Discussion on electrode reaction in partial equilibrium state by EMF measurements

Conference Dates

March 10-14, 2019


Nanocrystalline porous oxides and hydroxides are known to exhibit high proton and hydroxyl-ion conductivity in wet atmospheres. After a substantial number of challenges to improve the conductivity, it is well established that the surface protonic conduction is related to the hierarchical adsorbed water layer and the proton activity on the surface. However, details of electrode reaction for protonic conduction, which can be alternatively interpreted as a connection of ion formed by an electrode reaction to an ionic bridge, has never been discussed in previous studies. Recently, Stub et al. have measured the emf of the following water vapor concentration cell, Ag |porous-YSZ |Ag, under small water vapor gradients at a constant oxygen pressure, suggesting that the charge carrier is H3O+ in higher relative humidity (RH > 0.6) and a single proton hopping migration at lower RH region[1]. In their work, they assumed that two electrode reactions for H+ and H3O+ shown in the following equilibria, are reversible even at low temperature around room temperature.

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