Several synthetic and natural manganese dioxides are characterized in temrs of chemical composition, structural disorder and electrochemical activity; semi conducting propertie arre examined on pressed powdered samples. The reactivity scale established between structural disorder and electrochemical reactivity is paralleled by semi conducting properties and proton diffusivity. COnductivity values of 0.15 S.cm~(-1) for stoechiometric #beta#-MnO_2, 1.3 10 ~(-2), 2.5 10~(-2) and 3.7 10~(-2) s.Cm~(-1) for thedefect dioxides, respectvely synthetic-Ramsdellite,CMD and EMD are measured. Proton diffusivity sutyd by EIS provides, for lwo reduction rate, diffusion coeficient D values varying from 10~(-15) cm ~2/s value to 10~(-16) for he best reactive forms EMD and CMD; for NMD and #beta#-Md, D is respecitively 10~(-16) and 10~(-21) cm ~2/s. Redox reversibilityis obtained around 1.3 V for EMD for a one electron reduction in [KOH]<1M; at -0.4V for a 2 electrons redution in 9M KOH for Bi modified NMD.
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