Ni3V2O8/CNFs composite electrodes for flexible supercapacitors with excellent cycling stability

Herein, we report a nanoarchitectured nickel molybdate/carbon fibers@pre-treated Ni foam (NiMoO4 /CF@PNF) electrode for supercapacitors. The synthesis of NiMoO4 /CF@PNF mainly consists of a direct chemical vapor deposition (CVD) growth of dense carbon fibers (CFs) onto pre-treated Ni foam (PNF) as the substrate, followed by in situ growth of NiMoO4 nanosheets (NSs) on the CF@PNF substrate by means of a hydrothermal process. The NiMoO4 /CF@PNF electrode exhibits a high areal capacitance (5.14 F cm(-2) at 4 mA cm(-2) ) and excellent cycling stability (97 % capacitance retention after 2000 cycles at 10 mA cm(-2) ). Furthermore, we have successfully assembled NiMoO4 NSs//activated carbon (AC) asymmetric supercapacitors, which can achieve an energy density of 45.6 Wh kg(-1) at 674 W kg(-1) , and excellent stability with 93 % capacitance retention after 2000 cycles at 5 mA cm(-2) . These superior properties hold great promise for energy-storage applications.

Ni3S2 nanorods and three-dimensional reduced graphene oxide electrodes-based high-performance all-solid-state flexible asymmetric supercapacitors

All‐Solid‐State Cable‐Type Supercapacitors with Ultrahigh Rate Capability

The fabrication of supercapacitor electrodes with high energy density and excellent cycling stability is still a great challenge. A carbon aerogel, possessing a hierarchical porous structure, high specific surface area and electrical conductivity, is an ideal backbone to support transition metal oxides and bring hope to prepare electrodes with high energy density and excellent cycling stability. Therefore, NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid supercapacitor electrode materials were synthesized by assembling Ni-Co precursor needle arrays on the surface of the channel walls of hierarchical porous carbon aerogels derived from chitosan in this study. The 1D nanostructures grow on the channel surface of the carbon aerogel vertically and tightly, contributing to the enhanced electrochemical performance with ultrahigh energy density. The energy density of NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid asymmetric supercapacitors can reach up to 55.3 Wh kg-1 and 47.5 Wh kg-1 at a power density of 400 W kg-1, respectively. These asymmetric devices also displayed excellent cycling stability with a capacitance retention of about 96.6% and 92% over 5000 cycles.

Polypyrrole/SnCl2 modified bacterial cellulose electrodes with high areal capacitance for flexible supercapacitors

Flexible supercapacitors are attracting interest in wearable technologies as they can withstand mechanical deformations while delivering their energy storage function. Among frequently investigated electrode materials for flexible supercapacitors, polyaniline/graphene composites are favorable due to their synergistic properties that assure excellent specific capacitance, cycling stability, and high rate capability. This review highlights recent strategies to advance structural designs and synthesis methods of polyaniline/graphene electrodes for flexible supercapacitors. Firstly, the general mechanism and feature of the flexible supercapacitor will be discussed, followed by current challenges that focus on two key aspects, structural design and synthesis of the electrode. Next, by sorting the composites based on their morphological dimensionalities (i. e., one‐, two‐, and three‐dimensional), and focusing the discussion on the two key aspects, we evaluate recent and effective strategies to develop flexible supercapacitors with polyaniline/graphene composite electrode. Finally, future perspectives are given for broader applications of the flexible supercapacitors.

Interconnected Co 0.85 Se nanosheets as cathode materials for asymmetric supercapacitors

3D hierarchical transition-metal sulfides deposited on MXene as binder-free electrode for high-performance supercapacitors

Boosting hierarchical construction and charge storage capacity of polyaniline arrays grown on the surface of carbon cloth with the aid of graphene interlayer

The capacitance of an electric double‐layer capacitor (EDLC) is largely determined by the surface area and the electrical conductivity of the electrode material. To enhance the performance of EDLCs, a separate activation procedure is commonly used to increase the porosity of the electrode. A facile and scalable method of producing highly porous carbon electrodes for high‐performance supercapacitors without a separate activation procedure via simple thermal treatment of potassium acetate is reported. Potassium acetate‐derived carbon (PAC) exhibits a high specific surface area of 1704 m2 g−1 and superior electrical conductivity of 22 950 S cm−1 without further treatment. When used for EDLC electrodes, PAC displays a high specific capacitance of 195 F g−1 at 0.5 A g−1 and excellent cyclic stability with capacitance retention of 99.0% over 80 000 charge/discharge cycles. Carbonization and simultaneous self‐activation of PAC demonstrates a facile and efficient method of producing carbon electrodes with a high surface area without an additional activation procedure, which provides an efficient solution for producing high‐performance supercapacitor electrodes at low cost.

