Jana Bludská

The role of water in hydrogen insertion into WO3

Abstract The accelerating role of water in the insertion of hydrogen into tungsten trioxide WO 3 was studied in non-aqueous aprotic and/or protic reaction media and in aqueous solutions of the sulfuric acid. The activation energies of hydrogen insertion in various reaction media were estimated. The partial molar heat of hydrogen insertion ΔH =8.7±1.2 kJ ⧸ mole of H 0.45 WO 3 was evaluated.

The electrochemical insertion of alkali metal into YBa2Cu3O7−δ superconductor

Abstract The electrochemical insertion of lithium into ceramic superconductor YBa2Cu3O7−δ was observed in potential range 3.15–2.15 V vs Li (in 1 M LiClO4/PC solution). The process is reversible. The estimated value of the diffusion coefficient, DLi = 10−12−10−11 cm2s−1, indicates a rather rigid bond between layers in the crystal lattice of the electrode material. The highest lithium concentration corresponds to the ratio Li: Y = 0.4–0.5.

Electrochemical insertion of lithium in manganese dioxide

Abstract The insertion of lithium into compact electrolytic MnO2 was studied by galvanostatic and admittance techniques. The diffusion coefficient, 3.4 × 10−14 m2/s at 20 °C, and its activation energy of 30 kJ were determined. The rate of the process is controlled mainly by the high resistivity of MnO2 and by the polarization of the electrode reaction itself. Similarly, the behaviour of MnO2C plastic bonded electrodes is controlled mainly by the high resistivity of MnO2 if the content of carbon black is not sufficient to form a conductive network, and by polarization on the grains of MnO2 at higher carbon black contents. The optimum concentration of carbon is 30 – 40% by volume.

Insertion of hydrogen into hexagonal ammonium tungsten bronze (NH4)0.3WO3

Insertion of hydrogen into the hexagonal ammonium tungsten bronze was carried out by electrochemical and “hydrogen spill-over” techniques. The coefficient x = 0.06 in the hydrogen bronze Hx(NH4)0.3WO3 and the diffusion coefficient of hydrogen DH = 2.29 × 10−17 m2s−1 were found by the hydrogen insertion in the absence of water.

The increase of stability of LixCoO2 electrodes of cointercalated sodium

Abstract Cyclic electrochemical deintercalation and intercalation of LiCoO 2 was studied in LiClO 4 /propylene carbonate electrolyte. The stability of the material was markedly improved if 10 to 20% of lithium atoms were replaced by cointercalated sodium. The increase of the stability is explained by preventing of complete deintercalation in anodic range due to essentially lower mobility of sodium ions in the van der Waals gaps.

Hydrogen photoevolution on InGaP polycrystalline and tandem-type electrodes

We report on preparation of p-In1−xGaxP polycrystalline, p-In0.5 Ga0.5P/p-GaAs, and p-In0.5 Ga0.5P/n-GaAs/n-InP tandem-type cathodes. The photovoltaic efficiency of InGaP tandem type epitaxial electrodes is two times higher than that of polycrystalline photocathodes. The most significant advantage of epitaxial electrodes is in their markedly better corrosion resistance in comparison with polycrystalline photocatodes.

The preparation and electrochemical properties of chromium oxides CrOx both in lithium and sodium aprotic electrolytes

Abstract Chromium oxides CrO x were prepared under various conditions from CrO 3 . Their capacity and reversibility as cathodic materials both in LiClO 4 /propylene carbonate and NaClO 4 electrolytes were measured. The charge density in lithium electrolyte (750 C/g) was higher than that in sodium one (400–600 C/g). Coin cells were assembled with CrO x cathode; their capacity was 0.1 A h for 2025 size, and the average voltage 3.0 V.

Sodium insertion in manganese dioxide electrodes

Abstract The insertion of sodium in manganese dioxide electrodes from 1M NaClO 4 -PC solution was observed. It starts at 2.8 V and is completed at 2.2 V (against Na reference electrode). The diffusion coefficient D = 5 × 10 −14 cm −2 s −1 was estimated. Limiting concentration is lower than that for lithium, which is explained as accommodation of sodium in broader tunnels in γ-MnO 2 lattice, while lithium enters both kinds of tunnels.

Intercalation of alkali metals in chromium oxide-chloride

Abstract The electrochemical reduction of CrOCl in NaClO 4 /PC or LiClO 4 /PC solutions is irreversible. At low current, it is controlled by stoichiometry and by diffusion of alkali metals. Formation of an unstable intercalation compound followed by its decomposition to LiCl (or NaCl) and oxide CrO is supposed. This was confirmed by chemical lithiation of CrOCl in Li solution in liquid NH 3 .

Insertion of lithium into RuO2TiO2 electrodes

Abstract The insertion of lithium into the solid system RuO 2 TiO 2 was investigated. Both the potential and the rate of insertion decrease with the increase of titanium concentration, due to lowering the density of electronic states.