Single-Entity Collisional Electrochemistry at the Micro- and/or Nano-Interface Between Two Immiscible Electrolyte Solutions

Single-entity collisional electrochemistry (SECE) is a branch of single-entity electrochemistry. It can directly characterize entities/particles with single particle resolution through random collisions between particles and electrodes in a solution, and obtain rich physicochemical information, thus becoming one of the frontiers of electroanalytical chemistry in the past two decades. Interestingly, the (micro/nanoscale) sensing electrodes have evolved from a polarizable liquid/ liquid (mercury/liquid) interface to a solid/liquid interface and then to a liquid/liquid interface (i.e., an interface between two immiscible electrolyte solutions, ITIES), as if they have completed a cycle (but in fact they have not). ITIES has become the latest sensing electrode in the booming SECE due to its polarizability (up to 1.1 V at the water/a,a,a-trifluorotoluene interface) and high reproducibility. The four measurement modes (direct electrolysis, mediated electrolysis, current blockade, and charge displacement) developed in the realm of SECE at solid/liquid interfaces have also been fully realized at the miniature ITIES. This article will discuss these four modes at the ITIES from the perspectives of basic concepts, operating mechanisms, and latest developments (e.g., discovery of ionosomes, blockade effect of Faradaic ion transfer, etc.), and look forward to the future development and direction of this emerging field.