The results in Figure also indicate that the electric current in the redox electrolyte mainly flows via electron-transfer reactions between Ri and Oxj, as previously described. In Figure , the period in which the electric current or the potential of the five Pt probes reaches the midpoint between the initial value and the steady-state value is ~5 s. This effect is most clearly observed for the potential of Pt probe P5. This period is much shorter than expected under the assumption that a steady state is attained by the diffusion of Ri and Oxi, thus supporting the aforementioned conclusion. In fact, the period of time, t, needed to attain a steady state by such diffusion can be estimated from the equation t = x 2 /D, where x is the diffusion distance and D is the diffusion constant, and is calculated to be 40 s when x = 0.2 mm and D = 1 × 10 -5 cm 2 s -1 . In the present work, multivalent and high-concentration redox couples are used and their diffusion constants are expected to be much smaller than 1 × 10 -5 cm 2 s -1 . In addition, the effective diffusion distance x, as expected on the basis of the cell structure in Figure , is much larger than 0.2 mm. Therefore, the actual time t should be much larger than the calculated value.