Electrochemical preparation of porous ZnCuNi by electrodeposition in Ethaline deep eutectic solvent followed by anodic or cathodic dealloying in alkaline aqueous solutions for higher nitrate reduction activity

Abstract Electrodeposition of zinc-rich ternary ZnCuNi alloys were potentiostatically studied from an Ethaline deep eutectic solvent (DES) (having a molar ratio of 1:2 choline chloride-ethylene glycol) containing ZnCl2, CuCl2 and NiCl2. Voltammetry was conducted to understand the cathodic deposition and anodic stripping occurred in this system as a function of potential before the deposition of the ternary alloys. Selective anodic dissolution of Zn from the as-deposited alloys in a NaOH aqueous solution produced porous structures; however, Cu was also dissolved from the alloys if the alloys are overoxidized. Alternatively, porous structures were also produced via cathodic dealloying of the Zn when the as-deposited alloy was subjected to the electroreduction of NaNO3. When used as electrode, both kinds of porous structure showed enhanced activities towards nitrate reduction. Because the cathodic dealloying did not consume Cu, the electrodes produced by cathodic dealloying exhibited activity and stability superior to the electrodes produced by anodic dealloying. More importantly, because the dealloying process and electrode activation could be simultaneously achieved in one step during the cathodic electrolysis of nitrate, the term “self-enhancing electrode formed by in-situ cathodic dealloying” was used in this study. The XPS analysis indicated that Ni-rich surfaces of ZnCuNi electrodes were produced with the anodic dealloying in contrast to the Cu-rich surfaces produced with the cathodic dealloying. This study demonstrates a facile approach to control the electrode surface compositions in dealloying zinc alloys. Although the application of the porous electrodes prepared in this study was tested for electroreduction of nitrate, this approach can be extended to the electrocatalysis of other systems.