Charge Storage Sites Research Articles

Controllable synthesis induced through cationic surfactant with two long hydrophobic chains from individual carbon spheres to 3D carbon frameworks for high performance supercapacitors

A one-step sol-gel synthesis of porous carbon micro/nanospheres (PCMNSs) through cationic surfactant with two long hydrophobic chains was reported to realize the tunable synthesis of carbon nanospheres with interconnected structures between the shell and shell. The unique pore structure of PCMNSs endows the material with efficient electrochemical energy storage performance. The abundant macropores and mesopores of PCMNSs can promote the transport of electrolyte by reducing diffusion distances and provide sufficient active sites for effective charge storage and the charge transfer can be greatly increased by the interconnected channel structure among the carbon spherical shells. By adjusting the amount of surfactant and the consumption of ethanol, the controllable synthesis of individual carbon spheres to three-dimensional carbon frameworks were successfully realized. The results showed that the representative sample A-PCMNSs-0.6-35 had excellent supercapacitive performance, excellent electrochemical specific capacitance (242 F g−1 at 1 A g−1), great capacitance retention (170 F g−1 at 100 A g−1) and superior cycle stability (93% at 10 A g−1 after 5000 cycles).

Multiple anionic Ni(SO4)0.3(OH)1.4 nanobelts/reduced graphene oxide enabled by enhanced multielectron reactions with superior lithium storage capacity

The multielectron reaction materials for lithium-ion batteries are interesting charge storage hosts for next-generation high-energy–density anodes. As a class of multiple-anion transition metal compounds (MATMCs), the layered Nickel hydroxide sulfate (NiSH) nanobelts integrate positive-charged cations and intercalated anions, can be expected to construct the advanced high-energy–density materials, but have not yet reported. Herein, the layered NiSH nanobelts grafting on the 3D porous reduced Graphene oxide (rGO) nanosheets were fabricated for the first time as the negative electrode of lithium-ion battery (denoted as NiSH@rGO) by a one-pot hydrothermal approach. As expected, the NiSH@rGO composite delivers a superior initial discharge capacity (1060 mAh g−1 at 200 mA g−1 after 230 cycles) and an exceptional rate capacity (991 mA g−1 at 2000 mA g−1). Through in-situ XRD, ex-situ SEM and TEM, we showed that the outstanding performance of NiSH@rGO anode originate from multielectron reaction mechanism and prominent structural, which render expose more active sites for charge storage, increase the surface wettability of anode, accelerate electron/ion diffusion and ensure the stability of the structure. Above that, it showed excellent lithium storage capacity and high-rate performance. Furthermore, a full cell composed of the NiSH@rGO anode and LiFePO4 cathode displays an impressive capacitance and low-capacity decay rate. Our findings fundamentally and experimentally provide insights into the multi-anionic compounds for markedly enhancing the performance of the multi-electron anodes for advanced high-capacity lithium-ion battery.

A bipolar organic molecule toward a universal pseudocapacitive cathode for stable dual ion charge storage

Organic molecules are promising electrode materials for green and sustainable rechargeable electrochemical energy storage due to their tunable theoretical capacity and environmental friendliness. However, the commercialization of organic electrode materials is impeded by high solubility in electrolytes and inherently low electronic conductivity. Herein, a series of bipolar organic molecules, [5,10,15,20-tetra(ethynyl)porphinato] M(II) (MTEPP, M= Cu, Zn, Mg, 2H), is proposed as new cathode for highly stable dual ion charge storage. The stacking property of the porphyrin molecules is significantly influenced by complex ions and the mixed valence state of cation (Cu+ and Cu2+) renders better charge storage performance in functionalized porphyrin cathode. Reversible capacity of 219 mAh g−1 is obtained for CuTEPP cathode based on a four-electrons transfer and it can be stably cycled up to 1000 times in lithium based organic batteries. Ex-situ spectroscopies as well as simulation studies evidence the multiple electron transfer and the charge storage sites. Highly reversible capability (> 160 mAh g−1) and stable cyclability (> 300 cycles) is also achieved as cathode in both sodium and potassium based organic cells. This study offers a new approach for developing ultrastable and universal organic cathode for electrochemical energy storage.

