An old workhorse of oxide investigations:: new features of Co3O4

The electrochemical behaviour of Co3O4 from exhaustive cobalt nitrate decomposition (T = 260-850 degrees C) is investigated on graphite-supported electrodes, 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 estimated by voltammetry in 'wet' conditions and depends on preparation temperature as in ex situ solid state data. Adsorption of surface intermediates involved in charge transfer is examined. Langmuir and Temkin-type adsorption isotherms are obeyed for the Co2+/Co3+ and Co3+/Co4+ redox systems, respectively. Unusually negative (attractive) lateral interaction parameters are calculated for the latter system. Separation of oxide and graphite currents is achieved to permit real electrode surface area determination. (C) 1999 Elsevier Science S.A. All rights reserved.