Giant permittivity and low dielectric loss of Fe doped BaTiO3 ceramics: Experimental and first-principles calculations

Fe doped BaTiO₃ ceramics with giant permittivity and low dielectric loss were synthesized in N₂/H₂ atmosphere started with BaTiO₃ powders and iron powders. XRD analysis exhibited the tetragonal-pseudocubic phase transition when the Fe content is 3 mol%. XPS spectra confirmed the iron oxides with mixed-valence structure of Fe²⁺/Fe³⁺, while Ti-ions maintain Ti⁴⁺3d⁰ states without any oxidization-reduction. For the case of ceramics with 5 mol% Fe, the dielectric constant was 66,650 at 1000 Hz at room temperature, 19 times higher than that of pure BaTiO₃ ceramics, while the dielectric loss tangent was 0.13. Comparison with other giant-permittivity materials demonstrated the superior potential of present ceramics. First-principles calculations investigated the interfacial interaction of Fe-[TiO₂] interface and Fe-[BaO] interface. Giant dielectric constant was induced by the interfacial polarization between insulating ferroelectrics and semiconducting iron oxides with mixed-valence states, as well as the contribution from the generated electron hopping conduction.     

Hydrothermal synthesis and crystal structure of the first layered iron molybdate KH3Fe2Mo2O10

The layered iron molybdate compound, KH₃Fe^II₂Mo^VI₂O₁₀, has been hydrothermally synthesized and structurally characterized for the first time. The compound crystallizes in monoclinic space group C2/m with a=9.6448(7), b=6.5946(4), , β=115.950(1)°, , Z=2, and R1=0.0313, wR2=0.0817. The structure consists of FeO₆ octahedra and MoO₄ tetrahedra. Each FeO₆ octahedron shares edges with its adjacent FeO₆ octahedra and leads to a chain consisting of edge-sharing FeO₆ octahedron. The parallel chains are linked through MoO₄ tetrahedra. Each MoO₄ tetrahedron shares corners with two adjacent Fe octahedra through the vertical oxygen atoms of each FeO₆, and two adjacent Fe octahedra through an oxygen atom bridging the two adjacent Fe octahedra of its neighboring chain, respectively. A ∞-like 2D layers and pseudo-six-side tunnels are formed and the potassium cations are located in the pseudo-channels.     

Room temperature in situ chemical synthesis of Fe3O4/graphene

A simple, cost-effective, efficient, and green approach to synthesize iron oxide/graphene (Fe₃O₄/rGO) nanocomposite using in situ deposition of Fe₃O₄ nanoparticles on reduced graphene oxide (rGO) sheets is reported. In the redox reaction, the oxidation state of iron(II) is increased to iron(III) while the graphene oxide (GO) is reduced to rGO. The GO peak is not observed in the X-ray diffraction (XRD) pattern of the nanocomposite, thus providing evidence for the reduction of the GO. The XRD spectra do have peaks that can be attributed to cubic Fe₃O_4. The field emission scanning electron microscopy (FESEM) images show Fe₃O₄ nanoparticles uniformly decorating rGO sheets. At a low concentration of Fe²⁺, there is a significant increase in the intensity of the FESEM images of the resulting rGO sheets. Elemental mapping using energy dispersive X-ray (EDX) analysis shows that these areas have a significant Fe concentration, but no morphological structure could be identified in the image. When the concentration of Fe²⁺ is increased, the Fe₃O₄ nanoparticles are formed on the rGO sheets. Separation of the Fe₃O₄/rGO nanocomposite from the solution could be achieved by applying an external magnetic field, thus demonstrating the magnetic properties of the nanocomposite. The Fe₃O₄ particle size, magnetic properties, and dispersibility of the nanocomposite could be altered by adjusting the weight ratio of GO to Fe²⁺ in the starting material.     

