Electrochemical Studies and Absolute Work Function Measurements in Gas Ambient

A simple, direct and convenient method for making absolute work function measurements in gas ambient is presented. The method consists of making measurements with a kelvin probe that has been calibrated using the clean solution surface of an electrochemical half-cell. It is shown here that the outer potential of the half-cell solution surface is constant, reliable and readily reproducible. This makes the method possible. This method for making absolute work function measurements in gas ambient requires a knowledge of the absolute work function of the half-cell. This is related to the absolute half-cell potential. The absolute half-cell potential is discussed. Previous measurements of its value disagree and are controversial. The work function of clean Hg in gas ambient is studied. Using the work function of mercury as measured in vacuum as a reference, the absolute half-cell potential for the SCE (saturated calomel electrode) is measured to be E_{rm SCE}(abs) = -4.670 +/-.027 V. A carbon sample was also used as a reference to measure the SCE. The carbon sample's work function was measured in vacuum photoelectrically immediately before comparing to the SCE in gas ambient. Using this method, the absolute half-cell potential for the SCE was measured to be E _{rm SCE}(abs) = -4.635 +/-.050 V. Measurements on gold show that its work function decreases rapidly when removed from vacuum and that it is unstable in air. A study of the chi (chi) potential of solution-gas ambient surface (electrostatic potential difference across the interphase) is included. It was found that chi is constant for many different electrolyte solutions at varying concentrations. This allows liquid junction potentials to be measured. Also, an acoustically modulated kelvin probe was designed and built for use in gas ambient on liquid and solid surfaces.