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• The interconnected petal-like morphology of Co-MOFs on a flexible stainless steel substrate (FSS) was synthesized by using a cost-effective Reaction Diffusion Framework method. • The electrochemical properties of Co-MOFs/FSS were examined in different aqueous electrolytes. • The performance of supercapacitors using Co-MOFs/FSS was evaluated under varying concentrations of LiOH electrolyte. • A high-performance symmetric paper-soaked Co-MOFs/FSS//Co-MOFs/FSS device was designed and fabricated for supercapacitor applications. The electrolyte is a crucial component in supercapacitors (SCs), along with the electrode material, which can affect the electrochemical parameters, such as specific capacitances (C s), energy density (ED), cyclic stability, and potential window. Therefore, the present work explores the effect of different electrolytes on the performance of Co-MOFs/FSS electrodes for SCs. The Co-MOFs/FSS electrode was synthesized on a flexible stainless-steel (FSS) substrate using the reaction-diffusion framework method, and its structural, morphological, and compositional characteristics were analyzed. The SCs performance of Co-MOF/FSS was examined across multiple electrolytes (1M KOH, 1M LiOH, and 1M NaOH). The SCs performance of Co-MOFs/FSS increased in the following sequence: 1M LiOH > 1M NaOH > 1M KOH. Furthermore, the dependence of concentration variation of LiOH electrolyte on Co-MOFs/FSS for SCs was studied. In 2M LiOH electrolyte, the Co-MOFs/FSS demonstrated a maximum C s of 650 F g − 1 and specific capacity (C sp) of 262 C g − 1 at 5 mV s − 1. Furthermore, it exhibited a favourable retention rate of 71 % over 5000 GCD cycles at 10 mA cm−2. It also possessed higher ED and Power Density (PD) of 14.10 Wh kg−1 and 666 W kg−1 at 1 mA cm−2 respectively. Further, a flexible symmetric paper-soaked Co-MOFs/FSS//Co-MOFs/FSS device was fabricated, and its electrochemical performance was assessed. The fabricated device exhibited a higher C s of 122 F g − 1 and C sp of 171 C g − 1 at 10 mV s − 1. Additionally, it showed good retentivity of 46 % after the 3000th cycle at 15 mA; and exhibited higher ED of 6.78 Wh kg−1 and PD of 1500 W kg−1 at 6 mA. This study highlights the importance of selecting the appropriate electrolyte for enhancing the electrochemical performance of Co-MOFs/FSS electrode material. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract In this study, cathodic electrodeposition of manganese oxide onto reduced graphene oxide paper is carried out to prepare flexible and binder-free electrodes for electrochemical capacitors. Effects of electrodeposition potential and the amount of deposited mass on the electrochemical performance are examined. Hausmannite phase manganese oxide coated electrodes exhibit promising performance in charge-discharge and cyclic voltammetry measurements with specific capacitance of 546 F g−1 at current density of 0.5 A g−1 and 308 F g−1 at scan rate of 1 mV s−1, respectively. During potential cycling, phase transformation of Mn 3 O 4 to mixed-valent MnO x is observed. Consequently, MnO x nanostructures on self-standing reduced graphene oxide electrodes have 154% capacitance retention at 10000 cycles of cyclic voltammetry. Graphical abstract Image [ABSTRACT FROM AUTHOR]

Flexible and robust amino-functionalized glass fiber filter paper/polyaniline (A-GFFP/PANI) composite films were fabricated as free-standing tensile-tolerant electrodes for high performance supercapacitors, by facile in-situ chemical oxidative polymerization of aniline on the surface of glass fiber filter paper (GFFP) in sulfuric acid solution, after surface modification. The results showed that the surface modification of GFFP with (3-aminopropyl)triethoxysilane played a role as bridge for connecting the polyaniline and glass fiber, resulting to unique polyaniline (PANI) coating and subsequently better electrochemical properties. The specific capacitance and electrical conductivity of the A-GFFP/PANI-1 electrode, which was fabricated via the conventional chemical oxidative polymerization of aniline with concentration of 0.18 mol/L, were 391.3 F/g and 2.78 S/cm, while the A-GFFP/PANI-2 electrode, prepared via rapid-mixing chemical oxidative polymerization under the same preparation condition, possessed the specific capacitance and electrical conductivity of 490.6 F/g and 1.83 S/cm. The capacitance retention of the A-GFFP/PANI-2 electrode (106. 8%) was also better than that of the A-GFFP/PANI-1 electrode (98.0%) after 2000 CV cycles at a scan rate of 100 mV/s, also owing to the bridging function of the functional silane. The A-GFFP/PANI-2 electrode retained 72.6% of its initial specific capacitance under the stress of 0.70 MPa for 1 h, indicating its good tolerance to tensile. [ABSTRACT FROM AUTHOR]

A novel polyprrole (PPy)-decorated hierarchical NiCo 2 O 4 nanoneedles was grown on highly conductive carbon fiber paper (CFP) for high performance asymmetric supercapacitor applications. The PPy-decorated hierarchical NiCo 2 O 4 nanoneedle on CFP (PPy-NiCo 2 O 4 @CPF) was grown by two steps. At first, NiCo 2 O 4 nanoneedle was grown by hydrothermal process and followed by the deposition of PPy through electrochemical method. The fabricated PPy-NiCo 2 O 4 @CPF electrode displayed the higher electrochemical performance. The specific capacitance was ∼910 F g-1 at a current density of 1 A g −1 and cyclic stability was ∼88% after 10,000 cycles. To explore real performance of the electrode, we have fabricated solid state asymmetric supercapacitor using PPy-NiCo 2 O 4 @CFP as positive and nitrogen doped reduced graphene oxide (N-rGO) as negative electrodes. The fabricated asymmetric device delivered a specific capacitance of 118.6 F g-1 at a current density of 1.0 A g −1 with a maximum energy density of 40.81 Wh Kg −1 (at a power density of 738.27 W Kg −1 ) and maximum power density of 3746.77 W Kg −1 (at an energy density of 13.53 Wh Kg −1 ). The impressive results suggest that flexible PPy-NiCo 2 O 4 @CFPs can be a promising electrode material for supercapacitor applications. [ABSTRACT FROM AUTHOR]

• 1T-MoS 2 was applied as a flexible and functional "spacer" to hybridize with Ti 3 C 2 T X MXene, forming flexible capacitive freestanding films. • The insertion of electrically neutral pseudocapacitive could mitigate the restacking of Ti 3 C 2 T X MXene layers and improves the capacity of the composite paper. • The supercapacitor fabricated with acidic gel electrolyte and composite electrode with randomly stacked MXene and 1T-MoS 2 in a mass ratio of 6:1 demonstrated optimal performance. In the case of increasing shortage of non-renewable resources, developing high-efficiency and high-capacity energy storage devices is critical. Supercapacitors have the potential of high-efficiency and high-capacity. MXene and 1T-MoS 2 are two kinds of high performance pseudocapacitive materials. However, the stacking and aggregation of MXene nanosheets greatly reduce its capacity. The poor conductivity of 1T-MoS 2 also limits the full expression of its excellent pseudocapacitive performance. A flexible MXene/1T-MoS 2 composite paper electrode is designed and prepared in this work where the restacking of MXene can be relieved and the whole electrode maintains the conductivity. The interior stacking structure of MXene and 1T-MoS 2 in the composite paper, as well as the gel electrolyte type are explored. The device constructed with the electrode composed of randomly stacked MXene and 1T-MoS 2 (mass ratio 6:1) and acidic electrolyte (PVA/H 2 SO 4 gel electrolyte) demonstrates the optimal performance. The specific areal and volumetric capacitances reach 561.2 mF cm−2 and 1268.17 F cm−3 at the current density of 0.8 mA cm−2 respectively, outperforming most of the previously reported values for MXene based supercapacitors tested in gel electrolyte. The supercapacitor has excellent deformation durability and long cycle stability, demonstrating promising prospect in future flexible electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we design a novel FeCo 2 S 4 @Ni(OH) 2 core-shell hollow nanotube arrays on carbon paper for superior capacitance of supercapacitors. FeCo 2 S 4 hollow nanotube arrays vertically grow on carbon paper via hydrothermal reaction served as a "core" to shorten the ion transport path, Ni(OH) 2 nanosheets modified on the hollow nanotube arrays based on constant voltage electrodeposition reveal outstanding pseudocapacitance characteristic. The ultrathin Ni(OH) 2 nanosheets act as a "shell" layered to expand the specific surface area, effectively increasing the active sites of the faraday reaction. The subtle heterogeneous synergistic effects significantly improve their electrochemical performance. The unique core-shell structure of FeCo 2 S 4 @Ni(OH) 2 displays a superior capacity of 239.72 mA h g−1 at 1 A g−1, even at 8 A g−1 still has a capacity of 128.0 mA h g−1, indicating the excellent rate performance. Significantly, the asymmetric supercapacitor assembled by the FeCo 2 S 4 @Ni(OH) 2 nanoarrays positive electrode and activated carbon (AC) negative electrode exhibits superior electrochemical performance with ultra-high energy density (55.33 Wh Kg−1 at 800 W kg−1) and power density (8000 W kg−1 at 15.78 Wh Kg−1). After 10000 charge-discharge cycles, the device still has capacitance retention of 93.8%. Therefore, FeCo 2 S 4 @Ni(OH) 2 nanoarrays can be widely used in high-performance supercapacitors as potential and promising electrode materials. Composition of FeCo 2 S 4 @Ni(OH) 2 //AC two-electrode supercapacitor with ultra-high electrochemical performance (55.33 Wh Kg−1 at 800 W kg−1) and still retains 93.8% capacitance after 10,000 cycles，Charging to 3.2 V in tens of seconds, the device can light up the circular blue LED for a period of time. Image 1 [ABSTRACT FROM AUTHOR]

