Cu/Zn bimetallic catalysts prepared by facial potential steps electrodeposition favoring Zn deposition and grain boundary formation for efficient CO2ER to ethylene

Abstract

Electro-reduction of CO2 (CO2ER) is a promising way to reduce atmospheric CO2 meanwhile gaining high-value-added products (e.g. ethylene). Introducing zinc, a kind of cheap, non-hazardous metal into copper, can perform tandem catalytic functions to overcome the disadvantage of pure Cu. However, due to the quite different theoretical reduction potentials of Cu2+ and Zn2+, Cu/Zn bimetallic catalysts are difficult to be synthesized using the electrochemical method. Here, a facial Potential Steps electrodeposition (PSE) method was proposed to prepare Cu/Zn bimetal catalyst supported on a gas diffusion layer (CuZn/GDE), during which, a lower voltage only suitable for Cu’s deposition was firstly applied, and then a higher voltage was imposed. Worthy mentioned, during the first step, Zn2+ could also transfer to the cathode from the bulk solution and then be embedded by the deposited Cu, forming a capsule-analogous micro-reaction environment composed of highly electron-conductive Cu and enriched Zn2+, thus decreasing the over-potential of Zn’s deposition, further promoting the reduction of Zn & the formation of Cu/Zn grain boundary and the stabilization of Cu(I) in the second step. The optimized CuZn/GDE could achieve a high faradaic efficiency to ethylene (40.2 %) at −1.36 V vs RHE in H-cell. The DFT calculations showed that the *CO formation energy at Cu/Zn and Cu(0)/Cu(I) was lower than at pure Cu and that the formation of *COCOH at Cu(0)/Cu(I) was more thermodynamically favorable than at pure Cu. This work supplies a facial and effective strategy to synthesize copper-based bimetallic catalysts for CO2ER, which could decrease the over-potential of the metal with high deposition potential, and meanwhile form grain boundary, in favor of generation of C2 products.