Comparative study of the electrical characteristics of ALD-ZnO thin films using H2O and H2O2 as the oxidants

ZnO thin films were deposited via atomic layer deposition (ALD) using H₂O and H₂O₂ as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H₂O₂ (H₂O₂-ZnO) showed lower growth rates than those deposited with H₂O (H₂O-ZnO) at these temperature range due to the lower vapor pressure of H₂O₂, which produces fewer OH⁻ functional groups; the H₂O₂-ZnO films exhibited higher electrical resistivities than the H₂O-ZnO films. The selection of H₂O₂ or H₂O as oxidants was revealed to be very important for controlling the electrical properties of ALD-ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H₂O-ZnO, H₂O₂-ZnO exhibited poor crystallinity within a growth temperature range of 100-200°C, while H₂O₂-ZnO showed a strong (002) peak intensity. Photoluminescence showed that H₂O₂-ZnO had more interstitial oxygen and fewer oxygen vacancies than H₂O-ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.     

Electronic Structure and Properties of the O2+2, SO2+ and S2+2 Diatomic Dications

Multiply charged ions show novel energetic features which can potentially have useful photophysical properties. In order to investigate these interesting type systems, energy interaction curves for the ground and excited electronic states of O²⁺₂, SO²⁺, and S²⁺₂ have been generated by the ab initio complete active space multiconfiguration self-consistent field (CAS-MCSCF) method. The calculations were carried out in a triple-zeta sp plus double-zeta d Gaussian function basis set using compact effective potentials to replace the core electrons. In order to gauge the accuracy of the results, analogous calculations were carried out on the valence isoelectronic N₂ and NO⁺ systems for which experimental information is available for comparison of geometric and spectroscopic properties. Diverse high energy spectroscopy experiments on O²⁺₂ are interpreted and reconciled using the calculated ground and excited state energy interaction curves. Special attention is paid to the ₃Σ₊^u state, whose location and character have been particularly puzzling. Almost all the dication molecular states studied show the characteristic avoided crossing of diabatic states which gives a trapped equilibrium structure and a barrier to dissociation. These features make the dication kinetically stable, but thermodynamically unstable with an exothermic dissociation energy. The spectroscopy experiments on O²⁺₂ show that these states are experimentally attainable.     

Imaging and probing catalytic surface reactions on the nanoscale: Field Ion Microscopy and atom-probe studies of O2–H2/Rh and NO–H2/Pt

We present dynamic studies of surface reactions using video-Field Ion Microscopy (FIM) along with Pulsed Field Desorption Mass Spectrometry (PFDMS). Catalytic water formation is followed using rhodium and platinum 3D field emitter crystals for the oxidation of hydrogen with either oxygen (Rh) or NO (Pt). Strongly non-linear dynamics are observed with nanoscale spacial resolution. For both reactions quasi-oscillatory behaviour exists under certain conditions of temperatures and partial pressures. An influence of the probing electric field is observed and possibly essential in establishing oscillatory behaviour. Local chemical probing of selected surface areas with up to 400 atomic surface sites proves catalytic water formation to take place. Since water ions (H₂O⁺/H₃O⁺) cause image formation of the O₂–H₂ reaction on Rh, respective videos provide space-time resolved information on the catalytically active sites. Atom-probe data also reveal that the surface of the Rh sample reversibly switches from a metallic to an oxidized state during oscillations. As to the NO–H₂ reaction on Pt, fast ignition phenomena are observed to precede wave fronts. After catalytic water formation, NO molecules diffuse into emptied areas and cause high image brightness. Depending on the size of the Pt crystal, the reaction may ignite in planes or kinked ledges along the <100> zone lines. Thus FIM provides clear experimental evidence that kinks are more reactive than steps in the catalytic NO + H₂ reaction. Pt surface oxidation occurs and has probably been underestimated in previous FIM studies.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

Thermal Behavior of M +B5O6(OH)4 · 2H2O (M + = K, Rb, Cs) and Polymorphic Transformations of CsB5O8

