  A flexible technique is developed using hydrochloric acid to modify the redox
reaction between potassium permanganate and sodium nitrite in order to grow
ultrafine alpha-MnO2 nanorods, hydrothermally. The nanorods grown were 10-40 nm
diameters in range. Not any crack, fissure, imperfection or dislocation is
observed in the nanorods suggesting it to be finely ordered. Structure, phase
and purity of as developed nanorods were determined using X-ray diffraction
(XRD), Fourier transform infrared spectroscopy (FTIR) and Energy-dispersive
X-ray spectroscopy. Peseudocapacitance of alpha-MnO2 nanorods was tested using
a three electrode system. Considerably very high pseudocapacitance value of
643.5 F/g at 15 A/g current density was calculated from the galvanostatic
discharge current measurement. Also excellent cyclability is observed with high
retention of 90.5% after 4000 cycles. Highly uniform and confined morphology of
the nanorods helps smooth the electron dynamics between electrode/electrolyte
interfaces resulting in superior performance. Most importantly, the use of
potassium ferricyanide as redox additive to KOH electrolyte was proved to be
quite effective as it provides extra redox couple [Fe(CN)6]3n/[Fe(CN)6]4n which
helps in further smoothening of electron transition thereby resulting in
considerably superior pseudocapacitive performance.
