Brief review of external physical field-boosted low-temperature electrodeposition for metals and alloys

Abstract

Electrochemical metallurgy at low temperature (<473 K) shows promise for the extraction and refinement of metals and alloys in a green and sustainable manner. However, the kinetics of the electrodeposition process is generally slow at low temperature, resulting in large overpotential and low current efficiency. Thus, the application of external physical fields has emerged as an effective strategy for improving the mass and charge transfer processes during electrochemical reactions. This review highlights the challenges associated with low-temperature electrochemical processes and briefly discusses recent achievements in optimizing electrodeposition processes through the use of external physical fields. The regulating effects on the optimization of the electrodeposition process and the strategies for selecting various external physical fields, including magnetic, supergravity, and ultrasonic fields are summarized from the perspectives of equipment and mechanisms. Finally, advanced methods for in-situ characterization of external physical field-assisted electrodeposition processes are reviewed to gain a deeper understanding of metallic electrodeposition. An in-depth exploration of the mechanism by which external physical fields affect the electrode process is essential for enhancing the efficiency of metal extraction at low temperatures.

1. Introduction

Electrochemical metallurgy is a key method for producing many kinds of metal materials, including aluminum, titanium, and vanadium [1–6]. In industries, high-temperature electrochemical metallurgy is primarily used to extract alkaline earth metals [7]. Due to the high melting points of most molten salt systems result in substantial electricity consumption for maintaining these temperatures during production. In contrast, ionic liquid and organic solvent systems offer advantages such as wide electrochemical windows and pressure stability of liquid and vapor at room temperature, making them promising alternatives for achieving low-temperature metallurgy [8–9]. This low-temperature approach has attracted considerable attention due to its low energy consumption and high conversion efficiency [10].

Molten salt electrolysis has been successfully utilized to extract metals (aluminum, titanium, and rare earth elements) at room temperature by selecting a suitable solvent system [11–12]. However, the relatively slow mass transfer process at low temperatures is a major challenge hindering the further application of low-temperature metallurgy in engineering [13–15]. This limitation is particularly crucial in solvent systems such as ionic liquids (ILs), which possess viscosities that are two to three orders of magnitude higher than those of water or molecular organic solvents [16–18]. The slow mass transfer rate limits the reaction kinetics, reducing the suitability of electrochemical extraction in ILs for large-scale industrial applications. Direct interventions such as stirring have been employed to partially alleviate the issue of slow mass transfer [19–22]. However, these methods provide only limited improvement. Therefore, researchers have shifted their focus toward the application of external physical fields, such as magnetic fields, supergravity, and ultrasonic waves, to facilitate low-temperature metallurgical processes. These fields offer potential solutions for enhancing electrolysis efficiency and improving the morphology of the deposited products. Thus, extensive knowledge of electrode processes through in-situ visualization and quantitative characterization techniques is essential for understanding the kinetic processes of low-temperature electrochemical metallurgy. Despite these advancements, no systematic review summarizing the studies on field-assisted low-temperature electrodeposition has been published, highlighting the need for this comprehensive review.