In Situ Construction of Zn2Mo3O8/ZnO Hierarchical Nanosheets on Graphene as Advanced Anode Materials for Lithium-Ion Batteries.

Transition-metal oxides as anodes for lithium-ion batteries (LIBs) have attracted enormous interest because of their high theoretical capacity, low cost, and high reserve abundance. Unfortunately, they commonly suffer from poor electronic and ionic conductivity and relatively large volume expansion during discharge/charge processes, thereby triggering inferior cyclic performance and rate capability. Herein, a molybdenum-zinc bimetal oxide-based composite structure (Zn2Mo3O8/ZnO/rGO) with rectangular Zn2Mo3O8/ZnO nanosheets uniformly dispersed on reduced graphene oxide (rGO) has been prepared by using a simple and controllable cyanometallic framework template method. The Zn2Mo3O8/ZnO rectangular nanosheets with desirable porous features are composed of nanocrystalline subunits, facilitating the exposure of abundant active sites and providing sufficient contact with the electrolyte. Benefiting from the composition and structural merits as well as the induced synergistic effects, the Zn2Mo3O8/ZnO/rGO composite as LIB anodes delivers superior electrochemical properties, including high reversible capacity (960 mA h g-1 after 100 cycles at 200 mA g-1), outstanding rate performance (417 mA h g-1 at 10,000 mA g-1), and admirable long-term cyclic stability (862 mA h g-1 after 400 cycles at 1000 mA g-1). The mechanism of lithium storage and the formation of SEI film are systematically elucidated. This work provides an effective strategy for synthesizing promising Mo-cluster compound-based anodes for high-performance LIBs.

Facile construction of ZnWO4/ZnO porous nanoplates on reduced graphene oxide for superior lithium storage.

Zinc tungstate (ZnWO4) shows great promise as an anode material for lithium-ion batteries (LIBs) owing to its reversible multi-electron redox reactions and high theoretical capacity. Nevertheless, the low conductivity and big strain during cycling can lead to the inferior electrochemical properties of the ZnWO4 anode, hindering its practical application. Herein, we report a novel composite with ZnWO4/ZnO porous nanoplates in-situ constructed on reduced graphene oxide (rGO) by a metal-organic framework template strategy. The nanoplates with good porosity are composed of nanoparticles and nanorods, providing a short Li+-diffusion distance and plentiful Li+ storage active sites. The introduction of rGO can accelerate charge transfer and reinforce structural stability. As a result of these advantages, the ZnWO4/ZnO/rGO composite as LIBs anode delivers a high reversible capacity of 811 mAh g after 100 cycles at 200 mA g-1, excellent rate capability (437 mAh g at 5000 mA g-1), and good long cycling stability (485 mAh g after 500 cycles at 2000 mA g-1). Notably, the rate capability of the composite far precedes the previously reported ZnWO4-based anodes. This work provides an efficient approach for designing and fabricating advanced metal tungstate-based anodes for high-performance LIBs.

Decoration of nickel hexacyanoferrate nanocubes onto reduced graphene oxide sheets as high-performance cathode material for rechargeable aqueous zinc-ion batteries.

Prussian blue analogues (PBA) have attracted much attention in energy research due to their unique three-dimensional open framework structure, adjustable metal ions, and facile synthesis. However, the application of PBA as a cathode material for aqueous zinc-ion batteries (ZIBs) is restricted by its poor cycling performance and lower capacity. In this paper, we develop a new PBA-based hybrid cathode material for aqueous ZIBs by loading uniform nickel hexacyanoferrate (NiHCF) nanocubes onto reduced graphene oxide (RGO) sheets. In the NiHCF/RGO hybrid, NiHCF nanoparticles are well anchored on the RGO layers, forming a conductive network. The strong synergy between NiHCF and highly conductive RGO effectively increases the specific surface area, accelerates the electron and ion transport, and inhibits the structural collapse of the NiHCF/RGO electrode during the Zn2+ insertion/extraction process. Benefiting from the above advantages, the NiHCF/RGO hybrid exhibits a remarkable reversible capacity of 94.5 mAh g-1 at a current density of 5 mA g-1, excellent rate performance of 50.1 mAh g-1 at 200 mA g-1, and enhanced cycling stability with a capacity retention of 80.3% after 1000 cycles at 200 mA g-1. This work provides a simple and effective way to improve the electrochemical performance of PBA-based cathodes for aqueous ZIBs application.

