MnCo Layered Double Hydroxide Based Pseudocapacitor: Effect of Morphology and Electrochemical Cycling

Abstract

Layered double hydroxides (LDHs) attract considerable attention for use in supercapacitors owing to their unique features such as good anion exchange abilities, high redox activities, easily tunable chemical compositions, high chemical stabilities, and large surface areas. Among the LDHs, MnCo-LDH, CoAl-LDH, and NiMn-LDH are very promising electrode materials for supercapacitors as a class of two-dimensional metal hydroxides. MnCo-LDH is the most desirable electrode material for energy storage applications in the LDH class, as cobalt can be introduced in the LDH to improve the conductivity of the electrode material; Co2+ can be oxidized to the conductive CoOOH during the electrochemical reactions. Similarly, the introduction of manganese helps improve the electrochemical activity owing to its multiple oxidation states. We report a stepwise morphological evolution of MnCo-layered double hydroxide (LDH) cubes with the hydrothermal reaction time. The electrochemical performance of the fabricated electrode at each step was studied in detail. The obtained MnCo-LDH exhibited maximum areal capacitances of 3.17 Fcm-2 (at a scan rate of 5 mVs-1) and 3.78 Fcm-2 (at an applied current of 3 mA), good rate capability (74% at a scan rate of 100 mVs-1), and excellent energy efficiency (80% at an applied current of 4.5 mA). The electrochemical performances of all synthesized electrodes were enhanced during the electrochemical cycling, which led to morphological modifications. In addition, for practical applications, we fabricated a symmetric supercapacitor based on the MnCo-LDH electrode and studied its electrochemical performance in detail. Keywords: MnCo, Layered double hydroxide, electrochemical cycling, pseudo-capacitor, hydrothermal.