Electrocatalytic determination of hydrazine by a glassy carbon electrode modified with PEDOP/MWCNTs-Pd nanoparticles

The electrocatalysis of hydrazine oxidation by poly-ethylenedioxy pyrrole (PEDOP)-coated MWCNTs-palladium nanoparticles [PEDOP/MWCNTs-Pd] was investigated as an electrochemical sensor on the surface of glassy carbon electrode (GCE) in aqueous medium. Electrochemical oxidation of hydrazine in phosphate buffer (pH 7.4) was performed using cyclic voltammetry (CV) and chronoamperometry (CA) methods. Using the proposed electrode, the catalytic oxidation peak current of hydrazine was high and the overpotential of its oxidation decreased. Based on the obtained results, a mechanism for electrooxidation of hydrazine at [PEDOP/MWCNTs-Pd/GCE] demonstrated an irreversible diffusion-controlled electrode process and a four-electron transfer involved in the overall reaction. The experimental results showed that the mediated oxidation peak currents of the hydrazine were linearly dependent on the concentration of hydrazine in the range of 1.0 × 10⁻⁷ to 5.0 × 10⁻³ M. The detection limit (S/N = 3) was found to be 4 × 10⁻⁸ M with a fast response time of 10 s.     

CTAB assisted immobilization of RuO2 nanoparticles on graphene oxide for electrochemical sensing of hydrazine

A novel method has been presented to modify glassy carbon electrode (GCE) with graphene oxide (GO) nanocomposite without introducing any electrode binder such as chitosan and Nafion. First, modify GCE with RuO₂ nanoparticles which have been dispersed in cetyltrimethyl ammonium bromide (CTAB) aqueous solution. Then, highly adhesive RuO₂/CTAB/GO nanocomposite membrane formed on GCE by immersing RuO₂/CTAB modified GCE in GO suspension. CTAB plays significant roles not only in the preparation of the nanocomposite but also in the immobilization of nanocomposite on GCE surface. First, CTAB was used as the dispersant of RuO₂ nanoparticles. Second, CTAB acted as the molecular linker to bind RuO₂ nanoparticles on graphene sheets. Third, CTAB formed CTAB/GO nanocomposite which is highly adhesive on the surface of electrodes such as GCE and ITO (indium tin oxide). The obtained RuO₂/CTAB/GO/GCE shows excellent electrocatalytic ability towards the oxidation of hydrazine. The oxidation of hydrazine on RuO₂/CTAB/GO/GCE is an adsorption-controlled process and the oxidation current is linear with the concentration of hydrazine in the range of 1 × 10^?5～1 × 10^?3 M with a detection limit of 2.3 × 10^?6 M. The application of this sensor in the sensing of hydrazine in real water samples confirmed its reliability and accuracy.     

Self-supported iron-doped nickel sulfide as efficient catalyst for electrochemical urea and hydrazine oxidation reactions

The electrochemical oxidation of urea and hydrazine over self-supported Fe-doped Ni₃S₂/NF (Fe–Ni₃S₂/NF) nanostructured material is presented. Among the various reaction conditions Fe–Ni₃S₂/NF-2 prepared at 160 °C for 8 h using 0.03 mM Fe(NO₃)₃ shows the best results for the hydrazine and urea oxidation reactions. The potential values of 0.36, 1.39, and 1.59 V are required to achieve the current density of the 100 mA cm^?2 in 1 M hydrazine (Hz), 0.33 M urea, and 1 M KOH electrolyte, respectively. The onset potential in 1 M KOH, 0.33 M Urea +1 M KOH, and 1 M Hz + 1 M KOH values are 1.528, 1.306, and 0.176 respectively. The Fe–Ni₃S₂/NF-2 shows stable performance at 10 mA cm^?2 until 50 h and at 60 mA cm^?2 over the 25 h. A cell of PtC//Fe–Ni₃S₂/NF-2 requires the potential of 0.49, 1.46, and 1.59 V for the hydrogen production in 1 M Hz + 1 M KOH, 0.33 M Urea +1 M KOH, and 1 M KOH electrolyte, respectively, at a current density of 10 mA cm^?2, and almost 90% stable for the hydrogen production over the 80 h in all electrolytes. The improvement of the chemical kinetics of urea and hydrazine oxidation is due to the synergistic effect of the adsorption and fast electron transfer reaction on Fe–Ni₃S₂/NF-2. The doped Fe ion facilitates the fast electron transfer and the surface of Ni₃S₂ support to the urea and hydrazine molecule adsorption.     

