The rise of supercapacitor diodes: Current progresses and future challenges

Supercapacitor has been widely known as a representative electrochemical energy storage device with high power density and long lifespan. Recently, with the deeper understanding of its charge storage mechanism, unidirectional-charging supercapacitor, also called supercapacitor diode (CAPode), is successfully developed based on the ion-sieving effect of its working electrode towards electrolyte ions. Because CAPode integrates mobile ion and mobile electron in one hybrid circuit, it has a great potential in the emerging fields of ion/electron coupling logic operations, human-machine interface, neural network interaction, and in vivo diagnosis and treatment. Accordingly, we herein elucidate the working mechanism and design philosophy of CAPode, and summarize the electrode materials that are suitable for constructing CAPode. Meanwhile, some other supercapacitor-based devices beyond CAPode are also introduced, and their potential applications are instructively presented. Finally, we outline the challenges and chances of CAPode-related techniques.