Tunnel-dependent supercapacitance of MnO2: effects of crystal structure

A proportional relationship between the specific capacitance of MnO2 and the percentage of effective Mn centers that act as active sites in the Faradaic charge storage has been established on the basis of a tunnel structure–crystallization behavior correlation. A quantitative relationship between the effective Mn centers at the surfaces and in the tunnels can distinguish the specific capacitance values that arise from the adsorption/desorption and insertion/extraction processes, respectively, of different MnO2 crystallographic forms in the Faradaic charge storage. The different specific capacitance values between the MnO2 crystallographic forms are mainly attributed to the different effective utilizations of Mn centers in the size-limited tunnels. The present model demonstrates that increasing the percentage of effective Mn centers via decreasing the crystal size can facilitate obtaining MnO2-based electrode materials with higher specific capacitance values.

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Nickel Cobaltite Functionalized Silver Doped Carbon Xerogels as Efficient Electrode Materials for High Performance Symmetric Supercapacitor

Materials ◽

10.3390/ma13214906 ◽

2020 ◽

Vol 13 (21) ◽

pp. 4906

Author(s):

Madlin A. Wasfey ◽

Abdalla Abdelwahab ◽

Francisco Carrasco-Marín ◽

Agustín F. Pérez-Cadenas ◽

H. H Abdullah ◽

...

Keyword(s):

Electron Microscopy ◽

Specific Capacitance ◽

Surface Area ◽

Active Sites ◽

Electrode Materials ◽

Hybrid Composites ◽

High Energy ◽

Equivalent Series Resistance ◽

Carbon Xerogels ◽

Nickel Cobaltite

Introducing new inexpensive materials for supercapacitors application with high energy density and stability, is the current research challenge. In this work, Silver doped carbon xerogels have been synthesized via a simple sol-gel method. The silver doped carbon xerogels are further surface functionalized with different loadings of nickel cobaltite (1 wt.%, 5 wt.%, and 10 wt.%) using a facile impregnation process. The morphology and textural properties of the obtained composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen physisorption analysis. The silver doped carbon xerogels display a higher surface area and larger mesopore volume compared to the un-doped carbon xerogels and hierarchically porous structure is obtained for all materials. The hybrid composites have been utilized as electrode materials for symmetric supercapacitors in 6 M KOH electrolyte. Among all the hybrid composites, silver doped carbon xerogel functionalized with 1 wt.% nickel cobaltite (NiCo1/Ag-CX) shows the best supercapacitor performance: high specific capacitance (368 F g−1 at 0.1 A g−1), low equivalent series resistance (1.9 Ω), high rate capability (99% capacitance retention after 2000 cycles at 1 A g−1), and high energy and power densities (50 Wh/Kg, 200 W/Kg at 0.1 A g−1). It is found that the specific capacitance does not only depend on surface area, but also on others factors such as particle size, uniform particle distribution, micro-mesoporous structure, which contribute to abundant active sites and fast charge, and ion transfer rates between the electrolyte and the active sites.

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A novel ligand with –NH2 and –COOH-decorated Co/Fe-based oxide for an efficient overall water splitting: dual modulation roles of active sites and local electronic structure

Catalysis Science & Technology ◽

10.1039/d0cy01109f ◽

2020 ◽

Vol 10 (18) ◽

pp. 6266-6273

Author(s):

Yalan Zhang ◽

Zebin Yu ◽

Ronghua Jiang ◽

Jung Huang ◽

Yanping Hou ◽

...

Keyword(s):

Electronic Structure ◽

Water Splitting ◽

Energy Demand ◽

Active Sites ◽

Electrode Materials ◽

Global Energy ◽

Overall Water Splitting ◽

Local Electronic Structure ◽

Electrochemical Water Splitting

Excellent electrochemical water splitting with remarkable durability can provide a solution to satisfy the increasing global energy demand in which the electrode materials play an important role.

