Abstract
Cobalt oxide films, fabricated by reactive sputtering in a 100% pure O2 plasma are highly nonstoichiometric with a bulk oxygen to cobalt ratio of ∼ 1.15. Conversely, surface XPS studies indicate an oxygen to cobalt ratio ranging from 1.8 to 3.0 and show the presence of Co3+ only in the surface region of the as formed films. Infrared and Raman spectra however confirm the presence of both Co3+ and Co2+ in the bulk and indicate that these highly defective films possess the spinel structure. Photoelectrochemical and impedance studies show that the sputtered oxide is a highly doped p-type semiconductor with an indirect bandgap of Eg ∼ 1.50 eV. The electrocatalytic properties of these oxide films for oxygen reduction and evolution are reported.
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