Among metals used for CO2 electroreduction in water, Cu appears to be unique in its ability to produce C2+ products like ethylene and ethanol. Bimetallic combinations of Cu with other metals have been investigated with the goal of steering selectivity via creating a tandem pathway through the CO intermediate or by changing the surface electronic structure. Here, we report a facile cation exchange method to synthesize bimetallic Cu-Ag electrocatalysts for CO2 reduction using Cu2-xS as a growth template. Beginning with Cu2-xS hexagonal nanosheets (100 nm lateral dimension, 10 nm thick), the Ag cation concentration was varied, with a gradual change in crystal structure from Cu7S4 to Ag2S, as the Ag/Cu ratio varies from 0.1 to 10. After cation exchange, the nanosheet morphology remains but with increased shape distortion as the Ag fraction is increased. Interestingly, the control Cu2-xS nanosheets and cation exchanged nanosheets have very high faradaic efficiency (FE) for formate at low overpotential (-0.2 V vs. RHE) although the current density is small. The primary effects of Ag incorporation are increased C2/C1 ratio with higher current densities and suppression of hydrogen evolution at intermediate values and dominant production of CO and methane at higher values. Cation exchange can also be used to modify the surface of Cu foil. A two-step electro-oxidation/sulfurization process was used to produce Cu2-xS. With lower Ag+ concentrations, cation exchange produces uniformly dispersed Ag; however, at higher concentrations, we observe nucleation of Ag on the surface. The depletion of sulfur during the CO2 reduction also induces the morphology change towards nest structure for Cu/Ag sulfides on Cu foil and filament structure for CuAgS nanosheets that increased the roughness of the catalyst, which is beneficial for multi-carbon products.

Copper sulfide as the cation exchange template for bimetallic catalysts for CO2 electroreduction

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.