A simple template-free strategy to synthesize nanoporous manganese and nickel oxides with narrow pore size distribution, and their electrochemical properties

A facile method has been developed to synthesize nanoporous manganese and nickel oxides with polyhedron particle morphologies, high surface areas and narrow pore distributions by controlled thermal decomposition of the oxalate precursors. This method can be extended to using other kinds of salt precursors to prepare a series of nanoporous metal oxides. The heating rate, calcination temperature and controlled particle size of the oxalate precursors are important factors to get well-defined pore structures. XRD, TG-DTA, TEM, SEM, XPS, wet chemical titration and N₂ sorption isotherm techniques are employed for morphology and structure characterizations. High surface area microporous manganese oxide (283 m² g^-1) and mesoporous nickel oxide (179 m² g^-1) with narrow pore distribution at around 1.0nm and 6.0nm, respectively, are obtained. Especially, we can tune the pore size of manganese oxides from microscope to mesoscope by controlling the thermal procedure. Electrochemical properties of manganese and nickel oxides are studied by cyclic voltammetry measurements in a mild aqueous electrolyte, which shows a high specific capacitance of 309 F g^-1 of microporous manganese oxide and a moderately high specific capacitance of 165 F g^-1 of mesoporous NiO due to their nanoporous structure, presenting the promising candidates for super capacitors (SC).