Cs0.86(NH4)1.14SO4Te(OH)6 in porous anodic alumina for micro fuel cell applications

Cs_0.86(NH₄)_1.14SO₄Te(OH)₆ supported by anodic alumina membranes (AAMs) has been characterized for the first time in H₂/O₂ fuel cell. The fabricated membrane electrode assemblies are able to produce peak power densities in the range 15–30 mW cm⁻² under mild conditions (room temperature, low humidity and low Pt loading) and show an increased durability with cycling with respect to previous results obtained with AAM-based fuel cell. The physico-chemical characterization of the electrolytes has been carried out through X-ray diffractometry, scanning electron microscopy and micro-raman analysis. An estimation of the composite membranes conductance under fuel cell operation has been carried out from I–V characteristics and EIS measurements at room temperature.     

Effect of the addition of NH4F on anodic behaviors of DSA-type electrodes in H2SO4-(NH4)2SO4 solutions

The effect of NH₄F addition on the high-anodic behaviors of various DSA-type electrodes was investigated in a mixture of sulfuric acid and ammonium sulfate. The pronounced effect of NH₄ addition was observed on DSA-type Ti/RuO₂, Ti/IrO₂?TiO₂ electrodes, but not observed on the other electrodes studied. The close relationship was found between the increment of the electrode potential caused by the NH₄ addition and the quantity of F^? adsorbed on the electrode surface. The effect of NH₄F addition was considered to be resulted from the adsorption of F^? on the electrode surface, and the presence of adsorbed F^? was directly proved.     

Oxygen reduction mechanism on copper in a 0.5 M H2SO4

The mechanism of the oxygen reduction reaction (ORR) in a naturally aerated stagnant 0.5 M H₂SO₄ was studied using electrochemical methods. The cathodic polarization curve showed three different regions; electrochemical impedance spectroscopy (EIS) measurement was used accordingly. The EIS data were analyzed, and the mechanism for the ORR was proposed consequently. The three regions include a limiting current density region with the main transfer of 4e⁻ controlled by diffusion (−0.50 V < E < −0.40 V), a combined kinetic-diffusion region (−0.40 V < E < −0.20 V) with an additional 2e⁻ transfer due to the adsorption of the anions, and a hump phenomenon region (−0.20 V < E < −0.05 V), in which the chemical redox between the anodic intermediate and the cathodic intermediate , together with the electrochemical reaction, synergistically results in the acceleration of the ORR. Therefore, a coupled electrochemical/chemical process (the EC mechanism) in the hump phenomenon region was proposed, and a good agreement was found between the experimental and fitted results. The EC mechanism was confirmed by the deaerated experiments.     

Control of morphology and composition of self-organized zirconium titanate nanotubes formed in (NH4)2SO4/NH4F electrolytes

We investigated the formation of self-organized zirconium titanate nanotubes by anodizing a Ti-35Zr alloy in 1 M (NH₄)₂SO₄ + 0.1-2.0 wt.% NH₄F electrolytes. The morphology and composition of the zirconium titanate nanotube are controlled by the applied electrochemical conditions. The outer diameter of nanotubes is controlled by the anodization potential in the range between 1 and 100 V (versus Ag/AgCl). Tubes with diameters from 14 to 470 nm can be grown. The nanotube length correlates with the anodic charge up to a length where significant dissolution of the nanotube layer is observed. The wall thickness, composition of the nanotubes and porosity of the nanotube layer are significantly affected by the fluoride ion concentration. The length limiting factor of the nanotube growth is found to be the diffusion of ionic species in the electrolyte.     

Synthesis, crystal structure and magnetic properties of a new three-dimensional porous framework: [Gd2(BDA)3(DMF)2(H2O)4] · 2DMF

The open framework compound of [Gd₂(BDA)₃(DMF)₂(H₂O)₄] · 2DMF (1), prepared by heating GdCl₃ with 2,2′-bipyridyl-4,4′-dicarboxylatic acid (BDA) in mixed solvent, is constructed from BDA linking up polymeric [GdO₅(DMF)(H₂O)₂]_n tethers. The 1D channels are filled with coordinated and uncoordinated DMF molecules hydrogen bonding to terminal aqua ligands. The study of the temperature dependent magnetic susceptibilities revealed that there are ferromagnetic interactions between intra-chain Gd^III atoms and weak antiferromagnetic interactions between inter-chain Gd^III atoms.     