Phase transformations (dehydration, amorphization, crystallization, polymorphic transitions) and thermal expansion of M ⁺B₅O₆(OH)₄ · 2H₂O (M ⁺ = K, Rb, Cs) compounds and the polymorphic transformations of the CsB₅O₈ compound are investigated using the methods of glass crystallization, thermal X-ray diffraction, and differential thermal analysis (DTA). It is shown that the dehydration of RbB₅O₆(OH)₄ · 2H₂O and CsB₅O₆(OH)₄ · 2H₂O, like KB₅O₆(OH)₄ · 2H₂O, proceeds in two stages. After the first stage of the dehydration (with a loss of three water molecules), all three compounds transform into the amorphous state. At the second stage, the fourth water molecule leaves the amorphous phase. At temperatures above the glass transition point, anhydrous pentaborates MB₅O₈ (M = K, Rb, Cs) crystallize and subsequently undergo polymorphic transformations.     

Bactericidal Effectiveness of O3, O3/H2O2 and O3/TiO2 on Clostridium perfringens

The purpose of this research is to evaluate the bactericidal capacity of different Advanced Oxidation Treatments (AOTs) based on ozone: ozone, ozone/hydrogen peroxide and ozone/titanium dioxide on a wild strain of Clostridium perfringens, a fecal bacterial indicator in drinking water. The dose of ozone consumed ranges from 0.6 mg L^?1 min^?1 to 5.13 mg L^?1 min^?1 depending on the process and on the sample. In the treatments combined with O₃, H₂O₂ dose utilized is 0.04 mM and TiO₂ dose, 1 g L^?1. In order to evaluate the influence of natural organic matter and suspension solids over the disinfection rate, treatments are performed with two types of water – natural water from Ebro River (Zaragoza, Spain) and NaCl solution 0.9%. To achieve 4 log units of inactivation, 3.6 mg O₃ L^?1 is necessary in O₃ treatment, 4.25 mg O₃ L^?1 in O₃/TiO₂ system and 2.7 mg O₃ L^?1 in O₃/H₂O₂ after processing the natural water. In NaCl solution, to get the same inactivation, 0.42 mg O₃ L^?1 is necessary in O₃ treatment, 1.15 mg O₃ L^?1 in O₃/TiO₂ system and 0.06 mg O₃ L^?1 in O₃/H₂O₂ process. Even though the three treatments studied have a high bactericidal activity due to the number of surviving bacteria decreases to non-detectable levels, O₃/H₂O₂ is the most effective system for eliminating C. perfringens cells in a lower contact time, followed by O₃ and finally O₃/TiO₂ system.     

A comparison of ethanol and water as the liquid phase in the direct formation of H2O2 from H2 and O2 over a palladium catalyst

Ethanol and water have been compared as the media in which hydrogen peroxide is produced from the reaction of H₂ and O₂ over a palladium catalyst. There are significant differences between the reaction in the two media with respect to the net rate of H₂O₂ formation, the state of the active Pd and the mechanism of the reaction. The reactions were carried out at atmospheric pressure and at 10 °C, with O₂ and H₂ being introduced in a 4/1 ratio through a glass frit. In ethanol, using 50 mg of 5 wt % Pd/SiO₂, 1.8 wt% H₂O₂ was attained in 7 h; whereas, about half this amount was attained in water. In addition, the net formation rate did not remain constant in water. Both systems were 0.17 N in HCl, which facilitated the formation of colloidal Pd in water but not in ethanol. The loss of activity in water is attributed to the instability of the colloid, which has been shown previously to be the active state of Pd. By contrast, these results show that supported Pd is the active state of the metal in the ethanol system. The mechanism for the formation of the nonselective product, water, also is affected by the media in which the reaction is carried out. In ethanol, water is formed by the direct reaction of H₂ and O₂, while in the aqueous phase, water appears to be formed both by the direct pathway and by the reduction of H₂O₂.     

