Performance of Nickel-Iron nanostructured electrodes at different temperatures

In recent years, the whole world has been trying to reduce CO2 emissions through the global decarbonization of energy processes. In this view, the interest towards green hydrogen has drastically increased. One way to produce green hydrogen is by water electrolysis using only electricity from renewable sources. The storage of renewable solar or wind electricity is a major challenge to build a sustainable future energy system. The electrochemical production of hydrogen, through electrolysers, is a viable strategy to take advantage of the surplus electricity coming from renewable energy sources. Its production is pollution-free but is not economically viable. The development of more efficient electrolysers with low-cost electrode materials plays a key role. Catalysts must have such as good electrocatalytic properties, high conductivity, high availability, low cost, and good chemical stability. Nowadays, research is focused on improving the Alkaline Water Electrolysis (AE) to reduce the cost of electrode production. In alkaline environment it was demonstrated that, transition metals, and in particular Nickel or nickel based alloy nanostructured electrodes, have good and stable performances. Furthermore, industrial alkaline electrolysers work at temperatures between 40 and 90°C. Therefore, electrodes must be mechanically and chemically stable at these temperatures. An approach to improve AE performance consists on the fabbrication of nanostructured electrodes because they are characterized by high electrocatalytic activity due to the very high surface area. Starting from the results obtained in a previous work, the nanostructured alloy of NiFe was tested both as cathode and anode at three different temperatures (25 °C, 40 °C, 60 °C). Nanostructured electrodes were obtained through a simple and cheap method, template electrosynthesis, using a polycarbonate membrane as a template. NiFe electrodes morphology was studied by scanning electrode microscopy (SEM) and their composition was evaluated by energy diffraction spectroscopy (EDS) analyses. Later, the electrodes were characterized using various electrochemical techniques: Cyclic Voltammetry (CV), Quasi Steady State Polarization (QSSP) and Galvanostatic Step. To evaluate the mid-term behavior of the electrodes, especially at high temperatures, a constant current density was applied for 6 hours. In particular, -50 mA cm-2 for Hydrogen Evolution Reaction (HER) and 50 mA cm-2 for Oxygen Evolution Reaction (OER). All the tests were performed in 30% w/w KOH aqueous solution. Temperature increase plays a key role in increasing the efficiency of both anode and cathode reactions. As expected, the best result was obtained at 60 °C. Acknowledgments This research was funded by MUR, CNMS Centro Nazionale per la Mobilità sostenibile grant number CN00000023