Tuning the performance of switchable electrochemical capacitors: The role of gate electrode size in G-Cap functionality

• Gate electrode: counter electrode surface-area ratio governs potential distribution and switching behavior in in-plane G-Caps. • A larger gate electrode enhances ion depletion, enabling stronger “on/off” capacitance modulation. • Dynamic potential shifts under applied bias directly correlate with capacitance retention and switching efficiency. • Competing effects of ion depletion and electrolyte decomposition define the apparent capacitance under bias. • Comparison of NaCl/gelatin and PVA/H₂SO₄ electrolytes confirms the universality of the potential-shift mechanism and highlights the critical role of electrolyte properties. Establishing technologies and device architectures for functional ionic electroadsorption devices is essential for advancing a wide range of fields, from microelectronics and iontronics to biointerfacing and neuromodulation. Therefore, monolithic integration is one of the key goals for the future miniaturization of iontronic systems. The monolithic in-plane G-Cap (gated-capacitor), a novel iontronic element, functions as a switchable electrochemical capacitor with gating characteristics similar to transistors in electronic circuits. Its switching behavior (switchable capacitance) is based on ionic currents and ion electroadsorption, enabled by the introduction of a third “gate” electrode. This gate allows for reversible ion depletion and injection from/into the two-electrode "working" micro-capacitor inter-electrode space in response to the applied bias voltage. This study investigates the influence of gate electrode size, specifically the ratio of between its geometric surface area and that of the counter electrode, on the G-Cap performance. Understanding this behavior is crucial for the precise control of the G-Cap’s electrochemical behavior.