Green Synthesis of Three-Dimensional MnO₂/Graphene Hydrogel Composites as a High-Performance Electrode Material for Supercapacitors

Abstract

Graphene hydrogels (GHs) and their composites have attracted wide attention because of the special structure of graphene assembly and exceptional electrochemical performance as electrodes for energy storage devices. Here, we report a GH with three-dimensional architecture prepared by a hydrothermal method via a self-assembled process in glucose and ammonia system as well as subsequent freeze-drying. The δ-MnO/GH composite was then obtained by immersing GH in KMnO solution with a certain concentration under heat treatment. The asymmetric supercapacitor MnO/GH//GH consisting of pseudocapacitive nanosheet-like δ-MnO/GH as the cathode and electric double-layer capacitive GH as the anode provides high energy density of 34.7 W h/kg at a power density of 1.0 kW/kg. Importantly, it is found that the pseudocapacitive behavior of MnO has great effects on the rate performance of the supercapacitor, which is identified by kinetic analysis.

Defect Promoted Capacity and Durability of N‐MnO2–x Branch Arrays via Low‐Temperature NH3 Treatment for Advanced Aqueous Zinc Ion Batteries

“…Raman test was used to further check the phase and composition of active MnO 2 (Figure b). For the MnO 2 @TiC/C sample, Raman bands located at 570 and 634 cm −1 are in good agreement with the stretching vibration of MnO 6 groups of δ‐MnO 2 , and the band at 495 cm −1 is due to the stretching vibration of MnO bond . After NH 3 treatment, these bands shift to lower wave numbers for the N‐MnO 2– x @TiC/C sample, owing to the N doping and introduction of oxygen vacancy.…”

“…For the MnO 2 @TiC/C sample, Raman bands located at 570 and 634 cm −1 are in good agree ment with the stretching vibration of MnO 6 groups of δMnO 2 , and the band at 495 cm −1 is due to the stretching vibration of MnO bond. [30] After NH 3 treatment, these bands shift to lower wave numbers for the NMnO 2-x @TiC/C sample, owing to the N doping and introduction of oxygen vacancy. The pres ence of N doping and oxygen vacancy was further verified by Xray photoelectron spectroscopy (XPS) and electron paramag netic resonance (EPR) analysis.…”

High‐Stability MnOxNanowires@C@MnOxNanosheet Core–Shell Heterostructure Pseudocapacitance Electrode Based on Reversible Phase Transition Mechanism

“…The capacity retention of the supercapacitor can still retain at 94% after 2000 cycles, indicating the excellent long‐term cycling performance. As shown in Table 1 , compared with the materials in previous works such as Na x MnO 2 @CNF//AC, GF/CNT/MnO 2 //GF/CNT/PPy, MnO 2 /PPy//NC, and so on, although our results are not the most prominent compared with the work in references 31 or 34, the preparation process of electrode materials is simple, cheap and environmentally friendly. Therefore, the integrated electrochemical behaviors are promising to bridge the energy‐power gap between traditional batteries and capacitors.…”

Electro-Oxidation and Simultaneous Determination of Indole-3-Acetic Acid and Salicylic Acid on Graphene Hydrogel Modified Electrode

“…In recent years, they have gained great attention because of their high specific surface area, good electron mobility, porous, and 3D-networked structure [27][28][29]. Graphene hydrogel (GH) is a 3D graphene material that can be prepared easily by hydrothermal reduction [30][31][32] and chemical reduction [33,34]. To date, GH has been used in supercapacitors [30,34,35] and electrochemical sensors [36][37][38][39].…”

“…Graphene hydrogel (GH) is a 3D graphene material that can be prepared easily by hydrothermal reduction [30][31][32] and chemical reduction [33,34]. To date, GH has been used in supercapacitors [30,34,35] and electrochemical sensors [36][37][38][39]. GH-based nanocomposites show excellent electrocatalytic activity to the oxidation of ascorbic acid (AA), dopamine (DA), and uric acid (UA), which has been used in their simultaneous detection in human serum samples [31,32].…”