Pavel Stopka

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.

Attempt to verify experimental Einstein A-coefficient used for O2(1Δg) determination in COIL

This paper is a contribution to the current discussion on radiative lifetime, or the Einstein coefficient for spontaneous emission of singlet delta oxygen [O2(1(Delta) g)]. A verification of widely-used the A-coefficient by Badger et al. (2.58 X 10-4 s-1) in emission spectroscopy for determination of O2(1(Delta) g) concentration in Chemical Oxygen-Iodine Laser (COIL) was examined. Two independent comparative techniques, the EPR and emission spectroscopy, completed by a proposed mathematical model for calculation of O2(1(Delta) g) concentration from emission measurements, were employed. Singlet oxygen was generated chemically by a conventional way used in COIL. Within the accuracy of the both experimental techniques, the value of the Einstein A-coefficient estimated by this investigation is equal to (2.31 plus or minus 0.51) X 10-4 s-1, that is slightly less than the Badger et al. value.

ESR Study of Hydroxyl Radicals, Superoxide Anion Radicals and Molecular Singlet Oxygen Generated by Mercaptoundecahydro-closo-Dodecaborate(2-) Solution Irradiated by Neutrons under Conditions of Boron Neutron Capture Reaction

Recently, we have reported the generation of superoxide anion-radicals by neutron irradiation and UV light irradiation of mercaptoborates in water solutions at room temperature1. Now, we have irradiated 2.10-3 molar aqueous solutions of two types of mercaptoborates: Na2B12H11SH, [N(CH3)4]2B12H11SH and, for comparison Na2B4O7by thermal neutron flux on LVR-15 reactor in Řež/Czech Rep./ with total doses 5 Gy and 18 Gy, respectively. The generation of hydroxyl radicals ·OH, superoxide anion-radicals O2·−, and singlet molecular oxygen 1O2 were identified and determined by electron spin resonance spectroscopy. The quantity of generated radicals depend on initial oxygen concentration in irradiated solutions and on the energy of used neutron beam. The generation of radicals on the BNCT conditions could play an important role in therapeutical mechanism.