The doping of porous carbon materials with nitrogen is an effective approach to enhance the electrochemical performance of electrode materials. In this study, nitrogen-doped porous carbon derived from peanut shells was prepared as an electrode for supercapacitors. Melamine, urea, urea phosphate, and ammonium dihydrogen phosphate were employed as different nitrogen dopants. The optimized electrode material PA-1-1 prepared by peanut shells, with ammonium dihydrogen phosphate as a nitrogen dopant, exhibited a N content of 3.11% and a specific surface area of 602.7 m2/g. In 6 M KOH, the PA-1-1 electrode delivered a high specific capacitance of 208.3 F/g at a current density of 1 A/g. Furthermore, the PA-1-1 electrode demonstrated an excellent rate performance with a specific capacitance of 170.0 F/g (retention rate of 81.6%) maintained at 20 A/g. It delivered a capacitance of PA-1-1 with a specific capacitance retention of 98.8% at 20 A/g after 5000 cycles, indicating excellent cycling stability. The PA-1-1//PA-1-1 symmetric supercapacitor exhibited an energy density of 17.7 Wh/kg at a power density of 2467.0 W/kg. This work not only presents attractive N-doped porous carbon materials for supercapacitors but also offers a novel insight into the rational design of biochar carbon derived from waste peelings.

Metal organic frameworks (MOFs) as electrode materials for supercapacitors have attracted extensive attention due to their porous structure. However, the poor conductivity of MOFs limits the charge transfer. In this work, Mn-MOF/carbon nanotube (CNT) composites were grown directly on carbon cloth (CC) in one step by the traditional hydrothermal synthesis of MOFs to improve the electrical conductivity of Mn-MOFs. The structural and performance tests show that CNTs, as a conductive backbone, can connect Mn-MOFs to each other, which can obviously solve the problem of poor conductivity of MOF materials. The Mn-MOFs/CNTs/CC electrodes show a larger specific capacitance and excellent cycling stability by electrochemical tests. Compared to the original Mn-MOF electrode, the surface capacitance obtained increases from 188.8 mF·cm−2 to 385.8 mF·cm−2 at a current density of 0.8 mA·cm−2 and maintains a high capacitance retention of 118% after 5000 charge/discharge cycles at a current density of 5 mA·cm−2. This work confirms that the in- situ synthesis of MOFs and CNTs has promising applications in fabric-based flexible supercapacitors.

CdSe-nanoparticles-regulated synthesis of ZnCo-MOFs derived conductive porous carbon nanoflakes on carbon cloth for flexible sodium-ion supercapacitors

Via the activation treatment of carbonized almond shells with HNO3 and KOH, activated microporous carbon (AMC-3 and AMC-2) was successfully synthesized. These two AMC electrodes demonstrate remarkable electrochemical behaviors such as high rate capability, high specific capacitance, and excellent cycle stability when serving as electrodes for supercapacitors. More importantly, through the use of a Zn-Ni-Co ternary oxide (ZNCO) positive electrode and the AMC negative electrode, asymmetric supercapacitors (ASC) were assembled that deliver superior energy density (53.3 Wh kg(-1) at a power density of 1126.1 W kg(-1) for ASC-2 and 53.6 Wh kg(-1) at a power density of 1124.5 W kg(-1) for ASC-3) and excellent stability (82.7% and 83.4% specific capacitance retention for ZNCO//AMC ASC-2 and ZNCO//AMC ASC-3, respectively, after 5000 cycles). Through these two methods, low-cost, renewable, and environmentally friendly electrode materials can be provided for high energy density supercapacitors.

Mesoporous Zr-doped CeO2 nanostructures as superior supercapacitor electrode with significantly enhanced specific capacity and excellent cycling stability