Metals intercalated in graphite. V. A concentration cell with intercalated bromine

Abstract

JFAN-MARC LAL~NCFTTE and ROGER ROUSSEL. Can. J. Chem. 54, 3541 (1976) Bromine intercalates can be used as electrodes in concentration cells. Voltages of the order of 50 mY can be obtained with thermal gradients of 60-75 " C , in the range 0-100 "C. The cell can be operated on a continuous basis by allowillg the high activity electrode to distill bromine to the low activity electrode. JEAN-MARC LALANCETTE et ROGER ROUSSEL. Can. J. Chem. 54, 3541 (1976). Les composCs d'insertion du brome dans le graphite peuvent jouer le rBle d'ilectrodes dans une pile B concentration. Des voltages de l'ordre de 50 mV sont observes en appliquant un gradiant de 60-75 "C se situant dans la rCgion 0-100 "C. La cellule peut opCrer en continue si I'on permet la distillation du brome de 1'Clectrode B haut niveau d'activite vers I'Clectrode B basBromine can be intercalated in graphite. This intercalation is spontaneous when bromine is in contact with graphite at room temperature, the intercalation being accompanied by an important expansion of the volume of graphite which then assumes a typical blue color. Rudorff (1) has shown, by X-ray diffraction studies, that the compound CsBr corresponding to the saturation of the lattice of graphite with bromine is, in fact, a stack of alternating layers of b r~m i n e and carbon, two layers of bromine (7.05 k ) alternating with two layers of carbon (3.38 A).The bromine intercalates are not stable and will decompose spontaneously if not left in equilibrium with bromine vapor. The isotherms of fixation of bromine by graphite have been reported and Hooley (2) has shown the important influence of the size of graphite particles on such isotherms. The intercalation of bromine in graphite is not entirely reversible, however. Depending on the source of graphite (3) variable amounts of bromine in the range of 5-107, remain strongly held by the lattice and can be removed only by strong heating, with the formation of volatile derivatives of carbon incorporating bromine.The electronic state of intercalated bromine has been examined by several authors. According to Ubbelohde and co-workers (43, at low concentrations of bromine in graphite there must be a complete ionization of bromine. At higher concentrations of bromine, only a part of the bromine would exist in the ionic form. For Hennig ( 5 ) , in the case of CsBr one bromine atom exists in the ionic form for every seven bromine atoms. The residual bromine remaining in graphite would also be present in the form of partly dissociated and partly molecular entities.This paper, as part of a study of the chemistry of graphite intercalates (6), reports the use of bromine-graphite intercalates as electrodes in a concentration cell.The characteristics of a concentration cell are the following. The anode and the cathode call upon the same reversible system and the net energy withdrawn from the cell comes from the reaction of the system used to a difference in the activity of a common ion at the anode and at the cathode. The polarity of the concentration cell is su...

High Seebeck Coefficient Electrochemical Thermocells for Efficient Waste Heat Recovery

“…The Br 2 –Br – thermocell, which was first proposed by Lalancette and developed by Endo, and Shindo, , can exhibit a Seebeck coefficient of 5.68 mV K –1 when the hot side is operated above the boiling point of Br 2 . The vaporization of Br 2 increases the Seebeck coefficient; however, the extremely corrosive Br 2 vapor limits its application.…”

Phonon Dispersion Relation of Bulk Boron-Doped Graphitic Carbon

“…49,50 This process is only partially reversible in that the last 5−10% of the intercalated bromine can only be removed by strong heating to form volatile carbon derivatives that incorporate bromine. 51 In the present work, intercalated bromine and its destructive deintercalation process likely explains the larger d 002 and low values of L c and L a observed over the CBr x ′ temperature series, as seen in Figure 6a−c.…”

“…This is proposed to be a result of bromine atoms that have not been expelled from the material until it is heated above 950 °C. It is known that bromine forms stable intercalation compounds within graphite. , This process is only partially reversible in that the last 5–10% of the intercalated bromine can only be removed by strong heating to form volatile carbon derivatives that incorporate bromine . In the present work, intercalated bromine and its destructive deintercalation process likely explains the larger d 002 and low values of L c and L a observed over the CBr x ′ temperature series, as seen in Figure a–c.…”