Over-Reduction-Controlled Mixed-Valent Manganese Oxide with Tunable Mn²⁺/Mn³⁺ Ratio for High-Performance Asymmetric Supercapacitor with Enhanced Cycling Stability

Abstract

Manganese oxides composed of various valence states Mn x+ (x = 2, 3, and 4) have attracted wide attention as promising electrode materials for asymmetric supercapacitor. However, the poor electrical conductivity limited their performance and application. Appropriate regulation content of Mn x+ in mixed-valent manganese oxide can tune the electronic structure and further improve their conductivity and performance. Herein, we prepared manganese oxides with different Mn2+/Mn3+ ratios through an over-reduction (OR) strategy for tuning the internal electron structure of mixed-valent manganese, which could make these material oxides a good platform for researching the structure–property relationships. The Mn2+/Mn3+ ratio of manganese oxide could be precisely tuned from 0.6 to 1.7 by controlling the amount of reducing agent for manipulating the redox processes, where the manganese oxide electrode with the most appropriate Mn2+/Mn3+ ratio, as 1.65 (OR4) exhibits large capacitance (274 F g–1) and the assembling asymmetric supercapacitors by combining OR4 (positive) and the commercial activated carbon (as negative) achieved large 2.0 V voltage window and high energy density of 27.7 Wh kg–1 (power density of 500 W kg–1). The cycle lifespan of the OR4//AC could keep about 92.9% after 10 000-cycle tests owing to the Jahn–Teller distortion of the Mn­(III)­O6 octahedron, which is more competitive compared to other work. Moreover, a red-light-emitting diode (LED) can easily be lit for 15 min by two all-solid supercapacitor devices in a series.

A Critical Review of Carbon Quantum Dots: From Synthesis toward Applications in Electrochemical Biosensors for the Determination of a Depression-Related Neurotransmitter

“…For example, the quantum confinement effect and the popular property of the semiconductor quantum dot were not always observed in CDs [ 49 , 50 ]. To date, intrinsic (band-gap related) and extrinsic (surface related) recombination routes were proposed to explain the luminescence mechanism of CDs [ 44 , 51 , 52 ].…”

Multiple logic gates system based on dual‐wavelength triggered enhancing upconversion luminescence of Gd2(MoO4)3:Yb3+/Er3+

“…A D/Max-2500PC X-ray diffractometer (XRD) with CuKα was used to investigate the phase purity of sample by over the 2θ range of 10-80°. 42 A field emission scanning electron microscopy (SEM, S-3400N Ⅱ) was used to observe microstructural morphology and size of the sample. The UC emission spectra were considered to be determined by using a Jobin Yvon Fluorolog-3 fluorescence spectrometer system (Figure 1A).…”

“…[7][8][9]40,41 The chemical and volume changes that accompany ceramization of the polymer during pyrolysis have been documented in several studies. For example, see Refs [39][40][41][42]. Pyrolysis of polycarbosilane polymer has been modeled by Key et al 43 Ideally, the available individual models for polymer infiltration and pyrolysis should be combined to construct a model for the PIP process.…”

Preparation and Characterization of Ag@TiO2/α-Fe2O3 Ternary Nanocomposite for enhanced visible light photocatalytic performance

“…Generally, the most adopted methods to decompose pollutions such as chemical, heating, or biological process are found to be very expensive and ineffective mostly for the degradation of antibiotic. In recent years, nanomaterials are found to be very useful for different applications [2][3][4]. On the other side, photocatalytic reactions have been widely suggested as green solution to decompose many categories of pollutants under mild conditions and under solar light source [5][6][7][8][9][10][11].…”