Solar photoassisted anodic oxidation of carboxylic acids in presence of Fe using a boron-doped diamond electrode

This paper reports a comparative study on the anodic oxidation of 2.5 l of 50 mg l⁻¹ TOC of formic, oxalic, acetic, pyruvic or maleic acid in 0.1 M Na₂SO₄ solutions of pH 3.0 with and without 1.0 mM Fe³⁺ as catalyst in the dark or under solar irradiation. Experiments have been performed with a batch recirculation flow plant containing a one-compartment filter-press electrolytic reactor equipped with a 20 cm² boron-doped diamond (BDD) anode and a 20 cm² stainless steel cathode, and coupled to a solar photoreactor. This system gradually accumulates H₂O₂ from dimerization of hydroxyl radical (OH) formed at the anode surface from water oxidation. Carboxylic acids in direct anodic oxidation are mainly oxidized by direct charge transfer and/or OH produced on BDD, while their Fe(III) complexes formed in presence of Fe³⁺ can also react with OH produced from Fenton reaction between regenerated Fe²⁺ with electrosynthesized H₂O₂ and/or photo-Fenton reaction. Fast photolysis of Fe(III)-oxalate and Fe(III)-pyruvate complexes under the action of sunlight also takes place. Chemical and photochemical trials of the same solutions have been made to better clarify the role of the different catalysts. Solar photoassisted anodic oxidation in presence of Fe³⁺ strongly accelerates the removal of all carboxylic acids in comparison with direct anodic oxidation, except for acetic acid that is removed at similar rate in both cases. This novel electrochemical advanced oxidation process allows more rapid mineralization of formic, oxalic and maleic acids, without any significant effect on the conversion of acetic acid into CO₂. The synergistic action of Fe³⁺ and sunlight in anodic oxidation can then be useful for wastewater remediation when oxalic and formic acids are formed as ultimate carboxylic acids of organic pollutants, but its performance is expected to strongly decay in the case of generation of persistent acetic acid during the degradation process.     

FeVO4 as a highly active heterogeneous Fenton-like catalyst towards the degradation of Orange II

The iron vanadate, FeVO₄, was prepared and characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM). It was found that FeVO₄ could effectively catalyze H₂O₂ to generate active hydroxyl radical OH, which was confirmed with electron spin resonance (ESR) spin-trapping technique. Therefore, it was employed as a heterogeneous Fenton-like catalyst in the present contribution, and its catalytic activity was mainly evaluated in terms of the degradation efficiency of Orange II. Compared with the conventional heterogeneous Fenton-like catalysts, α-Fe₂O₃, Fe₃O₄ and γ-FeOOH, FeVO₄ possessed a much higher catalytic activity. The high catalytic activity possibly involved in a special two-way Fenton-like mechanism, that is, the activation of H₂O₂ by both Fe(III) and V(V) in FeVO₄. Moreover, FeVO₄ possessed a wide applicable pH range and its catalytic activity was slightly affected by the solution pH values in the range of 3–8.     

The influence of iron on the precipitation behaviour of nickel powder

The effect of iron on the precipitation behaviour of nickel powder was investigated. Reduction experiments were conducted on a 0.5 L laboratory autoclave fitted with a Teflon reaction beaker and a double impeller configuration consisting of an upper axial impeller and lower Rushton turbine. Reduction was conducted in the presence of a morphology modifier at a temperature between 180 and and 2800 kPa pressure using a synthetic nickel ammine sulphate solution (, free NH₃:Ni²⁺ and (NH₄)₂SO₄:Ni²⁺ molar ratios of 2.0-2.1 and 2.2, respectively). Nickel seed was used to initiate reduction and iron was added to the reduction solution as ferrous sulphate solution (acidified to pH 2.5 to prevent oxidation) to give a reduction solution with Fe²⁺ concentration of 6, 20 and 200 mg/L. The effect of iron was investigated by studying the evolution of the moments, volume or mass moment mean D(4.3), number based mean size , nickel depletion rate and population balance in the absence of sampling between batch reductions. Iron was found to act as a growth promoter and nucleation agent through reversible adsorption and hydrolysis on the surface of the seed particles. Growth was preferentially favoured over nucleation up to a Fe²⁺ concentration of 6 mg/L, thereafter the extent of nucleation increased with increasing Fe²⁺ concentration up to 200 mg/L. Nucleation and growth promotion in the presence of high shear rates gave rise to rapid aggregation, which ceased at a critical size of approximately and in the presence of iron and without. However, the sharp increase in the D(4.3) towards the end of the cycle and the general decrease in surface area shows that aggregation of larger particles plays a major role in size enlargement. Comparison of the scanning electron microscopy (SEM) micrographs of the powder with undesirable morphology produced in industrial practice and that produced in the laboratory in the presence of iron showed that iron was one of the factors responsible for the production of powder with undesirable morphology. Based on these laboratory scale experiments, iron levels in reduction solutions should not exceed 6 mg/L for effective control of particle morphology.     

