Asymmetric Supercapacitors based on 1,10-phenanthroline-5,6-dione Molecular Electrodes Paired with MXene.

An efficient approach to increase the energy density of supercapacitors is to prepare electrode materials with larger specific capacitance and increase the potential difference between the positive and negative electrodes in the device. Herein, an organic molecular electrode (OME) is prepared by anchoring 1,10-phenanthroline-5,6-dione (PD), which possesses two pyridine rings and an electron-deficient conjugated system, onto reduced graphene oxide (rGO). Because of the electron-deficient conjugated structure of PD molecule, PD/rGOs exhibit a more positive redox peak potential along with the advantages of high capacitance-controlled behaviour and fast reaction kinetics. Additionally, the small energy gap between the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) leads to increased conductivity in PD/rGO. To assemble the asymmetric supercapacitor (ASC), a two-dimensional metal carbide, as known as MXene, with a chemical composition of Ti3C2Tx is selected as the negative electrode due to its exceptional performance, and PD/rGO-0.5 is employed as the positive electrode. Consequently, the working voltage is expanded up to 1.8 V. Through further electrochemical measurements, the assembled ASC (PD/rGO-0.5//Ti3C2Tx) achieves a remarkable energy density of 36.8 Wh kg-1. Remarkably, connecting two ASCs in series can power 73 LEDs, showcasing its promising potential for energy storage applications.

COF-Based Electrodes with Vertically Supported Tentacle Array for Ultrahigh Stability Flexible Energy Storage.

As an emerging porous crystal polymer, covalent organic frameworks (COFs) possess unique characteristics, such as high porosity, excellent stability, diverse topologies, designable open channels, and functional tunability. However, limited by the solid powder form, most COFs display low active site utilization and weak binding force with the current collector. In this pioneering research, we integrate redox-active COFs onto carbon fiber surfaces (AC-COFs) via strong covalent bridging. The 2,6-diaminoanthraquinone (DAAQ) pillars embedded on the carbon fiber surface are the key to precisely controlling the growth direction of COFs. The obtained tentacle-like array vertically supported on the surface of the carbon fiber can effectively induce charge transfer and prevent COFs from aggregating/collapsing. The strong covalent coupling and increase of accessible active sites contributed to the high specific capacitance of AC-COFs electrode (1034 mF cm-2). In addition, the COF-based flexible electrode retains an initial capacitance of 98% after 20000 charge-discharge cycles. The flexible all-solid-state symmetric supercapacitor is assembled by PVA/H2SO4 gel electrolyte with an areal capacitance of 715 mF cm-2. Besides, a red LED can be easily powered by three-bending AC-COFs//AC-COFs devices. The innovative synthesis strategy opens up new opportunities to develop high-performance flexible energy storage devices based on COFs.

Organic Small-Molecule Electrodes: Emerging Organic Composite Materials in Supercapacitors for Efficient Energy Storage.

Organic small molecules with electrochemically active and reversible redox groups are excellent candidates for energy storage systems due to their abundant natural origin and design flexibility. However, their practical application is generally limited by inherent electrical insulating properties and high solubility. To achieve both high energy density and power density, organic small molecules are usually immobilized on the surface of a carbon substrate with a high specific surface area and excellent electrical conductivity through non-covalent interactions or chemical bonds. The resulting composite materials are called organic small-molecule electrodes (OMEs). The redox reaction of OMEs occurs near the surface with fast kinetic and higher utilization compared to storing charge through diffusion-limited Faraday reactions. In the past decade, our research group has developed a large number of novel OMEs with different connections or molecular skeletons. This paper introduces the latest development of OMEs for efficient energy storage. Furthermore, we focus on the design motivation, structural advantages, charge storage mechanism, and various electrode parameters of OMEs. With small organic molecules as the active center, OMEs can significantly improve the energy density at low molecular weight through proton-coupled electron transfer, which is not limited by lattice size. Finally, we outline possible trends in the rational design of OMEs toward high-performance supercapacitors.

Heterogeneous Ni3S2@FeNi2S4@NF nanosheet arrays directly used as high efficiency bifunctional electrocatalyst for water decomposition.