Controlled nanostructure of a graphene nanosheet‐TiO 2 composite fabricated via mediation of organic ligands for high‐performance Li storage applications

A graphene nanosheet-TiO2 nanoparticle composite (L-GNS-TiO2) was prepared for an application as a high-performance lithium storage device (or lithium-ion battery anode). The composite features a well-defined hybrid structure of GNS and homogeneously distributed anatase TiO2 nanoparticles due to nanoparticulation and modification by organic ligands (polyacrylic acid, tartaric acid, and diethylene glycol). Despite its low overall carbon content (~8.4%), the L-GNS-TiO2 composite-based anode exhibited highly reversible lithiation/delithiation (Coulombic efficiency >97%), excellent capacity retention (206 (92%) and 331 (147%) mAh g−1 after 50 and 450 cycles, respectively, at 0.15 A g−1) and decent rate capability (164 mAh g−1 at 0.75 A g−1). In addition, the stable morphology/structure of the composite after lengthy cycle tests reflected its mechanical robustness and electrochemical reversibility. The excellent performance of L-GNS-TiO2 was attributed to the enhanced electronic conductivity, retained charge storage sites, and a short Li+ diffusion pathway enabled by the unique composite structure constructed through optimized ligand mediation. Highlights A graphene nanosheet-TiO2 nanoparticle composite (L-GNS-TiO2) was prepared for Li storage applications. L-GNS-TiO2 possesses a structure containing uniformly distributed anatase TiO2 nanoparticles on GNS due to optimized mediation and nanoparticulation by organic ligands. L-GNS-TiO2 exhibits enhanced conductivity, retains charge storage sites, and facilitates Li+ transport/charge transfer. Excellent cycle stability (>100% capacity retention, 331 mAh g−1) and Coulombic efficiency (>99%) were realized after 450 cycles at 0.15 A g−1. Decent rate capability was achieved with a high capacity (164 mAh g−1) at 0.75 A g−1.

Amorphous phase induced high phosphorous-doping in dandelion-like cobalt sulfides for enhanced battery-supercapacitor hybrid device

Abstract Phosphorus (P) doping is considered to be an effective method for regulating the physicochemical properties of transition metal sulfides (TMSs) through triggering lattice distortion, improving electronic conductivity, and providing additional active sites for charge storage. However, the large P atom makes it difficult to be incorporated in TMSs, particularly at high doping level. Herein, we develop an amorphous phase induced strategy for efficient P doping in dandelion-like cobalt sulfides, reaching a high concentration of 18 at%. The obtained P-CoS1.097-6 displays remarkable specific capacity of 536 C g−1 and 502 C g−1 at the current density of 5 A g−1 and 20 A g−1, respectively, due to the enhanced electrical conductivity and rapid ion diffusion. This performance is higher than that of P-CoS1.097-48 with a low doping level of 7 at% (400 C g−1), the primeval Co1−xS-6 (345 C g−1), and CoS1.097-48 (335 C g−1). Based on P-CoS1.097-6 and activated carbon, the battery-supercapacitor hybrid (BSH) device delivers an electrochemical performance of 22 Wh kg−1 (energy density) and good stability with 88% capacity retained over 6000 cycles.

