Copper and tin electrodeposition from deep eutectic solvents using pulse current

In the past, metal electrodeposition has mainly been performed using aqueous electrolytes. However, such system often suffers from performance limitations and environmental concerns. Deep eutectic solvents (DES) are a type of ionic melt that has recently being proposed for electrodeposition metals and alloys. In addition, most electrodeposition studies are performed using direct current (DC) plating method. However, metal plated using this method often suffers from issues such as poor deposit quality and low Faradaic efficiency, which lead to the adoption of pulse plating method as an alternative. Currently, most studies of metal plating from DES have been carried out using DC plating and there have been relatively few studies of pulse plating. Therefore, the main objective of this study is to investigate aspects of pulse deposition from DES. Copper and tin were studied in this piece of research. The plating experiments of both metals were conducted in the ethaline-based DES using pulse current. The electrochemical characteristics were studied first, followed by the examination of the effects of pulse parameters on various aspects. Material characterization were also performed. It was found that copper reduction reaction in ethaline is a two-step single electron transfer process. While acceptable deposits were obtained, the current efficiency for pulse-plated copper was low in many cases. The occurrence of comproportionation (corrosion) reaction between cupric ions and copper: CuCl42- + Cu -->2CuCl2- was purposed and further tested via independent metal dissolution experiments. Two mathematical models were proposed to explain the relationship between the metal deposition and dissolution effect qualitatively, yet a more complex model needs to be developed to account for the results. Benzotriazole (BTA) was also tested and it was found the corrosion behaviour was suppressed to some extent. In the study of tin plating, the reduction of Sn2+ species takes place in a single two-electron transfer process. Pulse deposition experiments were carried out and the deposits showed high current efficiency with acceptable deposit properties and no corrosion behaviour was observed. However, no direct relationship was found between the deposit properties with the pulse parameters. The grain size ranged between 2.9 μm to 6.2 μm and oxygen was incorporated in some pulse conditions. In conclusion, this study has shown that it is possible to deposit both copper and tin from DES using pulse plating methods. Corrosion behaviour was observed in copper but not in tin. Collectively, the results showed that combining the technique of pulse plating and the use of DES solution can be a novel way to plate copper and tin. Currently, they do not offer superior advantages in terms of deposit quality and microstructure compared to the conventional methods, and it is clear that further optimisation of the process is required.In the past, metal electrodeposition has mainly been performed using aqueous electrolytes. However, such system often suffers from performance limitations and environmental concerns. Deep eutectic solvents (DES) are a type of ionic melt that has recently being proposed for electrodeposition metals and alloys. In addition, most electrodeposition studies are performed using direct current (DC) plating method. However, metal plated using this method often suffers from issues such as poor deposit quality and low Faradaic efficiency, which lead to the adoption of pulse plating method as an alternative. Currently, most studies of metal plating from DES have been carried out using DC plating and there have been relatively few studies of pulse plating. Therefore, the main objective of this study is to investigate aspects of pulse deposition from DES. Copper and tin were studied in this piece of research. The plating experiments of both metals were conducted in the ethaline-based DES using pulse current. The electrochemical characteristics were studied first, followed by the examination of the effects of pulse parameters on various aspects. Material characterization were also performed. It was found that copper reduction reaction in ethaline is a two-step single electron transfer process. While acceptable deposits were obtained, the current efficiency for pulse-plated copper was low in many cases. The occurrence of comproportionation (corrosion) reaction between cupric ions and copper: CuCl42- + Cu -->2CuCl2- was purposed and further tested via independent metal dissolution experiments. Two mathematical models were proposed to explain the relationship between the metal deposition and dissolution effect qualitatively, yet a more complex model needs to be developed to account for the results. Benzotriazole (BTA) was also tested and it was found the corrosion behaviour was suppressed to some extent. In the study of tin plating, the reduction of Sn2+ species takes place in a single two-electron transfer process. Pulse deposition experiments were carried out and the deposits showed high current efficiency with acceptable deposit properties and no corrosion behaviour was observed. However, no direct relationship was found between the deposit properties with the pulse parameters. The grain size ranged between 2.9 μm to 6.2 μm and oxygen was incorporated in some pulse conditions. In conclusion, this study has shown that it is possible to deposit both copper and tin from DES using pulse plating methods. Corrosion behaviour was observed in copper but not in tin. Collectively, the results showed that combining the technique of pulse plating and the use of DES solution can be a novel way to plate copper and tin. Currently, they do not offer superior advantages in terms of deposit quality and microstructure compared to the conventional methods, and it is clear that further optimisation of the process is required