A, and (d) FE distribution of the CORR products for the Ag_0.875%-pCuO at different currents in a reaction system with two cells in parallel. The gas source of all of the tests is simulated CCFS and (e) chronopotentiometry stability test of Ag_0.875%-pCuO at −4 A (−111.11 mA cm^–2) in MEA.

5

Auger patterns (a) of Ag_0.875%-pCuO materials after the 110 h CORR reaction and Auger patterns (b) of Ag-pCuO materials after the 4.5 h CORR reaction.

6

(a) In situ Raman spectroscopy studies of Ag_0.875%-pCuO in a flow cell with the electrodes in contact with 1 M KOH; (b) schematic illustration of the possible reaction pathway of CO reduction over Ag_0.875%-pCuO.