Inductive effect in Mn-doped ZnO nanoribon arrays grown on Ni foam: A promising key for boosted capacitive and high specific energy supercapacitors

Transition metal oxides have been explored in supercapacitor applications owing to their safety, low cost, high specific capacitance and high electrochemical activity. Among all transition metal oxides, zinc oxide based materials show remarkable response for designing the supercapacitors with high electrochemical activity. Here in, Mn doped ZnO (Zn_1-xMn_xO₃ with x = 0, 0.25, 0.50, 0.75 and 1) was synthesized by a facile hydrothermal method. Doping of Mn into the ZnO increased the surface area and decease the charge transfer resistance for the Zn_0.5Mn_0.5O₃. All the synthesized materials were characterized by x-ray diffraction (XRD), scanning electron microscopy SEM), BET, electrochemical tests and other various analytical techniques to confirm the structural, morphological, textural and suprcapacitive properties. The synthesized material Zn_0.5Mn_0.5O₃ having the porous nanoribons structure with BET surface area (2490 cm²/g). The electrochemical studies showed significantly enhanced response toward pseudocapacitive nature. The synthesized material exhibited the excellent specific capacitance (515F/g), specific energy (28.61 Wh/kg) and specific power (1000 W/kg) at current density of 2 mA/g. Such impressive and superior properties make the MnZnO₃ material as promising candidate for new generation supercapacitor applications.     

Experimental investigation of Co and Fe-Doped CuO nanostructured electrode material for remarkable electrochemical performance

The current research work presents a facile and cost–effective co-precipitation method to prepare doped (Co & Fe) CuO and undoped CuO nanostructures without usage of any type of surfactant or capping agents. The structural analysis reveals monoclinic crystal structure of synthesized pure CuO and doped-CuO nanostructures. The effect of different morphologies on the performance of supercapacitors has been found in CV (cyclic voltammetry) and GCD (galvanic charge discharge) investigations. The specific capacitances have been obtained 156 (±5) Fg^?1, 168(±5) Fg^?1 and 186 (±5) Fg^?1 for CuO, Co-doped CuO and Fe-doped CuO electrodes, respectively at scan rate of 5 mVs^?1, while it is found to be 114 (±5) Fg^?1, 136 (±5) Fg^?1 and 170 (±5) Fg^?1 for CuO, Co–CuO and Fe–CuO, respectively at 0.5 Ag^-1 as calculated from the GCD. The super capacitive performance of the Fe–CuO nanorods is mainly attributed to the synergism that evolves between CuO and Fe metal ion. The Fe-doped CuO with its nanorods like morphology provides superior specific capacitance value and excellent cyclic stability among all studied nanostructured electrodes. Consequently, it motivates to the use of Fe-doped CuO nanostructures as electrode material in the next generation energy storage devices.     

Microcystis aeruginosa supported-Mn catalyst as a new promising supercapacitor electrode: A dual functional material

In the present study, a Mn-supported catalyst material developed from Microcystis aeruginosa microalgae for hydrogen generation was tested as a supercapacitor electrode material for the first time. The catalyst material (MA-HCl-Mn) was examined for hydrogen generation through methanolysis of NaBH₄, and it demonstrated good catalytic activity. Symmetric and asymmetric supercapacitor cells were prepared using MA-HCl-Mn as the electrode material. The electrochemical performance of the cells were evaluated by a two-electrode system using 2 M KOH as the electrolyte. The gravimetric capacitance of the symmetric and asymmetric cells found to be 40 F/g and 71 F/g, respectively. It was concluded that MA-HCl-Mn served as a sustainable, dual functional material showing a high catalytic activity for the hydrogen generation and a promising electrochemical performance as the supercapacitor electrode.     

