Cobalt hydroxide as a capacitor material: Tuning its potential window

Research activities on various supercapacitor materials have grown enormously in recent years. Capacitor studies of Co(OH)(2) over a limited potential window in alkaline electrolytes are reported. A high potential window of a capacitor material is desirable for use in a device. Furthermore, as the specific energy and specific power of a capacitor depend strongly on its voltage, experiments are conducted in the present work to understand the reason for a low potential window for Co(OH)(2) as a capacitor material and also to increase its potential window. Experiments are conducted in NaOH and Na2SO4 electrolytes of various concentrations using electrochemically precipitated Co(OH)(2) on stainless steel current collectors in an aqueous Co(NO3)(2) electrolyte. Based on the potential window, specific capacitance, and specific energy, it is found that 0.05 M NaOH electrolyte is more appropriate for capacitor properties of Co(OH)(2) than the rest of the electrolytes studied. Using a Co(OH)(2) electrode with a specific mass of 1.0 mg cm(-2) in 0.05 M NaOH, a specific capacitance of about 380 F g(-1) is obtained with a potential window of 0.85 V at a charge-discharge current density of 10 A g(-1) (10 mA cm(-2)). (c) 2008 The Electrochemical Society.