Stainless steel-like FeCrNi nanostructures via electrodeposition into AAO templates using a mixed-solvent Cr(III)-based electrolyte

Electrodeposition of stainless steel-like materials such as FeCrNi alloy into micro- and nanotemplates provides a sustainable framework for creating biomedical-oriented micro- and nanocomponents with outstanding characteristics. While Cr(III)-based electrodeposition represents a 'green' alternative to toxic Cr(VI), its use is limited by Cr(III) aqueous chemistry which leads to the incorporation of impurities and the hydrogen evolution reaction (HER). These factors are responsible for low deposition efficiencies, brittleness and porosity. The current work sought to investigate the use of 'green' Cr(III)-glycine electrolyte to improve FeCrNi electrodeposition from Cr(III) precursors. Mixed-solvent electrolyte containing ethylene glycol (EG) was employed to reduce HER aftereffects. FeCrNi mixed EG electrolytes were compared to their aqueous counterparts to observe differences in Cr(III)-glycine complexation, coatings' composition and current efficiency. The feasibility of this method for creating nanostructures was verified by template-assisted electrodeposition using anodic aluminium oxide (AAO) templates. This study established that mixed-solvent electrolytes are an effective strategy to improve Cr(III)-based plating of alloys into miniaturised moulds. For the first time, electrodeposited FeCrNi nanowires (NWs) and nanotubes (NTs) were achieved via the framework developed in this work. The possible mechanisms controlling the morphological variations in FeCrNi nanostructures were discussed in relation to the kinetic and growth models in single metal electroplating into nanotemplates.