Rational design of MXene-based films for energy storage: Progress,prospects

Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides (MXenes) have been synthesized and developed into a wide range of applications including energy storage, optoelectronics, electromagnetic interference shielding, biomedicine, and sensors, etc. Compared to other 2D materials, MXenes possess a unique set of properties such as superior mechanical strength, outstanding hydrophily, and excellent dispersion quality, making them particularly suitable for fabricating films/membranes featuring designed microstructures and tunable nanochannels. 2D MXene-based films (MBFs) have demonstrated excellent ion storage, electron transport and ionic selectivity properties for electrochemical energy storage and have received enormous interest in recent years. Compared with conventional electrode materials and structures, MBFs show great advantages in the aspects of flexibility, tailorability and functionality, which are suitable for flexible, portable, and highly integrated energy storage systems. This review summarizes recent advances and well-developed strategies of the MBFs design and fabrication toward applications of metal-ion batteries (MIBs, including Li, Na, K-ions), lithium-sulfur (Li-S) batteries and supercapacitors (SCs). Special attentions are given to the design principles of MBFs based microstructures, inter-layer nanochannels and in-plane nanochannels for energy storage. Finally, the current challenges and promising perspectives of the MBFs for energy storage devices are presented.     

Construction of MnO2 nanosheets@graphenated carbon nanotube networks core-shell heterostructure on 316L stainless steel as binder-free supercapacitor electrodes

Carbon nanotubes are regarded as typical and promising electrode materials in supercapacitors. However, small specific capacitance of carbon nanotubes restricts the practical application in high energy density devices. Herein, MnO₂ nanosheets@graphenated carbon nanotube networks are synthesized directly on 316L stainless steel as binder-free electrodes for high-performance supercapacitors. Graphenated carbon nanotube networks are grown in-situ on stainless steel by chemical vapor deposition method followed by annealing treatment. Subsequently, MnO₂ nanosheets are uniformly deposited on graphenated carbon nanotube networks to construct core-shell heterostructure based on the facile hydrothermal reaction using KMnO₄ as the precursor. Core carbon nanotube networks can offer a stable structural backbone and shell MnO₂ nanosheets can shorten diffusion paths of ions. The MnO₂ nanosheets@graphenated carbon nanotube networks exhibit a high specific capacitance of 575.4 F g⁻¹ (areal capacitance of 274 mF cm⁻²) at the current density of 0.5 mA cm⁻² and good cycling stability (93% of capacity retention after 6000 cycles), due to the synergistic effects between pseudocapacitive MnO₂ nanosheets and conductive carbon nanotube networks. The developed synthetic strategy offers design guidelines for the construction of advanced binder-free electrodes for high-performance supercapacitors.     

MWCNTs-GONRs/Co3O4 electrode with needle-like arrays for outstanding supercapacitors

Multiwalled carbon nanotubes-graphene oxide nanoribbons (MWCNTs-GONRs) exhibit high specific surface area and good electroconductivity because of their unique three-dimensional cross-linking structure with the properties of both CNTs and GONRs. In this study, a hydrothermal method was employed to anchor MWCNTs–GONRs onto a Ni foam (NF) to obtain a precursor substrate. Subsequently, Co₃O₄ arrays were grown on the NF substrate to synthesize a MWCNTs–GONR/Co₃O₄ electrode. The electrode showed a capacitance of 846.2 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 90.1% after 3000 cycles. Furthermore, MWCNTs–GONRs/Co₃O₄ and active carbon (AC) were used as the positive and negative electrodes, respectively, to assemble a supercapacitor, which delivered a maximum energy density of 38.23 W h kg⁻¹ and a high power density of 6.80 kW kg⁻¹. In addition, the specific capacitance of the device reached a maximum of 91.5% after 9000 cycles. Thus, the MWCNTs–GONRs/Co₃O₄ electrode showed huge potential for supercapacitor applications.     

High-density oxygen-enriched graphene hydrogels for symmetric supercapacitors with ultrahigh gravimetric and volumetric performance

The contradiction between the porous structure and density of graphene materials makes it unable to meet the dual requirements of the next generation supercapacitors for gravimetric capacitance and volumetric capacitance. Herein, we successfully synthesized high-density oxygen-enriched graphene hydrogels (HOGHs) by a one-step hydrothermal method using high concentration graphene oxide (GO) solution and trometamol as precursors. The as-prepared HOGHs samples present a dense 3D network structure and moderate specific surface areas, which leads to a high packing density. In addition, the HOGHs samples also contain abundant oxygen-containing functional groups and some nitrogen-containing functional groups. These heteroatomic functional groups can provide pseudocapacitance for the electrode materials. Therefore, the HOGH-140 based symmetric supercapacitor shows ultrahigh gravimetric and volumetric specific capacitance (325.7 F g⁻¹, 377.8 F cm⁻³), excellent rate performance and cycling stability. Simultaneously, the symmetric binder-free supercapacitor exhibits high gravimetric specific energy density (11.3 Wh kg⁻¹) and volumetric specific energy density (13.1 Wh L⁻¹) in 6 M KOH, respectively. These outstanding properties make the material have a good application prospect in the field of compact energy storage devices.     

