Interfacial assistant role of amine additives on zinc electrodeposition from deep eutectic solvents: an in situ X-ray imaging investigation

The morphological and interfacial evolution processes of electrodeposited zinc were studied from deep eutectic solvents based on choline chloride (ChCl) and ethylene glycol (EG) by using the synchrotron radiation X-ray imaging. The effect of three amine additives including thiourea, aqueous ammonia and ethylenediamine on zinc deposits was compared, respectively. Raman spectra show that the presence of ammonia or ethylenediamine results in the formation of chlorozinc complexes with low chloride coordination number besides of the ZnCl42− species. The voltammetric and chronopotentiogram behaviors were assessed to understand the effect of amine additives on the deposition mechanism of zinc. The results indicate that the initial nucleation of zinc can be inhibited by the adsorption of thiourea on the electrode surface, whereas the addition of aqueous ammonia and ethylenediamine could improve the mass transport of active Zn species towards the cathode surface. The in situ X-ray imaging reveals the evolution process of mossy zinc deposits from the deep eutectic electrolytes without additive. The addition of thiourea and ethylenediamine can effectively modify the interfacial morphology of deposited Zn, and the compact layer-like films appear along the lateral direction of electrode. However, in the presence of ammonia, the scattered dendritic deposits are observed accompanying with zinc electrodeposition process.