Interface-dependent electrochemical behavior of nanostructured manganese (IV) oxide (Mn₃O₄)

We report on the crystallographic orientational dependence of the electrochemical behaviour in nanostructured manganese oxide. Manganese Oxide (Mn₃O₄) nanocrystals have been deposited on Nb-doped Strontium Titanate (Nb:SrTiO₃) substrate via pulsed laser deposition. (001), (101) and (112) orientated nanocrystals were successfully grown on (100), (110) and (111) Nb:SrTiO₃ substrates respectively. Analysis of the lattice arrangements suggests that nanostructure growth may be driven more by polarity rather than the epitaxial strain such that electrostatic repulsion can be minimised. Cyclic voltammetry (CV) in 1 M Na₂SO₄ electrolyte was performed to understand how specific capacitance values vary with changing lattice orientations. The maximum specific capacitance calculated for the (100) orientation was 34 F/g, obtained after the 3000^th cycle. Beyond this the CV loop plateaus rapidly and structural analysis of this sample revealed a morphological transformation from the (001) orientation to the (101) platelet structures. The maximum specific capacitance obtained was for the (112) sample (120F/g) suggesting that such non-primary planes in spinel oxides may be most attractive for electrochemical applications.