Behavior of a forest of NiFe nanowires in KOH and NaCl solution for water electrolysis

Abstract

In the present work, the behaviour of nanostructured electrodes consisting of an array of nanowires made of NiFe alloy is studied in a KOH + 0.5 M NaCl solution. The aim is to explore the possibility of using these electrodes for hydrogen production by seawater electrolysis. The splitting of sea water requires a highly selective electrode on the anode side, where the evolution of molecular chlorine or the formation of other active chlorine compounds can compete with the oxygen evolution reaction. Nanostructured electrodes obtained by template electrosynthesis were tested at room temperature in KOH + 0.5 M NaCl solution and the results were compared with those obtained in pure KOH. The results showed that the electrocatalytic behaviour of the nanostructured NiFe alloy was not affected by the presence of NaCl. Furthermore, the chemical-physical characterisations carried out after the long-term galvanostatic tests have shown that the nanostructured electrodes are also stable in terms of morphology and composition. In addition, the solution used to perform the long-term galvanostatic tests was analysed to investigate the possible formation of chlorine compounds. The absence of these compounds, together with the measurement of the potential value for the oxygen evolution reaction, which was always lower than the thermodynamic redox potential for the hypochlorite formation reaction, leads us to conclude that these electrodes are potentially suitable for seawater electrolysis.