Construction of rGO-Encapsulated Co3 O4 -CoFe2 O4 Composites with a Double-Buffer Structure for High-Performance Lithium Storage.

Transition metal oxides (TMOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). Nevertheless, their poor electronic and ionic conductivity as well as huge volume change leads to low capacity release and rapid capacity decay. Herein, a reduced graphene oxide (rGO)-encapsulated TMOs strategy is developed to address the above problems. The Co3 O4 -CoFe2 O4 @rGO composites with rGO sheets-encapsulated Co3 O4 -CoFe2 O4 microcubes are successfully constructed through a simple metal-organic frameworks precursor route, in which Co[Fe(CN)5 NO] microcubes are in situ coated by graphene oxide sheets, followed by a two-step calcination process. As anode material of LIBs, Co3 O4 -CoFe2 O4 @rGO exhibits remarkable reversible capacity (1393 mAh g-1 at 0.2 A g-1 after 300 cycles), outstanding long-term cycling stability (701 mAh g-1 at 2.0 A g-1 after 500 cycles), and excellent rate capability (420 mAh g-1 at 4.0 A g-1 ). The superior lithium storage performance can be attributed to the unique double-buffer structure, in which the outer flexible rGO shells can prevent the structure collapse of the electrode and improve its conductivity, while the hierarchical porous cores of Co3 O4 -CoFe2 O4 microcubes can buffer the volume expansion. This work provides a general and straightforward strategy for the construction of novel rGO-encapsulated bimetal oxides for energy storage and conversion application.

Nitrogen-doped carbon dots anchored NiO/Co3O4 ultrathin nanosheets as advanced cathodes for hybrid supercapacitors.

Herein, we demonstrate an advanced cathode of nitrogen-doped carbon dots (NCDs) anchored NiO/Co3O4 ultrathin nanosheets for hybrid supercapacitors by a facile hydrothermal-calcination route. Owing to the well defined thin-plate structure and ternary composition, the optimized NiO/Co3O4/NCDs nanosheets demonstrate a high specific capacity of 976.3 C g-1 (1775 F g-1) at 1 A g-1, and a splendid cycling stability of approximately 95.7% retention over 10,000 continuous cycles (15 A g-1). In addition, a hybrid supercapacitor is constructed by using NiO/Co3O4/NCDs nanosheets as cathode and reduced graphene oxide (RGO) supported NCDs composites as anode. The obtained NiO/Co3O4/NCDs//RGO/NCDs hybrid supercapacitor delivers a maximum energy density of 41.6 Wh kg-1, together with outstanding cycling stability (no decay after 10,000 cycles at 10 A g-1). Therefore, the ultrathin sheet-like structured NiO/Co3O4/NCDs cathode presents a great potential for supercapacitor application.

Facile synthesis of novel tungsten-based hierarchical core-shell composite for ultrahigh volumetric lithium storage.

The development of novel high volumetric capacity electrode materials is crucial to the application of lithium-ion batteries (LIBs) in miniaturized consumer electronics. In this work, a novel tungsten-based octahedron (CoWO4/Co3O4) with unique hierarchical core-shell structure is successfully fabricated by simply calcinating a cyanide-metal framework precursor. Benefitting from the heavy element W, the CoWO4/Co3O4 octahedrons show a high mass density of 5.18 g cm-3. When applied as anode materials for LIBs, the CoWO4/Co3O4 octahedrons exhibit an ultrahigh volumetric capacity (6226 mAh cm-3 after 350 cycles at 0.4 A g-1), superior rate capability (3165 mAh cm-3 at 3.0 A g-1) and outstanding long-term cycling performance (4703 mAh cm-3 at 1.0 A g-1 after 800 cycles). The extraordinary lithium storage performance can be ascribed to the unique hierarchical core-shell structure and the possible synergistic effect between W and Co, which provide more Li+ insertion sites and effectively buffer the volume variation during cycling. This work not only provides an ultrahigh volumetric lithium storage anode, but also gives a simple and general strategy for the synthesis of novel anode materials for high volumetric energy density LIBs.

