An old workhorse of oxide investigations: new features of Co3O4

The electrochemical behaviour of Co3O4 from exhaustive cobalt nitrate decom position (T = 260-850 degrees C) is investigated on graphite-supported elec trodes, mainly relying on quasi-reversible results. Two well defined 1-e(-) redox systems are observed related to Co2+/Co3+ and Co3+/Co4+ reactions of non-equivalent oxide surface sites. Oxide stoichiometry is directly estima ted by voltammetry in 'wet' conditions and depends on preparation temperatu re as in ex situ solid state data. Adsorption of surface intermediates invo lved in charge transfer is examined. Langmuir and Temkin-type adsorption is otherms are obeyed for the Co2+/Co3+ and Co3+/Co4+ redox systems, respectiv ely. Unusually negative (attractive) lateral interaction parameters are cal culated for the latter system. Separation of oxide and graphite currents is achieved to permit real electrode surface area determination. (C) 1999 Els evier Science S.A. All rights reserved.