Low‐lying energy isomers and global minima of aqueous nanoclusters: Structures and spectroscopic features of the pentagonal dodecahedron (H2O)20 and (H3O)+(H2O)20

We rely on a hierarchical approach to identify the low‐lying isomers and corresponding global minima of the pentagonal dodecahedron (H₂O)₂₀ and the H₃O⁺(H₂O)₂₀ nanoclusters. Initial screening of the isomers is performed using classical interaction potentials, namely the Transferable Interaction 4‐site Potential (TIP4P), the Thole‐Type Flexible Model, versions 2.0 (TTM2‐F) and 2.1 (TTM2.1‐F) for (H₂O)₂₀ and the Anisotropic Site Potential (ASP) for H₃O⁺(H₂O)₂₀. The nano‐networks obtained with those potentials were subsequently refined at the density functional theory (DFT) with the Becke‐3‐parameter Lee–Yang–Parr (B3LYP) functional and at the second order Møller–Plesset perturbation (MP2) levels of theory. For the pentagonal dodecahedron (H₂O)₂₀ it was found that DFT (B3LYP) and MP2 produced the same global minimum. However, this was not the case for the H₃O⁺(H₂O)₂₀ cluster, for which MP2 produced a different network for the global minimum when compared to DFT (B3LYP). The low‐lying networks of H₃O⁺(H₂O)₂₀ correspond to structures having 9 ‘free’ OH bonds and the hydronium ion on the surface of the nanocluster. The IR spectra of the various networks are further analysed in the OH stretching (‘fingerprint’) region and the various bands are assigned to structural arrangements of the underlying hydrogen bonding network. © 2012 Canadian Society for Chemical Engineering     

Oxidation of Herbicides in Groundwater by the Fenton Process: A Realistic Alternative for O3/H2O2 Treatment?

Oxidation with O₃/H₂O₂ and Fe²⁺/H₂O₂ are optional for the degradation of herbicides and pesticides in water. The choice of which process will be applied depends upon the degree of degradation of organic micropollutants and the process conditions related to the formation of oxidation by-products, and also on the total costs and the safety and reliability of the process. Under real conditions, atrazine and some phenylureaherbicides were oxidized with O₃/H₂O₂. Comparable experiments under conditions of different pH, iron and DOC content were performed with Fe²⁺/H₂O₂, in order to gain information on the influence of these parameters. The oxidation results of both processes as well as the formation of bromate as one of the oxidation by-products are described. It was found that 80% of atrazine and >99% of some phenylureaherbicides could be degraded with O₃/H₂O₂ at pH 7.8 (H₂O₂/O₃ ratio 3.7 g/g). Under these conditions, bromate was formed up to 5 μg/1. Comparable results were obtained with Fe²⁺/H₂O₂ at a pH value of 5.5, whereas the formation of bromate was kept below 0.2 μg/L.     

Direct synthesis of H2O2 from H2 and O2 over Pd/H-beta catalyst in an aqueous acidic medium: Influence of halide ions present in the catalyst or reaction medium on H2O2 formation

The influence of different halide ions present in the catalyst or reaction medium on the performance of Pd/H-beta catalyst in the direct H₂O₂ synthesis in an aqueous acidic (0.03 M H₃PO₄) reaction medium at 27 °C and atmospheric pressure has been thoroughly investigated. The results showed a strong influence of both the bulk Pd oxidation state in the catalyst and the halide ions added to the reaction medium on the performance of the catalyst in the H₂ to H₂O₂ oxidation, H₂O₂ decomposition/hydrogenation reactions. The different ammonium halides impregnated reduced Pd/H-beta catalyst calcined in inert (N₂) and oxidizing (air) gaseous atmospheres also revealed that the bulk Pd oxidation state and nature of the halide ions present in the catalyst together control the overall performance of the catalyst in the H₂O₂ formation reaction. The presence of halide ions in reaction medium or in the catalyst significantly changes the selectivity for H₂O₂ formation in the direct H₂O₂ synthesis. Bromide ions are found to remarkably enhance the H₂O₂ selectivity in the direct H₂O₂ synthesis irrespective of the Pd oxidation state in the catalyst. The promoting action of Br⁻ is attributed mainly to the large decrease in the H₂O₂ decomposition and hydrogenation activities of the catalyst and also inhibition for the non-selective H₂-to-water oxidation over the catalyst.     