CF4 plasma-treated porous silicon nanowire arrays laminated with MnO2 nanoflakes for asymmetric pseudocapacitors

High energy density is a necessity of the electrochemical energy storage (EES) systems for practical application in many fields, including implantable devices, backup systems, sensors, and portable electronics. In the present work, we developed a simple and up-front method to achieve high energy- and power-density asymmetric pseudocapacitors (APCs) from silicon nanowires (SiNW)-laminated intrinsic pseudocapacitive two-dimensional (2D) nanoflakes. Initially, the impermeable SiNWs are treated with carbon tetrafluoride (CF4) plasma to form porous silicon nanowires (pSiNWs). 2D intrinsic pseudocapacitive MnO2 (2D MnO2) nanoflakes were decorated on the pSiNWs to fabricate core–shell-structured 2D MnO2/pSiNWs for high-energy APCs. The nanostructuring over the one-dimensional (1D) SiNWs via the plasma process and the 2D nature of the MnO2 nanoflakes simultaneously provided large active sites for charge storage and transport processes. As a result, the optimized 2D MnO2/pSiNW electrode material exhibited a specific capacitance of 311.89 F/g at an applied current density of 2 A/g and 100% coulombic efficiency at all current densities, with excellent cycling durability. To evaluate the actual cell applicability of the prepared core–shell electrode, APCs were designed using the 2D MnO2/pSiNWs as the positive electrode and activated carbon (C) as the negative electrode. The assembled APC showed a maximum energy density of 93.31 mWh/cm2 and a power density of approximately 1.51 mW/cm2, with a large operational voltage window (2.2 V) and capacitive retention of 89.5% over 10,000 cycles. The strategic construction of the 2D MnO2/pSiNWs and the extracted output demonstrated that the fabricated electrodes and/or devices are promising candidates for next-generation high-performance pseudocapacitors.

A new neodymium-phosphine compound for supercapacitors with long-term cycling stability.

A new neodymium-phosphine compound (Nd-(Ph)3P) was used for the first time as an electrode for supercapacitors and exhibited an extraordinary capacitance of 951 F g-1 at 0.5 A g-1 with a high capacitance retention of 96% after 10 000 cycles at 10 A g-1, which is the highest capacitance for rare earth based materials in SCs. Such an excellent performance might be due to the fact that this material can provide plenty of electron-active sites for charge storage and electrolyte diffusion can be efficiently promoted.

Modified sol-gel synthesis of Co3O4 nanoparticles using organic template for electrochemical energy storage

The demand for economic and efficient electrode for energy storage devices has been increased with the rapid advancements in the sustainable synthesis of active material. Herein, bioactive compounds as fuel for the synthesis of electrode material (Co3O4 NPs), were investigated. Functionalization of Co3O4 NPs via organic extract of Euphorbia cognata Boiss have not only revealed the rapid and efficient growth of active materials but also ensured an effective interaction between the fabricated electrode and electrolyte solution for charge storage reactions. The synthesized Co3O4 NPs were scrutinized for its optical, structural, compositional and chemical properties and then investigated by galvanostatic charge discharge, cyclicvoltammetry for determination of its energy storage potential. The fabricated electrode was tested at range of scan rates and current densities to evaluate its charge storage potential at different scan rates and current densities. The phytofunctionalized Co3O4 NPs offered a large accessible active sites for charge storage with capacitance of 103 Fg-1, a maximum energy density of 1.9 Whkg−1, and higher power density of 4.7 KWkg−1. Thus, we have demonstrated the sustainable fabrication of electrode for energy storage applications.

Flexible all-solid-state supercapacitor based on polyhedron C-ZIF-8/PANI composite synthesized by unipolar pulse electrodeposition method

In this work, the unipolar pulse electrodeposition (UPED) method is used to electrodeposit the conductive polyaniline (PANI) on the carbonized polyhedron zeolitic imidazole particles (C-ZIF-8). The composite film of C-ZIF-8/PANI coated on the flexible substrate stainless steel wire mesh (SSWM) offers large contact area between the electrode material and the electrolyte, which provides enough active sites for charge storage. The obtained flexible electrode exhibits efficient-specific capacity of 363 F g−1 with 300° stretching angle and excellent long-term cycling stability after 10,000 cycles at 5 mA g−1 in 1 M H2SO4 electrolyte. It is found that the flexible electrode shows obvious improvement in the electrochemical properties when it was bent or stretched. Asymmetrical all-solid-state supercapacitor device is fabricated by using polyvinyl alcohol (PVA) solid gel as electrolyte and separator, which shows general gravimetric capacitance of 147, 156, and 156 F g−1 with energy densities of 8.66, 9.16, and 9.16 W kg−1 at stretching angle of 0°, 120°, and 300°, respectively, and stable power density of 162.5 W kg−1 in the different conditions. It indicates that such a composite C-ZIF-8/PANI/SSWM is a favorable material for portable and flexible energy storage.

