Cyanide-Free Electroplating for Gold Coatings: A Review

Electroplating gold coating is very important for both jewelry industry and fabrication of functional materials. The traditional process for gold plating is fulfilled in the cyanide-containing solution, which can potentially produce hazardous HCN gas during electrodeposition and generate hazardous CN−-containing wastewater. In addition, the residual CN− ions in substrate can damage the post-coated microelectronics. Cyanide-free processes for electroplating gold are springing up these years, showing great potential for replacing the environmentally unfriendly cyanide process. In this review, the types of gold coatings are first summarized. Then the physicochemical properties of various cyanide-free complexing agents for electroplating gold film are compared. Subsequently, cyanide-free systems that have great potential for industrialization are introduced, with other novel cyanide-free systems still on its infant being also suggested. Finally, the existing problems and future developments are anticipated. The contents can hopefully provide comprehensive understanding of the cyanide-free gold electroplating process.