473by electron exchange between the adjacent redox centers. Whichever explanation is correct, the new design of electrode should allow electrochemical ESR to be used first to study shorter lived intermediates and second to study intermediates and products in the kinetics of modified electrodes. Experimental SectionThe ESR spectrometer used was a Bruker ER 200 tt. The spectrometer has a dual cavity. In the second cavity a solid solution of Mn2+ in MgO serves as a permanent standard to calibrate the sensitivity of the spectrometer. The flow system and the method of construction of the tube electrode have been described previously.6 The nonelectroactive part of the semiannular or the missing sector electrodes was made of Teflon and assembled in the same way as a complete annular electrode. Except where stated, all chemicals and reagents were of AnalaR grade. Dimethylsulfoxide (BDH) was purified and dried as described previously.I6 Acetonitrile (Fison's dried distilled) was refluxed with 1% (w/v) CaH2 for 2 h and then fractionally distilled. TEAP (Fluka, purum) was recrystallized once from water. TBAT (Fluka, purum) was recrystallized once from a mixture of ethanol and petroleum ether. TMPD (BDH, L. R. grade) was recrystallized as described by Michaelis." Poly(nitro-(16) Mann, C. K. Electroanal. Chem. 1969, 4, 57. (17) Michaelis, L.; Schubert, M. P.; Granick, S. J. Am. Chem. Soc. 1939, 61, 1981.styrene) was synthesized by the method of Wiley and Smith.'* It was coated on to the platinum tube electrode by using the method of Miller.'3Vinylanthraquinone was synthesized by the method of Manecke and Storck.I9 The monomer was polymerized by using benzoyl peroxide initiator in tolulene solution at 100 'C for 240 h. The modified electrode was made by dip coating the platinum electrode in a 1 % (w/v) solution of polymer in CH2C12.All electrochemical experiments were controlled by a purpose built potentiostat of modular construction. Acknowledgment. W e thank the SERC and the WolfsonFoundation for financial support. W e are grateful to Mr. Michael Pritchard for his assistance in making the electrodes, to Mr. John Hooper for constructing the potentiostat, to Dr. S. Wilson for synthesizing poly(nitrostyrene), and to Mr. S. Jawaid for synthesizing poly(viny1anthraquinone). This is a contribution from the Wolfson Unit for Modified Electrodes.Registry No. Pt, TMPD, TMPD radical cation,, 24936-54-7; poly@-nitrostyrene) radical anion, 87842-91-9; poly(2-vinylanthraquinone), 73546-39-1; poly-(2-vinylanthraquinone) radical anion, 87842-93-1.Abstract: Electrochemical methods for the dispersion of Pt microparticles at microgram levels in polymeric matrices of poly(viny1acetic acid) glassy carbon electrodes, Pt-PVAA/GC, are described. The PVAA film was formed on a GC surface by refluxing neat VAA monomer under nitrogen. Cyclic voltammetry and single and double potential step electrolysis were
Recent progress in the development of rechargeable alkaline zinc-manganese dioxide cells is described. The advantages and limitations of the system are evaluated. Laboratory tests run on commercial primary alkaline cells as well as model simulations of a bipolar MnO~ electrode show that the rechargeable alkaline battery may be able to compete with lead-acid, nickel-cadmium, and secondary lithium cells for low-to moderate-rate applications. However, because of its poor performance at high rates and low temperatures, the alkaline MnO~ battery is not suitable for present automotive starting applications.
Several commercial grade electrolytic manganese dioxides (EMD's) of gamma variety were converted to normalbeta‐MnO2 by digesting in 1M sulfuric acid containing Mn2+ at various temperatures. The transformation was found to be catalyzed by Mn2+ and accelerated at high temperatures. The pseudo first‐order rate constants of EMD transformation were evaluated and an activation energy determined to be in the range of 98–115 kJ/mol. This value was very close to the activation energy of 94–100 kJ/mol for desorption of the type II water in EMD lattice. A mechanism involving the equilibrium between EMD and Mn2+, and liberation of the bound water was, thus, proposed.
Lab prepared gamma‐electrolytic manganese dioxide (γ‐EMD) of various particle size was converted to beta phase (betafication) by digesting in sulfuric acid containing Mn(II). The pseudo‐first order rate constant evaluated was found to be a function of temperature and particle size. The activation energy evaluated, however, is independent of the particle size. A proposed mechanism involving nucleation of β‐MnO2 at EMD surface via equilibration with Mn(II) in the electrolyte followed by the growth of β‐MnO2 into the core of EMD particles is discussed.
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