Monolithic in-plane integration of gate-modulated switchable supercapacitors (ipG‐Cap)

Abstract Monolithic integration of iontronic devices is a key challenge for future miniaturization and system integration, in particular the interconnection of multiple functional elements as required for ion computing. The G-Cap, a novel iontronic element, is a switchable supercapacitor with gating characteristics comparable to transistors in electronic circuits, but switching relies on ionic currents and ion electroadsorption. We report here the first monolithic in-plane G-Cap integration through 3D-inkjet printing of non-toxic nanoporous carbon precursors. The printed G-Cap has a three-electrode architecture integrating a symmetric "working" micro-supercapacitor (W-Cap) and a third "gate" electrode (G-electrode) that reversibly depletes/injects electrolyte ions into the system, effectively controlling the "working" capacitance. The printed precursor structures were directly converted into nanoporous carbon materials with a specific surface area of 544 m2 g−1. The symmetric W‐Cap operates with a proton conducting hydrogel electrolyte based on PVA/H2SO4 and shows a high capacitance (1.3 mF cm−2) that can be switched “on” and “off” by applying a DC bias potential (- 1.0 V) at the G-electrode. This effectively suppresses AC electroadsorption in the nanoporous carbon electrodes of the W-Cap, resulting in a high capacitance drop from an "on" to an "off" state. Printing offers far-reaching freedom of design for varying the device structure achieving superior device performance. The new monolithic structures achieve high rate performance, reversible on-off switching with an off-value as low as 0.5 % surpassing values reported so far. Establishing technologies and device architectures for functional ionic electroadsorption devices is crucial for diverse fields ranging from microelectronics and iontronics to biointerfacing and neuromodulation.