Increasing anhydrous chromium chloride concentration in AlCl3-EMIC ionic liquid: a step towards non-hydrogen-embrittlement chromium electroplating

Non-hydrogen-embrittlement chromium electroplating has wide applications in industry. Using an ionic liquid (AlCl3-1-ethyl-3-methyl-imidazolium chloride, AlCl3-EMIC) as the electrolyte provides a viable way for metal electrodeposition. However, the low solubility of anhydrous chromium chloride salt in acidic AlCl3-EMIC IL makes the electrodeposition process essentially impractical. We propose a new method for dissolving CrCl3 or CrCl2, which effectively increases the concentration of anhydrous chromium salts in AlCl3-EMIC IL. Moreover, we demonstrate for the first time that the electroless deposition of BCC Cr can be realized on an Al substrate using this solution, which indicates that the reduction potential of chromium ions in AlCl3-EMIC IL is more positive than that of aluminum ions. This proves the thermodynamic possibility of electroplating metallic Cr. Therefore, our work paves the way for the engineering application of electroplating non-hydrogen-embrittlement chromium.