Sol-gel template synthesis of highly ordered MnO2 nanowire arrays

In this paper, anodic aluminum oxide (AAO) templates with uniform pore diameter and periodicity were fabricated using a two-step oxidizating method at a constant current of 1.5 A dm−2 in a mixed solution of 0.5 M sulfate acid and 5 g L−1 oxalic acid at room temperature, pore-widening was done in 5 wt.% phosphoric acid. Then, arrays of manganese dioxide nanowires were prepared by combining the AAO template and a sol-gel solution containing Mn(CH3COO)2 and citric acid. SEM was used to characterize the structure of AAO and MnO2 nanowires. The results show that uniform length and diameter of MnO2 nanowires were obtained, and the length and diameter of MnO2 nanowires are dependent on the pore diameter and the thickness of the applied AAO template. The pore diameter of the AAO was about 70 nm, the diameter of the MnO2 nanowires was 70 nm and the length of the MnO2 nanowires was about 500-700 nm. XRD analysis indicate the MnO2 nanowires was α-MnO2 polymorph. The results of cyclic voltammetry indicated that the α-MnO2 nanowires are promising electrode materials for application in supercapacitors, the specific capacity of the electrode was 165 F g−1.