Abstract: Multi-walled carbon nanotubes grown on the carbon paper substrate are prepared by in situ growth in a chemical vapor deposition system. Co(OH)2 is deposited on carbon nanotubes/carbon paper by electrodeposition methods. SEM images show that the successful growth of nanometer-sized Co(OH)2 nanosheets on the surface of carbon nanotubes/carbon paper substrate. The electrodes of Co(OH)2/carbon nanotubes/carbon paper composite are investigated for their use in supercapacitors with cyclic voltammograms, chronopotentiometric measurements and electrochemical impedance spectroscopy. The composite electrode shows the largest specific capacitance of 1083Fg−1 at a current density of 0.83Ag−1 in 6M KOH electrolyte. Furthermore, this composite exhibits good cycling stability and lifetime. The implanted CNTs between carbon paper and Co(OH)2 act as a good conductive medium for electrodes in supercapacitors, and the interconnected nanosheets of the Co(OH)2 can facilitate the contact of the electrolyte with active materials, and thus increase the capacitance. [Copyright &y& Elsevier]

Layered α-Co(OH) 2 nanosheets have been widely investigated as one of the promising supercapacitor materials owing to its high theoretical specific capacitance (3,460 F g −1 ). However, their poor electrical conductivity, poor stability, and unclear charge storage mechanism limit their practical use in energy storage systems. To address the first two drawbacks of layered Co(OH) 2 , conductive silver nanoparticles (AgNPs) with a finely tuned loading content were for the first time incorporated to the layered Co(OH) 2 structure coated on a flexible reduced graphene oxide (rGO)paper substrate. In situ electrochemical X-ray absorption spectroscopy (XAS) was also used to investigate the charge storage mechanism of AgNPs/Co(OH) 2 electrode. It was found that the incorporation of AgNPs with an average diameter of <10 nm can significantly enhance the charge storage capacity of Co(OH) 2 due to high electrical conductivity leading to fast charge transport. The charge storage mechanism of the Ag-doped α - Co(OH) 2 energy storage cell is based on an intercalation/de-intercalation process (a battery-like behavior) and a physical adsorption of solvated ions (a supercapacitor-like behavior). The incorporation of AgNPs to the layered Co(OH) 2 nanosheets in this work can overcome the current drawbacks of the Co(OH) 2 , which may lead to practical use as a hybrid energy storage device. [ABSTRACT FROM AUTHOR]

Although functionalized carbon-based materials have been widely used as the supercapacitor electrodes, the optimum contents of the functional groups, the charge storage mechanisms, and the effects of electrolytes and operating temperature have not yet been clearly investigated. In this work, carboxylate-modified hollow carbon nanospheres (c-HCN) with different functional group contents synthesized by an oxidation process of carbon nanospheres with nitric acid were coated on flexible carbon fibre paper and used as the supercapacitor electrodes. An as-fabricated supercapacitor of the c-HCN with a finely tuned 6.2 atomic % of oxygen of the oxygen-containing groups in an ionic liquid electrolyte exhibits a specific capacitance of 390 F g −1 , a specific energy of 115 Wh kg −1 , and a maximum specific power of 13548 W kg −1 at 70 °C. The charge storage mechanism investigated is based on the chemical adsorption of the ionic liquid electrolyte on the c-HCN electrode. This process is highly reversible leading to high capacity retention. The supercapacitor in this work may be practically used in many high energy and power applications. [ABSTRACT FROM AUTHOR]

Although carbon fiber paper (CFP) or nonwovens are widely used as a non-corrosive and conductive substrate or current collector in batteries and supercapacitors as well as a gas diffusion layer in proton exchange membrane fuel cells, the CFP cannot store charges due to its poor ionic conductivity and its hydrophobic surface. In this work, the chemically functionalized CFP ( f -CFP) consisting of hydroxyl and carboxylic groups on its surface was produced by an oxidation reaction of CFP in a mixed concentrated acid solution of H 2 SO 4 :HNO 3 (3:1 v/v) at 60 °C for 1 h. Other amide and amine groups modified CFP were also synthesized for comparison using a dehydration reaction of carboxylic modified CFP with ethylenediamine and n-butylamine. Interestingly, it was found that hydroxyl and carboxylic groups modified CFP behave as a pseudocapacitor electrode, which can store charges via the surface redox reaction in addition to electrochemical double layer capacitance. The aqueous-based supercapacitor of f -CFP has high areal, volumetric, and specific energy (49.0 μW.h/cm 2 , 1960 mW.h/L, and 5.2 W.h/Kg) and power (3.0 mW/cm 2 , 120 W/L, and 326.2 W/Kg) based on the total geometrical surface area and volume as well as the total weight of positive and negative electrodes. High charge capacity of the f -CFP stems from high ionic charge and pseudocapacitive behavior due to hydroxyl and carboxylic groups on its surface and high bulk electronic conductivity (2.03 mS/cm) due to 1D carbon fiber paper. The acid treatment process here could be used to improve the charge storage capacity of other carbonaceous materials such as carbon nanotubes. [ABSTRACT FROM AUTHOR]

The development of polypyrrole (PPY) flexible supercapacitors has been recognized as one of the most effective strategies for preparing advanced flexible energy storage devices. However, they are still limited by low mass loading and poor areal capacitance during charge-discharge process. Here, freestanding conductive film is designed and prepared by PPY/bacterial cellulose (BC) nanofibers in combination with graphene (RGO) through a simple in situ polymerization and filtering method. The porous and flexible BC nanofiber is used as a substrate and template for successive polymerization of PPY, which is responsible for such a large areal mass of 13.5 mg cm −2 . Thus, the high areal capacitance of 3.66 F cm −2 at 1 mA cm −2 and 2.59 F cm −2 at 50 mA cm −2 are achieved. The assembled symmetric supercapacitor by coupling of two freestanding electrodes delivers high areal capacitance of 1.67 F cm −2 , high areal energy density of 0.23 mWh cm −2 and a maximum power density of 23.5 mW cm −2 . Therefore, it is believed that this strategy holds great promise for design of freestanding conductive polymer electrodes on high performance flexible supercapacitors. [ABSTRACT FROM AUTHOR]

