Electrocatalytic oxidation of cyanide on copper-doped cobalt oxide electrodes

Copper and copper oxides are well-known excellent catalysts in several chemical processes, but their low mechanical and electrochemical stability restrict their direct utilization as electrodes in electrolytic processes. In this work, the incorporation of copper into cobalt oxide (CuxCo3−xO4) is presented as an excellent approach to obtain highly active and robust copper-based electrocatalysts. Particularly, the electrocatalytic performance of Ti-supported CuxCo3−xO4 electrodes (with 0 ≤ x ≤ 1.5) has been studied for the oxidation of cyanide in alkaline media. Cyclic voltammetry and electrolysis runs show an outstanding effect of Cu on the activity, efficiency and kinetics of spinel CuxCo3−xO4 electrodes for CN− electro-oxidation. Despite being active oxides with high activity towards water oxidation, copper saturated (x = 1.0) and oversaturated (x = 1.5) spinels exhibit unprecedented 100% current efficiencies for the electro-oxidation of CN− in aqueous electrolyte. In situ surface enhanced Raman spectroscopy (SERS) reveals the specific adsorption of CN− ions on surface Cu species to be involved in the electrocatalytic oxidation mechanism. This electrocatalytic activity has been attributed to surface Cu(II) in the spinel lattice. Furthermore, the CuxCo3−xO4 electrodes also display high electrochemical stability. Therefore, they are considered excellent candidates for the sustainable electrochemical elimination of highly toxic cyanides.Financial support from the Spanish Ministerio de Economía y Competitividad and FEDER funds (MAT2016-76595-R, IJCI-2014-20012) and from the Generalitat Valenciana (PROMETEO2013/038) is gratefully acknowledged