pH measurement technique on cathodes during electrolysis

Abstract

Many transition metals and transition metal alloys deposit in the presence of high hydrogen overvoltage. This is accompanied by increase of pH near the cathode. By following the pH changes at the cathode, it is possible to gain much better understanding of the mechanism of metal deposition and of the effect of bath constituents on the electrodeposition process and the nature of deposits. A simple technique was developed for measuring pH changes at the cathode using commercially available glass electrodes in contact with a fine mesh metal screen used as a cathode. A flat bottom glass electrode is used in connection with the metal screen cathode as a back side pH sensor. Measurements were made in solutions containing copper, which should not exhibit pH increase during plating, and in solutions containing nickel and iron, which exhibit large increase of pH at the cathode being plated.