Influence of ionic equilibrium in the CuSO4-H2SO4-H2O system on the formation of irregular electrodeposits of copper

The relative concentration of hydrogen ion (H⁺) as a function of sulfuric acid (H₂SO₄) concentration (calculated using Pitzer's model) and the electrochemical processes by which irregular copper deposits are formed were correlated. Irregular deposits are formed by potentiostatic electrodeposition at a high overpotential where the hydrogen evolution reaction occurs parallel to copper electrodeposition. Two sets of acid sulfate solutions were analyzed. In one set of experiments, the concentration of CuSO₄ was constant while the concentration of H₂SO₄ was varied. The other set of experiments was performed with a constant concentration of H₂SO₄ and different concentrations of CuSO₄. Then, the volumes of the evolved hydrogen (calculated as the average current efficiencies of hydrogen evolution) and the morphologies of copper deposits, characterized by the SEM technique, obtained for the same ratio of CuSO₄/H₂SO₄ were mutually compared and discussed in terms of the relative concentrations of hydrogen ions (H⁺) as a function of the H₂SO₄ concentration. Good agreement between the ionic equilibrium in the CuSO₄-H₂SO₄-H₂O system and the results of the electrochemical processes was obtained. In this way, it was shown how this ionic equilibrium can be applied to predict and analyze the solution composition in electrolytic copper deposition processes.     

Synthesis, crystal structure and thermal stability of tetrahydroborate sodalite Na8[AlSiO4]6(BH4)2

Tetrahydroborate sodalite formation was investigated in the system Na₂O–SiO₂–Al₂O₃–NaBH₄–H₂O under mild hydrothermal conditions. Due to the high degree of decomposition of hydroborates in aqueous solutions synthesis conditions were tuned by variation of the parameters alkalinity, liquid/solid ratio, reaction temperature and reaction time. The insertion of 8–16 molar NaOH solution was crucial for the higher stability of pure tetrahydroborate salt under strong alkaline conditions. Synthesis at 393 K and 24 h reaction time reveal tetrahydroborate sodalite Na₈[AlSiO₄]₆(BH₄)₂ beside a small amount of amorphous material within the total batch. Structure, composition and thermal stability of this new sodalite was investigated using XRD, NMR, infrared and TG/DTA methods. The crystal structure of tetrahydroborate sodalite has been refined in the space group P-43n with a = 891.61(2) pm. The Si- and Al-atoms of the aluminosilicate framework are completely ordered. The boron atoms of the tetrahydroborate anions are located at the centre of the sodalite cage whereas the hydrogen atoms are positionally disordered. Na₈[AlSiO₄]₆(BH₄)₂ shows a high stability under inert gas conditions. At atmospheric conditions the group can be oxidized to borate and boroxide anions suggesting the formation of hydrogen which leaves the sodalite cages. Future investigation of reloading properties of the oxidized form could be highly interesting for the hydrogen storage capabilities of these sodalites.     

The mechanism of the anodic formation of S2O2−8 ions on a Ti-supported IrO2 electrode in mixed aqueous solutions of H2SO4, (NH4)4SO4 and NH4F

The mechanism for the anodic formation of peroxydisulfate ion on a Ti-supported IrO₂ electrode was investigated in mixed aqueous solutions of H₂SO₄, (NH₄)SO₄ and NH₄F.Peroxydisulfate ion can be formed in higher yield at lower overpotential on the Ti-supported IrO₂ electrode, compared with smooth Pt electrode. The most probable mechanism under Langmuir conditions of intermediate adsorption was proposed as

     

Enhanced mechanical property of Ca5(PO4)2SiO4 bioceramic by a biocompatible sintering aid of zinc oxide

In the present work, a biocompatible additive ZnO was used to enhance the sintering of calcium phosphate silicate (CPS)¹ bioceramic and improve its mechanical property. Sol-gel prepared CPS powders were mechanically mixed with various amount of ZnO and then sintered at high temperatures to prepare Zn-CPS bioceramics. The effects of ZnO content and sintering temperature on microstructure and bending strength of Zn-CPS bioceramics were investigated and the related mechanism was also discussed. The results showed that ZnO could significantly enhance the sintering of CPS and improve its bending strength accordingly. The Zn-CPS bioceramic with 1?wt% ZnO sintered at 1300?°C exhibited a highest bending strength of 80.8?MPa. The enhanced densification of Zn-CPS bioceramics might be attributed to the liquid phase appeared during the sintering process and the formation of Ca₂ZnSi₂O₇² (HT) nano-grains at grain boundaries. It is expected that Zn-CPS bioceramics could have both good mechanical property and excellent bioactivity.     

Hydrogen evolution on RuxTi1−xO2 in 0.5 M H2SO4

Hydrogen evolution from 0.5 M H₂SO₄ on Ti electrodes coated with a Ru_xTi_1−xO₂ (x=0.04-0.5) layer has been studied by potentiostatic polarisation, cyclic voltammetry and ac-impedance spectroscopy. The results indicate that after a certain activation period the performance of such an electrode coating is comparable to platinum. The addition of small amounts of sodium molybdate increased the capacitance of the electrode and a reduction of the performance was observed. Increasing the temperature of the pure electrolyte from 20 to 75 °C caused an increase in the rate of the hydrogen evolution and in addition an increase of the electrode capacitance. The electrodes have been found to be rather tolerant to chloride and Fe²⁺ ions, and could hence be promising candidates as catalyst materials for solid polymer water electrolysis systems. From steady state measurements the Tafel slopes were found to change from −105 mV/decade for pure titanium to about −40 mV/decade for the (RuTi)O₂ coated electrodes. The exchange current densities were calculated from the steady state curves, as well as from impedance data, to be about 10⁻⁴ A cm⁻² after activation.     

