Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO Via Bimetallic Silver-Copper Electronic Engineering

Abstract

Electrocatalytic CO2 reduction reaction (E-CO2RR) provides a sustainable way to convert greenhouse gases into value-added chemicals and small-molecule fuels[1, 2]. However, the efficient production of a single product remains a challenge. To this end, we have constructed the Ag-Cu bimetallic system as an experimental platform to investigate the process of electronic effects on the selectivity and activity of CO products in more detail. Specifically, metallic Ag is used as the matrix and different levels of Cu (Ag, Ag99Cu1, Ag96Cu4, Ag70Cu30, Ag30Cu70, Cu) are added as modifiers of the 3d orbital electron density of the system to adjust the adsorption strength of *H (key intermediates for H2 formation), *COOH and *CO (the key intermediate of CO formation) intermediates. Combining the electrochemical test results with the DFT calculations, we obtain the following trends: The addition of trace amounts of Cu (Ag99Cu1, Ag96Cu4) can greatly enhance the catalytic potential of Ag for the selective production of CO products at low potentials, achieving near 100% selectivity for CO products (Ag96Cu4, -1V vs. RHE).The observed rate determining step of the reaction on Ag30Cu70 from CO2–*COOH to *COOH–*CO implies that adding too much Cu or leading to strong adsorption of *CO results in poisoning.It was observed that Ag96Cu4 had the optimum CO selectivity and Ag70Cu30 had the optimum CO activity current, which is different from previous concentrations on the same catalyst. (Figure 1a, b) We attribute the above findings to Ag96Cu4 effectively reducing the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction (HER), thus achieving the best CO selectivity (Figure 1c, d). While the Ag70Cu30 together activates the CO2RR and HER processes and shows relatively low formation energies of *COOH and *H, the compromised thermodynamic barrier and product selectivity allows for the best CO partial current density to be exhibited (Figure 1c, d). We believe that the electron effect will serve as an effective platform for screening selective and active catalysts. Figure1. a) FECO and b) jCO as a function of the proportion of Cu in AgxCu100-x series catalysts. c, d) The calculated free energy diagrams of CO2RR to CO and HER on fcc Ag (111), Ag96Cu4 (111), Ag70Cu30 (111), Ag30Cu70 (111) and Cu (111) surfaces at 0 V vs. RHE, respectively. Reference Grätzel, M., Nature 2001, 414 (6861), 338-344. DOI 10.1038/35104607.Zheng, Y.; Vasileff, A.; Zhou, X.; Jiao, Y.; Jaroniec, M.; Qiao, S.-Z., Journal of the American Chemical Society 2019, 141 (19), 7646-7659. DOI 10.1021/jacs.9b02124. Figure 1