INSITU SURFACE PH MEASUREMENT DURING ELECTROLYSIS USING A ROTATING PHELECTRODE

An in situ technique has been developed for measuring the surface pH a djacent to a solid electrode/liquid interface during electrolysis. Mea surements of the surface pH can be used to obtain insights regarding t he electrodeposition of various transition metals and to obtain a bett er understanding of associated in situ surface chemistry effects. Many transition metals and alloys deposit with simultaneous hydrogen evolu tion and, as a result, are accompanied by a pH rise near the cathode, thereby affecting the reactivity of the nearby metal-ion species. Meas urements of the surface pH of a solution containing simple salts durin g hydrogen evolution from a cathode were performed. The surface pH of a cathode during Ni and NiFe electrodeposition was also measured. The experiments demonstrated that, in the absence of buffers or metal ions , the surface pH rises many pH units above the bulk value. During Ni a nd NiFe electrodeposition, however, the surface pH of solutions consis ting of simple salts and starting from a bulk pH level of 2 does not i ncrease more than 3 pH units from the bulk value. In the case of Ni an d NiFe electrodeposition, surface buffering occurs because of the hydr olysis of the metal-ion species present. Additionally, it is found tha t during the anomalous codeposition of NiFe, the surface pH is much lo wer than that required by the Dahms-Croll hypothesis.