Calorimetric and nuclear byproduct measurements in electrochemical confinement of deuterium in palladium

We present the results of a new experiment with our multicell set-up implemented with mass spectrometric measurements of⁴He and a highly improved neutron detector. The excess heat measured is comparable with the results of other laboratories, but no neutrons were found and the tritium excess was lower than expected from the power excess. ⁴He has been measured in the electrolysis gases and a tentative correlation of ⁴He with excess power is presented and discussed.     

Concrete-like high sulfur content cathodes with enhanced electrochemical performance for lithium-sulfur batteries

Nowadays,lithium-sulfur batteries have attracted numerous attention due to their high specific capacity,high energy density,low cost and environmental benignancy.However,there are some critical challenges to be overcome such as low electronic conductivity and capacity fading caused by shuttle effect.Many attempts have been conducted to improve the electrochemical performance by designing effective sulfur hosts.In this paper,we synthesize a concrete-like sulfur/carbon cathode with high sulfur content(84%)by using 3D macroporous hosts with high pore volume.Sophisticated strategies of using polarized carbon framework and polymer coating are applied to synergistically control the dissolution of polysulfides so that the capacity retention and high rate performance can be remarkably enhanced.As a result,the composite exhibits a specific discharge capacity of 820 mAhg~(-1)at a discharge current of 800 mAg~(-1)(approximate to 0.5 C)after 100 cycles,calculated on the integrated mass of composite,which is superior to most report results.     

High temperature solid state catalytic isotope exchange with deuterium and tritium

A method for synthesizing tritium- or deuterium-labeled amino acids, peptides and biogenic amines through high temperature solid state catalytic isotope exchange (HSCIE) is proposed. The dependence of the degree of isotope exchange in HSCIE on the structure of the compound, the reactivity of hydrogen at different carbon atoms and the conditions of the process has been examined. If HSCIE is performed in the temperature range of 373 to 413K, the selectivity of isotopic label incorporation comes to 70% or higher. When the tritium label is introduced into peptides, they retain the configuration of asymmetric atoms, even upon the substitution of tritium for hydrogen at the -carbon atoms of the amino acid residues. HSCIE at 453–513K leads to an even distribution of the isotopic label over the organic compound molecule. The results of³H NMR spectroscopy highlighting the distribution of the tritium label in the organic compound molecules are presented. The configuration of asymmetric atoms in amino acids is preserved to a high extent upon 80–90% substitution of isotopes for hydrogen atoms.Presented at the 12th Radiochemical Conference, Marianské Lazné May 7–11, 1990.     

Miniaturization of flow-through generation cells for electrochemical hydride generation in AAS

The construction and optimization of five new types of miniaturized flow-through electrolytic cells with lead cathode and platinum anode for electrochemical hydride generation in atomic absorption spectrometry (HG-QFAAS) were achieved during this research study. The ion-exchange membrane was not part of these cells and only one carrying electrolyte for both electrode chambers was used. Hydride generation efficiency achieved was either comparable or higher than the one recorded for the classic thin-layer generation cell. The inner volume of the cathode chamber was reduced to a quarter of the classic thin-layer flow-through cell. Compared to the commonly used thin-layer flow-through cell, higher sensitivity (7.32×10³ dm³ μg⁻¹) and better limit of detection (0.32 μg dm⁻³) were obtained for selenium determination using two of these new generators.      

Radiospectroscopic method for determining contents of deuterium and tritium in aqueous solutions

Radio-wave emission spectra in the microwave region are registered for the first time for ordinary water (H₂O), heavy water (D₂O), and D₂O with a low content of T₂O. The obtained spectra are analyzed according to a special program using a hardware–software complex. Measurement results show that the proposed method allows us not only to determine differences between substances in terms of composition and concentration, but to determine the presence of heavy and superheavy hydrogen isotopes in ordinary water as well.     

Preparation of substituted cinnamic acids labelled with deuterium and tritium at the ring positions

A series of substituted cinnamic acids labelled at the ring positions with deuterium or tritium has been easily obtained via the Doebner modification of Knoevenagel condensation reaction between labelled benzaldehyde derivatives and malonic acid in pyridine. The substituted benzaldehyde precursors were synthesized by isotope exchange method in deuterated or tritiated water at 80 °C in acidic medium. Ring-tritiated substituted cinnamic acids with specific activity ranging from 207 GBq /5.6 Ci/ mol^–1 to 4366 GBq /118 Ci/ mol^–1 was obtained using ca. 37 GBq /1 Ci/ of HTO.     

Allylation of N-heterocycles with allylic alcohols employing self-assembling palladium phosphane catalysts

The first palladium catalyst system that allows the direct allylation of indoles with allylic alcohols as substrates with water being the only byproduct is presented. The application of self-assembling ligands based on complementary hydrogen bonding was the key to success.     