Graphitic layer of carbon has been deposited on the surface of cellulose paper by simple pencil drawing approach. The edges of exfoliated multilayer graphene sheets formed during pencil drawing on the rough paper surface causes the enhancement of electrochemical capacitance. One step chemical polymerization technique has been adopted to fabricate polyaniline nanofibers on hydrophobic pencil drawn graphitic layer on the cellulose paper. These polyaniline coated pencil drawn paper electrodes were used to fabricate all-solid-state symmetric supercpapcitors with superior performance in comparison to similar pencil drawn paper electrodes without polyaniline. All-solid-state symmetric supercapacitor with paper based multilayer graphene-polyaniline nanofiber electrodes exhibits specific capacitance of 28.37 F g−1, areal capacitance of 93.64 mF cm−2, energy density of 8.32 µW h cm−2, and power density of 39.97 µW cm−2. It also shows excellent cyclic stability with initial increment to a maximum value and then decrease to 91.5 % of the maximum value after 5000 cycles. It is interesting to note that it retains 134.28 % of initial areal capacitance after 5000 cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Symmetric paper-based supercapacitor devices containing polypyrrole (PPy)–cellulose composite electrodes and aqueous electrolytes can be charged using either potential step or constant current charging. Potential step charging provides better control of the charging and can result in significantly shorter charging times, enabling charging in 22s for devices with cell capacitances of 12.2F when charged to 0.8V. The paper-based electrode material was compatible with charging currents as large as 5.9Ag−1 due to the rapid counter ion mass transport resulting from the porous composite structure and the thin PPy coatings. The charging times were controlled by the RC time constants of the devices and the cell resistance was found to decrease with increasing electrode area. For small cells, the cell resistance was determined to a large extent by the electrolyte resistance and contact resistances, whereas the resistance of the current collectors dominated for larger cells. The specific cell capacitance was 38.3Fg−1 or 2.1Fcm−2, normalized with respect to the total electrode weight and electrode cross section area respectively, and the devices showed 80–90% capacitance retention after 10000 potential step charge and discharge cycles. These results, which demonstrate that potential step charging can be advantageous for conducting polymer based energy storage devices, are very encouraging for the development of new up-scalable paper-based energy storage devices. [Copyright &y& Elsevier]

Vertically stacked thorn-like nanostructured NiCo 2 S 4 arrays are designed to in-situ grow on the electrochemical oxidized graphite paper by a two-step hydrothermal method where graphite papers act as heterogeneous nuclear sites to rationally construct the unique features of NiCo 2 S 4. Bimetal synergistic effect and the presence of sulfur atoms can improve the ionic and electron conductivity of NiCo 2 S 4. The unique structure of NiCo 2 S 4 fabricated in such way can allow more active sites exposed to reversible redox reactions, as well as provide relatively short ions/electrons transport pathways within the broken crystal structure and rich porous structure. As such, graphite paper supported NiCo 2 S 4 as a self-supported electrode (NiCo 2 S 4 @EGP) shows an extraordinarily high rate capability with the specific capacitance of 1276 F g−1 at 1 A g−1, and even 1218 F g−1 at 20 A g−1, as well as the excellent cycle stability with capacitance retention of 86 % after 5000 cycles. When assembling into a flexible asymmetric all-solid-state supercapacitor device, this device reaches a high-power density of 55.3 Wh kg−1 at a power density of 747.6 W kg−1, together with a superior high cycle stability (retained 95 % in 5000 cycles). These results obviously open interesting perspectives of using NiCo 2 S 4 @EGP as self-supported electrodes to become an advanced flexible power device. Vertically stacked thorn-like nanostructured NiCo 2 S 4 arrays are designed to in-situ grow on the electrochemical oxidized graphite paper, giving an extraordinarily high rate capability for supercapacitor electrodes with the specific capacitance of 1276 F g−1 at 1 A g−1, and even 1218 F g−1 at 20 A g−1. [Display omitted] [ABSTRACT FROM AUTHOR]

• Report a mass production paper-making method for flexible electrodes. • The HWF supported paper electrodes show high volumetric capacitance of 246.4 f cm−3 and good flexibility. • The HWF supported ASCs achieve a high energy density of 10.1 mWh cm−3 with power density of 93.9 mW cm−3. In this study, paper supported flexible electrodes for supercapacitors are prepared by paper-making process with the hardwood fiber (HWF), multi-walled carbon nanotube (MWCNT) and NiCo 2 S 4 powder. Compared with previous reported cellulose nanofiber (CNF), nickel foam and carbon cloth supported electrodes, the HWF supported paper electrodes demonstrate its advantages of low-cost, mass production, low-thickness and superior flexibility. It can achieve a high specific capacitance of 1725 F g−1 at 1 A g−1, a remarkable rate retention of 79.3 % from 1 A g−1 to 10 A g−1, an ultrahigh volumetric specific capacitance of 246.4 F cm−3 at 1 mA cm−2 and an excellent cycling stability at 20 A g−1 after 5000 cycles. The as-fabricated HWF supported flexible asymmetric supercapacitors (ASCs) have achieved excellent volumetric specific capacitance of 10.25 F cm−3 and energy density of 10.1 mWh cm−3 with power density of 93.9 mW cm−3. All results suggest that the paper-making method and the HWF supported paper electrodes provide great opportunity for developing high-performance flexible energy-storage electrodes with the feasibility of mass production. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this work, the composite papers, containing carbon nanotubes (CNTs) and nickel oxides, possess high specific capacitance because of the formation of synergistic effect by adopting a conductive CNT network structure as the supporting architecture and nickel oxide as the primary material of the supercapacitor. The presence of CNT network improves the poor electrical conductivity of the nickel oxides and benefits the electron transfer during the charge/discharge processes, as a result, achieves a high specific capacitance. The CNT/NiO hybrids are synthesized via hydrothermal treatment and subsequently mixed with different amounts of pristine CNTs during the filtration process to form multilayered CNT/NiO hybrid paper electrodes, which possess a stable lamellar structure without binder. The hybrid paper electrode shows a high specific capacitance of 713.9 F/g at a scan rate of 2 mV/s. By paring the as-fabricated paper electrode with commercial activated carbon/CNT hybrid paper as anode and using the 6 M KOH solution as electrolyte, an asymmetric supercapacitor was assembled. The materials in hybrid paper electrodes can be used not only as electrode's active materials, but also as current collectors. The supercapacitor shows an energy density of 23.9 Wh kg−1 and a power density of 698.6 W kg−1 as well as good stability of 88.2% capacitance retention after 3000 cycles. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this work, Na+/K+- inserted MnO 2 (Na x K y MnO 2) nanosheets are synthesized on Ni foam via a facile and efficient route based on an electro-deposition and electro-oxidation reaction process. The Na x K y MnO 2 nanosheet arrays has a broad potential window, which can be extended to 1.0 V versus standard calomel electrode (vs. SCE). The Na x K y MnO 2 with iso-oriented feature and unique nanoarchitectures provides shortened diffusion path lengths for both Na+, K+ and electronic transport, and reduces the stress associated with Na+, K+ insertion and extraction. The layered Ti 3 C 2 T x paper on Ni foam (Ti 3 C 2 T x @NF) are also synthesized successfully that can act as a negative electrode, stably in a negative potential window of −0.8−0 V (vs. SCE). Subsequently, an aqueous asymmetric supercapacitor is demonstrated with a high potential of 1.8–2.0 V by using Na x K y MnO 2 @NF as the positive electrode and Ti 3 C 2 T x @NF as the negative electrode. The asymmetric device achieves a high power density of 9.396 mW/cm2 and improved energy density of 0.11 mWh/cm2, as well as great cycling performance. [ABSTRACT FROM AUTHOR]

Hematite (α-Fe 2 O 3) is considered a promising electrode material due to its cost-effectiveness and high theoretical specific capacity. In this paper, we prepared Fe 2 O 3 nanoparticles by hydrothermal method. To improve the drawbacks such as poor conductivity and low practical capacity, NiCo 2 O 4 nanorods and graphene oxide (rGO) are added to Fe 2 O 3 nanoparticles. The composite exhibits a specific capacity of 644 F g−1 at a current density of 1 A g−1. The higher ion diffusion rate can improve the specific capacity and energy density in optimized composites. At a current density of 1 A g−1, compared to Fe 2 O 3 , the specific capacity and energy density of Fe 2 O 3 /NiCo 2 O 4 /rGO were increased by 278.8 % and 304.5 %, respectively. In order to stimulate more potential applications, we encapsulated Fe 2 O 3 /NiCo 2 O 4 /rGO-//Co 3 O 4 asymmetric supercapacitors with binder-free Co 3 O 4 as the counter electrode. Determining the optimal positive and negative active substance mass ratio by controlling the amount of charge, the device can deliver a high specific capacity of 280.6 F g−1 at a current density of 1 A g−1 and power density of 354.8 W Kg−1 while providing a high energy density of 56.1 Wh Kg−1. These results indicate that Fe 2 O 3 /NiCo 2 O 4 /rGO has potential for electrochemical energy storage, which could provide new ideas for new commercial supercapacitors. [ABSTRACT FROM AUTHOR]

