Analysis of capacitance and charge accumulation for an electric double layer on porous electrode

The configuration of an electric double layer transistor (EDLT) allows for a very high surface charge density that cannot be achieved by solid dielectrics. Novel phases and superconductivity have been explored using the EDLT technique. The channel in an EDLT typically consists of single crystals or two-dimensional materials. When polycrystalline materials with porous surfaces are used as channel materials in an EDLT, it may not be easy to prepare gate electrodes that have a larger surface area than that of the channel to accumulate significant charge on the channel. Based on the impedance measurements, we estimated the electric double layer (EDL) capacitance on porous YBa2Cu3Oy (YBCO), which can be used as a gate electrode. The ratio of the EDL capacitances on YBCO and Au per unit area was found to be larger than 10, implying that the large surface area is associated with the YBCO porosity. The accumulated electrostatic charge on the YBCO electrodes estimated from double-step chronocoulometry is consistent with the EDL capacitance obtained from impedance measurements. Our work should broaden the applicability of EDLT to a wide range of materials, including porous materials.