Anomalous electrochemical behaviour of palladium in base

Noble metal hydrous oxides are known to be recalcitrant systems, i.e. they either undergo reduction at high overpotential or fail to undergo this reaction, due to the intervention of high-energy, virtually isolated atom or nanocluster states of the element as primary reduction products. Hydrogen absorption by activated palladium in base results in enhanced levels of surface activation and eventually to the spontaneous generation of recalcitrant hydrous oxide species which deactivate the electrode surface. Hydrous oxide behaviour at palladium in base is significantly more complicated than in acid; the deposits in question are less readily formed in base, and the main component of a multilayer oxide film grown in acid (HO2) seems to alter to a more readily reducible form (HO1) on transferring the electrode to base. However, evidence was obtained serendipitously in the present work for the formation of a recalcitrant oxide deposit on palladium in base; the involvement of metastable metal and hydrous oxide states provides the basis of energy storage and anomalous heat emission behaviour which is a controversial topic in the case of this electrode system.     

The one-electron cleavage of benzylic bromides at palladium and palladized cathodes: Benzyl radicals generation and immobilization onto solid interfaces

Benzyl bromide 1 and 4-nitrobenzyl bromide 2 are reduced at solid electrodes in propylene carbonate (PC) and dimethylformamide (DMF) containing tetraalkylammonium salts. Palladium electrodes and these covered with layers of Cu–Pd, Ag–Pd, Au–Pd, and Ni–Pd were especially found to favour the one-electron scission of the C–Br bond. Under these conditions, 1 and 2 are reduced in two separated steps assigned to the transient formation of a free radical capable to couple or to add onto the cathodic material. The formation of benzyl radical allows the in situ addition onto unsaturated organic systems (mono- and di-benzylations). The formation of benzylic radical was confirmed by ESR technique (trapping the paramagnetic intermediate with nitrones). Lastly, preliminary experiments were achieved in order to test the grafting feasibility of benzyl radicals onto cathodic interfaces.     

Study of exchange of hydrogen for deuterium and tritium in α-aminoalkylphosphonous acids

The kinetics of isotope exchange of hydrogen for deuterium in -aminoalkylphosphonous acids as a function of the pH were investigated by PMR spectroscopy. Tritiumlabeled -aminoalkylphosphonous acids were obtained as a result of direct hydrogen- tritium exchange between T₂O and hydrophosphoryl compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1966–1969, September, 1990.     

Coulometric generation of H(+) and D(+) ions in aqueous media by anodic oxidation of hydrogen and deuterium dissolved in palladium

Coulometric generation of H(+) and D(+) ions in aqueous media by the oxidation of hydrogen and deuterium dissolved in palladium, is described. Hydrogen and deuterium dissolved in palladium were found to be oxidized at more negative potentials than the oxidation potentials of water and other components present. The H(+) and D(+) ions generated were used for the titration of tris(hydroxymethyl) aminomethane, piperidine, triethylamine and sodium tetraborate, the end-point being determined potentiometrically with a glass electrode and an SCE. In titrations of 0.001-0.1M solutions of the bases, the current efficiency was 100%.     

兼具高孔隙率和梯度孔隙结构的多孔钯块材的制备、表征及其电化学性能研究

钯材料广泛用于氢同位素储存和分离、催化和传感等领域.传统的负载钯催化材料具有优异的乙醇和甲醇等电化学催化氧化性能.除此之外,负载钯催化材料还具有优异的甲烷催化燃烧性能.然而,很多研究显示负载钯催化材料存在很多不足,例如在工程应用过程中不稳定,纳米颗粒会发生聚集和长大,进而引起材料性能急剧下降等.不同于钯片、海绵钯粉末和负载钯催化材料,多孔钯具有三维连通的孔隙结构,可避免团聚现象的发生.同时,多孔钯还具有一些特殊的物理化学性能.研究表明,梯度孔隙结构是一种高效的电化学催化结构.因而近年来很多研究者都致力于探索具有高孔隙率和梯度孔隙结构多孔钯块材的制备方法.已有的研究包括造孔剂法和模板法等,但上述方法制得的多孔钯块材均存在比表面积低或难以获得块体材料缺点.我们研究组发展了一种制备兼具高孔隙率和梯度孔隙结构的多孔钯块材的新方法.即通过以一定粒度的NaCl颗粒作为造孔剂放电等离子烧结制备PdAl合金复合块材,然后通过去离子水溶解获得多孔PdAl合金,最后经过在盐酸溶液中去合金化得到具有数十微米的宏观大孔和约10纳米的纳米孔等梯度孔隙结构的多孔钯块材.当造孔剂添加量为20 vol.%,制得了孔隙率高达88%且完整的多孔钯块材.对该多孔钯块材的力学性能进行了测试,其压缩强度为0.5 MPa.对该块材进行氮吸附测试,测试结果显示其比表面积达到54 m2/g.我们进一步对该多孔钯块材的乙醇电化学催化氧化性能进行了研究.对不同扫描速度下多孔钯块材在KOH(1 mol/L)+乙醇(0.8 mol/L)溶液中电催化活性进行分析.随着扫描速率从10 mV/s提高到50 mV/s,正扫描峰电流密度也逐渐提高,且峰电位向正电位方向移动.对峰电流密度和扫描速率的平方根进行拟合,发现它们之间存在明显的线性关系,表明该电催化氧化行为是一个受扩散控制的过程.随着溶液中乙醇浓度不断增加,正扫描方向乙醇氧化峰的峰电流呈现出先增大后减小的趋势.这是因为乙醇基和羟基在钯表面的竞争性吸附造成的.当乙醇浓度较高时,乙醇基会占据钯表面大量的活性位,从而阻碍和抑制羟基的吸附.此时,羟基在钯表面的吸附成为电氧化反应的控制因素.因此,只有选择合适的乙醇浓度,才能更好地发挥材料的电催化性能.当乙醇浓度为2 mol/L时,峰电流最大,达到120 mA/cm2,表明多孔钯块材具有优异的电催化性能,这与该材料的梯度孔隙结构、高比表面积和高孔隙率密切相关.进一步对多孔钯块材的催化稳定性进行研究.该多孔钯块材显示出了优异的催化稳定性,当经过50次循环后,乙醇氧化峰的峰电流仅下降到~110 mA/cm2.     

