Selective Electrochemical Reduction of CO2 to CO on Zn-Based Foams Produced by Cu2+ and Template-Assisted Electrodeposition

In this work, we aim to develop a Zn-based metal foam catalyst with very large specific area suitable for efficient CO production. Its manufacture is based on the dynamic hydrogen bubble template method that consists of the superposition of metal deposition and hydrogen evolution at the solid liquid interface. We employed Cu ions in the Zn2+-rich electroplating bath as foaming agent. The concentration of Cu as foaming agent was systematically studied and an optimized Zn94Cu6 foam alloy was developed, which, to the best of our knowledge, is the most selective Zn-based CO2 electrocatalyst toward CO in aqueous bicarbonate solution (FECO = 90% at -0.95 V vs reversible hydrogen electrode). This high efficiency is ascribed to the combination of high density of low-coordinated active sites and preferential Zn(101) over Zn(002) texturing. X-ray photoelectron spectroscopy investigations demonstrate that the actual catalyst material is shaped upon reduction of an oxide/hydroxide-terminating surface under CO2 electrolysis conditions. Moreover, intentional stressing by oxidation at room conditions proved to be beneficial for further activation of the catalyst. Identical location scanning electron microscopy imaging before and after CO2 electrolysis and long-term electrolysis experiments also showed that the developed Zn94Cu6 foam catalyst is both structurally and chemically stable at reductive conditions.