Influence of Alloying on CO2 Electroreduction on Ag-Zn System

Abstract

Electrochemical reduction of CO2 is an attractive pathway for the sustainable production of fuels and chemicals, as it allows for the effective use of renewable energy sources while mitigating the effects of CO2 in the atmosphere. While significant decrease in overpotentials and increase in reaction rates have been reported for the two-electron reduction products, reports on improved activity and selectivity for the products that require more than two electrons (> 2 e- products) have been limited on monometallic transition metal catalysts. Recent theoretical work indicates that this difficulty of reducing CO2 to > 2 e- products is due to the linear scaling of the binding energies of CO2 reduction intermediates on transition metal catalysts, and the necessity of catalyst systems that can break such scaling has been emphasized.(1) Alloys, which can provide bifunctional sites that selectively stabilize intermediates, are a promising class of materials, and a large amount of effort has been focused on the investigation of their effectiveness as CO2 reduction catalysts. Recent works have reported on improved CO2 reduction activity and selectivity on alloy systems, which were attributed to the synergy between the two metal atoms at the surface. However, most improvements reported in these works are pertaining to two-electron products, and alloy systems that demonstrate improvements for > 2 e- products remain elusive. Here, we report on the investigation of polycrystalline AgZn foil, which resulted in the observation of enhanced activities and selectivities for methane and methanol productions compared to Ag and Zn foils. Although CO is the main CO2 reduction product as expected of an alloy between two metals active for CO production, the selective enhancement observed for the > 2 e- products is noteworthy, as it indicates that alloys are promising candidates in the development of effective CO2 electroreduction catalysts. The production of CO as major product is explained by the binding energies of intermediates, and the importance of optimal binding energies are discussed. Reference 1. A. A. Peterson and J. K. Nørskov, The Journal of Physical Chemistry Letters, 3, 251 (2012).