A platinum counter electrode with high electrochemical activity and high transparency for dye-sensitized solar cells

Ultra-thin platinum films were deposited on indium tin oxide (ITO) substrates in a sputtering process and used as counter electrodes of dye-sensitized solar cells. The nano-structured Pt film not only has a high transmittance (75%), but also has a lower charge-transfer resistance compared with that of thick Pt films. Under front-side illumination, the synergistic effects of the nano-structured Pt film (1.4 nm) and a reflective aluminum foil can increase the efficiency of a normal cell from 6.8 to 7.9%. For the back-side illumination, the efficiency achieved by using the present strategy is 6.6%, which is comparable to the front-side illuminated efficiency of DSSCs using thick Pt films (ca. 6.8%).     

Disulfide-polyaniline composite cathodes for rechargeable batteries with high energy density

A composite cathode was prepared from a solution containing 2,5-dimercapto-1,3,4-thiadiazole (DMcT) and polyaniline (PAn). The resulting cathode exhibits 80% of the theoretical capacity. Furthermore, an energy density of over 600 Wh/kg-cathode and a discharge voltage of 3.4 V are obtained, when it is coupled with a lithium anode. Additional advantages of the present cathode material over the conventional metal oxides are the ease in disposal by incineration, the low pollution and the low cost. Current capability of 137 A/kg-cathode is achieved by adding a polypyrrole derivative to the DMcT-PAn composite and coupling it with a copper current collector.     

Controllable synthesis of high loading LiFePO4/C nanocomposites using bimodal mesoporous carbon as support for high power Li-ion battery cathodes

Mesoporous LiFePO₄/C composites containing 80 wt% of highly dispersed LiFePO₄ nanoparticles (4–6 nm) were fabricated using bimodal mesoporous carbon (BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO₄, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO₄ and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g^?1 at 0.1 C of the high loading electrode and 42 mAh·g^?1 at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO₄ loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO₄ displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.     

Oxide cathodes for electrochemical devices made with the use of a nanostructured composition material

The possibility of using the LnO _x mischmetal (Ln = Ce, La, Nd, Pr, Sm) for preparation of cathodes for solid-oxide fuel cells with the supported YSZ electrolyte is studied. The electrical and electrochemical characteristics of Ln-Mn-O electrodes with the ratio of all lanthanides contained in the mischmetal except for cerium to manganese Ln: Mn = 1: 1 and also of a material comprised of Ln-Mn-O and La_0.8Sr_0.2MnO₃ are studied. The latter electrode material that contains 35?C40 wt % of Ln-Mn-O and was sintered at 1200°C has the specific ohmic resistance of 0.1 ?? cm at 800°C. The polarization conductivity is compared for electrodes made of 100% Ln-Mn-O, 40 wt % Ln-Mn-O + 60 wt % La_0.8Sr_0.2MnO₃, and 100% La_0.8Sr_0.2MnO₃ in the initial state and after their modification through the introduction of an electrocatalyst (PrO_{2 ? x} ). The highest polarization conductivity is typical of Ln-Mn-O + (La, Sr)MnO₃ electrodes containing 40 wt % Ln-Mn-O and PrO_{2 ? x} . The polarization conductivity of these electrodes is found to be 25 S/cm² at 800°C.     

Porous single-crystalline palladium nanoparticles with high catalytic activities

Palladium's pore cousin: a facile approach is described for the size-controlled preparation of porous single-crystalline Pd nanoparticles. These porous Pd nanoparticles exhibit size-independent catalytic activities for the Suzuki coupling and are more active than commercial Pd/C catalysts.     

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application.A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst.Activated carbon modified with palladium catalyst (AC-Pd) was prepared for electrochemical dechlorination.For the 4-chloropbenol wastewater of initial concentration 200 mg L~(-1),the removal efficiency could nearly reach 100% in less than 30 min.Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration.OH radicals,generated by electrochemical reaction,played a critical role in self-regeneration of AC-Pd.High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment.