Towards cleaner production of trivalent chromium electrodeposition: Mechanism, process and challenges

The chromium electrodeposition process produces functional chromium layers and high-purity chromium metal, which are used in a wide range of industries. Compared with the traditional process using Cr(VI), the chromium electrodeposition process of Cr(III) has the advantages of low toxicity, low energy consumption, and low impact on the environment, which has a broad prospect for development. Nevertheless, the nature of Cr(III) in aqueous solution and the mechanism of electrodeposition make the preparation of thick chromium layers challenging, thus hindering the development of trivalent chromium electrodeposition technology. Hence, it is crucial to analyze the properties of Cr(III) in aqueous solution and the principle of electrodeposition, investigate methods to disrupt the inert structure of [Cr(H2O)(6)](3+), prevent Cr(VI) formation and control the pH stability near the cathode to promote the sustained electrodeposition of Cr(III). This paper systematically overviews Cr(III) properties in aqueous solutions and the challenges encountered during electrodeposition. It focuses on the research advancements in utilizing coordination agents to disrupt the structure of [Cr(H2O)(6)](3+). The measures to enhance the sustained electrodeposition of Cr(III) (including the selection of electrodes, the improvement of electrolytic cells, the exploration of additives, etc.) are discussed. Finally, some recommendations are provided to facilitate the development of Cr(III) electrodeposition.