Abstract A simple hydrothermal method is developed for the growth of NiCo 2 O 4 nano-needle arrays on a filter paper carbon (FC) substrate for use as a high performance electrode for supercapacitors. The as-synthesized NiCo 2 O 4 /C composites exhibited high specific capacitance (995.2 F g−1 at a current density of 10 A g−1) and excellent cycling performance (no capacitance loss after 3000 cycles). The 3D framework of the FC substrate not only prevents the aggregation of NiCo 2 O 4 nanoparticles, but also improves its electrical conductivity, thus leading to excellent electrochemical performance. Moreover, an asymmetric supercapacitor was assembled by using the NiCo 2 O 4 /C composites and activated carbon as the positive and negative electrode, respectively, and provided a maximum energy density of 20.87 Wh kg−1 at a power density of 374.6 W kg−1 and a maximum power density of 7.48 kW kg−1 at an energy density of 11.43 Wh kg−1 within a potential window of 0–1.5 V, demonstrating the potential of the composites for use in high performance energy storage systems. Highlights • Filter paper derived carbon (FC)/NiCo 2 O 4 was prepared by hydrothermal method. • The FC with open channels increased the electron and ion transport rates. • The FC-based supercapacitor exhibited good capacity and cycling stability. [ABSTRACT FROM AUTHOR]

Abstract We report the development of flexible self-supported metal-free electrodes based on non-oxidized graphene multilayer (MLG) paper, utilized to assemble bendable electrochemical supercapacitors. Using a simplified production method various electrodes exhibiting high conductivity were prepared and its structural, morphological, chemical and electrical properties characterized. Measurements in supercapacitors assembled from MLG electrodes and PANI-coated MLG electrodes show excellent electrochemical characteristics, with specific capacitances of 58 mF cm−2 and 451 F g−1 with 84% and 103% of capacitance retention after 1000 cycles, respectively. The energy and power density obtained for the PANI/MLG flexible supercapacitor reached 17.0 Wh g−1 and 3.61 kW kg−1, respectively. Moreover, in bending tests, the supercapacitors displayed an excellent mechanical and electrochemical stability. As an important result of this study, MLG electrodes appear as an interesting material for flexible high performance energy storage devices. Graphical abstract Image 1 Highlights • Flexible self-supported metal-free electrodes based on multilayer graphene paper. • PANI-coated MLG electrodes reached specific capacitances 451 F g−1. • The energy and power density of 17.0 Wh g−1 and 3.61 kW kg−1. • PANI/MLG supercapacitor exhibited 103% of capacitance retention after 1000 cycles. [ABSTRACT FROM AUTHOR]

The emerging field of wearable electronic devices has propelled the demand for advanced energy storage solutions. Among these, wearable supercapacitors have garnered significant attention due to their intrinsic advantages, including high stability, rapid charging discharging capabilities, and cost-effectiveness. This paper unveils the latest strides in flexible and wearable supercapacitors, placing a spotlight on the exceptional performance of a novel V 2 O 5 -pBOA-Graphene nanocomposite. Synthesized through a straightforward chemical approach, the material is meticulously characterized using X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The electrochemical behavior of the fabricated wearable supercapacitor devices is scrutinized, revealing an outstanding specific capacitance of 986 Fg−1 in a two-electrode system, coupled with an impressive energy density of 49 Whkg−1. The nanocomposite's robust cycling stability is showcased, with a capacitance retention of 93.47 % over 2000 cycles. Moreover, the device's flexibility is assessed by bending it at various angles, and it retains more than 91 % capacitance even at a 90° angle, underscoring its suitability for wearable applications. The choice of electrode materials, encompassing vanadium pentoxide (V 2 O 5), poly benzoxazole aniline (pBOA), and graphene, synergistically contributes to the nanocomposite's remarkable electrochemical performance. V 2 O 5 , with its pseudocapacitive behavior, is complemented by the conductivity and mechanical stability offered by pBOA and graphene. The ternary V 2 O 5 -pBOA-Graphene nanocomposite emerges as a frontrunner for wearable supercapacitor applications, promising enhanced flexibility, efficiency, and practical utility in real-world scenarios. The findings underscore the potential of the V 2 O 5 -pBOA-Graphene nanocomposite as a key player in the future of wearable energy storage, opening avenues for further exploration, optimization, and integration into practical applications. [ABSTRACT FROM AUTHOR]

The accurate estimation of state-of-charge (SOC) is crucial for the supercapacitor (SC) management system of electric vehicles. In this paper, a salp swarm algorithm (SSA)-optimized high and low degree cubature Kalman filters (CKFs) for SC SOC estimation is proposed. Firstly, the key parameters are identified for the Thevenin model by SSA under SC test data. Secondly, a temperature-varied model with temperature uncertainty is constructed by polynomial fitting. Thirdly, an adaptive rule based on SSA is designed to regulate the noise covariance matrix information in real time. Combining this rule and CKFs, SSA-based generalized high-degree CKF (SSA-GHCKF) and SSA-based low-degree CKF (SSA-CKF) are developed with the minimum prediction error as the objective. Finally, the effectiveness of improved CKFs is evaluated by the urban dynamometer driving schedule in varying temperatures. The simulation results show that the root mean square errors of SOC estimation by CKF, GHCKF, and SSA-CKF are kept within 1.4553 %, 1.2880 % and 1.2152 %, while for SSA-GHCKF, this metric is merely 1.1933 %. The proposed SSA-GHCKF enables superior accuracy and robustness for SOC estimation at extreme temperatures. [ABSTRACT FROM AUTHOR]

• Partially transformation growth of PBA on NiFe-MOF to obtain dual-MOF heterostructure. • NiFe-MOF/PBAs have an ultra-high specific capacity of 4270.19 c g−1 at 1 a g−1. • NiFe-MOF/PBAs//AC device has a high specific capacity up to 1996.01 c g−1 at 1 a g−1. • The device has excellent cycling stability of only 1.14 % decay rate (20,000 cycles). Metal organic framework (MOF) is considered as an excellent electrode material for supercapacitors due to its low cost and homogeneous nanostructure, but the drawbacks of single MOF, such as low specific capacity and stability, limit its development, so the design of bimetallic MOF structural composites is a challenging but favourable strategy for the development of supercapacitors. In this paper, NiFe-MOF/PBAs heterostructure, a bimetallic MOF material with a granular rod-like structure, is successfully prepared by using bimetallic MOF as a precursor and introducing [Co(CN) 6 ]3− ions to further convert it into PBAs (Prussian blue analogs). Due to the special macroporous structure of PBAs, the composite combines the advantages of the two MOF materials, and the specific capacity is as high as 4270.19 C g−1 at 1 A g−1. The composite still has excellent electrochemical properties when assembled into devices. The specific capacity is 1996.01 C g−1 at 1 A g−1, the energy density reached 749.99 W h kg−1 at a power density of 415.85 W kg−1, and the decay rate is only 1.14 % after 20,000 cycles at 10 A g−1. These results indicate that the designed dual MOFs composite electrodes have good application prospects in the field of electrochemical energy storage. [Display omitted] [ABSTRACT FROM AUTHOR]

• A simple and fast hydrothermal synthesis method was proposed in this paper to synthesize an electrode material with a heterostructure of NiMoO 4 nanoneedles and high-performance flower-shaped NiCoZn-LDH on a foam nickel substrate. • The electrochemical performance of the NiCoZn-LDH@NMO@NF nanoneedle composite electrode material, treated with CTAB, is significantly superior to that of the untreated NiMoO 4 @NF electrode. • It shows excellent electrochemical properties, including a specific capacitance of 3541 mF/cm2 in KOH solution and an outstanding capacity retention of 83.04 % after 10,000 cycles. Transition metal hydroxides have attracted wide attention as promising composite nanomaterials due to their numerous active sites and large specific surface areas. In this study, a two-step hydrothermal synthesis method is proposed to generate a heterostructure (NiCoZn-LDH@NiMoO 4 @NF) consisting of nanoflowers coated with nanoneedles on a foam nickel substrate. The aggregation issue of NiCoZn-LDH is effectively improved by immersing it in CTAB solution after one-step hydrothermal synthesis of NiMoO 4 nanoneedles on Ni Foam (NF). The heterostructure between NiMoO 4 nanoneedles and NiCoZn-LDH significantly enhances the material stability and electrochemical performance. Activated carbon is used as the negative electrode, and the NiCoZn-LDH@NiMoO 4 @NF composite material is used as the positive electrode to assemble an asymmetric supercapacitor (ASC) device for electrochemical testing. The device exhibits a specific capacitance of 3541 mF/cm2 at a current density of 6 mA/cm2. Furthermore, the capacity retention rate remains at 83.04 % after 10,000 cycles of charge and discharge, and a high specific energy density of 0.735 mWh/cm2 is achieved at a power density of 1.6 mW/cm2. The experimental results demonstrate that transition metal hydroxides play a crucial role in enhancing the electrochemical performance of supercapacitors. This study provides new insights into Supercapacitor (SC) active materials and offers a promising experimental approach for synthesizing new nanomaterials. [ABSTRACT FROM AUTHOR]

