Cobalt-based compounds and composites as electrode materials for high-performance electrochemical capacitors

Abstract

Recent progress, achievements, challenges and outlook in the (re)search of high performance cobalt-based compounds and composites for electrochemical capacitors.

Quantifying the Role of Nanotubes in Nano:Nano Composite Supercapacitor Electrodes

“…We observe a pair of peaks around 0.17 V (vs Hg/HgO) which correspond to the oxidation/reduction of Co(OH)2. [4] The areas enclosed by the CVs show almost no change as the scan-rate increased 6 500-fold. The ultrathin film has a specific capacitance of 164 F g -1 at 10 mV s -1 and it retains 76% (125 F/g) at 5000 mV s -1 , confirming its good rate performance.…”

“…[4] However, manuscripts following such strategies generally report performance enhancements rather than exploring the physical nature of the improvements. We argue that by applying Equations (1) and (2), it is possible to gain an insight into the mechanisms behind the performance increases associated with nanotube addition.…”

“…This may be due to partial oxidation of the Co(OH)2 to CoOOH, a material which is considerably more conductive (in plane conductivity ~500 S m -1 ). [4] Access to Equations (1) and (2) allow us to consider the limitations of low-conductivity electrode materials which result in high- electrodes. By expanding Equation (1) to second order, it can easily be shown that, at high rate, the measured areal capacitance is given by (2) and (3), we can show that:…”

“…[9] We note that LPE has not previously been used to exfoliate Co(OH)2 and was chosen due to its scalability and versatility. [10] This method involves sonicating the layered power in an aqueous sodium cholate solution, coupled with a centrifugation regime [11] designed to retain only the thinnest 4 nanosheets, and yields a dispersion of nanosheets with a pale pink color as expected for -…”

Spinel CoMn2O4 nanosheet arrays grown on nickel foam for high-performance supercapacitor electrode

“…In efforts to improve electrochemical performance, various binder-free supercapacitor electrodes supported by Ni foam have been studied [6][7][8]. Ni foam (NF) with free-standing interconnected network has been widely used as substrate owing to its high surface area, high electron conductivity, low cost and facility to practical application.…”