Electronic Effects Determine the Selectivity of Planar Au–Cu Bimetallic Thin Films for Electrochemical CO₂ Reduction

Abstract

Au–Cu bimetallic thin films with controlled composition were fabricated by magnetron sputtering co-deposition, and their performance for the electrocatalytic reduction of CO2 was investigated. The uniform planar morphology served as a platform to evaluate the electronic effect isolated from morphological effects while minimizing geometric contributions. The catalytic selectivity and activity of Au–Cu alloys was found to be correlated with the variation of electronic structure that was varied with tunable composition. Notably, the d-band center gradually shifted away from the Fermi level with increasing Au atomic ratio, leading to a weakened binding energy of *CO, which is consistent with low CO coverage observed in CO stripping experiments. The decrease in the *CO binding strength results in the enhanced catalytic activity for CO formation with the increase in Au content. In addition, it was observed that copper oxide/hydroxide species are less stable on Au–Cu surfaces compared to those on the pure Cu surface, where the surface oxophilicity could be critical to tuning the binding strength of *OCHO. These results imply that the altered electronic structure could explain the decreased formation of HCOO– on the Au–Cu alloys. In general, the formation of CO and HCOO– as main CO2 reduction products on planar Au–Cu alloys followed the shift of the d-band center, which indicates that the electronic effect is the major governing factor for the electrocatalytic activity of CO2 reduction on Au–Cu bimetallic thin films.

Operando Insight into the Correlation between the Structure and Composition of CuZn Nanoparticles and Their Selectivity for the Electrochemical CO2 Reduction

“…59 Such shift results in a weakening of the binding strength of *CO due to the occupancy of antibonding states. 18,60 Therefore, product selectivity in the Zn-rich CuZn NPs seems to be controlled by the ligand effect rather than strain effects, leading to the loss of the functionality of the Cu site for further reduction of CO intermediates.…”

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

“…The switch in the catalytic behavior of this system was explained in refs ( 25 and 111 ) by the interplay of geometric and electronic effects. The expansion of the interatomic distances was found to result in a more favorable stabilization of the reaction intermediates, leading to the formation of products beyond *CO. 319 Furthermore, changes in the electronic structure due to Cu and Zn alloying resulted in a shift of the d -band center of Cu away from the Fermi level, 438 and a weakening of the *CO binding 111 , 439 , 440 during the gradual Cu and Zn reduction and alloying, leading to different catalytic selectivity and stability for Cu-rich and Cu-poor samples. In fact, it was suggested that the Cu-M interatomic distances might constitute a convenient descriptor of the catalyst properties in these bimetallic NPs, with NPs with shorter interatomic distances (similar to that in metallic Cu) favoring the production of CH 4 , while NPs with longer Cu—M distances favor the production of CO.…”

Potential Link between Cu Surface and Selective CO2 Electroreduction: Perspective on Future Electrocatalyst Designs

“…By combining these metals with Cu to form alloy or bimetallic structures, the CO 2 RR activity was increased. While previous works using these alloyed nanoparticles further improved the selectivity and activity of CO 2 RR toward CO at lower overpotential, [ 80,128 ] bimetallic structures have shown promising synergistic effects that lead toward the CC coupling reaction. Based on a previous report by Kuhl et al about the electrocatalytic conversion of CO 2 using several transition metal surfaces, including Au, Ag, Zn, Cu, Ni, Pt, and Fe, it was revealed that Cu may not be the only metal that has the ability to catalyze hydrocarbon and alcohol formation.…”