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The dynamics of individual solvated ions near solid surfaces is the driving force behind numerous interfacial processes, from electrochemical reactions to charge storage, mineral growth, biosignalling and bioenergetics. The precise system behaviour is delicately dependent on the atomistic and molecular details of the interface and remains difficult to capture with generalisable, analytical models. Reported dynamics can vary by orders of magnitude depending on microscopic details of the solvent, ions and/or surface chemistry. Experimentally, tracking single solvated ions as they move at or along interfaces remains highly challenging. This is, to some extent, offset by simulations that can provide precise atomistic insights, but usually over limited timescales. The aim of this review is to provide an overview of this highly interdisciplinary field, its achievements and remaining challenges, reviewing both experimental and computational results. Starting from the well accepted continuum description of dissolved ions at solid-liquid interfaces, we outline the challenges of deriving local information, illustrating the discussion with a range of selected studies. We explore the challenges associated with simultaneously achieving the spatial and temporal resolution needed to gain meaningful, yet contextual insights of single ions' dynamics. Based on the current studies, we anticipate the future developments in the field, outlining remaining challenges and opportunities.
Trewby et al. (Fri,) studied this question.