Three-dimensional graphene network deposited with mesoporous nitrogen-doped carbon from non-solvent induced phase inversion for high-performance supercapacitors.

Three-dimensional graphitic carbon materials with controllable composition and hierarchically porous structure are promising electrode materials for supercapacitors. In this work, a modified phase inversion method combined with a calcination process was developed to prepare three-dimensional graphene networks embedded with nitrogen-doped carbon nanoparticles. When used as electrode for supercapacitors, the as-prepared material delivered a high capacitance of 431.9 F g-1 at 0.1 A g-1 and 156.8 F g-1 at 20 A g-1, as well as a stable cyclic behavior with no capacitance decay after 5000 cycles. Such a remakable capacitive performance was attributed to its hierarchically porous structure and proper nitrogen doping content (9.68 ±â€¯0.24 at%), which facilitated the migration of electrolyte ions and provided abundant redox active sites for the faradic reactions. The synthetic strategy may be exploited for the rational design and synthesis of new carbon materials with controlled doping level and three-dimensional porous structure.

MOF derived CoP-decorated nitrogen-doped carbon polyhedrons/reduced graphene oxide composites for high performance supercapacitors.

ZIF-67 derived CoP-decorated nitrogen-doped porous carbon (CoP-NPC) polyhedra anchored on reduced graphene oxide (RGO) sheets have been successfully prepared through an efficient pyrolysis-phosphidation-assembly strategy. The resulting CoP-NPC/RGO composite as an electrode for supercapacitors shows an enhanced electrochemical performance with high capacitances of 466.6 F g-1 at 1 A g-1 and 252 F g-1 at 20 A g-1, as well as 94.7% of capacitance retention after 10 000 cycles in 1 M H2SO4 solution. Moreover, the symmetrical two-electrode device assembled from CoP-NPC/RGO electrodes delivers a high energy density of 12 W h kg-1 at a power density of 500 W kg-1 and excellent long-term cycling stability (93% of the initial capacitance after 10 000 cycles at 10 A g-1). This superior electrochemical performance of CoP-NPC/RGO can be ascribed to its 3D interconnected porous structure and the synergistic effect between CoP and the nitrogen-doped carbon matrix. The unique architecture of the composites can effectively enhance the electrochemical performance by shortening the diffusion distance of electrolyte ions and improving the electrical conductivity and the contact area between active materials and the electrolyte. The excellent electrochemical performances make CoP-NPC/RGO a promising electrode material for high-performance supercapacitors.

Flower-like silver bismuthate supported on nitrogen-doped carbon dots modified graphene oxide sheets with excellent degradation activity for organic pollutants.

In this study, a new ternary AgBiO3/GO/NCDs composite (GO = graphene oxide, NCDs = nitrogen-doped carbon dots) has been successfully prepared through in-situ growth of flower-like AgBiO3 on GO/NCDs complex support. The AgBiO3/GO/NCDs composite exhibits significantly enhanced degradation activities towards organic pollutants of rhodamine B, phenol and tetracycline. Especially, the refractory tetracycline (20 mg L-1) can be completely removed within 6.0 min with a dosage of 30 mg of AgBiO3/GO/NCDs under the assistance of peroxymonosulfate (PMS, 0.2 mM). It is revealed that GO in the composite can facilitate the quick and efficient electron transfer and improve the generation of reactive oxygen species during the degradation process, while the NCDs may play double roles as both the electron-acceptor and the reactive site. Besides, the electrons can be captured by PMS to produce plenty of sulfate radicals (SO4-) with very strong oxidation ability. All these factors collaboratively promote the degradation efficiency of AgBiO3/GO/NCDs towards organic pollutants. The excellent degradation activities of AgBiO3/GO/NCDs endow it with potential application in wastewater purification.

Ionic liquid directed construction of foam-like mesoporous boron-doped graphitic carbon nitride electrode for high-performance supercapacitor.