• The synthesized ILs were used as novel green electrolytes for supercapacitors. • Among the ILs, the smallest anion, formate, exhibited the highest performance. • The highest value of energy density of 70 Wh kg−1 was related to the farmate anion. Supercapacitors are promising technologies for extremely effective energy storage and power management, which is a critical and major area of worldwide technological advancement. Ionic liquids (ILs) are an environmentally benign promising emerging class of versatile solvent systems. In this paper, for the first time, a new approach to the application of monoethanolamine-based ILs with anions formate, acetate, and propionate ([HEA]F, [HEA]A, and [HEA]P) as eco-friendly, affordable, and easy synthesis electrolytes are proposed for activated carbon (AC)-based supercapacitors. The ionic conductivity and the electrochemical stable potential window (ESPW) of ionic liquids were assessed. The electrochemical performance of synthesized ILs as an electrolyte in AC-based supercapacitors was compared. Electrochemical properties were performed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), linear sweep voltammetry (LSV), and galvanostatic charge-discharge (GCD) methods to evaluate the electrolytic performance of ionic liquids in supercapacitors. The charge transfer resistance (R ct) and solution resistance (R s) decreased with decreasing anion size of ILs. At a scan rate of 10 mVs−1, the prepared supercapacitors using [HEA]F, [HEA]A, and [HEA]P ionic liquids deliver specific capacitance of 114, 95, and 73 F g−1, respectively. The maximum power density 2941 W kg−1 and maximum energy density 70 Wh kg−1 were obtained for the prepared supercapacitor using [HEA]F ionic liquid. The supercapacitors prepared with [HEA]F, [HEA]A and [HEA]P electrolytes show capacitance retention of 96%, 91% and 87% after 5000 charge-discharge cycles, respectively. [ABSTRACT FROM AUTHOR]

• Combination of unilateral solution impregnation with laser induction in one-step process to get manganese-assisted graphene electrodes. • The modifier under the laser is cleverly used to achieve the enhancement of the electric double layer capacitance and the incorporation of pseudocapacitance. • Nitrogen, oxygen and manganese in superhydrophilic graphene with high yield, large surface area and low impedance. • The capacitance of as-prepared device is performing ∼25 times of the control. • Balancing cycling performance and capacity improvement of supercapacitors. Laser-induced graphene (LIG) technology has made it possible to prepare graphene-based supercapacitors on a large scale and at low cost. However, the performance of graphene-based supercapacitors fabricated solely by laser still has a great potential for improvement. In this work, we obtained high-performance supercapacitors based on manganese-assisted laser-induced multi-layer graphene-like carbon (MLIGC) by a simple process. Poly-(m-phenylene isophthalamide) (PMIA) papers treated with modifier (KMnO 4) were used as substrates. Modifier not only deepened the cross-sectional carbonization and achieveed uniform dispersing of manganese oxide nanoparticles, but also changeed the surface properties of MLIGC. Benefit from the hybrid structure of manganese oxide nanoparticles uniformly dispersed inside multi-layer graphene-like carbon (LIGC) prepared by one-step laser process, the combination of electric double-layer capacitance and pseudocapacitance allows for a further breakthrough in capacity while maintaining excellent cycling stability. Specifically, the supercapacitors achieve an area capacity of 72.4 mF cm−2 at 0.2 mA cm−2, which is 25 times higher than the control. In addition to the significant capacity increase, the addition of the modifier also achieveed a significant impedance reduction (almost one ninth of the control) and demonstrateed excellent cycling stability (nearly 100 % capacity retention after 7500 cycles at 10 mA cm−2). More importantly, the method is simple, fast, low-cost and high-efficiency, which provides a new path for the large-scale preparation of planar carbon-based supercapacitors. [Display omitted] [ABSTRACT FROM AUTHOR]

• Multilayer MnO 2 /B-containing CNF was prepared by sequential electrospinning. • B-related functional groups and MnO 2 exist independently in different nanosheets. • Each component acts independently to maximize the electrochemical properties. • B-related functional groups and MnO 2 optimize the pseudocapacitance. • The large number of mesopores leads to a high rate response and stable cycle life. One major challenge in capacitor development is achieving high capacitance and large energy density with rapid charge and discharge rates of minutes to seconds. This paper reports boron-containing trilayer structured MnO 2 /carbon nanofiber composites(PPMnB) as promising supercapacitor electrodes with high electrochemical properties under rapid charge and discharge conditions. Multilayer carbon nanofiber(CNF) composites are designed to maximize the advantages of CNF, MnO 2 , and boron functional groups when applying functionalized porous CNF containing transition metal composites to supercapacitor electrodes. The PPMnB electrode exhibits a high specific capacitance (215 Fg−1 at 1 mAcm−2), good rate capability (83 % capacity retention at 20 mAcm−2), high energy density (23.5 Whkg−1 at 400 Wkg−1), and good cycling stability (only 6.0 % loss after 10,000 cycles at 1 mAcm−2). In addition, the asymmetric capacitor of the PPMnB(25) and PPB(0) used as the positive and negative electrode shows excellent electrochemical performance, including an excellent energy density of 46.3 Whkg−1 at a maximum voltage of 1.4 V. High electrochemical performance is achieved through the combined effects of the hierarchical porosity of CNF, high electrochemical activity of MnO 2 , and increased electrical conductivity by boron functional groups in each layer. [Display omitted] [ABSTRACT FROM AUTHOR]

In a pursuit to satisfy the rising energy demand, researchers to create novel, environmentally safe electrode materials for several energy storage devices. The electrochemical performance could be compromised as a result of the polymer binders employed in the electrode coating procedure. Binder-free electrode materials accelerate electron transport pathways by providing enough room to accommodate the active material's large volume changes during charging and discharging. Lower electronegativity of sulphur compared to oxygen provides increased flexibility in the structure of transition metal sulphides which makes them stand out as the promising candidates in the search for innovative electrode materials. Likewise, although PANI possess high conductivity and specific capacitance, it's ineffective to be used in the purest form for practical applications owing to its inability to retain the capacitance when it undergoes multiple charging/discharging cycles. In this work, we describe the development of binder-free Cu-Mn mixed sulphide and its nanocomposite with PANI on carbon fibre paper (CP) substrates. Characterization techniques such as XPS, FE-SEM along with elemental mapping helped in understanding the successful formation of the nanocomposite. In contrast to pure PANI and Cu-Mn mixed sulphide at the same current density in a neutral 1 M Na 2 SO 4 electrolyte, the composite of Cu-Mn mixed sulphide and PANI demonstrated an enhanced areal capacitance of 550.95 mF cm−2 at 1 mA cm−2. Incorporating PANI with Cu-Mn mixed sulphides has not only improved their capacitance but also reduced the rate at which pristine PANI's capacitance degrades when subjected to a greater number of charge/discharge cycles which is reflected in the enhanced capacity retention property of the nanocomposite, wherein the composite maintained 99.02% of its original capacitance at a current density of 10 mA cm−2 than of pure PANI on CP substrates. [Display omitted] [ABSTRACT FROM AUTHOR]

Porous structures grown in situ increase the electrode contact area with the electrolyte, reduce ion diffusion distance, and enhance electrode material electrochemical properties. In this paper, we have adopted a dual-channel electrodeposition strategy with simultaneous electrodeposition and phosphorylation to construct metal-semiconductor contact heterostructures by depositing Ni@NiCo phosphate microspherical nanostructures directly on a copper foam (CF) (Ni@NiCoP/CF) framework at room temperature. The results show that Ni@NiCoP/CF has excellent electrochemical performance with a high specific capacity of 200 mAh g –1 at 1 A g –1, 147.2 mAh g –1 at 20 A g –1 and 93.6 % after 5000 cycles, showing excellent ration performances and cycling stability. In addition, the hybrid supercapacitor composed of Ni@NiCoP/CF as the positive electrode and activated carbon as the negative electrode achieves a high energy density of 48.7 Wh kg−1 at 874 W kg−1 and has excellent cycling stability with 113.23 % capacity retention after 30,000 charge/discharge cycles at a high current density of 10 A g –1. This study serves as a guide for the development of high-performance capacitor cathode materials with high electrochemical activity and capacity. [ABSTRACT FROM AUTHOR]