Electrocatalyst materials for fuel cells based on the polyoxometalates—K7 or H7[(P2W17O61)Fe(H2O)] and Na12 or H12[(P2W15O56)2Fe4(H2O)2]

Free acids of the iron substituted heteropoly acids (HPA), H₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (HFe1) and H₁₈[(P₂W₁₅O₅₆)₂Fe^III₂(H₂O)₂] (HFe2) were prepared from the salts K₇[(P₂W₁₇O₆₁)Fe^III(H₂O)] (KFe1) and Na₁₂[(P₂W₁₅O₅₆)₂Fe^III₄(H₂O)₂] (NaFe4), respectively. The iron-substituted HPA were adsorbed on to XC-72 carbon based GDLs to form HPA doped GDEs after water washing with HPA loadings of ca. 1 μmol. The HPA was detected throughout the GDL by EDX. Solution electrochemistry of the free acids are reported for the first time in sulfate buffer, pH 1-3. The hydrogen oxidation reaction was catalyzed by KFe1 at 0.33 V, with an exchange current density of 38 mA/cm². Moderate activity for the oxygen reduction reaction was observed for the iron substituted HPA, which was dramatically improved by selectively removing oxygen atoms from the HPA by cycling the fuel cell cathode under N₂ followed by reoxidation to give a restructured oxide catalyst. The nanostructured oxide achieved an OCV of 0.7 V with a Tafel slope of 115 mV/decade. Cycling the same catalysts in oxygen resulted in an improved catalyst/ionomer/carbon configuration with a slightly higher Tafel slope, 128 mV/decade but a respectable current density of 100 mA/cm² at 0.2 V.     

Phenol photodegradation with oxygen and hydrogen peroxide over TiO2 and Fe-doped TiO2

Photodegradation of phenol was investigated with two types of oxidant agents in water, oxygen and hydrogen peroxide, at two different reaction pH with a series of nanosized iron-doped anatase TiO₂ catalysts with different iron contents. The catalysts have been prepared by a sol–gel/microemulsion method. Firstly, iron-doped titania catalysts were studied with respect to their activity behavior when oxygen was used as oxidant agent in the photocatalytic degradation of aqueous phenol in comparison with un-doped reference catalysts. Secondly, two catalysts (TiO₂ and 0.7 wt.% Fe-doped TiO₂) were selected to extend the study for the employment of hydrogen peroxide as oxidant at different concentrations and two initial reaction pHs. An enhancement of the photocatalytic activity is observed only for relatively low doping level (ca. 0.7 wt.%) in catalyst calcined at 450 °C preferably using hydrogen peroxide as oxidant agent which is attributable to the partial introduction of Fe³⁺ cations into the anatase structure. Nevertheless, it has been demonstrated that catalyst surface properties can play an important role during phenol photodegradation process on the basis of the analysis of differences found in the photoactivity as a function of reaction pH.     

Catalytic degradation of phenol in sonolysis by coal ash and H2O2/O3

This study demonstrated that coal ash, as widely distributed solid waste disposal, would function as a media for organic pollutants removal in the presence or absence of H₂O₂/O₃ under ultrasonic radiation. Coal ash could act as a catalyst to generate OH radicals with the presence of H₂O₂/O₃ and consequently enhance the phenol degradation. Experimental results showed that when using coal ash as a catalyst under ultrasonic irradiation, 83.4% and 88.8% of phenol was degraded in the presence of H₂O₂ or O₃, respectively. The degradation rate of phenol would increase with increasing amount of O₃, while there was an optimal concentration of H₂O₂ (1.5 mM) for phenol degradation. Higher dosage of coal ash could result in higher phenol degradation rates. H₂O₂/coal ash/ultrasonic system could achieve better performance for phenol degradation under more acidic conditions, while more alkaline condition in O₃/coal ash/ultrasonic system favored phenol degradation. This study provides a new approach for wastewater treatment especially when contaminated with phenolic pollutants.     

