Fig. 3

Schematic diagram of the sample holder (modified from Ohta et al. 2018) used in this study. The characters W, WS, R, and C, respectively, indicate Working, Working Sense, Reference, and Counter electrode. a Information about shapes and dimensions with dashed lines representing probes leading to the electrode, released outward between stopper and rubber jacket. b Layout of electrodes in the sample holder. Each electrode is geometrically separated by acrylic rings. c Layout of the entire measurement system. The white arrows represent the circumferential confining pressure, exerted by the band to prevent water leakage from the rubber jacket and to marginalize the interfacial currents on the sides of the sample. The black arrows represent the load of 10 N for tightening the electrode set to the sample