Towards Sustainable Gold Depositions: Sulfite‐Based Cyanide‐Free Au‐Coatings Under Acidic Electrochemical Operation for PEM Electrolysis

ABSTRACT Sulfite‐based gold electrodepositions are explored as a cyanide‐free route for protective and conductive coatings in proton exchange membrane (PEM) water electrolysis. Multilayered Au/Ni/Cu coatings exhibit dense microstructures, well‐defined interfaces, and typical Au reflections of the fcc crystal system. Contact resistance remains low across the relevant compaction range, reaching 9.39 mΩ cm 2 at 150 N cm −2 , consistent with the performance of commercial cyanide‐derived coatings, meeting the international standards. Corrosion testing showed similar corrosion potentials and currents for both systems, whereas chronoamperometry revealed an under 2 mA current at 2 V and a more stable course for the sulfite‐based coating. In situ cell measurements under representative PEMWE operating conditions with polarization up to 2 A cm −2 reached cell potentials of under 1.9 V and no indication of significant mass‐transport limitations. Operation exceeding 160 h showed overlapping polarization curves before and after chronoamperometry testing and a degradation rate 11.8 µV h −1 , indicating stable electrochemical behavior. Overall, the sulfite‐complexed deposition approach delivers physical characteristics and acidic electrochemical behavior consistent with established industrial gold coatings while eliminating cyanide from the process.