Highly active, selective and stable electroreduction of carbon dioxide to carbon monoxide on a silver catalyst with truncated hexagonal bipyramidal shape

To improve the activity, selectivity and stability of silver electrodes towards CO 2 electroreduction to CO, three-dimensional frameworks comprised of the metallic silver electrocatalyst particles were constructed on bulk silver surfaces using a successive double-potential pulses method. With the help of X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, it was found that the as-synthesized silver particles exhibited a truncated hexagonal bipyramidal morphology, which was assembled from silver seeds with two {111} bases as well as laterally exposed {100} and {111} facets. Potential-dependent results revealed that the modified electrode exhibited an earlier onset potential, higher Faradaic efficiency and greater current density for CO evolution when compared to its smooth-surface counterpart. Moreover, as opposed to the bulk silver electrode losing its activity as a function of time, the activity of the improved electrode was durably stable over three successive 4   h periods. It is proposed that, in addition to the relatively vast electrochemical surface area, the exposed edges of the silver particles play a major role in enhancing the intrinsic activity and selectivity of the silver electrocatalyst by stabilizing the surface-adsorbed COOH species. Meanwhile, the existence of a large proportion of low-index {111} planes facilitates the desorption of the reduction intermediates of adsorbed CO species, suppressing the deactivation of the silver electrode towards CO 2 reduction.