1Department of Chemistry, University of Oxford, United Kingdom
2Physical and Theoretical Chemistry Laboratory, United Kingdom
In this lecture I will give a personal viewpoint on several fundamental outstanding scientific problems which each have their roots in understanding concentrated electrolytes.
First, I will justify and define the term ‘concentrated electrolyte’, as distinct from dilute electrolyte, as the important category which unifies many of the materials to be discussed in this congress. Concentrated electrolytes include ionic liquids, solvate ionic liquids, deep eutectic solvents, molten salts, and certain simple electrolyte solutions. The defining feature is that the distance between neighbouring charges in the fluid is smaller than the Bjerrum length, causing the ions to be strongly coupled together. I will explain how this leads to collective properties distinct from other classes of fluids.
Next, I will present two general scenarios involving the interface of a solid and a concentrated electrolyte, one from the natural world and one from the world of technology. The first scenario is the nucleation of minerals from saturated solutions, occurring ubiquitously in inorganic and living matter. The second scenario is the interface in energy storage devices wherein synthetic electrolytes of relatively simple composition respond to a polarisable electrode. I will point out some important questions for the community which must be answered to facilitate progress in these disciplines.
Finally, I will review the unexpected observation of ‘anomalous underscreening’ in highly concentrated electrolytes and ionic liquids and clarify the outstanding questions in this direction as well as updating on new experimental insights.
The talk will include many highlights from the literature as well as results from our own experimental investigations made using a surface force balance (SFB) in our laboratory in Oxford. Altogether, I hope the lecture will be of interest to a wide audience and will stimulate future work in some of the key difficult areas relating to the fascinating field of concentrated electrolytes.