Monitoring Nanostructural Dynamics During the Electrochemical Growth of Metal Hydroxide Thin Films by in-situ Small-Angle X-Ray Scattering

Understanding structural dynamics on the nanoscale is essential for progress in current research areas such as catalysis, energy storage, and nanotechnology. In this study, we introduce an in-house electrochemical flow cell for real-time small-angle X-ray scattering (SAXS) experiments to monitor cobalt hydroxide (Co(OH)₂) electrocrystallization under controlled conditions. Co(OH)₂ films were produced via cathodic electrochemical deposition (CED) from a Co(NO₃)₂ solution. SAXS data, complemented by electron microscopy and spectroscopy, reveal the formation of nanoscale Co(OH)₂ platelets with an average thickness of ~13 nm and a lateral size of ~600 nm. Time-resolved in-situ SAXS tracks the steady growth of these platelets, from 7.8 nm to 15.7 nm thickness over 120 min. In addition, SAXS measurements demonstrate the influence of citrate ligands, which initially suppress platelet formation and stabilize spherical nanostructures. As citrate depletes in the electrolyte, platelets begin to form, indicating a dynamic shift in crystallization mechanism. By employing in-situ SAXS, we successfully monitor the temporal evolution of nanoscale structures, offering insights into the mechanisms governing crystallization under electrochemically controlled conditions. These findings underscore the versatility of in-house SAXS setups for real-time analysis of material formation and growth processes, with implications for tailoring the synthetic parameters towards materials with dedicated nanostructures for various technological applications.