One-step electrodeposition of CoMn-LDH with core-shell configuration for enhancing charge storage capabilities of on-chip microsupercapacitor

Abstract

Enhancing capacitance of electrode materials in microsupercapacitors is crucial for their application in microdevices. However, the small size of electrodes poses a significant challenge in regulating interfacial structure of electrode material. In this study, we propose a novel approach that leverages the difference in solubility products (K_sp) of cations to construct gradient composition for regulating electrical structure of MnCo-Layered double hydroxides (CoMn-LDH). It was evidenced that the K_sp of the metal hydroxides decreased with deposition temperature, resulting in the composition evolution of CoMn-LDH from uniformly distributed Co, Mn nanoflakes to core-shell-like distribution with a Co-rich core and Mn-rich shell as the temperature decreased from 25 °C to 0 °C. The locally concentrated composition of CoMn-LDH regulates the electronic state density of Co, Mn, and O, forming a electron-deficient region around the low-valence Co. This facilitates the adsorption of charges on active sites and enhances the conductivity of CoMn-LDH. Additionally, the low deposition temperature also reduces the nucleation and growth rate of nanoflakes. As the deposition temperature decrease, the size and thickness of CoMn-LDH decrease gradually, which shortens the charge diffusion route during charge-discharge process. In this respect, the CoMn-LDH deposited at 5°C exhibits superior specific capacitance, with an area capacitance of 192.7 mF cm⁻² at the current density of 1 mA cm⁻², as well as good rate performance. Moreover, due to the promoted charge storage kinetics, the diffusion-contributed capacitance retained 77.7 % at scan rate of 20 mV s^-1 compared to that obtained at the scan rate of 5 mV s^-1. Herein, this work presents an efficient route for regulating charge adsroption capabilities of metal hydroxides.