Magnetic, optical and electrocatalytic properties of urchin and sheaf-like NiCo2O4 nanostructures

Abstract

Using soft hydrothermal approach we tune the morphology of spinel NiCo2O4 and show that the magnetic, optical and electrocatalytic properties depends on the morphology. The electrochemical oxidation of methanol was investigated on urchin and sheaf-like morphologies of NiCo2O4 electrodes in alkaline media using cyclic voltammetry, chronoamperometry and linear sweep voltammetry techniques. The urchin and sheaf-like NiCo2O4 electrodes show excellent electrocatalytic activity towards methanol oxidation and exhibits current densities of about 8.85 mA cm−2 and 7.31 mA cm−2 at bias potential of 0.6 V in 1 M KOH and 0.5 M methanol electrolytes. More importantly, the urchin-like NiCo2O4 retained the current density by 97% of its original after 1000 CV cycles at a scan rate of 20 mV s−1, which is higher than sheaf-like NiCo2O4 electrode (only 85%). The Ni and Co species in the binary metal oxide are deduced to be the electroactive sites. The unique mesoporous surface morphologies of NiCo2O4 favor the enhancement of electrocatalytic activity. There is a strong influence of crystallite size and morphology on the magnetic and optical band gap energies of nickel cobaltite. The estimated band gap energies from the UV–vis absorption are 2.07 and 3.04 eV for urchin-like NiCo2O4, and 1.98 and 2.95 eV for sheaf-like NiCo2O4.