UV-Enhanced Exchange of O2with H2O Adsorbed on TiO2

Ultraviolet light dramatically increases the rate of isotope exchange between gas-phase O₂and water adsorbed on TiO₂at room temperature, but it does not affect the rate of CO₂–water exchange. Both ethanol and acetaldehyde, when coadsorbed with H₂¹⁸O, dramatically decrease the rate of O₂exchange, but not CO₂exchange, with adsorbed H₂¹⁸O. This decrease is attributed to a combination of competition for adsorbed oxygen between exchange and photocatalytic oxidation of the adsorbed organic and blocking of the oxygen adsorption sites by the organic. The same oxygen species participate in O₂-H₂¹⁸O exchange and photocatalytic oxidation.     

Synthesis,structural characterization and properties of a novel 1D helical chain arsenomolybdate {[Cu(en)2][Cu(en)(H2O)][(Cu(en)2(H2O)] [AsIIIAsVMo9O34)]} · 2H2O

An organic–inorganic hybrid 1D helical chain arsenomolybdate {[Cu(en)₂][Cu(en)(H₂O)][(Cu(en)₂(H₂O)] [As^IIIAs^VMo₉O₃₄)]} · 2H₂O (1) (en = ethylenediamine) has been hydrothermally synthesized and characterized by elemental analyses, IR, UV and CD spectrum, powder X-ray diffraction, TG-DTA and single-crystal X-ray diffraction. The asymmetric unit of 1 consists of a monocapped trivacant Keggin [As^IIIAs^VMo₉O₃₄]^6 − subunit, a pendant [Cu(en)₂(H₂O)]^2 + cation, a pendant [Cu(en)(H₂O)]^2 + cation, one bridging [Cu(en)₂]^2 + cation and two lattice water molecules. It should be noted that 1 illustrates a one-dimensional (1D) helical chain assembled by {[Cu(en)(H₂O)][(Cu(en)₂(H₂O)][As^IIIAs^VMo₉O₃₄)]}^2 − clusters and [Cu(en)₂]^2 + linkers.     

The Active Phase in the Direct Synthesis of H2O2 from H2 and O2 over Pd/SiO2 Catalyst in a H2SO4/Ethanol System

In an effort to determine the active state of supported palladium for the direct formation of H₂O₂ from H₂ and O₂, the catalytic behavior of Pd⁰/SiO₂, PdO/SiO₂ and partially reduced PdO/SiO₂ was determined. The results obtained in an ethanol slurry, with chloride ions and H₂SO₄ being present, showed that the PdO/SiO₂ catalyst was almost completely inactive for the formation of H₂O₂ at 10 °C. The Pd⁰/SiO₂ catalyst exhibited the highest activity for H₂O₂ formation, and the PdO/SiO₂ material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd⁰ (the metal phase) and PdO were observed on Pd⁰/SiO₂ and PdO/SiO₂, respectively. As expected, with the partially reduced PdO/SiO₂ catalyst, both Pd⁰ and PdO phases were evident. The TEM results revealed that the Pd⁰ particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H₂O₂.     