Oxidation pathways of malachite green by Fe-catalyzed electro-Fenton process

A very detailed scheme for the Fe³⁺-catalyzed electro-Fenton mineralization of malachite green as a model triarylmethane dye is presented. Bulk electrolyses of 250-mL aqueous solutions of 0.5 mM malachite green with 0.2 mM Fe³⁺ as catalyst have been carried out at room temperature and pH 3.0 under constant current in an undivided cell equipped with a graphite-felt cathode and a Pt anode to assess the performance of the electro-Fenton system. In situ electrogeneration of Fe²⁺ and H₂O₂ from quick cathodic reduction of Fe³⁺ and dissolved O₂ (from bubbled compressed air), respectively, allows the formation of the very oxidizing species hydroxyl radical (OH) in the medium from Fenton's reaction. A pseudo-first-order decay kinetics with an apparent rate constant of k_1,MG = 0.244 min⁻¹ was obtained for total destruction of malachite green by action of OH at 200 mA, requiring 22 min for total decoloration of the solution. In the same experimental conditions, overall mineralization was reached at 540 min. Up to 15 aromatic and short-chain carboxylic acid intermediates were identified along the treatment. The evolution of current efficiency was calculated from the chemical oxygen demand (COD) removal. Based on the time course of most of the by-products and the identification of inorganic ions released, some plausible mineralization pathways are proposed and thoroughly discussed. It has been found that the electro-Fenton degradation of malachite green proceeds via parallel pathways, all of them involving primary splitting of the triaryl structure initiated by attack of OH on the central carbon, thus yielding two different N-dimethylated benzophenones. Successive cleavage of the aromatic intermediates generates oxalic acid as the ultimate short-chain carboxylic acid, whereas N-demethylation of some of them produces formic acid as well. Oxalic acid and its Fe²⁺ complexes, as well as formic acid, can be slowly but totally mineralized by OH.     

Influence of Fe2O3 content on the dielectric behavior of aluminous porcelain insulators

Due to the increasing availability of substitute materials for electrical porcelain, research is needed to adapt formulations involving these materials to the current economic realities of the industry. This study assessed the effect of iron oxide concentration (0, 1, 2, 3, 5, and 8 wt%) on the dielectric properties of an aluminous porcelain composition commonly employed for electrical insulation based on different values of temperature and frequency. Samples with iron oxide contents of 0, 3, and 5 wt% were analyzed using dilatometry, X-ray diffraction, and scanning electron microscopy to evaluate the thermal, structural, and microstructural changes related to their Fe₂O₃ concentrations. Both the dielectric constant (ε_r) and the loss tangent (tan δ) were measured and evaluated in every sample. Results indicated that the presence of Fe₂O₃ increased the dielectric constant and loss tangent, which could result in an increase in heating by dielectric losses. Fe₂O₃ contents of up to 5 wt% had no significant effect on the performance of these insulators at room temperature (∼30 °C) and a high frequency (1 MHz), especially when the hematite phase was completely solubilized in the porcelain phases.     

Frequency, temperature and In dependent electrical conduction in NiFe2O4 powder

A series of polycrystalline spinel ferrites with the composition NiIn_xFe_2-xO₄ (0 ≤ x ≤ 0.3) were prepared by the solid state reaction to study the effect of In³⁺ ions substitution on their dc electrical resistivity and dielectric properties. The dc resistivity has been investigated as a function of temperature and composition. The indium ion increases the dc resistivity and activation energy of the system. A study of the dielectric properties of these mixed ferrites, as a function of composition, frequency and temperature, has been undertaken. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) all decreases with frequency as well as with the composition. The dielectric constant (ε′) and dielectric loss tangent (tanδ) were increases with increasing temperature. AC conductivity increases with increase in applied frequency. The dielectric behavior of the present samples is attributed to the Maxwell-Wagner type interfacial polarization. The conduction mechanism in these ferrites is due to electron hopping between Fe²⁺ and Fe³⁺ ions on adjacent octahedral sites.     

