Nanostructured Ni-Co Alloy Electrodes Fabrication and Characterization for both Hydrogen and Oxygen Evolution Reaction in Alkaline Electrolyzer

Abstract

Sun and wind as power sources are becoming more and more relevant owing to the progressive abandoning of the fossil fuels [1,2]. Additionally, worldwide public authorities are encouraging the use of renewable energies by promoting laws and guidelines [3,4]. In this scenario, a fundamental role can play hydrogen that besides being a valuable energy carrier, it can also act as a storage medium to balance the discontinuity affecting the renewable energy sources production [5]. As a consequence, cheap and abundant availability of hydrogen is crucial. Electrochemical water splitting is likely one of the most valuable technique to produce hydrogen because the process is environmentally friendly being electron a reagent, which, unfortunately, enhances the cost. The minimum energy requested is 39.67Wh per g of hydrogen. This value increases more or less owing to the electrodes overvoltage that depends on the current density passing through the electrolyzer. One approach to improve the performance of a water splitting electrochemical cell is based on the development of nanostructured electrodes distinguishing for low cost and high electrocatalytic activity. By template electrosynthesis, we have fabricated Ni nanowires featured by very high surface area. In previous works, we have shown that water-alkaline electrolyzer with Ni nanowires electrodes covered by nanoparticles of IrO2 as an anode and Pd as a cathode have good and stable performance also at room temperature [6-7]. In this work, the attention has been focused on the fabrication of nickel-cobalt electrodes. In particular, starting from aqueous solutions containing both elements at different concentrations, alloyed electrodes with different compositions were fabricated through electrodeposition into a template. The chemical and morphological features of these nanostructured electrodes will be presented and discussed. Furthermore, electrochemical and electrocatalytic tests aimed to establishing the best alloy composition were carried out for both hydrogen and oxygen evolution reaction. Then, long term test conducted at a constant current density in aqueous solution of potassium hydroxide (30% w/w) will be also reported.