Abstract
A series of MOx (M = Co, Ni, Zn, Ce)-modified lamellar MnO2 electrode materials were controllably synthesized with a superfast self-propagating technology and their electrochemical practicability was evaluated using a three-electrode system. The results demonstrated that the specific capacitance varied with the heteroatom type as well as the doping level. The low ZnO doping level was more beneficial for improving electrical conductivity and structural stability, and Mn10Zn hybrid nanocrystals exhibited a high specific capacitance of 175.3 F·g−1 and capacitance retention of 96.9% after 2000 cycles at constant current of 0.2 A·g−1. Moreover, XRD, SEM, and XPS characterizations confirmed that a small part of the heteroatoms entered the framework to cause lattice distortion of MnO2, while the rest dispersed uniformly on the surface of the carrier to form an interfacial collaborative effect. All of them induced enhanced electrical conductivity and electrochemical properties. Thus, the current work provides an ultrafast route for development of high-performance pseudocapacitive energy storage nanomaterials.
Highlights
The energy storage of pseudocapacitors is based on both ion adsorption and fast surface redox reactions, which can beneficially endow high specific capacitance and energy density compared to electrochemical double-layer capacitors [1,2]
The phase composition and morphology of the synthesized layered MOx -δ-MnO2 (M = Co, Ni, Zn, Ce) materials were studied by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) (Figure 2)
It can be observed that the MOx -δ-MnO2 (M = Co, Ni, Zn) samples with the same doping levels featured the typical characteristic diffraction peaks at the 2θ values of 12.3 and 24.9◦ (Figure 2a), which can be attributed to the crystal planes of (001) and (002) of the parent lamellar MnO2 (JCPDS no. 43-1456) [17]
Summary
The energy storage of pseudocapacitors is based on both ion adsorption and fast surface redox reactions, which can beneficially endow high specific capacitance and energy density compared to electrochemical double-layer capacitors [1,2]. Poor inherent electronic conductivity (10−5 –10−6 S/cm) usually imparts the bulk of MnO2 materials with low practical capacitances (less than 100 F·g−1 ), well below the theoretical value [8]. This severely hampers the practical delivery of MnO2 as high-performance pseudocapacitive electrode nanomaterials. To dispose of this problem, MnO2 -based composites combined with conductive materials, such as carbon materials, polymers, metals, and some transition metal oxides, have attracted much attention [9,10]. The promotion of MnO2 conductivity through external conductive improvements is very limited, due to the weak interactions of the
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