Developing and designing bifunctional electrocatalysts are very important for the production of hydrogen from water electrolysis. The reasonable interface modulation can effectively lead to the optimization of electronic configuration through the interface electron transfer in the heterostructures and thus resulting in the enhanced efficiency. In this work, self-supported and heterogeneous interface-rich Ni3S2@FeNi2S4@NF electrocatalyst for overall water splitting was designed and prepared through a controllable step-wise hydrothermal process. Density functional theory calculations suggest that heterogeneous interface formed between Ni3S2 and FeNi2S4 can optimize the Gibbs free energy for H* adsorption (ΔGH*). Benefiting from the open structure of the nanosheet arrays, the abundant heterogeneous interfaces in Ni3S2@FeNi2S4@NF composite, the positive synergistic effect between Ni3S2 and FeNi2S4, and the good conductivity of foamed nickel (NF) substrate, the optimized Ni3S2@FeNi2S4@NF nanoarray catalyst displayed excellent electrocatalytic activities, the overpotential is only 83 mV and 235 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at 10 mA cm-2, respectively. Importantly, an alkaline electrolyser directly using the Ni3S2@FeNi2S4@NF as both the anode and cathode achieved an ultralow cell voltage of 1.46 V, accompanied by outstanding stability. The performance is better than that of most other transition-metal sulfides electrocatalysts. This work may provide a useful strategy for reasonably regulating heterogeneous interfaces to effectively improve the performance of materials, thus accelerating the practical application of transition-metal sulfides electrocatalysts for overall water splitting.

Application of multi-active center organic quinone molecular functionalized graphene in fully pseudocapacitive asymmetric supercapacitors.

5, 7, 12, 14-pentacenetetrone (PT), polycyclic quinone derivatives, are rich in carbonyl, which were investigated as a novel organic electrode material for supercapacitors. PT with aπconjugated system, is a flat molecule, generating strongπ-πinteractions between molecules. PT molecules were uniformly fixed on conductive reduced graphene oxide (rGO) throughπ-πinteraction by one-step solvothermal method, forming a three-dimensional cross-linked PT@rGO hydrogel. This composite structure was conducive to reducing the charge transfer resistance and promoting the Faraday reaction of electrode, which achieved the superposition of electric double-layer capacitance and pseudocapacitance. Appropriate organic molecular loading can effectively improve electrochemical performance. The optimal PT@rGO electrode material displayed the specific capacitance of 433.2 F g-1at 5 mV s-1with an excellent rate capability in 1 mol l-1H2SO4electrolyte. Finally, the fully pseudocapacitive asymmetric supercapacitor has been assembled by using PT@rGO as positive electrode and benz[a]anthracene-7,12-quinone (BAQ) modified rGO(BAQ/rGO)as negative electrode, which exhibited the good energy storage performance in a cell voltage of 1.8 V.

2-Amino-3-chloro-1,4-naphthoquinone-covalent modification of graphene nanosheets for efficient electrochemical energy storage.

Green and renewable organic redox molecules are greatly advantageous over conventional inorganic intercalation electrode materials in terms of electrochemical reversibility and cycling stability. However, their electrical insulation prevents them from being used alone as electrode materials for supercapacitors. Herein, 2-amino-3-chloro-1,4-naphthoquinone (ACNQ) molecules were covalently grafted onto graphene nanosheets (GNS) via diazotization. The ACNQ-functionalized GNS (CNQ-GNS) electrode material exhibited a high specific capacitance of 364.2 ± 10 F g-1 at a current density of 1 A g-1, which is much larger than that of bare GNS (190 ± 6 F g-1). Moreover, the electrode exhibited an outstanding rate capability (capacitance retention of 76.8% at 100 A g-1). Finally, an asymmetric supercapacitor device was fabricated using graphene nanosheets as the positive electrode and the optimized CNQ-GNS as the negative electrode, which displayed a high energy density of 19.1 W h kg-1 at a power density of 0.8 kW kg-1 with a long cycling life span (nearly no loss after 10 000 cycles at 5 A g-1) in 1 M H2SO4 electrolyte. Briefly, the highly conductive GNS scaffold delivers a high electrical double-layer capacitance, while the organic functional groups covalently bonded on the GNS contribute additional faradaic pseudocapacitance, resulting in outstanding electrochemical energy storage.