Electrochemical oxidation of ammonia (NH4/NH3) on thermally and electrochemically prepared IrO2 electrodes

The electrochemical oxidation of ammonia (NH₄⁺/NH₃) in sodium perchlorate was investigated on IrO₂ electrodes prepared by two techniques: the thermal decomposition of H₂IrCl₆ precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(III) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.On both electrodes, ammonia is oxidized in the potential region of Ir(V)/Ir(IV) surface redox couple activity, thus, may involve Ir(V). During ammonia oxidation, TDIROF is deactivated, probably by adsorbed products of ammonia oxidation. To regenerate TDIROF, it is necessary to polarize the electrode in the hydrogen evolution region. On the contrary, AIROF seems not to be blocked during ammonia oxidation indicating its fast regeneration during the potential scan. The difference between both electrodes results from the difference in the activity of the iridium oxide surface redox couples.     

Effect of potassium hydrogen phthalate (C8H5KO4) on the one-step electrodeposition of single-phase CuInS2 thin films from acidic solution

The effect of potassium hydrogen phthalate (C₈H₅KO₄) as a special additive on the one-step electrodeposition of single-phase CuInS₂ thin films from acidic solution (pH 2.5) was investigated in detail. The XRD, SEM and UV-vis-NIR characterization confirms that the addition of an adequate concentration of C₈H₅KO₄ (23 mM) to the electrolytic bath containing 12.5 mM Cu²⁺, 10 mM In³⁺, 40 mM S₂O₃²⁻ and 100 mM LiCl can contribute greatly to the controllable growth of pure chalcopyrite CuInS₂ films with uniform surfaces and an ideal band gap of approximately 1.54 eV. Complexation studies of C₈H₅KO₄ with Cu²⁺ and In³⁺ in electrolytic solutions indicated that C₈H₅KO₄ can complex Cu²⁺ more strongly than In³⁺ and move the electrode potentials of Cu²⁺ and In³⁺ near each other as determined by polarization analysis. Furthermore, the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis performed in a series of solution systems revealed a three-step reaction mechanism for CuInS₂ deposition and considerable adsorption of C₈H₅O₄⁻ and Cu(C₈H₅O₄)⁺ to the cathode surface. This deposition shows that the synergetic effects of complexation and adsorption originated from the additive on the Cu²⁺ electro-reduction, thus promoting the co-deposition of copper, indium and sulfur in the form of single-phase CuInS₂.     

A new (3,4,7)-connected topology framework based on [Cd2(CO2)3O4N2] second building unit

A new 3D coordination polymer [Cd₂(L³)(BTC)(H₂O)] (1) (HL³ = 3,5-bis(pyridin-3-ylmethoxy)benzoic acid, H₃BTC = 1,3,5-benzenetricarboxylic acid), has been isolated under hydrothermal condition and characterized by single-crystal X-ray diffraction. Compound 1 is constructed from Cd₂-based second building units (SBUs) [Cd₂(CO₂)₃O₄N₂] and displays a 3D (3,4,7)-connected net with (4²·6)(4³·6³)(4⁵·6¹¹·8⁵) topology. In addition, the photoluminescent spectra indicate compound 1 may be a good candidate for blue-luminescent materials.     

Solid state protonic conductor NH4PO3–(NH4)2Mn(PO3)4 for intermediate temperature fuel cells

A new proton-conductive composite of NH₄PO₃–(NH₄)₂Mn(PO₃)₄ was synthesized and characterized as a potential electrolyte for intermediate temperature fuel cells that operated around 250 °C. Thermal gravimetric analysis and X-ray diffraction investigation showed that (NH₄)₂Mn(PO₃)₄ was stable as a supporting matrix for NH₄PO₃. The composite conductivity, measured using impedance spectroscopy, improved with increasing the molar ratio of NH₄PO₃ in both dry and wet atmospheres. A conductivity of 7 mS cm⁻¹ was obtained at 250 °C in wet hydrogen. Electromotive forces measured by hydrogen concentration cells showed that the composite was nearly a pure protonic conductor with hydrogen partial pressure in the range of 10²–10⁵ Pa. The proton transference number was determined to be 0.95 at 250 °C for 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte. Fuel cells using 2NH₄PO₃–(NH₄)₂Mn(PO₃)₄ as an electrolyte and the Pt–C catalyst as an electrode were fabricated. Maximum power density of 16.8 mW/cm² was achieved at 250 °C with dry hydrogen and dry oxygen as the fuel and oxidant, respectively. However, the NH₄PO₃–(NH₄)₂Mn(PO₃)₄ electrolyte is not compatible with the Pt–C catalyst, indicating that it is critical to develop new electrode materials for the intermediate temperature fuel cells.     