Abstract: Graphene films (G films) were obtained by direct vacuum filtration of a highly dispersed graphene suspension (G suspension) on filter paper. After the complete removal of the filter paper, the stand-alone G films were directly used as electrodes for supercapacitors, without any binder or electrochemical active additives. The thicknesses of the G films were controlled by varying the volume of filtrated G suspension. The stable G suspension was prepared by chemically reducing the graphite oxide together with the aryl diazonium salt solution. A small amount of charged sulphonate groups introduced by this process can effectively prevent the graphene nanosheets from aggregating during reduction. It was found that the best performing thin G film exhibited a high capacitance of 117.9 F/g at a high scan rate of 1000mV/s, with no deterioration observed after 15,000 cycles at this scan rate, and its energy density reached 16.38 Wh/Kg when the highest power density was 58.97 KW/Kg at the high scan rate. [Copyright &y& Elsevier]

In this paper, a porous free-standing nitrogen-doped graphene (NG) film for high energy density supercapacitor is prepared via a facile hydrogel strategy. Taking advantage of the hydrogel behavior together with the mechanical stability of GO sheets, an interconnected macro-porous nitrogen-doped free-standing film is constructed. The nitrogen doping structure ensures sufficient pseudocapacitance and conductivity of the film, while the macro-porous structure favors fast ion adsorption. When assembled in a symmetric two-electrode supercapacitor, not any conductive agent or binder is used. The free-standing NG film shows specific capacitance of 455.4 F g−1 based on the mass of whole electrode, while no capacitance loss after 5000 cycles. Furthermore, an asymmetric supercapacitor is assembled with this NG film as negative electrode and a macro-porous graphene/polypyrrole composite film synthesized using the similar strategy as positive electrode. An energy density of 34.51 Wh kg−1 at a power density of 849.77 W kg−1 is obtained, suggesting great potential of this film for application in energy storage field. [ABSTRACT FROM AUTHOR]

This paper describes a hybrid capacitor based on identical activated carbon (AC) electrodes and the 1-ethyl-3-methylimidazolium selenocyanate, [EMIm][SeCN], liquid salt as redox-active electrolyte. [EMIm][SeCN] is a fluorine-free ionic liquid (IL) which combines good charge and mass transport properties (σ = 25 mS cm−1 and η = 17 mPa s−1), as well as redox activity originating from the pseudohalide anion. Owing to the impact of the SeCN−/(SeCN) 2 redox couple, the AC/AC capacitor based on this electrolyte displays remarkable discharge (from 1.5 V) capacitance of 49 and 56 F g−1 (expressed per total active mass of electrodes) using aluminum and stainless steel (SSt) current collectors, respectively. Although higher capacitance values were displayed for the hybrid capacitor with SSt components, more advantageous E 0 localization for cell hybridization was observed when using Al current collectors. [ABSTRACT FROM AUTHOR]

In this paper, thin-walled 3D alcoholic hydroxyl functionalized partially reduced graphene oxides (APRGs) with high alcoholic hydroxyl content are easily prepared using graphene oxide (GO) dispersions via an eco-friendly one-step hydrothermal method. A small amount of Tris(hydroxymethyl)methyl aminomethane (THAM) is used as the alcoholic hydroxyl source, 3D structural modifier, nitrogen doping and reducing agents, at the same time. The externally introduced alcoholic hydroxyl groups cannot only improve the wettability of the APRGs samples, but also increase their specific capacitances. Most importantly, because the chemical nature of the alcoholic hydroxyl group is stable, it imparts the APRGs sample excellent cycle stability. The APRG-30 sample with high alcoholic hydroxyl content (9.34 at%) in the wet state exhibits a high specific capacitances of 260.2 F g-1 at 0.3 A g-1 in 6 M KOH aqueous electrolyte with an excellent rate capability of 89.8% at 10 A g-1. In particular, a specific capacitance increasing of 4.7% after 10,000 cycles at 10 A g-1 is obtained, demonstrating its outstanding long-term cycle stability. These results imply that the APRG-30 sample is suitable for use as supercapacitor electrode materials. • APRGs samples are successfully prepared by a one-pot hydrothermal method. • APRGs samples have a thin-walled 3D porous structure. • APRGs samples have high content of alcoholic hydroxyl group. • The APRG-30 based electrode exhibits a high specific capacitance of 260.2 F g-1. • The APRG-30 based symmetric supercapacitors present outstanding long-term cycle stability. [ABSTRACT FROM AUTHOR]

This paper reports on the long-term performance of electrochemical capacitor operating in 1 mol⋅L−1 KI solution subjected to two ageing protocols, i.e., galvanostatic cycling and potentiostatic floating. Ageing tests have been performed at similar voltage conditions (1.5 V), estimated from the coulombic and energetic efficiency as well as the self-discharge analysis. The end-of-life criterion (80% of initial capacitance retained) was the same for both procedures. The influence of the ageing methodology on the structural and textural changes in electrode material has been discussed. The results obtained allowed for failure mechanisms description in the floating tests in comparison to traditional galvanostatic cycling. It has been stated that de facto the structural changes do not diminish the long-time performance. Notwithstanding, it has been found that galvanostatic cycling has a definitely stronger and detrimental impact on the carbon structure. Interestingly, both ageing methodologies affect the electrode porosity in a similar way. The nitrogen adsorption measurements indicated that the specific surface area decrease correlates with the capacitance fade. Changes observed in the pore size distribution allowed us to conclude that the porosity of both electrodes is blocked by adsorbed and/or deposited species. It looks that floating causes higher pore clogging especially for positive electrode. • Different ageing mechanism was proposed for capacitor failure during cycling and floating. • Decrease of electrode porosity after ageing tests was significant especially for (+) electrodes. • Iodide species were confined in both electrodes. • Electrochemical capacitor with a redox active electrolyte (I-/I 2) shows moderate self-discharge for optimal voltage. [ABSTRACT FROM AUTHOR]

Abstract In this paper, hierarchical Co 3 O 4 -SnO@SnO 2 nanostructures flexible supercapacitor electrodes were fabricated by hydrothermal routine. Owing to the introduction of Co 3 O 4 as well as a cleverly PN junction hierarchically skeleton, the Co 3 O 4 -SnO@SnO 2 electrode presents a structure of nanospheres covered by nanoparticles, offering a low internal resistance (0.6 Ω) and high electrical conductivity. Without the use of a binder and complicated manufacturing process, the hierarchical nanostructures can be directly used as the working electrode in the three-electrode system. In addition, the electrode demonstrates a high specific capacitance (1.056 F cm−2 at 1 mA cm−2) and excellent stability (only 8.5% was lost in initial specific capacitance at 1 mA cm−2 after 2000 cycles). Therefore, the hierarchical Co 3 O 4 -SnO@SnO 2 nanostructures provide an opportunity for the coordinated development of novel energy density and power density of supercapacitor. Highlights • Metal oxides are introduced into the skeleton by a cleverly PN junction hierarchical nanostructure. • Built-in electric field in hierarchical nanostructure can reduce the electrode internal resistance to 0.6 Ω. • The hierarchical nanostructure electrode exhibits excellent discharge time, good cycle stability and higher capacitance. [ABSTRACT FROM AUTHOR]

Abstract Electrochemical capacitor (EC) technology has advanced considerably since the first products were commercially introduced more than forty years ago. Products today, on both a mass and a volume basis, store considerably more energy and deliver significantly higher power than did the earlier ECs. Plus products today are available with much higher ratings. Today modules containing many kF-sized ECs are used to store energy in a wide variety of industrial applications. Worldwide, fifty companies are estimated to manufacture EC products. This paper reports initial electrical characteristics of eight popular, state-of-the-art electrochemical capacitor cells. Large-signal, small-signal, and functional-test performance is compared among these ECs. A goal was to identify fundamental strengths of each of the eight technologies as expressed by the eight samples evaluated. [ABSTRACT FROM AUTHOR]