Hydrogen adsorption and interactions in self-reducing shell hosted palladium nanoparticles on magnetite support

The nanoparticles (NP), consisting of hydrazine grafted organo-silica with PdNPs embedded shell on the Fe₃O₄ core, were prepared to study the adsorption and interactions of hydrogen in PdNPs and their support matrix. This material is expected to find the applications in the hydrogen technology including catalysis. The PdNPs were formed spontaneously in the organo-silica shell on magnetite nanoparticles by the reduction of Pd²⁺ ions with grafted hydrazine in the organo-silica shell. Thus formed NPs, termed as Fe₃O₄-GTEOS@PdNPs, were also thermally treated at 1033 K in Ar atmosphere to convert organic components to carbon. The chemical composition, physical structure, and magnetic properties were studied by high resolution transmission electron microscopy, X-rays diffraction, Mössbauer spectroscopy and X-ray photoelectron spectroscopy for the characterizations of physical, chemical and magnetic changes occurred in the Fe₃O₄-GTEOS@PdNPs after hydrogen adsorption-desorption at varying temperatures with respect to that in unused one. The hydrogen adsorption pressure-composition (PC) isotherms in Fe₃O₄-GTEOS@PdNPs followed the expected trend from 173 to 303 K as expected from PdNPs. However, thermally treated Fe₃O₄-GTEOS@PdNPs were found to adsorb lower amount of hydrogen due to oxidation of Pd⁰ to PdO and morphological changes during heating in Ar atmosphere. The comparison of n_H/n_Pd value (0.49) obtained for the PdNPs in Fe₃O₄-GTEOS@PdNPs with the values those reported in the literature for different Pd materials showed the decrease in n_H/n_Pd value with decrease in the size of Pd particles. This was attributed to stronger Pd–H bond in a nanoscale palladium, which prevented hydrogen transfer to interior matrix as compared to bigger Pd particles. The hydrogen adsorption PC isotherm at 373 K in Fe₃O₄-GTEOS@PdNPs could not be obtained as the unknown chemical reaction happened in the sample during the experiment. The considerably higher H₂ consumption in the Fe₃O₄-GTEOS@PdNPs occurred at 373 K than that expected from the hydrogen adsorption in the PdNPs alone.     

La(OH)3-decorated NiFe nanoparticles as efficient catalyst for hydrogen evolution from hydrous hydrazine and hydrazine borane

Ultrafine NiFe nanoparticles (NPs) decorated by La(OH)₃ have been successfully prepared via a facile one-step co-reduction method without the help of surfactant or support. It was found that after being decorated with La(OH)₃, the NiFe–La(OH)₃ NPs have a smaller particle size and lower crystallinity. The resultant NiFe–La(OH)₃ nanocatalyst exhibits an excellent catalytic activity, 100% H₂ selectivity, and satisfied recyclability for hydrogen evolution from hydrous hydrazine (N₂H₄·H₂O) at 343 K under alkaline conditions, giving a high turnover frequency (TOF) value of 100.6 h⁻¹, which is more than 35 times higher than pure NiFe NPs (2.8 h⁻¹). The kinetics study shows that with respect to the concentration of catalyst and N₂H₄, the N₂H₄ dehydrogenation reaction follows fist-order kinetics and zero-order kinetics, respectively. Furthermore, NiFe–La(OH)₃ also exhibits an outstanding performance and excellent recycle stability during high dehydrogenation of hydrazine borane (N₂H₄BH₃). The excellent performances for the dehydrogenation of N₂H₄ and N₂H₄BH₃ could be attributed to the strong interaction between La(OH)₃ and NiFe NPs, as well as ultrafine and low crystalline NiFe NPs due to the addition of La(OH)₃.     

Cesium hydrazinidoborane,the last of the alkali hydrazinidoboranes,studied as potential hydrogen storage material

Alkali hydrazinidoboranes MN₂H₃BH₃ (M = Li, Na, K, Rb) have been developed for hydrogen storage. To complete the family of MN₂H₃BH₃, we focused on cesium hydrazinidoborane CsN₂H₃BH₃ (CsHB). It has been synthesized by reaction of cesium with hydrazine borane (N₂H₄BH₃) at −20 °C under inert atmosphere, and it has been characterized. A crystalline solid (monoclinic, s.g. P2₁ (No. 4)) has been obtained. Its potential for hydrogen storage has been studied by combining different techniques. It was found that, under heating at constant heating rate (5 °C min⁻¹) or at constant temperature (e.g. 120 °C), CsHB decomposes rather than it dehydrogenates. It releases several unwanted gaseous products (e.g. NH₃, B₂H₆) together with H₂, and transforms into a residue that poses safety issues because of shock-sensitivity and reactivity towards O₂/H₂O. Though the destabilization brought by Cs⁺ onto the anion [N₂H₃BH₃]⁻ has been confirmed, the effect is not efficient enough to avoid the aforementioned drawbacks. All of our results are presented herein and discussed within the context of solid-state hydrogen storage.     

