MnOx/C composites as electrode materials.: I.: Synthesis, XRD and cyclic voltammetric investigation

MnOx/C composite material was obtained by precipitation on suspended carbon black particles from dissolved KMnO4. Doped composites were obtained by addition of Ca, Mg, Ni and other ions to the reaction mixture. The resulting solids are XRD amorphous or very poorly crystalline, but their chemical composition, Mn valence and electrochemical behaviour are very similar to those reported for birnessite, 7-A layered manganate(III,IV). We tested the electrochemical reduction/oxidation of the composite in 2 M KOH using cyclic voltammetry with three kinds of electrodes: microparticles immobilised on a carbon electrode (voltammetry of microparticles, vmp), carbon paste electrodes (cpee) and PTFE-bonded electrodes (tbe). Each technique has been used for its own merit: vmp is the best pilot technique, cpee enables fast quantification of the charge/mass relations, and tbe is the most reliable, but the slowest and the most laborious one. All the employed techniques yield directly comparable results. The composite can be discharged/recharged several tens of times at approximately 1 e(-)/Mn efficiency. (C) 1999 Elsevier Science Ltd. All rights reserved.