Effect of magnetic catalysts on the kinetic behaviour of Reactive Black 5 decomposition by an O3/H2O2 process

BACKGROUND: Particles are often too small to be separated from a reaction system and recycled, especially in waste‐water treatment via a catalytic ozonation process. Therefore, the objective of this study was to prepare a magnetic catalyst (SiO₂/Fe₃O₄) that can be recycled by using an external magnetic field. The characteristics of the magnetic catalyst and kinetics of decomposition of Reactive Black 5 (RB5) using a magnetic catalyst/H₂O₂/O₃ have been investigated. Magnetic catalysts (SiO₂/Fe₃O₄) were characterized by X‐ray diffraction (XRD), vibrating sample magnetometry (VSM) and Fourier transform infrared (FTIR) spectroscopy. RESULTS: In the case of the decomposition of RB5 by the SiO₂/Fe₃O₄/H₂O₂/O₃ process, the contribution of the destruction by the indirect oxidation of OH· caused by the chain reaction of H₂O, OH^?, and H₂O₂ was found to be larger than that of the direct attack of O₃. The kinetic behaviour of the reacting species during the decomposition of RB5 by catalytic ozonation could be well modelled under various experimental conditions. CONCLUSIONS: The paramagnetic behaviour of the prepared SiO₂/Fe₃O₄ led to the formation of the magnetic catalyst SiO₂/Fe₃O₄, which could be separated more easily by the application of a magnetic field. More than 90% of the magnetic catalyst was recovered and easily redispersed in a solution for reuse by mixing with a flat‐bladed turbine. Copyright © 2010 Society of Chemical Industry     

Influence of nature/concentration of halide promoters and oxidation state on the direct oxidation of H2 to H2O2 over Pd/ZrO2 catalysts in aqueous acidic medium

The nature/concentration of halide promoters and influence of the Pd oxidation state on the promoted reaction system has been investigated on the direct H₂O₂ process over a 2.5 wt.% Pd/ZrO₂ catalyst in an aqueous acidic reaction medium. The oxidation state of Pd had a profound influence on the H₂O₂ synthesis process. Interestingly, the nature of the halide determined the magnitude/type of influence the Pd oxidation state exerted on the overall process. While the effect of the oxidation state on the H₂O₂ yields was large for the reaction systems containing F⁻ or no halide, the effect was significantly smaller for the reaction systems containing Br⁻ and Cl⁻. The nature of the halide also strongly influenced the H₂O₂ synthesis process. Br⁻ strongly enhanced the H₂O₂ yields, while F⁻ had a negative influence on the H₂O₂ yields. The ability of the halides to enhance the H₂O₂ process was found to strongly depend on its propensity to suppress the secondary H₂O₂ decomposition reaction. The influence of Br⁻ and Cl⁻concentration studies revealed that the optimum halide concentration for the direct H₂O₂ synthesis process was dependent on the nature of the halide. While the maximum in H₂O₂ yields for the Br⁻ containing reaction medium corresponded to a concentration of ∼0.9 mmol/dm³ (KBr) the maximum for the Cl⁻ containing solution was obtained at ∼1.5 mmol/dm³ (KCl). Such knowledge is crucial from the viewpoint of optimization (catalyst/reaction system screening studies) of the direct H₂O₂ process. The qualitative trends (H₂O₂ selectivity/yield) observed in case of the incorporated halide catalysts were similar to those observed with halides in reaction medium over the Pd/ZrO₂ catalyst.     

Role of O3 and OH· Radicals in Ozonated Aqueous Solution for the Photoresist Removal of Semiconductor Fabrication

The role of direct oxidation by aqueous O₃ and advanced oxidation by OH^· in the removal of photoresist was studied by chemical kinetic simulation and experiments of O₃ reactivity and decomposition in homogeneous aqueous solutions. O₃ is the main species responsible for the removal of conventional photoresist in the ozonated water cleaning process, and the timing of initiator addition to ozonated water is important to maintain high O₃ concentration. Simulation using t-butanol implies that maintenance of a high OH^· concentration is required to remove highly implanted photoresists that O₃ itself cannot easily remove.     