Hierarchically porous and heteroatom self-doped graphitic biomass carbon for supercapacitors.

Here we report a simple, low-cost and environment friendly method, in which Black locust seed dregs and potassium ferrate (K2FeO4) are used as starting raw materials and activation agent. The hierarchically porous carbons (BDPC) with high special surface area and abundant mesopores (SBET = 2010.1 m2 g-1 and Vmeso = 1.457 cm3 g-1) are obtained through hydrothermal treatment and chemical activation. The BDPC electrode exhibits excellent electrochemical performances by virtue of unique architecture and heteroatoms pseudocapacitance contribution. In the three-electrode system, the optimized carbon material (BDPC-2) achieves a high specific capacitance of 333 F g-1 at 1 A g-1 and displays the high rate capability (81.1% capacitance retention at 100 A g-1) in 6 M KOH electrolyte. The symmetric supercapacitor based BDPC-2 exhibits energy density as high as 26.2 Wh kg-1 (at a power density of 0.79 kW kg-1) and excellent long-term cycling stability (only 8% decrease after 10,000 cycles) in 6 M KOH.

Horseradish peroxidase supported on porous graphene as a novel sensing platform for detection of hydrogen peroxide in living cells sensitively.

A viable and simple method for preparing porous graphene network using silver nanoparticles (AgNPs) etching was proposed, and a sensitive biosensor was constructed based on the porous graphene (PGN) and horseradish peroxidase (HRP) to measure the release of H2O2 from living cells. Owing to the large surface area and versatile porous structure, the use of nanoporous materials can significantly improve the analysis performance of the biosensor by loading large amounts of enzyme and accelerating diffusion rate. Meanwhile, the constructed electrode exhibited excellent electrochemical performance toward H2O2 with a determination limit as low as 0.0267nM and wide linear range of 7 orders of magnitude, which was superior to other H2O2 electrochemical sensors. Thus, this novel biosensor can detect the H2O2 release from living cells not only under normal physiological conditions (10-8-10-7M) but also in emergency state with the increased concentration (~10-4M). This work provides tremendous potential for real-time tracking of the secretion of H2O2 in different types of physiological and pathological investigations.

Cutting and unzipping multiwalled carbon nanotubes into curved graphene nanosheets and their enhanced supercapacitor performance.

We report a remarkable transformation of multiwalled carbon nanotubes (MWCNTs) to curved graphene nanosheets (CGN) by the Hummers method. Through this simple process, MWCNTs can be cut and unzipped in the transverse and longitudinal directions, respectively. The as-obtained CGN possess the unique hybrid structure of 1D nanotube and 2D graphene. Such a particular structure together with the improved effective surface area affords high specific capacitance and good cycling stability during the charge-discharge process when used as supercapacitor electrodes. The electrochemical measurements show that CGN exhibit higher capacitive properties than pristine MWCNTs in three different types of aqueous electrolytes, 1 M KOH, 1 M H(2)SO(4), and 1 M Na(2)SO(4). A specific capacitance of as high as 256 F g(-1) at a current density of 0.3 A g(-1) is achieved over the CGN material. The improved capacitance may be attributed to high accessibility to electrolyte ions, extended defect density, and increased effective surface area. Meanwhile, this high-yield production of graphene from low cost MWCNTs is important for the scalable synthesis and industrial application of graphene. Furthermore, this novel CGN nanostructure could also be promisingly applied in many fields such as nanoelectronics, sensors, nanocomposites, batteries, and gas storage.

Plasma degradation of dyes in water with contact glow discharge electrolysis.

Contact glow discharge electrolysis (CGDE) of two dyes, weak acid brilliant red B and weak acid flavine G, was investigated under different concentrations, temperature and mediums. From the variation of their concentration with the reaction time, it was demonstrated that the oxidation would be a first-order reaction. On the base line of UV spectra of solution in the degradation process, we deduced that two dyes underwent the oxidative degradation in CGDE. The rate constants, relevant coefficients and the decolorization degree were displayed under different conditions.