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Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

10.26434/chemrxiv.8150660 ◽

2019 ◽

Author(s):

Yan Wang ◽

Sagar Udyavara ◽

Matthew Neurock ◽

C. Daniel Frisbie

Keyword(s):

Electric Field ◽

Hydrogen Evolution ◽

Active Sites ◽

Density Functional ◽

Electrode Materials ◽

Density Functional Theory Calculations ◽

Electronic Charge ◽

Back Side ◽

Gate Electrode ◽

Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

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Poly(aniline-co-pyrrole)-coated Ni-doped manganese dioxide as electrode materials for supercapacitors

Functional Materials Letters ◽

10.1142/s1793604720510078 ◽

2020 ◽

Vol 13 (02) ◽

pp. 2051007

Author(s):

Jie Dong ◽

Qinghao Yang ◽

Qiuli Zhao ◽

Zhenzhong Hou ◽

Yue Zhou ◽

...

Keyword(s):

Electrochemical Performance ◽

Manganese Dioxide ◽

Specific Capacitance ◽

Electrode Materials ◽

High Specific Capacitance ◽

Cycle Stability ◽

Mass Ratio ◽

Scan Rate ◽

Poly Aniline ◽

Inorganic And Organic

Electrode materials with a high specific capacitance, outstanding reversibility and excellent cycle stability are constantly pursued for supercapacitors. In this paper, we present an approach to improve the electrochemical performance by combining the advantages of both inorganic and organic. Ni-MnO2/PANi-co-PPy composites are synthesized, with the copolymer of aniline/pyrrole being coated on the surface of Ni-doped manganese dioxide nanospheres. The inorganic–organic composite enables a substantial increase in its specific capacitance and cycle stability. When the mass ratio of Ni-MnO2 to aniline and pyrrole mixed monomer is 1:5, the composite delivers high specific capacitance of 445.49[Formula: see text]F/g at a scan rate of 2[Formula: see text]mV/s and excellent cycle stability of 61.65% retention after 5000 cycles. The results indicate that the Ni-MnO2/PANi-co-PPy composites are promising electrode materials for future supercapacitors application.

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Effect of redox additive in aqueous electrolyte on the high specific capacitance of cation incorporated MnCo2O4@Ni(OH)2 electrode materials for flexible symmetric supercapacitor

Composites Part B Engineering ◽

10.1016/j.compositesb.2021.108755 ◽

2021 ◽

pp. 108755

Author(s):

Prakas Samanta ◽

Souvik Ghosh ◽

Naresh Chandra Murmu ◽

Tapas Kuila

Keyword(s):

Specific Capacitance ◽

Electrode Materials ◽

Aqueous Electrolyte ◽

High Specific Capacitance ◽

Symmetric Supercapacitor

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A Hierarchical Architecture of Functionalized Polyaniline/Manganese Dioxide Composite with Stable-Enhanced Electrochemical Performance

Journal of Composites Science ◽

10.3390/jcs5050129 ◽

2021 ◽

Vol 5 (5) ◽

pp. 129

Author(s):

Yapeng Wang ◽

Yanxiang Wang ◽

Chengjuan Wang ◽

Yongbo Wang

Keyword(s):

Electrochemical Performance ◽

Manganese Dioxide ◽

Specific Capacitance ◽

Current Density ◽

Electrode Materials ◽

High Efficiency ◽

Scanning Speed ◽

Hierarchical Architecture ◽

Electrochemical Window ◽

A Current

As one of the most outstanding high-efficiency and environmentally friendly energy storage devices, the supercapacitor has received extensive attention across the world. As a member of transition metal oxides widely used in electrode materials, manganese dioxide (MnO2) has a huge development potential due to its excellent theoretical capacitance value and large electrochemical window. In this paper, MnO2 was prepared at different temperatures by a liquid phase precipitation method, and polyaniline/manganese dioxide (PANI/MnO2) composite materials were further prepared in a MnO2 suspension. MnO2 and PANI/MnO2 synthesized at a temperature of 40 °C exhibit the best electrochemical performance. The specific capacitance of the sample MnO2-40 is 254.9 F/g at a scanning speed of 5 mV/s and the specific capacitance is 241.6 F/g at a current density of 1 A/g. The specific capacitance value of the sample PANI/MnO2-40 is 323.7 F/g at a scanning speed of 5 mV/s, and the specific capacitance is 291.7 F/g at a current density of 1 A/g, and both of them are higher than the specific capacitance value of MnO2. This is because the δ-MnO2 synthesized at 40 °C has a layered structure, which has a large specific surface area and can accommodate enough electrolyte ions to participate the electrochemical reaction, thus providing sufficient specific capacitance.

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