The concept of electrochemical capacitance comprises both double-layer grounded capacitive (non-faradaic charging) and pseudocapacitive (faradaic charging) behaviours, as has been recently demonstrated [1–3]. In this paper, we demonstrate that nanostructured compounds possessing electrochemical capacitance can be used to design suitable interfaces for label-free biosensing applications, which, moreover, do not require a redox probe to be added to biological samples before assaying. This is possible when the capacitive transducer layer of the biosensor device is kept within an appropriate length scale (for instance, thicknesses lower than 10 nm) in which mesoscopic electrochemical properties prevail. Hence, we demonstrate how the capacitive signatures of Prussian Blue nanostructured films can be envisioned as transducer signals in biosensor devices in general, going beyond traditional redox monolayers, using aqueous electrolytes. This approach is illustrated using electroactive films made of Prussian Blue nanoparticles and modified with appropriate receptors, which successfully and specifically detected interleukin-6, a small biomarker, with a limit of detection of 5.6 ± 0.3 ng mL−1. In summary, the application of Prussian Blue pseudocapacitive properties in label-free biosensor devices were demonstrated as a proof-of-concept of how such applications can be engineered. [ABSTRACT FROM AUTHOR]

Abstract In recent years, the rapid development of portable equipment and flexible wearable devices urgently requires supercapacitor electrode material with high volumetric capacitance. Ti 3 C 2 T x , a member of MXenes family, is one of the most promising supercapacitor electrode material candidates. However, how to further enhance the volumetric capacitance of the Ti 3 C 2 T x is still a great challenge at present. In this paper, a simple and eco-friendly method is presented by preparing flexible Ti 3 C 2 T x supercapacitor electrode using self-assembly of few-layer Ti 3 C 2 T x followed by alkalinizing and annealing treatment. The alkalinized and annealed Ti 3 C 2 T x film (denoted as ak-Ti 3 C 2 T x film-A) exhibits an ultrahigh volumetric capacitance of 1805 F cm−3 at 1 A g−1, and an impressive cycling stability up to 98% capacitance retention after 8000 cycles. The significant improvement in volumetric capacitance performance is mainly due to the increase of redox-active sites exposed by removal of surface terminal groups during alkalinizing and annealing, and the enhancement in conductivity of the film owing to the annealing induced increase of crystalline order. Moreover, the supercapacitor fabricated with ak-Ti 3 C 2 T x film-A displays an outstanding volumetric energy density of 45.2 Wh L−1. This work provides a new strategy for design and development of other MXenes-based materials with high volumetric capacitance performance for flexible and highly integrated supercapacitors. Graphical abstract Image 1 Highlights • ak-Ti 3 C 2 T x film-A by using self-assembly of Ti 3 C 2 T x followed by alkalinizing and annealing treatment is presented. • ak-Ti 3 C 2 T x film-A show a significant enhancement in volumetric capacitance performance. • The symmetric supercapacitor fabricated with ak-Ti 3 C 2 T x films-A displays an ultrahigh volumetric energy density. [ABSTRACT FROM AUTHOR]

• A novel MoS 2 is prepared through facile hydrothermal method. • An interesting nano-worm based aggregates morphology and crystallinity of MoS 2 is obtained. • Excellent electrode material along good specific capacitance and high energy density is attained. • MoS 2 is believed to be a potential electrode material for asymmetric supercapacitor as shown in manuscript. Nowadays, supercapacitors and batteries are trending electrochemical energy storage devices. However, their low energy density and uncertain power density limited their applications, respectively. Recently, the latest innovation in energy storage devices, called hybrid supercapacitors, has appeared as an eventual energy storage device that demonstrates a hybrid storage mechanism of both supercapacitors and batteries. In this work, MoS 2 has been prepared by the facile hydrothermal method, characterized by different techniques, and applied as an electrode in supercapacitors and supercapatteries. The XRD patterns and EDX confirm the successful synthesis of MoS 2 with an average crystallite size of 62.25 nm, while the SEM images show the randomly oriented nanoworms of MoS 2. The XPS spectrum depicts the presence of variable oxidation states of molybdenum (Mo4+and Mo6+) in the MoS 2. The electrochemical performance shows that the highest specific capacitance and specific capacity reached 1866.66 F/g and 1119.99 C/g, respectively, at a scan rate of 5 mV/s for MoS 2. The asymmetric supercapacitor device is made from (Graphite/MoS 2) using as a working electrode and activated carbon as a cathode, which are separated by filter paper. Furthermore, the Dunn's model is utilized to evaluate of capacitive and battery mechanisms and shows the dominant role of diffusive and surface-controlled developments at low and high scan rates, respectively, owing to the change in diffusion time of electrolyte species. The fabricated device shows an energy density and power density of 103.51 Wh/kg and 3807.59 W/kg at a current density of 1 and 7 A/g, respectively, with 93.52% capacity stability and 99.8% coulombic efficiency. This excellent performance of MoS 2 is believed to be a potential electrode candidate for asymmetric supercapacitor applications. [ABSTRACT FROM AUTHOR]

Hierarchical microstructures are unique characteristic in various natural organisms with optimized functions. The anisotropic structure offers low-tortuosity with hierarchical porosity, providing sufficient multifunctional channels for mass/ion transport, which is desirable for the design of low temperature tolerant energy storage device. Conductive hydrogels are elastic crosslinked polymeric networks that adaptable in various environmental conditions, exhibiting promising potentials for energy storage and conversion devices. However, conventional hydrogel based energy storage devices would inevitably freeze at low temperatures (< 0 °C) due to the high content of solvent water, which fundamentally lead to the fatal deterioration of the ionic conductivity and limit their applications in extreme conditions. In this paper, a flexible solid-state supercapacitor was prepared using wood inspired anisotropic polyvinyl alcohol (PVA) hydrogel electrolyte via directional freezing strategy. The hierarchical channels are tuneable by varying the concentrations of PVA solutions. The ionic conductivity of hydrogel electrolyte was significantly enhanced in the full temperature range attributing to the hierarchical microstructures, specifically, the microscale vessel-like directional ion transport channels coupled with nanopores on the inner walls. With co-mixing of dimethyl sulfoxide/ethylene glycol as the organic solvent medium, the assembled solid-state supercapacitors exhibited excellent electrochemical performance of 65% capacity retention at -30 °C, remarkably flexibility and decent cycling stability of 75% capacity retention after 5000 cycles at -20 °C. This work demonstrates that the hierarchical anisotropic channels and organic anti-frozen additive could significantly enhance the low temperature performance of solid-state supercapacitors, opening up new strategy for advancing energy storage devices at extreme conditions via the bio-mimicked optimization of microstructure and electrolyte composition. [ABSTRACT FROM AUTHOR]

Flexible asymmetric supercapacitors (FASCs) have attracted increasing interest in portable and wearable electronics. The practical application of FASCs in high energy density devices is limited by their low specific capacity, which can be effectively addressed by designing electrode materials hierarchically on the micro-nanoscale. Herein, well-defined 3D porous hierarchical CuCo 2 O 4 @carbon quantum dots (CQDs) and Fe 2 O 3 @CQDs architectures are rationally synthesized through a simple CQDs-induced hydrothermal self-assembly technique. Both of the as-prepared CuCo 2 O 4 @CQDs and Fe 2 O 3 @CQDs electrodes exhibit improved specific capacity, desirable rate capability and complementary potential range. A FASC (CuCo 2 O 4 @CQDs//Fe 2 O 3 @CQDs) on graphite paper delivers a high operation voltage of 1.55 V, an energy density of 39.5 Wh kg −1 at 1203.7 W kg −1 , and long cycling lifespan. The excellent performance is ascribed to the good electronic conductivity with the assistance of CQDs and their unique 3D mesoporous structures with extraordinary specific surface area, which could provide fruitful active sites for electrochemical reactions. The newly developed FASC based on the Faradaic-type electrodes is inspiring, and would be promising for the applications in wearable electronic devices. [ABSTRACT FROM AUTHOR]

In this paper, we explore the successful hydrothermal approach to make Co 3 (PO 4 ) 2 ·4H 2 O/GF micro-flakes composite material. The unique sheet-like structure of the graphene foam (GF) significantly improved the conductivity of the pristine Co-based material, which is a key limitation in supercapacitors application. The composite electrode material exhibited superior capacitive conduct in 6 M KOH aqueous electrolyte in a 3-electrode set-up as compared to the pristine cobalt phosphate material. The material was subsequently adopted as a cathode in an asymmetric cell configuration with carbonization of Fe cations adsorbed onto polyaniline (PANI) (C-Fe/PANI), as the anode. The Co 3 (PO 4 ) 2 ·4H 2 O/GF//C-FP hybrid device showed outstanding long life cycling stability of approximately 99% without degradation up to 10000 cycles. A specific energy density as high as 24 W h kg −1 , with a corresponding power density of 468 W kg −1 was achieved for the device. The results demonstrated the efficient utilization of the faradic-type Co 3 (PO 4 ) 2 ·4H 2 O/GF composite along with a functionalized carbonaceous electric double layer (EDL)-type material to produce a hybrid device with promising features suitable for energy storage applications. [ABSTRACT FROM AUTHOR]

