However, understanding the mechanism and kinetics of chromium electrodeposition from this system is quite limited. Fundamental knowledge of the deposition process is key for industrial process optimization. Essential to determining the reaction mechanism and kinetics is the identification of the chemical species involved in the reaction. Using a hybrid multiscale experimental and computational approach, insights into chromium complexation in the bulk electrolytes and how this speciation influences the composition of the deposit have been gained.
Samples electroplated in electrolytes of varied formate concentrations were characterized using X-ray Fluorescence (XRF) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Results from these analyses show that metallic chromium is only deposited when the electrolyte contains formate ions. In the absence of formate, only oxide and carbide species are deposited. The characterization results also show a current efficiency of the TCCT process of ~ 40%. From observations from surface characterization as well as spectroscopic analysis and density functional theory (DFT) and ab initio molecular dynamics studies (AIMD) of the bulk electrolyte, the coordination and complexation of formate ion in the chromium complex responsible for metallic chromium deposition have also been identified. Voltammetric studies coupled with ex-situ XPS and scanning electron microscopy (SEM) surface characterization also lead to a clear definition of the reaction mechanism of metallic chromium deposition that the incorporation of formate in trivalent chromium electrolytes makes possible.