Ion transfer -that is the movement of an ion across a phase boundary along with modulation of the ion's solvation shell -is a fundamental process across many fields, from biology to electrochemical technology, whose kinetics govern many different functions. The mechanisms of ion transfer, particularly a chemical understanding of the reaction pathway(s), however, are poorly understood. The kinetics of ion transfer are often implicitly overlooked when electrochemical reaction rates are analyzed, for example, in the framework of electron-transfer models such as with the Marcus or Butler-Volmer formulations. For reactions where reactive ions must cross the electrochemical double layer -examples being desolvation and ion adsorption during hydrogen evolution 1 , metal corrosion, or Na/Li-ion insertion -electron transfer is unlikely to be the rate-controlling step. In these examples, interfacial ion transfer is the chargetransfer step that consumes the majority of the kinetic overpotential. Yet for many such reactions, theories that were developed for simple electron transfer are applied to analyze the kinetics and mechanism of interfacial ionic processes. Improved kinetic models for reactions where ion transfer is rate limiting can support the design of new catalysts to accelerate these processes. Significant progress in this area has been made by Bazant for classical electrochemical coupled ion-electron transfer and Hynes for the fully quantum mechanical coupled proton-electron transfer, yet there are few experimental platforms to straightforwardly test the predictions from these theories.