In situ real-time investigation of ruthenium electrodeposition behavior in HCl solution using EQCM

Industrial waste solutions are rich in precious metals, which are valuable secondary resources. In order to realize the separation and recovery of ruthenium by electrodeposition, this work used a combination of cyclic voltammetry (CV), chronoamperometry (I-t), and electrochemical quartz crystal microbalance (EQCM) to study the electrochemical behavior and electrodeposition mechanism of ruthenium in HCl solution. The results show that the reduction of ruthenium in HCl solution is influenced by hydrogen evolution reaction (HER) and chlorine evolution reaction, and the reduction process of ruthenium varies at different potentials. The reduction currents of Ru(VIII)/Ru(0) and Ru(IV)/Ru(III) are observed at 0.88 V and 0.6 V. The reduction of Ru(III) to Ru(0) at negative potentials starts at −0.2 V, with peak cathodic currents between −0.2 V and −0.5 V accompanied by a significant mass increase, which is confirmed to be the electrodeposition of metallic ruthenium by SEM and EDS. The microscopic morphology of the ruthenium coating is spherical particles, and the nucleation mode of electrodeposition is progressive nucleation. The HER leads to a macroscopic morphology of a cleaved lamellar structure, which is not tightly adhered to the substrate. The metallic ruthenium starts to oxidize and dissolve rapidly after 1.12 V, leading to a rapid degradation of the electrode surface quality.