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

The kinetic behavior in the direct synthesis of H₂O₂ with Pd–Me (Me = Ag, Pt) catalysts prepared by depositing the noble metals by electroless plating deposition (EPD) or deposition–precipitation (DP) methods on α-Al₂O₃ asymmetric ceramic membrane with or without a further surface coating by a carbon thin layer is reported. The effect of the second metal with respect to Pd-only catalysts considerably depends on the presence of the carbon layer on the membrane support. Several factors in the preparation of these membranes as well as the reaction conditions (temperature, concentration of Br⁻, pH) determine the selectivity in H₂O₂ formation, influencing the rate of the consecutive reduction of H₂O₂ (which is faster with respect to H₂O₂ decomposition on the metal surface) and/or of direct H₂ + O₂ conversion to H₂O. Defective Pd sites are indicated to be responsible for the two unselective reactions leading to water formation (parallel and consecutive to H₂O₂ formation), but the rate constants of the two reactions are differently influenced from the catalytic membrane characteristics. Increasing the noble metal loading on the membrane not only increases the productivity to H₂O₂, but also the selectivity, due to the formation of larger, less defective, Pd particles.     

The effect of Mg(OH)2 on furfural oxidation with H2O2

The oxidation of furfural in H₂O₂ and H₂O₂–Mg(OH)₂ system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)₂ suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H₂O₂ is homogeneous, and the synergy between dissolved Mg^2 + cations and OH⁻ ions facilitates the HOO⁻ attacking the carbon atom of HCO other than the CC bound of furan ring.     

ESR study of reactions of cellulose with ·OH generated by Fe+2/H2O2

It was demonstrated by ESR spectroscopy that the Fe⁺²/H₂O₂ system gave a reactive species which generated an ESR triplet spectrum or sorbitol similar to that generated by hydroxyl radicals from the Ti⁺³/H₃O₂ system. An ESR spectrum was obtained for the hydroxyl radicals generated by the latter system. However, the lifetime of hydroxyl radicals, generated by the Fe⁺²/H₂O₂ system, was apparently very short, and an ESR spectrum for the hydroxyl radicals, generated by this system, was not observed. The Fe⁺²/H₂O₂ system also generated triplet spectra with cotton cellulose I, cotton cellulose II, and microcrystalline cellulose, suggesting that a hydrogen atom had been abstracted from the hydroxyl group on carbon C₆, or possibly the hydrogen atom on carbon C₅. The ESR spectrum generated on microcrystalline cellulose was less intense than those generated on cellulose I and II. On initiation of graft polymerization of the activated cellulose with acrylonitrile, the triplet spectrum disappeared and was replaced by two strong singlet spectra. One of the singlet spectra was likely generated on carbon C₁ or C₄ on depolymerization of the cellulose molecule, and the other was probably generated on the end of the growing polyacrylonitrile molecular chain. The absence of a triplet spectrum gave direct evidence for the order in which the acrylonitrile monomer was being grafted onto the cellulose molecule. The mechanisms proposed by Haber and Weiss for the reactions generated in the Fe⁺²/H₂O₂ system were generally supported.     

Preparation of NiCo2O4 Nanosheet Arrays and its High Catalytic Performance for H2O2 Electroreduction

Ni foam supporting‐NiCo₂O₄ nanosheet arrays (NiCo₂O₄/Ni foam) are successfully prepared by electrodeposition of the hydroxide precursor, followed by a thermal treatment in air without any template and surfactant. The morphology of NiCo₂O₄ nanosheet arrays is characterized by scanning electron microscope and transmission electron microscopy. The structure is analyzed using X‐ray diffractometer, X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The catalytic performance of NiCo₂O₄/Ni foam electrode for H₂O₂ electroreduction in KOH solution is evaluated by means of cycle voltammetry and chronoamperometry, which exhibits an excellent catalytic performance and superior stability for H₂O₂ electroreduction. The reduction current density of H₂O₂ on NiCo₂O₄/Ni foam electrode is 0.378 A cm⁻² at –0.4 V in the solution containing 3.0 mol L⁻¹ KOH + 0.4 mol L⁻¹ H₂O₂, which is much larger than that on other metal oxides reported previously.