Carbon materials with controllable hierarchically porous structure and high doping level are expect to exhibit superior energy storage performance when used as electrode materials for supercapacitors. Herein, we report the preparation of a novel foam-like boron-doped carbon nitride material with hierarchically porous structure and high doping contents of nitrogen (21.45 ±â€¯0.93 at%) and boron (6.46 ±â€¯0.60 at%). Due to the unique compositional and structural features, this material exhibits high energy storage performance, including a large specific capacitance of ∼ 660.6 F g-1 at 0.1 A g-1 and a high capacitance retention after 10,000 cycles. This study can provide new ideas for the development of carbon based electrode materials with unique hierarchically porous structure and improved doping level.

Nitrogen-doped carbon dots modified dibismuth tetraoxide microrods: A direct Z-scheme photocatalyst with excellent visible-light photocatalytic performance.

In this work, an all solid direct Z-scheme photocatalyst of monoclinic dibismuth tetraoxide microrods/nitrogen-doped carbon dots (m-Bi2O4/NCDs) has been constructed through a simple one-step hydrothermal method. The m-Bi2O4/NCDs photocatalyst exhibits excellent photocatalytic activity for the degradation of methylene orange (MO) and phenol under visible light irradiation. The pollutants of MO (10 mg L-1) and phenol (45 mg L-1) could be efficiently degraded by m-Bi2O4/NCDs within 30 and 120 min, respectively, which is much better than that of the single m-Bi2O4, indicating that the introduction of NCDs into m-Bi2O4 can effectively improve the photocatalytic activity. Moreover, the m-Bi2O4/NCDs photocatalyst possesses a high photocatalytic stability and durability, and its photocatalytic activity did not show obvious decline after four photodegradation cycles. It is found that both O2- and direct h+ oxidation play important roles in the degradation process, and based on the experimental result a direct Z-scheme photocatalytic mechanism is proposed. This study suggests that the as-prepared m-Bi2O4/NCDs composite is a promising photocatalyst for environmental remediation.

Nitrogen-enriched carbon spheres coupled with graphitic carbon nitride nanosheets for high performance supercapacitors.

Three-dimensional (3D) nitrogen-doped carbon materials with a hierarchically porous structure are prepared by the introduction of nitrogen-doped carbon spheres (NCS) into the inter-sheet spaces of graphitic carbon nitride nanosheets (g-CN). The as-prepared graphitic carbon nitride/nitrogen-doped carbon sphere (g-CN/NCS) composites present a high nitrogen doping level, a unique hierarchically porous structure, and a high specific surface area of 448 m2 g-1. Such particular features make the g-CN/NCS composite an ideal material for supercapacitor electrodes, which could deliver a large specific capacitance of 403.6 F g-1 at 0.1 A g-1, an excellent rate capability of 220 F g-1 at 10 A g-1, and a high cycling stability with almost 100% capacitance retention after 5000 cycles at 20 A g-1. Furthermore, the g-CN/NCS electrode-based symmetric supercapacitors exhibit a decent energy density of 6.75 W h kg-1 at a power density of 1000 W kg-1. The enhanced performances are mainly attributed to the high nitrogen doping level and the hierarchically porous structure of the 3D structured g-CN/NCS composites, which provide an efficient pathway for transporting ions and electrons, and endow more active sites for electrochemical energy storage.

Metal-organic framework derived Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons as bifunctional electrocatalysts for hydrogen evolution and oxygen-reduction reactions.

The development of simple and cost-effective synthesis methods for electrocatalysts of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is critical to renewable energy technologies. Herein, we report an interesting bifunctional HER and ORR electrocatalyst of Fe/Fe3C@N-doped-carbon porous hierarchical polyhedrons (Fe/Fe3C@N-C) by a simple metal-organic framework precursor route. The Fe/Fe3C@N-C polyhedrons consisting of Fe and Fe3C nanocrystals enveloped by N-doped carbon shells and accompanying with some carbon nanotubes on the surface were prepared by thermal annealing of Zn3[Fe(CN)6]2·xH2O polyhedral particles in nitrogen atmosphere. This material exhibits a large specific surface area of 182.5 m2 g-1 and excellent ferromagnetic property. Electrochemical tests indicate that the Fe/Fe3C@N-C hybrid has apparent HER activity with a relatively low overpotential of 236 mV at the current density of 10 mA cm-2 and a small Tafel slope of 59.6 mV decade-1. Meanwhile, this material exhibits excellent catalytic activity toward ORR with an onset potential (0.936 V vs. RHE) and half-wave potential (0.804 V vs. RHE) in 0.1 M KOH, which is comparable to commercial 20 wt% Pt/C (0.975 V and 0.820 V), and shows even better stability than the Pt/C. This work provides a new insight to developing multi-functional materials for renewable energy application.

g-C3N4/AgBr nanocomposite decorated with carbon dots as a highly efficient visible-light-driven photocatalyst.

