Electrodeposition of Amorphous Mn3O4 and Ni-Mn3O4 on Activated Carbon for Enhanced Capacitive Deionization

Abstract

Capacitive deionization (CDI) is an emerging technology for desalination, water remediation, water treatment and water softening. Despite its long history, CDI still has challenges in identifying a good material to be utilized in the process. Several studies have shown the potential of metal oxide coatings as a way to increase and modify the adsorption performance of activated carbon. Mn and Ni oxides are promising materials not just in supercapacitors but also in capacitive deionization. These metal oxides has high theoretical capacitance, which could translate to a high adsorption capacity. Moreover, the precursors of both metals are inexpensive, which could pave the way for material commercialization. This study is focused on fabricating Mn3O4 coated activated carbon in order to improve the performance of activated carbons in CDI. Furthermore, the Mn3O4 coating is modified by incorporating Ni on it. The synthesis is performed through anodic electrodeposition. The surface of the samples were characterized by SEM, XRD, BET and contact angle. Its electrochemical performance was also determined through cyclic voltammetry and electrochemical impedance spectroscopy. The chemical oxidation state and composition of the samples were identified using X-ray photoelectron spectroscopy and Raman spectroscopy. Activated carbon symmetric cells and metal oxide-coated activated carbon asymmetric cells were constructed and tested for CDI. Both Mn3O4 and Ni-Mn3O4 yielded better performance than pristine activated carbon CDI cells. Furthermore, adding Ni to Mn3O4 showed that Ni has the capability to alter the morphology of Mn3O4. For both metal oxides, the improved performance is due to the tuned morphology and pore distribution, increased wettability, and pseudocapacitive adsorption mechanism. This illustrates that metal oxides and pseudocapacitive materials are excellent electrodes for CDI.