BN-codoped CNT based nanoporous brushes for all-solid-state flexible supercapacitors at elevated temperatures

Porous graphitic carbon based nanostructured electrodes offer several advantages for energy storage applications, such as, high specific surface area, high active charge storage sites, suitable ion diffusion and excellent charge transport properties. Vertically aligned carbon nanotubes (CNTs) have widely been exploited for electrochemical energy storage in different architectures using various electrolytes. However, a 3D carbon based electrode with high mechanical flexibility, reliability along with high charge storage capacity with solid-state electrolyte have yet to be realized. Here we develop a simple spray pyrolysis process for synthesizing nanoporous brush-like CNTs grown radially on individual carbon fibers of a carbon cloth (CC) substrate and simultaneously codoping with boron (B) and nitrogen (N) heteroatoms. The obtained BNCNT-CC electrodes were utilized to fabricate highly flexible all solid state symmetrical supercapacitor cells. The cells demonstrated high aerial capacitance of 106.8 mF/cm2 (~21.4 F/cm3), excellent flexibility without any performance degradation, attractive capacitance retention (86.4%) even after 5000 charge/discharge cycles, stability above room temperature, 741.8 mWh/cm3 specific energy at 25 W/cm3 specific power and conservation of 56% of its initial energy at specific power of 1 kW/cm3. The results are distinctly better than previous reports as a whole in terms of different performance parameters and are attributed to the unique nanoporous structure, low combined series resistance, BN-codoping and diffusion controlled modulation in electrochemical energy storage characteristics.

Fabrication of organic nanocomposite of polyaniline for enhanced electrochemical performance

Abstract Herein, we have developed a simple and facile technique at 210 °C to obtain nano-structured organic compounds, instead of making carbon dots at a relatively higher temperature. Taking the advantage of stable dispersion of organic nanostructures in an aqueous medium, composite of polyaniline has been developed and subsequently utilized as an active electrode material for supercapacitor application. This composite material confirms noteworthy enhancement in specific capacitance (779 F/g) and also divulges the attractive capacitance retention using three-electrode systems. The suitability of the materials for the solid-state device was tested with a prototype two-electrode device. The symmetric device exhibits 130 F/g gravimetric capacitance and 650 mF/cm2 areal capacitance. The improved performance in the specific capacitance is observed due to the generation of more active charge storage sites in the interfacial interaction of organic nanostructures and polyaniline in the composite. The cyclic stability of the symmetric device reveals excellent retention of 96% in specific capacitance over 5000 cycles.

Achieving Fast and Durable Lithium Storage through Amorphous FeP Nanoparticles Encapsulated in Ultrathin 3D P-Doped Porous Carbon Nanosheets.