Visible-light-driven photocatalysis as a green technology has attracted intense interest due to its potential applications in environmental remediation. However, the poor visible light utilization and low electron-hole separation efficiency of photocatalysts largely limited their practical application. In this work, a new ternary visible-light driven photocatalyst of g-C3N4/CDs/AgBr has been prepared by the introduction of carbon dots (CDs) onto the surface of g-C3N4, followed by in-situ growth of AgBr nanoparticles on CDs-modified g-C3N4 nanosheets. The g-C3N4/CDs/AgBr nanocomposite exhibits excellent photocatalytic efficiency for organic pollutant degradation, which is about 4.0, 5.3 and 2.3 times higher than that of AgBr, g-C3N4 and g-C3N4/AgBr, respectively. The result indicates the introduction of CDs into g-C3N4/AgBr can largely improve the photocatalytic activity since CDs act as the light absorber and the electron mediator between g-C3N4 and AgBr, which effectively promote the separation of photogenerated charge carriers and the utilization of visible light. Moreover, the photocatalytic activity of g-C3N4/CDs/AgBr has no obvious decrease after four photodegradation cycles, demonstrating a high photocatalytic stability. This study highlights the potential application of highly efficient CDs decorated photocatalysts in waste water purification.

Ionic Liquid Directed Mesoporous Carbon Nanoflakes as an Effiencient Electrode material.

Supercapacitors are considered to be the most promising approach to meet the pressing requirements for energy storage devices. The electrode materials for supercapacitors have close relationship with their electrochemical properties and thus become the key point to improve their energy storage efficiency. Herein, by using poly (vinylidene fluoride-co-hexafluoropropylene) and ionic liquid as the dual templates, polyacrylonitrile as the carbon precursor, a flake-like carbon material was prepared by a direct carbonization method. In this method, poly (vinylidene fluoride-co-hexafluoropropylene) worked as the separator for the formation of isolated carbon flakes while aggregated ionic liquid worked as the pore template. The obtained carbon flakes exhibited a specific capacitance of 170 F/g at 0.1 A/g, a high energy density of 12.2 Wh/kg and a high power density of 5 kW/kg at the current of 10 A/g. It also maintained a high capacitance retention capability with almost no declination after 500 charge-discharge cycles. The ionic liquid directed method developed here also provided a new idea for the preparation of hierarchically porous carbon nanomaterials.

Carbon nanotube and graphene-based bioinspired electrochemical actuators.

Bio-inspired actuation materials, also called artificial muscles, have attracted great attention in recent decades for their potential application in intelligent robots, biomedical devices, and micro-electro-mechanical systems. Among them, ionic polymer metal composite (IPMC) actuator has been intensively studied for their impressive high-strain under low voltage stimulation and air-working capability. A typical IPMC actuator is composed of one ion-conductive electrolyte membrane laminated by two electron-conductive metal electrode membranes, which can bend back and forth due to the electrode expansion and contraction induced by ion motion under alternating applied voltage. As its actuation performance is mainly dominated by electrochemical and electromechanical process of the electrode layer, the electrode material and structure become to be more crucial to higher performance. The recent discovery of one dimensional carbon nanotube and two dimensional graphene has created a revolution in functional nanomaterials. Their unique structures render them intriguing electrical and mechanical properties, which makes them ideal flexible electrode materials for IPMC actuators in stead of conventional metal electrodes. Currently although the detailed effect caused by those carbon nanomaterial electrodes is not very clear, the presented outstanding actuation performance gives us tremendous motivation to meet the challenge in understanding the mechanism and thus developing more advanced actuator materials. Therefore, in this review IPMC actuators prepared with different kinds of carbon nanomaterials based electrodes or electrolytes are addressed. Key parameters which may generate important influence on actuation process are discussed in order to shed light on possible future research and application of the novel carbon nanomateials based bio-inspired electrochemical actuators.

