Direct reversible voltammetry and electrocatalysis with surface-stabilised Fe2O3 redox states

Nanoparticle film voltammetry is employed to explore the presence and reactivity of surface-stabilised iron redox centers at the interface of immobilised Fe2O3 nanoparticles of ca. 4 nm diameter and aqueous buffer media. Mesoporous films of Fe2O3 nanoparticles on tin-doped indium oxide (ITO) substrates are formed in a layer-by-layer deposition process from aqueous colloidal Fe2O3 and aqueous cyclohexyl-hexacarboxylate followed by thermal (500 °C) removal of the organic binder content. Both reversible oxidation and reversible reduction responses for Fe(III) are observed in phosphate and carbonate buffer media in the “underpotential” zone. Higher oxidation states of iron formed anodically (here tentatively assigned to Fe(IV)) are shown to be inert in phosphate buffer media but reactive towards the oxidation of glucose in carbonate buffer media.