Conversion-type transition-metal phosphide anode materials with high theoretical capacity usually suffer from low-rate capability and severe capacity decay, which are mainly caused by their inferior electronic conductivities and large volumetric variations together with the poor reversibility of discharge product (Li3P), impeding their practical applications. Herein, guided by density functional theory calculations, these obstacles are simultaneously mitigated by confining amorphous FeP nanoparticles into ultrathin 3D interconnected P-doped porous carbon nanosheets (denoted as FeP@CNs) via a facile approach, forming an intriguing 3D flake-CNs-like configuration. As an anode for lithium-ion batteries (LIBs), the resulting FeP@CNs electrode not only reaches a high reversible capacity (837 mA h g-1 after 300 cycles at 0.2 A g-1) and an exceptional rate capability (403 mA h g-1 at 16 A g-1) but also exhibits extraordinary durability (2500 cycles, 563 mA h g-1 at 4 A g-1, 98% capacity retention). By combining DFT calculations, in situ transmission electron microscopy, and a suite of ex situ microscopic and spectroscopic techniques, we show that the superior performances of FeP@CNs anode originate from its prominent structural and compositional merits, which render fast electron/ion-transport kinetics and abundant active sites (amorphous FeP nanoparticles and structural defects in P-doped CNs) for charge storage, promote the reversibility of conversion reactions, and buffer the volume variations while preventing pulverization/aggregation of FeP during cycling, thus enabling a high rate and highly durable lithium storage. Furthermore, a full cell composed of the prelithiated FeP@CNs anode and commercial LiFePO4 cathode exhibits impressive rate performance while maintaining superior cycling stability. This work fundamentally and experimentally presents a facile and effective structural engineering strategy for markedly improving the performance of conversion-type anodes for advanced LIBs.

Hydrothermal synthesis of rod‐like CoMoO4 and its excellent properties for the anode of lithium‐ion batteries

AbstractCoMoO4 has attracted extensive interest as an anode for lithium‐ion batteries due to its high theoretical capacity and low cost. Nevertheless, achieving controlled synthesis of CoMoO4 with definite morphology by simply adjusting a certain synthesis condition is a very meaningful topic. Here, rod‐like CoMoO4 formed by lamellar stacking was successfully synthesized through the control pH value of one‐step hydrothermal route, and its excellent electrochemical performance was investigated. The rod‐like CoMoO4 prepared at 190°C and pH = 7 has a high initial discharge capacity of 1,482.8 mAh/g at 200 mA/g. The discharge capacity of 1,041 mAh/g was maintained after 500 cycles, and the capacity retention was 70.2%. The improved electrochemical performance of rod‐like CoMoO4 can be attributed to the rod structures, which could shorten ion diffusion and electronic conduction pathway, provide more efficient charge storage sites, and alleviate the volume changes during Li + intercalation/deintercalation.

Multicomponent design of Fe3O4 nanosheet-based binder-free anodes with a special substrate for supercapacitors

Magnetite (Fe3O4) is a promising anode material for supercapacitors with aqueous alkaline electrolytes, whereas its sluggish kinetics and poor cycling stability are still challenges for practical applications. In this work, we design a Fe3O4 nanosheet-based binder-free anode derived from bicomponent Fe3O4–Fe nanosheets. The Fe3O4–Fe nanosheets are grown on a special stainless steel by an electrochemical method. Coated with graphene oxide, the Fe3O4–Fe nanosheets are subjected to electrochemical activation, through which the Fe3O4–Fe nanosheets and the surface of the special stainless steel are simultaneously oxidized into Fe3O4, and thus an integrated electrode with sufficient active sites for non-insertion charge storage is obtained. The graphene oxide is reduced to electrochemically reduced graphene oxide at the same time. When used as a binder-free anode in KOH solutions, the Fe3O4 nanohseets@electrochemically reduced graphene oxide electrode demonstrates pseudocapacitive behavior with a high capacitance (442.0 F g−1 at 3 A g−1), superior rate capability (430.9 F g−1 at 30 A g−1), and excellent cycling stability (98.9% retention after 25000 cycles). The asymmetric supercapacitor assembled with the Fe3O4 electrode exhibits a high energy density and good cycling stability. These results suggest the high potential of the rationally designed Fe3O4 nanosheet-based electrode as an integrated anode for supercapacitors.

