Selective Electrochemical Reduction of CO 2 to CO on Zn-based Foams Produced by Cu 2+ and Template-Assisted Electrodeposition

In this work we aim at developing 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 (DHBT) method that consists of the superposition of metal deposition and hydrogen evolution at the solid-liquid interface. We employed Cu ions in the Zn -rich electroplating bath as foaming agent. The concentration of Cu as foaming agent was systematically studied and an optimized Zn Cu foam alloy was developed, which, to the best of our knowledge, is the most selective Zn-based CO electrocatalyst towards CO in aqueous bicarbonate solution (FE = 90 % at -0.95 V vs RHE). This high efficiency is ascribed to the combination of high density of low-coordinated active sites and preferential Zn(101) over Zn(002) texturing. XPS investigations demonstrate that the actual catalyst material is shaped upon reduction of an oxide/hydroxide terminating surface under CO electrolysis conditions. Moreover, intentional stressing by oxidation at room conditions proved to be beneficial for further activation of the catalyst. Identical location (IL) SEM imaging before and after CO electrolysis and long term electrolysis experiments also showed that the developed Zn Cu foam catalyst is both structurally and chemically stable at reductive conditions.