A facile one-pot hydrothermal method to produce SnS2/reduced graphene oxide with flake-on-sheet structures and their application in the removal of dyes from aqueous solution.

In this article, we report a novel one-pot synthesis of SnS2/reduced graphene oxide (rGO) flake-on-sheet nanocomposites via in situ reduction of graphene oxide (GO) by Sn(2+) under hydrothermal conditions. The morphology and structure of the obtained product were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction instrument (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The adsorption characteristics of the SnS2/rGO nanocomposites were examined using an organic dye Rhodamine B (RhB) as adsorbate. SnS2/rGO exhibited superior adsorption behavior for RhB. The adsorption kinetics and adsorption isotherm were investigated. The adsorption of RhB by SnS2/rGO was well fitted to the Langmuir isotherm model, and the resultant kinetic data were well described by pseudo-second-order model.

Constructing carbon-coated Fe3O4 microspheres as antiacid and magnetic support for palladium nanoparticles for catalytic applications.

Fe3O4 microsphere is a good candidate as support for catalyst because of its unique magnetic property and large surface area. Coating Fe3O4 microspheres with other materials can protect them from being dissolved in acid solution or add functional groups on their surface to adsorb catalyst. In this paper, a carbon layer was coated onto Fe3O4 microspheres by hydrothermal treatment using polyethylene glycol as the connecting agents between glucose and Fe3O4 spheres. Through tuning the added amounts of reactants, the thickness of the carbon layer could be well-controlled. Because of the abundant reductive groups on the surface of carbon layer, noble metal ions could be easily adsorbed and in situ reduced to nanoparticles (6-12 nm). The prepared catalyst not only had unique antiacid and magnetic properties, but also exhibited a higher catalytic activity toward the reduction of methyl orange than commercially used Pd/C catalyst.

Fabrication of Pt/polypyrrole hybrid hollow microspheres and their application in electrochemical biosensing towards hydrogen peroxide.

Pt/polypyrrole (PPy) hybrid hollow microspheres were successfully prepared by wet chemical method via Fe(3)O(4) template and evaluated as electrocatalysts for the reduction of hydrogen peroxide. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD), inductive coupled plasma emission spectrum (ICP) and Fourier-transform infrared spectra (FTIR) measurements. The results exhibited that ultra-high-density Pt nanoparticles (NPs) were well deposited on the PPy shell with the mean diameters of around 4.1nm. Cyclic voltammetry (CV) results demonstrated that Pt/PPy hybrid hollow microspheres, as enzyme-less catalysts, exhibited good electrocatalytic activity towards the reduction of hydrogen peroxide in 0.1M phosphate buffer solution (pH=7.0). The composite had a fast response of less than 2s with linear range of 1.0-8.0mM and a relatively low detection limit of 1.2microM (S/N=3). The sensitivity of the sensor for H(2)O(2) was 80.4mAM(-1)cm(-2).

Accurately tuning the dispersity and size of palladium particles on carbon spheres and using carbon spheres/palladium composite as support for polyaniline in H2O2 electrochemical sensing.

With an accurate control of the dispersity and size of the palladium nanoparticles (Pd NPs), carbon spheres/Pd NPs composite was prepared without any extra reducing agents. In order to fully understand the formation mechanism and find out the best condition for the fabrication of carbon/Pd composite spheres, the effects of temperature, reaction time, pH value, and the weight ratio of PdCl(2) to carbon spheres on the morphology of the final products were investigated. A superior product with small (d = 7.66 nm, sigma = 1.94 nm), homogeneously distributed Pd crystals was obtained at pH 7 and a reaction temperature of 70 degrees C in ethanol. The Pd NPs decorated carbon sphere was used as support for electroactive polyaniline (PANI) in our work because it could enhance their sensing properties which were afforded by catalytic Pd NPs and hydrophilic carbon spheres. The sensor based on carbon/Pd/PANI exhibited a high sensitivity of 656.0693 mA M(-1) cm(-2) and a detection limit of 5.48 microM toward the reduction of H(2)O(2). In addition, the carbon/Pd/PANI sensor also showed good selectivity between H(2)O(2) and ascorbic acid.