Emerging on-chip microcells in electrocatalysis: functions of window and circuit

An electrocatalytic process that efficiently converts the reactants into high-value-added chemicals has attracted increasing attention in renewable energy fields. Specifically, understanding such a process at a single-material level will be of fundamental importance for catalyst design and mechanism explorations as well. Thanks to the development of electronic devices, on-chip microcells have emerged as a powerful platform through which significant progress has been impressively made. Here, this review provides an overview of the progress based on on-chip microcells. We first introduce how the on-chip microcell develops from electronic transistors like field effect-based and electric double-layer-based ones. Next, we discuss current achievements relying on their two basic functions: the reaction window and the circuit; the former is mainly focused on the active sites, for example, identification of active sites as well as monitoring of their changes; the latter sheds light on its circuit characteristics, such as electrical-field modulation, contact engineering for charge injection, and in situ conductance measurement of metallic and nonmetallic catalysts. Finally, we give personal perspectives on this emerging field, including the current challenges and potential applications.