Direct measurements of local current distributions on electrodes covered with thin liquid electrolyte films

•Local current distribution in thin liquid films is directly measured.•Oxygen reduction and evolution reactions (ORR and OER) occur in different areas.•Active areas of electrodes for ORR is governed by ionic resistances in the film.

Thin liquid electrolyte films are frequently used in electrochemical systems, such as energy devices and sensors, where they play an important role in determining the performance of such devices. However, it is difficult to experimentally determine the electrochemical behavior of these thin liquid films on electrodes. Here we investigated the uneven distribution of currents on an electrode covered with a thin liquid electrolyte film using a segmented Pt array electrode. A combination of experimental and simulation studies revealed that local ionic resistances governed the active positions of electrodes for the oxygen reduction reaction. These results demonstrate that segmented array electrodes are powerful tools for investigating the unique electrochemical features of thin liquid electrolyte films.