Oxygen‐Deficient Homo‐Interface toward Exciting Boost of Pseudocapacitance

AbstractPseudocapacitors hold great promise as charge storage systems that combine battery‐level energy density and capacitor‐level power density. The utilization of pseudocapacitive material, however, is usually restricted to the surface due to poor electrode kinetics, leading to less accessible charge storage sites and limited capacitance. Here, tin oxide is successfully endowed with outstanding pseudocapacitance and fast electrode kinetics in a negative potential window by engineering oxygen‐deficient homo‐interfaces. The as‐prepared SnO2−x@SnO2−x electrode yields a specific capacitance of 376.6 F g−1 at the current density of 2.5 A g−1 and retains 327 F g−1 at a high current density of 80 A g−1. The theoretical calculation reveals that the oxygen defects are more favorable at homo‐interfaces than at the surface due to the lower defect formation energy. Meanwhile, as compared with the surface, the homo‐interface possesses more stable Li+ storage sites that are readily accessed by Li+ due to the occurrence of oxygen vacancies, enabling outstanding pseudocapacitance as well as high rate capability. This oxygen‐deficient homo‐interface design opens up new opportunities to develop high‐energy and power pseudocapacitors.

Two-Dimensional Layered Ultrathin Carbon/TiO2 Nanosheet Composites for Superior Pseudocapacitive Lithium Storage.

Intercalation of carbon nanosheets into two-dimensional (2D) inorganic materials could enhance their properties in terms of mechanics and electrochemistry, but sandwiching these two kinds of materials in an alternating sequence is a great challenge in synthesis. Herein, we report a novel strategy to construct TiO2 nanosheets into 2D pillar-layer architectures by employing benzidine molecular assembly as pillars. Then, 2D carbon/TiO2 nanosheet composite with a periodic interlayer distance of 1.1 nm was obtained following a polymerization and carbonization process. This method not only alleviates the strain arising from the torsion of binding during carbonization but also hinders the structural collapse of TiO2 due to the intercalation of the carbon layer by rational control of annealing conditions. The composite material possesses a large carbon/TiO2 interface, providing abundant active sites for ultrafast pseudocapacitive charge storage, thus displaying a superior high-rate performance with a specific capacity of 67.8 mAh g-1 at a current density of 12.8 A g-1 based on the total electrode and excellent cyclability with 87.4% capacity retention after 3000 cycles.

Aqueous lithium and sodium ion capacitors with boron-doped graphene/BDD/TiO2 anode and boron-doped graphene/BDD cathode exhibiting AC line-filtering performance

This paper reports our investigation of aqueous sodium and lithium ion capacitors (SIC and LIC, respectively) with a boron-doped graphene (BDG)/boron-doped diamond (BDD) cathode and BDG/nanocrystal BDD/TiO2 nanotube array anode. Vertically grown BDG nanosheets formed a porous three-dimensional morphology rich in charge storage sites with a short ion-diffusion distance and, high structural stability. In an aqueous NaCl solution, the potential windows are 0–1.1 V and −1.2–0 V for the cathode and anode, respectively, and their specific capacitances are 66.76 and 23.86 mF cm−2 at a current density of 3 mA cm−2, respectively. The devices exhibit high energy densities (SIC: 47.8 μWh cm−2; LIC: 33.9 μWh cm−2) and high power densities (SIC: 77.7 mW cm−2; LIC: 65.3 mW cm−2) at an operating voltage of 2.5 V. The SIC and LIC exhibited 100% coulombic efficiency over 10,000 cycles, with a capacitance retention of 99.5% and 97.8%, respectively, at a high current density of 90 mA cm−2 over 2000 cycles. Moreover, the capacitors exhibit effective AC current filtering over a wide frequency range of 50–10,000 Hz. The coulombic efficiencies and long-term stabilities of these aqueous devices are better at high current densities, and large energy densities are retained at high power densities, which is advantageous for high-frequency filtering.

Synthesis of Cyclopentadithiophene-Diketopyrrolopyrrole Donor-Acceptor Copolymers for High-Performance Nonvolatile Floating-Gate Memory Transistors with Long Retention Time.