Mo-doped Ni-based catalyst for remarkably enhancing catalytic hydrogen evolution of hydrogen-storage materials

Ni-based alloys are considered as the efficient catalyst for hydrogen-storage materials decomposition. Herein, we applied an in-situ melt-quenching method to dope Mo in Ni-based alloy for catalytic hydrogen evolution from hydrogen-storage materials. Importantly, Mo doped Ni-based catalyst exhibits more than 6 times higher TOF value than that of pure Ni both in AB hydrolysis and hydrazine decomposition, because Mo acts as an electron donor to improve the reducibility of Ni. Hydrogen evolution kinetics were studied over a range of temperatures (303–353 K) and initial feed concentrations (catalyst/hydrogen-storage materials (wt/wt) ratios = 0.2–10). Under optimal reaction conditions, the H₂ evolution rate reaches 1.92 mol H₂/(mol_cat min) and 0.05 mol H₂/(mol_cat min) in the hydrolysis of ammonia borane and decomposition of hydrazine, which are 6.42 and 6.44 times higher than undoped Ni catalyst, respectively. And the apparent activation energy of ammonia borane hydrolysis and hydrazine decomposition were evaluated to be 26.66 ± 3.31 kJ/mol and 40.01 ± 3.38 kJ/mol, respectively.     

Effect of palladium precursor and preparation method on the catalytic performance of Pd/SiO2 catalysts for benzene hydrogenation

Supported Pd catalysts on silica were prepared by different synthesis methods using Pd(Ac)₂ and PdCl₂ as salts precursors. The obtained materials were characterized by X-Ray Diffraction (XRD), H₂ chemisorption, and temperature programmed desorption of hydrogen (H₂-TPD). The catalytic performances of these catalysts have been evaluated in the hydrogenation of benzene. The obtained results show that metal dispersion and catalytic activity are strongly dependent on the salts precursor and the method of preparation of the catalyst. The catalysts prepared by hydrazine reduction exhibit higher activity in benzene hydrogenation than that by the polyol reduction method. Moreover, the catalyst prepared with palladium acetate showed higher catalytic activity than those prepared with palladium chloride. The superior catalytic performance of this catalyst in the hydrogenation of benzene was ascribed to a significantly better dispersion of Pd particles on the silica support.     

Effects of hydrazine addition on gas evolution and performance of the direct borohydride fuel cell

A fuel cell configuration using alkaline NaBH₄–N₂H₄ solutions as the fuel is suggested. Gas evolution behaviors and cell performances of alkaline NaBH₄–N₂H₄ solutions on different catalysts have been studied. It is found that gas evolution behaviors are influenced by the applied anodic catalysts and the concentration of NaBH₄ and N₂H₄. NaBH₄ is mainly electro-oxidized on Pd but N₂H₄ is mainly electro-oxidized on Ni and surface-treated Zr–Ni alloy when using NaBH₄–N₂H₄ solutions as the fuel and a composite of Pd, Ni and surface-treated Zr–Ni alloy as the anodic catalyst. The cyclic voltammetry results show that electrochemical oxidation potential of NaBH₄ is higher than that of N₂H₄. Adding hydrazine into alkaline sodium borohydride solutions can suppress gas evolution and improve the cell performance of the DBFC. The performances of fuel cells using NaBH₄–N₂H₄ solutions are comparable to that of fuel cell using N₂H₄ solution.     

有效微生物降解肼的试验研究

采用自配含肼污水直接投加EM法,可检测出不同条件(温度、pH、EM浓度、肼浓度)下肼浓度的变化,探讨了有效微生物降解肼的效果.复合培养基复壮的EM,在浓度为5%,温度为30℃、pH为8.0时,降解效果较好,3.5天内可将浓度在2～50mg/L肼降解至0.5mg/L以下,实践证明,EM在实验室条件下对肼浓度有较好的降解作用.