Stretchable ionics: How to measure the electrical resistance/impedance

Stretchable ionic conductors have attracted increasing interest in the field of sensors, actuators, bioelectronics, and flexible energy devices due to their high elasticity and biocompatibility. Ionic conductors conduct electrical charges via the migration of mobile ions and the "ion-electron" conversion on the electrode interfaces. Therefore, the measurement of electrical resistance or impedance of ionic conductors is normally carried out under AC mode. However, it seems that recently studied ionic devices, especially those "resistive mode" ionic strain sensors, often use DC mode for the characterization. This Matter of Opinion revisits the conduction mechanism of emerging stretchable ionics and discusses the methods to measure ionic resistance/impedance, aiming to attract more research attention to study the conduction mechanism and characterization protocols for stretchable ionic devices.