B. F. Lyakhov

Evidence for large hydrogen storage capacity in single-walled carbon nanotubes encapsulated by electroplating Pd onto a Pd substrate

We report a study of hydrogen storage in an alternative material, representing single-walled carbon nanotubes (SWCNTs) encapsulated by thin Pd layers onto a Pd substrate. A synergetic effect resulting in combination of the Pd and the SWCNTs properties with regards to hydrogen has been achieved. Adding SWCNTs increases the H{sub 2} capacity of the Pd-SWCNT composite by up to 25% relative to Pd metal alone under electrochemical loading. This results in a storage capacity of 8-12 wt %. with regard to the added SWCNTs.

Effect of cations of alkali metals and ammonium on the process of deposition and structure of iron-tungsten alloys

It is established that potassium ions facilitate expansion of the current density range where crystalline alloy deposits form. This is presumed to be connected with an increase in the hydrogen overvoltage, in connection with which alloy deposits turn amorphous at higher current densities and potentials corresponding to these, at which hydrogen evolution accelerates. A high alloy deposition rate and a sufficiently negative potential of its deposition are conditions not sufficient for transition from large-crystal to nanocrystalline and amorphous deposits. Here, a more important role is played by hydrogen that inserts itself into the crystal lattice. As one could assume, hydrogen in this case facilitates preservation of the emerging nonequilibrium structures, hindering crystallization processes as a result the iron hydride formation.

Effect of Hydrogen Absorption on Atomic-Electronic Structure of PdH System According to Positron Annihilation Data

The positron annihilation technique is used to investigate the atomic-electronic structure of the electrochemically hydrogenated palladium. Curves of the angular correlation of the annihilation gamma-quanta radiation (ACAR) were recorded on the original Pd specimen, electrochemically hydrogenated Pd, and dehydrogenated Pd. EF Fermi levels and free-electron concentrations were estimated based on the experimental ACAR curves. A substantial increase in the free-electron concentration from N/V = 4.6 × 1022 [22] cm−3 to N/V = 6.0 × 1022 cm−3 was found in the hydrogenated Pd specimen compared to that of the original palladium. This change is accompanied by a decrease in the Gaussian half-width of the ACAR curves, which indicates a certain loosening of the palladium crystal lattice upon the hydrogenation. Upon the electrochemical removal of hydrogen from palladium, the annihilation characteristics of the metal are almost completely restored.

Electrochemical sorption of hydrogen in single-wall carbon nanotubes encapsulated in palladium

The distribution of hydrogen in the palladium matrix and single-wall carbon nanotubes (SWCNs) in Pd-SWCN nanocomposite upon electrochemical hydrogenation is quantitatively studied in situ using voltammetry and chronoammetry. The high mobility of hydrogen in nanotubes is discovered and reflected in the low H-SWCN bond energy, which equals 0.073 ± 0.05 eV/H-atom and is close to the hydrogen activation energy (ɛH = 0.072–0.08 eV/H-atom) obtained using vacuum thermal desorption [7]. The presence of SWCN is shown to increase the hydrogen capacity of the Pd-SWCN composite compared to individual palladium by nearly 25%. The hydrogen storage capacity of nanotubes (CH) in Pd-SWCN composite increases with an increase in the Pd-to-SWCN volume ratio (V(Pd)/V(SWCN)). CH reaches the maximum limiting value of 12 wt % at V(Pd)/V(SWCN) > 12.

Diffusion of hydrogen atoms and the internal friction spectrum of the PdH x system

The temperature dependences of dissipative loss spectra were studied by the internal friction method for the polycrystalline Pd system and interstitial solid solutions PdHx. Four relaxation processes related to the structural peculiarities of the crystal lattice were observed in Pd; two additional relaxation processes were observed in PdHx solid solutions. The latter were related to the mobility of hydrogen atoms in different phases of the face-centered cubic crystal structure.

Electrodeposition, properties, and composition of rhenium–nickel alloys

The process of deposition of the Re–Ni alloy, its current efficiency, and the alloy composition are studied as a function of the current density and the solution temperature. The hydrogen content in the deposits, their surface morphology, internal structure, and properties as the cathodic material for HER are examined. It is assumed that besides the high rhenium content, the high catalytic activity of nickel–rhenium alloys is associated with the high degree of their structural disordering.

Electrodeposition of iron–molybdenum alloy from ammonium–citrate solutions and properties of produced materials

The structure and properties of Fe–Mo alloys is studied. It is shown that the iron–molybdenum alloys formed in the electrolysis are highly hydrogenated, and the content of hydrogen in them increases with increasing atomic fraction of molybdenum in the cathodic deposit. The kinetics of hydrogen evolution reaction in the alkaline solutions on the obtained materials is studied.

Gaseous products of dimethylamine borane oxidation in chemically catalyzed deposition of nickel-rhenium-boron coatings

The gaseous products of the oxidation of hydride hydrogen of the dimethylamine borane (DMAB) (CH3)2NH · BH3 reducer used for depositing Ni-Re-B coatings and hydrolysis of DMAB on them were studied by mass spectrometry of the isotope composition of the gas. The oxidation level of hydride hydrogen of the DMAB reducer was found to depend on the catalytic activity of the Ni-Re-B alloy, on which heterogeneous hydrolysis takes place. For Ni-Re-B alloys with low rhenium concentrations (0–13 at %), the heterogeneous hydrolysis of DMAB proceeds with hydride hydrogen oxidation to the atomic state, as it does in the deposition of the Ni-B alloy. In contrast, at high rhenium concentrations (40–46 at %), the oxidation proceeds to the proton H+, leading to an antibatic dependence of the hydrolysis and alloy reduction rates. An analysis of the partial rates of the process and isotope composition of the evolved gas revealed two different mechanisms of the chemical-catalytic reduction of Ni-Re-B alloys at concentrations of potassium perrhenate of 0–4 and 4–16 mM in solution.

Magnetic characterization of a hydrogen phase trapped inside deep dislocation cores in a hydrogen-cycled PdHx (x≈4.5 × 10 -4) single crystal

The magnetic characterization of Pd single crystals deformed by cycling in a hydrogen atmosphere has been performed. Based on evidence obtained from thermal desorption analysis, it is shown that the condensed hydrogen phase formed inside deep dislocation cores in PdHx (x = H/Pd ≈ 4.5 × 10−4) is tightly bound with a Pd matrix. The activation energy of hydrogen desorption from these cores was found to be as high as e = 1.6eV/H-atom, suggesting the occurrence of a strong band overlapping between Pd and H atoms. SQUID measurements carried out in a weak magnetic field (H < 5.0 Oe) showed an anomalous diamagnetic contribution to the DC and AC magnetic susceptibilities of the PdHx sample at T < 30 K resulting in the presence of the hydrogen phase. It is suggested that the anomalous diamagnetic response in PdHx is caused by the presence of a hydrogen dominant phase, tightly bound with a Pd matrix inside the dislocation cores (nanotubes).

Nuclear reactions in the Pd/PdO:Dx and Ti/TiO2:Dx systems excited by ionizing radiation

The yield of the products of nuclear reactions from deuterated palladium and titanium irradiated by an electron beam and X rays has been studied. Charged particles have been detected by CR-39 track detectors, which are not sensitive to electronic noise, electrons, and X-ray photons. To identify the type of particles and to estimate their energy, three detectors covered by aluminum and copper foils of various thicknesses have been used. It has been established with reliable statistics that 30-keV electrons and X rays initiate the synthesis of deuterons in the Pd/PdO:Dx and Ti/TiO2:Dx systems with the yield of 3-MeV protons.