Ionic conductivity of PEO9: Cu(CF3SO3)2: Al2O3 nano-composite solid polymer electrolyte

Cu⁺⁺ ion containing solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO₉:Cu(CF₃SO₃)₂ made by complexing copper triflate (CuTf₂) with PEO appears to show scientifically intriguing transport properties. Although some copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the species involved are yet to be established. In order to obtain enhanced ionic conductivities and also to contribute towards understanding the ionic transport process in Cu⁺⁺ ion containing, PEO based composite polymer electrolytes, we have studied the system PEO₉: CuTf₂: Al₂O₃ incorporating 10 wt.% of alumina filler particles of grain size 10 μm, 37 nm, 10–20 nm and also particles of pore size 5.8 nm. Thermal and electrical measurements show that the system remains amorphous down to room temperature. The composite electrolyte is predominantly an ionic conductor with electronic conductivity less than 2%. The triflate (CF₃SO₃⁻) anions appear to be the dominant carriers. The presence of alumina grains has enhanced the conductivity significantly from room temperature up to 100 °C. The nano-porous grains with 5.8 nm pore size and 150 m²/g specific surface area exhibited the maximum conductivity enhancement. This enhancement has been attributed to Lewis acid–base type surface interactions of ionic species with O²⁻ and OH⁻ groups on the filler grain surface.     

A novel (3,4,8)-connected 3D topology framework based on [Gd2(bpdc)3(H2O)3] second building units

A new 3D coordination polymer {[Gd₂(bpdc)₃(H₂O)₃]·H₂O}_n(1) has been isolated from the reaction of 2,2′-bipyridine-4,4′-dicarboxylic acid (H₂bpdc) and Gd(III) salts under hydrothermal conditions. Single-crystal X-ray diffraction study shows that compound 1 is constructed from Gd₂-based second building units (SBUs) [Gd₂(bpdc)₃(H₂O)₃] and displays a 3D (3,4,8)-connected net with (4²·6)(3²·4²·5²)(3²·4⁵·5⁴·6¹¹·7⁶) topology. A thermogravimetric analysis of 1 shows a high thermal stability. The magnetic behavior of 1 reveals a weak antiferromagnetic interaction between Gd(III) ions.     

Nickel foam-supported porous Ni(OH)2/NiOOH composite film as advanced pseudocapacitor material

A porous net-like β-Ni(OH)₂/γ-NiOOH composite film is prepared by a chemical bath deposition. The as-prepared porous composite film shows a highly porous structure built up by many interconnected nanoflakes with a thickness of about 20 nm. The pseudocapacitive behavior of the porous composite film is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 1 M KOH. The porous β-Ni(OH)₂/γ-NiOOH composite film exhibits a noticeable pseudocapacitance with 1420 F g⁻¹ at 2 A g⁻¹ and 1098 F g⁻¹ at 40 A g⁻¹, respectively, much higher than those of the dense Ni(OH)₂ film (897 F g⁻¹ at 2 A g⁻¹ and 401 at 40 A g⁻¹). The porous architecture is responsible for the enhancement of the electrochemical properties, and it increases electrochemical reaction area, shortens ions diffusion paths and relaxes volume change caused by the electrochemical reactions.     

亚硝酸钠与氯化铵反应动力学研究

研究了在盐酸催化的亚硝酸钠(NaNO2)与氯化铵(NH4C1)反应动力学,结果显示:亚硝酸钠与氯化铵在水中的反应为二级反应;其速率常数与该体系中氢离子的浓度成正比;活化能为50.26 kJ/mol;亚硝酸钠与氯化铵反应的动力学方程为dC/dt=-2.066×107CH+e-6045/TC2.     

Organically templated Np(IV) coordination polymer with in situ formed oxalate anion (ImidazoleH)[Np(C2O4)(CH3SO3)3(H2O)2]

The reaction of Np(V) methanesulfonate solution with imidazole led to the in situ formation of oxalic acid and the reduction of Np(V) to Np(IV). As a result, the novel organically templated organic polymer, (ImidazoleH)[Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂], was formed. The structure consists of infinite chains of [Np(C₂O₄)(CH₃SO₃)₃(H₂O)₂]⁻ and imidazolium cations. The crystal structure is confirmed by IR and UV–vis spectroscopic data. This complex is the first example of structurally characterized 1:1 An(IV) oxalate.