Cathodic deposition of Ni(OH)2 and Co(OH)2 for asymmetric supercapacitors: Importance of the electrochemical reversibility of redox couples

• Published in: Journal of power sources Vol. 221; pp. 128 - 133
• Main Authors: Hu, Chi-Chang, Chen, Jia-Cing, Chang, Kuo-Hsin
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.01.2013; Elsevier
• Subjects: Applied sciences; Asymmetric type; Asymmetry; Capacitors; Capacitors. Resistors. Filters; Cathodic deposition; Chlorides; Cobalt hydroxide; Density; Deposition; Electrical engineering. Electrical power engineering; Energy of formation; Exact sciences and technology; Nickel hydroxide; Scanning electron microscopy; Supercapacitors; Various equipment and components; Supercapacitors; Cathodic deposition; Cobalt hydroxide; Nickel hydroxide; Asymmetric type; Performance evaluation; Power density; Anode; Cathode; Energy density; Potential difference; Electrolytic capacitor; X ray diffraction; Redox couple; Transmission electron microscopy; Graphene; Energetic efficiency; Supercapacitor; Capacitance; Reversibility; Microstructure; Specific capacity; Double layers
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2012.07.111

This work demonstrates the influences of electrochemical reversibility of the pseudocapacitive materials on the performances of an asymmetric supercapacitor consisting of a pseudocapacitive cathode and an anode of the double-layer type. Thanks for the simple, one-step, cathodic deposition of nickel and cobalt hydroxide (denoted as Ni(OH)2 and Co(OH)2, respectively) films from their chloride precursor in aqueous media with the addition of 40 mM NO3− as the OH-donating agent. The specific capacitances of Ni(OH)2 and Co(OH)2 films (ca. 0.4 mg cm−2) deposited at 1.0 mA cm−2 for 1000 s are equal to 2217 and 549 F g−1, respectively while the electrochemical reversibility of Co(OH)2 is better than that of Ni(OH)2 based on peak potential difference and symmetry of charge/discharge curves. The Co(OH)2-graphene asymmetric supercapacitor shows higher capacitance retention and higher energy efficiency of charge–discharge than the Ni(OH)2-graphene system although the latter system exhibits higher energy and power densities than the former one. The microstructures of as-deposited Ni(OH)2 and Co(OH)2 films have been examined by scanning electron microscopic (SEM), transmission electron microscopic (TEM), and X-ray diffraction (XRD) analyses. ► Reversibility of redox materials determines CS retention and energy capture efficiency of asymmetric ECs. ► CS of Ni(OH)2 and Co(OH)2 prepared by cathodic deposition are 2217 and 549 F g−1, respectively. ► Ni(OH)2-graphene is an energy-oriented EC of the asymmetric type. ► Co(OH)2-graphene is a power-oriented EC of the asymmetric type.