Direct observation of the dynamics of single metal ions at the interface with solids in aqueous solutions

Ricci, M.; Trewby, W.; Cafolla, M.; Voïtchovsky, K.

Abstract

The dynamics of ions adsorbed at the surface of immersed charged solids plays a central role in countless natural and industrial processes such as crystal growth, heterogeneous catalysis, electrochemistry, or biological function. Electrokinetic measurements typically distinguish between a so-called Stern layer of ions and water molecules directly adsorbed on to the solid’s surface, and a diffuse layer of ions further away from the surface. Dynamics within the Stern layer remain poorly understood, largely owing to a lack of in-situ atomic-level insights. Here we follow the dynamics of single Rb+ and H3O+ ions at the surface of mica in water using high-resolution atomic force microscopy with 25 ms resolution. Our results suggest that single hydrated Rb+ions reside τ1 = 104 ± 5 ms at a given location, but this is dependent on the hydration state of the surface which evolves on a slower timescale of τ2 = 610 ± 30 ms depending on H3O+ adsorption. Increasing the liquid’s temperature from 5 °C to 65 °C predictably decreases the apparent glassiness of the interfacial water, but no clear effect on the ions’ dynamics was observed, indicating a diffusion-dominated process. These timescales are remarkably slow for individual monovalent ions and could have important implications for interfacial processes in electrolytes.

Citation

Ricci, M., Trewby, W., Cafolla, M., & Voïtchovsky, K. (2017). Direct observation of the dynamics of single metal ions at the interface with solids in aqueous solutions. Scientific Reports, 7, Article 43234. https://doi.org/10.1038/srep43234

• Journal Article Type: Article
• Acceptance Date: Jan 23, 2017
• Online Publication Date: Feb 23, 2017
• Publication Date: Feb 23, 2017
• Deposit Date: Nov 21, 2016
• Publicly Available Date: Mar 2, 2017
• Journal: Scientific Reports
• Publisher: Nature Research
• Peer Reviewed: Peer Reviewed
• Volume: 7
• Article Number: 43234
• DOI: https://doi.org/10.1038/srep43234