Ion conducting polymers play a central role in the development of safer and more efficient electrochemical devices such as batteries, fuel cells, and electrolyzers. Self-assembling polymeric materials with multiple components offer pathways to simultaneously optimize more than one material function, as well as control structure at the nanoscale. In the first part of my talk, I will highlight the advantages and new information that can be derived from the use of custom microfabricated interdigitated electrodes (IDEs) as a platform to probe bulk and interfacial electrochemical properties of polymer electrolytes films through electrochemical impedance spectroscopy (EIS). The second part of my talk will address the use block copolymer electrolytes (BCEs) as ion conducting membranes. BCEs provide the means to realize high ionic conductivity and mechanical robustness by judicious choice of block chemistry. To understand the potential of these materials, however, transport properties through BCEs, with domain structure at the nanoscale, must be understood at a fundamental level at the device scale, 10s to 100s of microns. Transport across grain boundaries and defects must be taken into account. Here, we report the direct measurement of structure–electrochemical property relationships in BCEs by using thin-films and IDEs. Conductivity is found to be directly proportional to the number and length of domains of the BCE that are connected from one electrode to the other. Any conducting domain within the film impeded with even a single non-conducting defect (e.g. a dislocation) does not contribute to the conductivity and increases the capacitance of the material. Finally, by completely aligning the conductive domains between electrodes, we can quantitatively investigate intrinsic ion transport differences between BCEs and their homopolymer analogs. We conclude that the interfacial mixing between the blocks at domain interfaces is the dominant factor in reducing ionic mobility in well-aligned BCEs at low charge carrier concentrations.