Anodic oxidation and electro-Fenton treatment of rotenone

Rotenone, a widely used botanical insecticide submitted to strong restrictions regarding its environmental hazards, was studied as a target compound for electro-Fenton (EF) treatment in aqueous-acetonitrile mixture (70:30) of pH 3.0. In this system, the degradation of organic pollutants occurs by attack of hydroxyl radicals (OH) which are produced from the reaction of added ferrous catalyst (Fe²⁺) and hydrogen peroxide (H₂O₂) electrogenerated by oxygen reduction at carbon felt cathode. The degradative efficiency of EF system was comparatively studied versus anodic oxidation method (AO) in absence and presence of H₂O₂. It was found that only EF is sufficiently powerful to induce fast and efficient mineralization of rotenone and its degradation intermediates.The mineralization of rotenone was found to depend largely on organic solvent type, metal ion catalyst, applied current and initial rotenone concentration. The best operative conditions are achieved using aqueous-acetonitrile mixture of pH 3.0 in the presence of 0.2 mM Fe²⁺ catalyst with a current intensity of 100 mA. Under these optimized conditions, 30 min were sufficient to completely degrade rotenone in 100 mL of a 20 mg L⁻¹ solution. A nearly complete mineralization (∼96% of COD removal) was achieved after 8 h treatment.Rotenone removal kinetic was found to obey the pseudo-first order model and the absolute second order rate constant (k_Rot = 2.49 × 10⁹ M⁻¹ s⁻¹) for the reaction between the substrate and OH was derived.HPLC-MS and HPLC-DAD analysis were applied to identify and follow the evolution of rotenone oxidation products. Three stable aromatic intermediates were observed and two of these were identified as 12aβ-hydroxyrotenone and hydroquinone. Subsequent attack of these intermediates by OH radicals leads to the formation of aliphatic carboxylic acids such as succinic, acetic, oxalic and formic, quantified by ion-exclusion chromatography.     

Electrodeposition of Mackinawite films on Ti: effects of the S2O3/Fe mole ratio in the solution

Mackinawite films have been deposited on Ti supports from aqueous solutions containing ferrous and thiosulphate ions, using a potentiostatic double pulse technique. Studies on the influence of the electrolyte concentration ratio [S₂O₃²⁻]/[Fe²⁺] on the film properties were performed. Cyclic voltammetry was used as a diagnostic technique for the electrodeposition process. In situ characterisation of the deposits was performed by anodic stripping analysis. The structure and morphology of the films were investigated by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The experimental data provide evidence that Mackinawite deposits have been obtained from the entire electrodeposition baths although its purity is conditioned by the bath composition. Namely, when [S₂O₃²⁻]=[Fe²⁺], oxidation products such as α-S and γ-FeOOH were detected.     

Characteristics of Fe/AlPO4-5 catalyst prepared with organic solution

The Fe/AlPO₄-5 catalysts are prepared by impregnation with aqueous and organic solution (acetic acid, alcohol and acetone) of iron(III) nitrite respectively. The characterization of catalyst by means of XPS, Mössbauer spectroscopy, TPR and CO hydrogenation is reported. The catalyst prepared with the aqueous solution has no activity for CO hydrogenation because the Fe(III) in the catalyst cannot be reduced to -Fe. However, the catalysts prepared with organic solution possess obvious hydrogenation activity, in which -Fe is present in the initial reduced catalyst besides Fe³⁺ and Fe²⁺. The results may be explained by the interaction degrees between the metal and the support induced by the different impregnation solvents.     

Mercury removal from coal combustion by Fenton reactions – Part A: Bench-scale tests

This series of papers describes the development of technology to convert Hg(0) to Hg(II) in coal-derived flue gas based on the well-known Fenton reactions so that a Hg control strategy can be implemented in a wet scrubber. This effort consists of both bench-scale and pilot-scale work. This first paper reports on the bench-scale tests. The bench-scale results showed that Hg(0) oxidation can be achieved by the Fenton reactions and the oxidation rate is quantitatively dependent on the residence time of the Hg stream in the solution. An average of 75% oxidation of Hg(0) was achieved. Iron-based Fenton-type additives gave much more promising results compared to Cu-based Fenton-like additives for Hg(0) oxidation. The pH value of the sorbent solution also had a significant effect on the oxidation of Hg(0) and a suitable pH window was found to lie between 1.0 and 3.0 for this application. This may be attributed to the chain reaction mechanisms of Fe³⁺/H₂O₂ for Fenton reactions, i.e., the decomposition of H₂O₂ for the production of OOH radicals in the Fe³⁺/H₂O₂ system which is kinetically favoured under a wide range of conditions at pH values of 3 or less. At higher pH values, H₂O₂ is converted to H₂O instead of OOH radicals in the presence of Fe³⁺.     

