In this study, pH measurement was performed in a thin electrolyte droplet with a thickness <1000 µm by the measurement of the
equilibrium electrode potential of an Sb/SbxOy electrode used as a pH sensor. The equilibrium potential of the Sb/SbxOy electrode was evaluated
by using the Kelvin probe (KP) technique. To investigate the potential response of the Sb electrode in a thin electrolyte droplet, the dependency
of the Volta potential difference between the Sb and a gold wire as a KP on electrolyte droplet thickness was measured. The Volta potential
difference had a linear response with respect to the buffer solution pH, independent of the droplet thickness. This result indicates that the KP
technique, combined with an Sb electrode, is sensitive to the pH of a thin electrolyte droplet of thickness ²50 µm. This pH measurement
technique was also applied to measure pH in a corrosion model of steel. The corrosion model consisted of two steel plates in the same plane as
the anode and cathode, with a constant current between them. During the corrosion process, the pH value decreased from 6 to 5 near the anode
and increased from 6 to 12 at the cathode. The changes in pH measured in the thin electrolyte droplet were in good agreement with the color
changes of the solution containing pH indicators.
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