Oxygen functional groups are one of the most important subjects in the study of electrochemical properties of carbon materials which not only can change the wettability, conductivity and pore size distributions of carbon materials, but also can occur redox reactions. In the electrode materials of carbon-based supercapacitors, the oxygen functional groups have been widely used to improve the capacitive performance. In this paper, we systematically analyzed the reasons for the increase of the capacity that promoted by oxygen functional groups in the charge∕discharge cycling tests and the mechanism how the pseudocapacitance is provided by the oxygen functional groups in the acid/alkaline aqueous electrolyte. In addition, we in more depth discussed the effect of the oxygen functional groups in electrochemical impedance spectroscopy. [ABSTRACT FROM AUTHOR]

This paper addresses the development of an electrically conductive flexible nanocomposite membrane by the incorporation of an optimum amount of pyrrole into tetraethyl orthosilicate crosslinked poly(vinyl alcohol). The incorporated pyrrole underwent in-situ chemical oxidation in presence of iron(III) chloride. The resulting membrane was subjected to various techniques to understand its physico-chemical properties. The nanocomposite membrane demonstrated an excellent electrical conductivity of 4.56 S cm −1 with a desired flexibility. The electrochemical properties of the electrode membrane were systematically investigated using cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The resulting electrode membrane exhibited a specific capacitance as high as 484 F g -1  at a current density of 0.1 A g −1 with an excellent cycle life stability. Based on its excellent electrochemical performance, we have developed both interdigital micro-supercapacitor and sandwich-type supercapacitor devices; among these, the interdigital micro-supercapacitor exhibited a specific capacitance of 51.42 F g -1  at 0.05 A g −1 , which is two times higher than that of sandwich-type supercapacitor (25.49 F g −1 ). Furthermore, the method adopted here for the fabrication of an interdigital micro-supercapacitor device can be easily applied to large-scale fabrication of electrically conductive membranes and opens up new opportunities for flexible lightweight energy storage devices. [ABSTRACT FROM AUTHOR]

This paper deals with the synthesis of two new families of cationic poly(ionic liquid)s (PILs). The first one is obtained by free radical copolymerization of 1-[2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl]-3-methylimidazolium bis(trifluoromethylsul-fonyl)imide with poly(ethylene glycol) methyl ether methacrylate, while the second one by chemical modification of poly(epichlorohydrin- co -ethylene oxide) via quaternization with N-methylimidazole and subsequent ion exchange with lithium bis(trifluoromethylsulfonyl)imide. Both PILs demonstrated T g below 0 °C, bulk ionic conductivities in anhydrous state in the range of 8.4 × 10 −7 -1.5 × 10 −5  S/cm (25 °C) and electrochemical stability of 3.1–3.4 V (25 °C). These PILs were further applied in the construction of symmetric truly all-polymer pseudo-supercapacitors. The first PIL, possessing high ionic conductivity of 1.5 × 10 −5 S/cm at 25 °C, was chosen to play the role of separator, while the second one, demonstrating an ability to form good coatings, was used for the preparation of the thin electrode films via vapor phase polymerization of 3,4-ethylenedioxythiophene (EDOT), pyrrole (Py) or 3-methylthiophene (3 MT) in its solution. The varying of the electroactive polymer's nature allowed for the optimization of the devices parameters resulting in the assembly of PPy+PIL2/PIL1/PPy+PIL2 pseudo-capacitor showing best characteristics in terms of specific capacitance (2.8 and 7.0 F/g at 30 mV/s scan rate and 25 and 70 °C, respectively), energy and power (E max  = 1.39 Wh/kg and P max  = and 286 W/kg at 70 °C and 30 mV/s scan rate). Such flexible device was cycled for 1000 cycles with 96% of capacitance retention at a voltage up to 1.2 V at 25 °C. To be clear, this level of electrochemical performance is not as high as other systems that have been reported in the literature. However, we emphasize that the novelty of these proof-of-concept experiments is the fact that they demonstrate the possibility, for the first time and to the best of our knowledge, to create pseudo-supercapacitors based on polymeric materials alone, with no low molecular weight components. This is significant because it represents a path to highly efficient, lightweight and safe devices requiring no sealing and tolerant of a much broader range of application conditions (reduced pressures, high temperature, etc.). [ABSTRACT FROM AUTHOR]

Porous noble metal nanostructures with highly porous and extended surface areas are a long-desired target in both industry and academia. Among them, noble metal aerogels have emerged as state-of-the-art catalysts and these exceptional structures play crucial roles in various applications such as catalysis, sensors, etc. Until now, various methods have been published for the creation of noble metal aerogels, while their development and synthesis suffer from time-consuming multistep procedures. In this paper, we present an efficient method for the creation of porous three-dimensional network of Pd aerogel by a self-assembly process. This method offers several advantages over other methods such as being one-pot synthesis, simplicity and fast. Pd aerogel is synthesized by reducing H 2 PdCl 4 in the presence of sodium carbonate using glyoxylic acid monohydrate as a reductant agent in a short time followed by supercritical drying. The Pd aerogel serves as an anode catalyst for the electrooxidation reaction of ethanol and exhibits superior electrocatalytic activity and durability compared to Pd/C catalyst. We believe that the Pd aerogel synthesized via this method is a promising catalyst for direct ethanol fuel cells (DEFCs) and will also open large opportunities for other applications. [ABSTRACT FROM AUTHOR]

Lithium manganese spinel, LiMn 2 O 4 (LMO), is a well-established active material for batteries, in which charge is stored via a two-stage insertion of Li + that manifests with coupled current peaks or voltage plateaus under voltammetric or galvanostatic conditions, respectively. The charge–discharge kinetics for LMO are significantly enhanced when the oxide is expressed in a nanoscale form, for example as an ultrathin coating of nanocrystallites at the surfaces of a 3D carbon substrate, such as fiber paper–supported carbon nanofoams (CNFs). In addition to expressing well-defined “battery-like” Li + -insertion peaks between ∼0.6 and 1 V vs . Ag/AgCl when cycled in aqueous lithium sulfate, LMO@CNF electrodes exhibit a pseudocapacitance envelop at more negative potentials (∼0.2–0.6 V). The pseudocapacitive character of LMO@CNF is further verified when cycled in aqueous sodium sulfate, where a broad capacitance envelop dominates the voltammetric response over the entire potential range at a current density an order of magnitude greater than expected for double-layer capacitance. Thus, the LMO@CNF electrode provides a prime example where multiple distinct charge-storage mechanisms are expressed in a single material. Herein, we apply voltammetry and impedance-based methods to deconvolve the respective contributions of double-layer capacitance, surface-based pseudocapacitance, and battery-like Li + insertion. The use of power-law analysis provides a general assignment of transport dynamics, while projecting impedance data as 3D Bode-style representations provides key mechanistic information regarding the time/frequency–potential response of LMO@CNF electrodes. [ABSTRACT FROM AUTHOR]

ZnMn 2 O 4 is regarded as one of the potential anode materials for lithium-ion batteries (LIBs), due to its high theoretical specific capacity (784 mAh g −1 ). Unfortunately, the bulk ZnMn 2 O 4 presents an inferior electrochemical performance resulting from the large volume change during the charge-discharge process. In this paper, we report the synthesis and electrochemical properties of ZnMn 2 O 4 nanoparticles (NPs) that are homogeneously distributed in connective network porous carbon nanofibers wrapped by reduced graphene oxide sheets. The distinctive structure of this composite not only provides enough voids to storage Li-ions and buffer the volume expansion of the ZnMn 2 O 4 NPs, but also offers a continuous conducting network for Li-ion and electron transportation, resulting in significantly improved electrochemical performances. As binder-free electrodes for LIBs, an optimized ZnMn 2 O 4 @rGO-CNFs sample exhibits a reversible capacity of 1142 mAh g −1 at 100 mA g −1 over 100 cycles, and a stable capacity of 659 mAh g −1 after 1000 cycles at a large current density of 2000 mA g −1 , enabling ZnMn 2 O 4 a promising electrode candidate for LIBs. [ABSTRACT FROM AUTHOR]