Organic flash memories that employ solution-processed polymer semiconductors preferentially require internal stability of their active channel layers. In this paper, a series of new donor-acceptor copolymers based on cyclopentadithiophene (CDT) and diketopyrrolopyrrole (DPP) are synthesized to obtain high performance and operational stability of nonvolatile floating-gate memory transistors with various additional donor units including thiophene, thiophene-vinylene-thiophene (CDT-DPP-TVT), selenophene, and selenophene-vinylene-selenophene. Detailed analyses on the photophysical, two-dimensional grazing incident X-ray diffraction, and bias stress stability are discussed, which reveal that the CDT-DPP-TVT exhibits excellent bias stress stability over 105 s. To utilize the robust nature of CDT-DPP-TVT, floating-gate transistors are fabricated by embedding Au nanoparticles between Cytop layers as a charge storage site. The resulting memory devices reveal bistable current states with high on/off current ratio larger than 104 and each state can be distinguished for more than 1 year, indicating a long retention time. Moreover, repetitive writing-reading-erasing-reading test clearly supports the reproducible memory operation with reversible and reliable electrical responses. All these results suggest that the internal stability of CDT-DPP-TVT makes this copolymer a promising material for application in reliable organic flash memory.

Surface modification of reduced graphene oxide‐polyaniline nanotubes nanocomposites for improved supercapacitor electrodes

AbstractIn the present work, irradiation with high energetic ions has been used for surface, structural, and morphological modifications of reduced graphene oxide (RGO) and polyaniline nanotubes (PAniNTs) nanocomposites with a view to enhance their electrochemical performance as supercapacitor electrode. High‐resolution transmission electron microscope micrographs depict defect induced fragmented morphology with stable inner hollow tubes up to a fluence of 2.2 × 1012 ions cm−2, above which drastic degradation of PAniNTs is observed. Irradiation induced annealing effects and structural disorder at varied irradiation fluences have been investigated by micro‐Raman spectroscopy. Formation of shorter PAniNTs of higher surface area due to generation of ion irradiation induced defects and their reorganization results in increased Brunauer‐Emmett‐Teller specific surface area and porosity. Surface energy and wettability of the electrodes increase upon ion irradiation, which improves electrode‐electrolyte interaction at the interface. Surface free energy calculations indicate increased concentration of polar groups on the nanocomposite electrode surface upon irradiation. Electrochemical performance studies indicate enhancement in specific capacitance and cyclic stability from 448 F g−1 and 89% for unirradiated nanocomposite to 482 F g−1 and 92%,, respectively, for the nanocomposite irradiated at 2.2 × 1012 ions cm−2 fluence, which is attributed to the increased surface energy and porosity upon irradiation giving rise to increased electrochemically active sites for charge storage in the electrode.

Ultrathin carbon layer-encapsulated TiN nanotubes array with enhanced capacitance and electrochemical stability for supercapacitors

Although titanium nitride (TiN) is promising as electrode material in supercapacitors due to the high conductivity, there are drawbacks such as the brittleness, low capacitance, and chemical stability. Herein, three-dimensional (3D) carbon-encapsulated mesoporous titanium nitride nanotubes (TiN/C NTs) arrays with carbon doping are prepared by one-step nitridation of anodic TiO2 NTs with organic electrolyte as the carbon source. In TiN/C NTs, 3D carbon matrix not only serves as a protective layer and mechanical support to mitigate electrochemical oxidation and structural collapse, but also provides a conductive network to facilitate electron transfer. The capacitance retention of the TiN NTs electrodes increases from 72.5 to 92.2% for 4000 cycles after carbon encapsulating. Moreover, the carbon doping increases the active charge storage sites of the TiN NTs. The TiN/C NTs electrode exhibits a large volumetric capacitance of 121 F cm−3 (0.83 A cm−3), which is one time larger than that of the pure TiN NTs (69 F cm−3). The symmetrical all-solid-state device assembled with two TiN/C NTs electrodes and polyvinyl alcohol electrolyte shows a large volumetric capacitance of 8.3 F cm−3. This finding provides a good potential application in flexible supercapacitor.