(Digital Presentation) Flattening of the Capacitance–Current Density Curve. the Effect of Surface Metallization of Ni(OH)2 on the Electrode for the Hybrid Supercapacitor

During the last decades, the development of supercapacitors (SCs) has become one of the main trends in electrochemistry. This can be explained by the requirements of some autonomous devices in high currents for a short time. Another reason is that the coupling of an accumulator and a SC can be used for the accumulator's lifetime prolongation and increase its performance as well. One of the best-known materials for SCs is nickel hydroxide. It is used in positive electrodes of asymmetric hybrid SCs. In this work, we used the direct formation of Ni(OH) 2 on nickel foam followed by its partial metallization by electroless nickel plating in order to define the effect of metallization on the electrochemical performance of formed electrodes. The formation of electrodes was carried out by means of the reaction of nickel ammonia complex decomposition [1]. Cleaned nickel foam substrates were submersed in nickel ammonia complex solution. Full complex self-decomposition was made for two days and certain Ni(OH) 2 mass was deposited on substrates. The next step for electrodes was rinsing with distilled water and drying in fresh air for one day. Formed in such a way electrodes were used to define electrode properties without metallization. Several formed electrodes were used for the further metallization step. For this electrodes with Ni(OH) 2 were immersed in electrolyte for electroless nickel plating. The composition and work conditions were the following: 30 g/L NiSO 4 ·7H 2 O, 10 g/L Na 2 H 2 PO 4 ·H 2 O, 30 g /L (NH 4 ) 2 SO 4 , pH=8.2, t=85 °C. As a result, several electrodes with different deposited nickel to nickel hydroxide were formed. Formed electrodes were rinsed with distilled water, and dried on air for one day. After that, cyclic voltammetry with different sweep rates (5, 10, 20, 50, 100, 500 mV/s) and charge-discharge cycling (1, 2, 3, 5, 10 A/g) were performed. All reactants were of analytical grade and used without further purification. For the formation of all electrodes, nickel foam (NF) substrates with sizes 1×3.5 cm and the following parameters were used: purity - 99.99%, thickness - 1.6 mm, density - 346 g/m 2 , porosity ≥95%, 80-110 ppi. In order to estimate morphology, an optical microscope with a digital camera (Hayear 16MP) was used. For electrochemical measurements, Gamry 1010E potentiostat was used. The platinum plate was used as a counter and Ag|AgCl in 3M KCl was employed as a reference electrode. 1M KOH solution was used as an electrolyte