Picture your electrode: A primer on scanning electrochemical microscopy

Every electrochemical energy storage and conversion device requires electrodes to exchange charge with the electrolyte and move electrons through an external circuit. We are used to describing electrode performance in terms of single-valued, averaged measurements: a peak current, a charge transfer resistance, a capacitance, and a charge capacity. However, these characterizations escape the complexity of most practical materials. Electrodes are not idealized current collectors but rather heterogeneous surfaces on which individual features strongly influence device performance by dictating local charge transfer. Thus, it would be desirable to understand reactivity at such locality, whatever its length scale.