Forces, structures, and ion mobility in nanometer-to-subnanometer extreme spatial confinements: Electrochemisty and ionic liquids

Being able to probe electrolyte structures and ion mobility in nanometer confined cavities/pores is central for the fundamental understanding and steering of various processes in biologic and material systems. Here, we review how force probe experiments were utilized for studying interfacial physics at solid/liquid/solid interfaces. We discuss recent technological achievements and show how micro-to-nano and ultimately subnanometer confinement can be achieved and probed using the surface forces apparatus. We discuss ion-mobility and structuring in confined spaces during reactive and nonreactive conditions. This includes ion-layering and confinement induced effects, such as enhanced reactivity, decreased ion-mobility, electric double layer overlapping and more. We limit the discussion to electrochemical and ionic liquid systems, yet we discuss the broader perspective how to develop the technique further, and how recent advances can already find new exciting applications, across sometimes unexpected fields. These range from studying physiologic processes to technologic application in catalysis, microfluidics, or geology.