Porous manganese dioxide film built from arborization-like nanoclusters and its superior electrochemical supercapacitance with attractive cyclic stability

A Novel High Entropy Hydroxide Electrode Material for Promoting Energy Density of Supercapacitors and Its Efficient Synthesis Strategy

In this work, a novel high entropy hydroxide NiCoMoMnZn-layered double hydroxide(LDH) is synthesized as an electrode material for supercapacitors using a novel template re-etching method to promote the energy density. As a positive electrode material for supercapacitors, NiCoMoMnZn-LDH has the advantage of a uniform distribution of elements, high specific surface area, porous and stable structure. More importantly, the specific capacitance can reach 1810.2 F g-1 at the current density of 0.5 A g-1, and the NiCoMoMnZn-LDH//AC HSC assembled from the material has an energy density of up to 62.1 Wh kg-1 at a power density of 475 W kg-1. Moreover, the influence of different compositions on their morphological, structural, and electrochemical properties is investigated based on the characterization results. Then, the synergistic mechanism among the components of the high entropy NiCoMoMnZn-LDH is revealed in detail by DFT calculations. In addition, the synthesis strategy proposed in this work for high-entropy hydroxides exhibits universality. Experimental results show that the proposed strategy successfully avoids not only phase separation and element aggregation in the formation of high entropy materials, but also reduces structural distortion, which is beneficial for efficient and large-scale synthesis of high entropy hydroxides.

Synthesis of Carbon-Supported MnO2 Nanocomposites for Supercapacitors Application

In this study, carbon-supported MnO2 nanocomposites have been prepared using the microwave-assisted heating method followed by two different approaches. The MnO2/C nanocomposite, labeled as sample S1, was prepared directly by the microwave-assisted synthesis of mixed KMnO4 and carbon powder components. Meanwhile, the other MnO2/C nanocomposite sample labeled as S2 was prepared indirectly via a two-step procedure that involves the microwave-assisted synthesis of mixed KMnO4 and MnSO4 components to generate MnO2 and subsequent secondary microwave heating of synthesized MnO2 species coupled with graphite powder. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectroscopy have been used for characterization of MnO2/C nanocomposites morphology, structure, and composition. The electrochemical performance of nanocomposites has been investigated using cyclic voltammetry and galvanostatic charge/discharge measurements in a 1 M Na2SO4 solution. The MnO2/C nanocomposite, prepared indirectly via a two-step procedure, displays substantially enhanced electrochemical characteristics. The high specific capacitance of 980.7 F g−1 has been achieved from cyclic voltammetry measurements, whereas specific capacitance of 949.3 F g−1 at 1 A g−1 has been obtained from galvanostatic charge/discharge test for sample S2. In addition, the specific capacitance retention was 93% after 100 cycles at 20 A g−1, indicating good electrochemical stability.