Electro-Fenton degradation of antimicrobials triclosan and triclocarban

The antimicrobials triclosan (2,4,4′-trichloro-2′-hydroxydiphenyl ether) and triclocarban (N-(4-chlorophenyl)-N′-(3,4-dichlorophenyl)urea) have been degraded by four electro-Fenton systems using undivided electrolytic cells with a Pt or boron-doped diamond (BDD) anode and a carbon felt or O₂ diffusion cathode. The main oxidant is hydroxyl radical (OH) produced both on the anode surface from water oxidation and in the medium by Fenton's reaction, which takes place between electrogenerated H₂O₂ and Fe²⁺ coming from cathodic reduction of O₂ and Fe³⁺, respectively. Triclosan from saturated aqueous solutions of pH 3.0 is completely removed in all cells, decreasing its decay rate in the order: Pt/carbon felt > BDD/carbon felt > Pt/O₂ diffusion > BDD/O₂ diffusion, in agreement with their OH generation ability from Fenton's reaction. Glyoxylic, maleic and oxalic acids are identified as aliphatic intermediates. Complexes between oxalic acid and iron ions persist largely in solution, although Fe²⁺-oxalato complexes are mineralized by OH in the medium and Fe³⁺-oxalato complexes are destroyed by OH on BDD. Analogous treatments of more concentrated triclosan solutions using a 20:80 (v/v) acetonitrile/water mixture as solvent evidence the role of hydroxyl radicals along the degradation. In this hydroorganic medium hydroxylated derivatives such as 2,4-dichlorophenol, 4-chlorocatechol, chlorohydroquinone and chloro-p-benzoquinone, and carboxylic acids such as maleic, oxalic, formic and acetic acids are detected as products. Complete destruction of iron-oxalato complexes and released Cl⁻ ion involves some oxidizing species coming from parallel acetonitrile oxidation. The same electro-Fenton systems also yield the overall removal of triclocarban in acetonitrile/water mixtures, giving rise to urea, hydroquinone, chlorohydroquinone, 1-chloro-4-nitrobenzene and 1,2-dichloro-4-nitrobenzene as primary intermediates.     

Cation distributions and magnetism of Al-substituted CoFe2O4 - NiFe2O4 solid solutions synthesized by sol-gel auto-combustion method

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000?°C for 1?h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160?nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al³⁺ ions substituting the other cations such as Co²⁺, Ni²⁺ and Fe³⁺ ions in the compounds. The room temperature Mössbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe³⁺) cations. The observed magnetic hyperfine field (B_hf) decreases with increase in Al-concentration due to the distribution of diamagnetic Al³⁺ in the environment of ⁵⁷Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of B_hf. The distributions of the cations obtained from the Rietveld refinement and Mössbauer spectroscopy results indicate an increase in Fe³⁺(Th)/Fe³⁺(Oh) occupancy-ratio on increasing Al³⁺ concentration, and Ni²⁺ cations prefer the octahedral site, whereas Co²⁺ and Al³⁺ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.     

Direct synthesis of H2O2 acid solutions on carbon cathode prepared from activated carbon and vapor-growing-carbon-fiber by a H2/O2 fuel cell

Direct synthesis of H₂O₂ acid solutions was studied using a gas-diffusion cathode prepared from activated carbon (AC), vapor-growing-carbon-fiber (VGCF) and poly-tetra-fluoro-ethylene (PTFE) powders, with a new H₂/O₂ fuel cell reactor. O₂ reduction to H₂O₂ was remarkably enhanced at the three-phase boundary (O₂(g)-electrode(s)-acid(l)) at the [AC + VGCF] cathode. Fast diffusion processes of O₂ to the active surface and of H₂O₂ to the bulk acid solutions were essential for H₂O₂ accumulation. Synergy of AC and VGCF was observed for the H₂O₂ formation. RRDE and cyclic voltammetry studies indicated that the surface of AC functioned as the active phase for O₂ reduction to HO₂, and VGCF functioned as an electron conductor and a promoter to convert HO₂ to H₂O₂. A maximum H₂O₂ concentration of 353 mM (1.2 wt%) was accomplished under short-circuit conditions (current density 12.7 mA cm⁻², current efficiency 40.1%, geometric area of cathode 1.3 cm², reaction time 6 h).