Nickel-Copper Alloys Modified Electrodes: an Electrochemical Study on their Interfacial and Supercapacitive Properties

Abstract

In this manuscript, we report the electrodeposition of nickel-copper alloys in a two steps methodology. Firstly, the copper electrode is oxidized to generate Cu 2+ ions followed by the reduction of both Ni 2+ and Cu 2+. The electrodes were further cycled in KOH to convert the metallic alloy into the respective electroactive hydroxide. This methodology created an electrode with high roughness and distinct electrochemical behavior. The modified electrodes were also characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Finally, the modified electrodes were studied in their supercapacitive properties by galvanostatic charge and discharge curves; the electrodes showed a good specific capacitance of 58 mF cm -2 . The results indicated a new strategy using a simple methodology to modified Cu-electrodes to develop supercapacitors at low cost. Keywords: nickel-copper hydroxides, supercapacitors, electrodeposition, interfacial properties IntroductionNowadays, the worldwide demand for energy impacts the research in new energy storage and conversion devices where it is intended an enhanced efficiency, low-cost and eco-friendly alternative.1-3 Among them, supercapacitors (SCs) arise as a good alternative due to their ease-preparation, long cycle life and fast and reversible redox reactions. [4][5][6] Supercapacitors, ultracapacitors or electrochemical capacitors are devices that combine the power delivery presented in the capacitors and the energy density presented by the batteries. 7 Based on the charge storage mechanism, supercapacitors can be divided into two categories: electrochemical doublelayer capacitors (EDLCs), where the capacitance arises from the charge accumulated at the electrode/electrolyte interface. Carbonaceous materials such as graphene and carbon nanotubes are typical examples vastly employed in EDLCs. 8,9 The second one are the pseudocapacitors, which the charge storage mechanism is based on both double layer capacitance and fast redox reactions at the electrode/electrolyte interface, increasing the overall density of current produced. Typical pseudocapacitors materials are transition metals oxide/hydroxide (TMOH) and conducting polymers. [10][11][12] Amongst the different TMOH used as supercapacitors electrodes, RuO 2 is by far one of the most investigated material due to its high theoretical specific capacitance, long cycle life and rate capability, electrochemical properties and conductivity. 13 However, its high-cost and scarcity is the main drawback related to RuO 2 based materials in commercial devices. In this way, in order to obtain more attractive materials, TMOH alloys based on low-cost metals have been extensively studied.14 Shinde et al.15 studied the incorporation of Mn in CuO/Cu(OH) 2 by successive ionic layer adsorption and reaction (SILAR) technique. The authors have found an improved specific capacitance of 600 F g -1 for the doped material that was ascribed to a change in the morphology occasioned by the Mn doping effect.Another TMOH of i...