Al-substituted α-cobalt hydroxide synthesized by potentiostatic deposition method as an electrode material for redox-supercapacitors

Al-substituted α-cobalt hydroxide was prepared by a potentiostatic deposition process at −1.0 V (vs. Ag/AgCl) onto stainless steel electrodes by using a mixed aqueous solution of cobalt nitrate and aluminum nitrate. Their structure and surface morphology were studied by using X-ray diffraction analysis, energy dispersive X-ray spectroscopy and scanning electron microscopy. The SEM images showed changes in the nanostructure of α-cobalt hydroxide by the addition of Al. Galvanostatic charge–discharge curves showed a drastic improvement in the capacitive characteristics of α-cobalt hydroxide, with a specific energy increase from 11.3 to 18.7 Wh kg−1 by the substitution of just 8 at.% Al, and a specific capacitance of 843 F g−1 between 0 and 0.4 V. The cycle stability data suggest no significant changes in the discharge characteristics of α-cobalt hydroxide by the addition of Al.