Metal phthalocyanine-linked conjugated microporous polymer hybridized with carbon nanotubes as a high-performance flexible electrode for supercapacitors

Metal phthalocyanine-linked conjugated microporous polymers (MPc-CMPs) have huge potential applications in energy conversion and storage systems. However, the inherent low conductivity limits their practical application. Herein, the MPc-CMPs are hybridized with highly conductive carbon nanotubes (CNTs) via the easy vacuum filtration method. Interestingly, the composite (denoted as CoPc-CMP/CNTs) shows the flexible feature, which can be served as the flexible binder-free electrode for supercapacitors (SCs). As expected, the flexible CoPc-CMP/CNTs exhibits a high specific capacitance of 289.1 F g⁻¹ at a current density of 1 A g⁻¹ and good capacity retention of 82.4% over 1350 cycles at a high current density of 10 A g⁻¹. Furthermore, First-principle calculations are used to elucidate the superiority of CoPc-CMP to other analogues. The good electrochemical performance could be attributed to the synergistic effect from the high pseudocapacitance and good conductivity of CoPc-CMP as well as the capacitive contribution and good conductivity of CNTs. Our strategy provides a new avenue to develop the high-performance SCs via rational integration of MPc-CMPs with highly conductive CNTs.     

Transforming waste sugar solution into N-doped hierarchical porous carbon for high performance supercapacitors in aqueous electrolytes and ionic liquid

Waste sugar solution is a by-product in the process of manufacturing vitamin C. Nowadays, the unused industrial waste residues are transformed into high efficient energy storage devices, such as supercapacitors electrodes, which are worth exploring because they are consistent with the concept of green and sustainable development. In this paper, a nitrogen-doped hierarchical porous carbon are obtained via pre-carbonization and KOH activation. The as-prepared material, possessed proper pore size distribution, large specific surface area and nitrogen-doping, exhibits good electrochemical performance, such as a high specific capacitance of 342 F g⁻¹ (0.1 A g⁻¹), good stability with 95% capacitance retention after 15,000 cycles in 6 M KOH. Moreover, the supercapacitors deliver a high energy density of 25.6 and 65.9 W h kg⁻¹ in the 1 M Na₂SO₄ and EMIMBF₄, respectively. The good electrochemical performance illustrates that the nitrogen-doped hierarchically porous carbon derived from the waste sugar solution is a potential candidate for energy storage.     

Biomass-derived graphene-based nanocomposite: A facile template for decoration of ultrathin nickel–aluminum layered double hydroxide nanosheets as high-performance supercapacitors

One promising approach to design of high performance supercapacitors is based on the coupling the conductive porous carbon matrixes and the electroactive components. However, the main challenge to this goal is the maintaining the long cycling life, high power and high energy densities of the related capacitors. Herein, we reported on an electroactive composite based on biomass derived 3D graphene coupled with nickel-aluminum layer double hydroxides for manufacturing a cathode material in a supercapacitor. The electrode exhibits a remarkable specific capacitance of 1390 F g⁻¹ at 1 Ag^-1, and ultrahigh rate capability of 60% from 1 to 30 Ag^-1, as well as excellent cycling stability with a capacitance retention of 92% after 5000 cycles. Furthermore, the electrode was used as the positive electrode against a Vulcan XC-72R as the negative electrode to assemble an asymmetric supercapacitor. The asymmetric supercapacitor device exhibited a maximum energy density of 173 Wh kg⁻¹ and power density of 28.8 kW kg⁻¹ as well as excellent cycling stability of 92% after 5000 cycles. The asymmetric supercapacitor could lighted up LED lamps with different colors more than 24 min. The work showed promising performance of further application in electrochemical devices.