Applications of Redox Contacts for Metal and Semiconductor Rotating Ring-Disk Electrodes

A design of a rotating ring-disk electrode with an electrolytic back-contact ell for the disk has been implemented and tested. Both the disk, acting as a bipolar electrode between a conventional cell and back compartment, and the back-electrolyte are made readily interchangeable. The most significant application is to semiconductor disks where ohmic contacts may be intricate to fabricate, as for the p-InP example xperimentally investigated here. However, control of the back-cell characteristics when there is a front metallic disk allows blocking current flow (anodic or cathodic) in a selected direction over some potential range. Application of this principle to amperometric end-point detection in titrimetry illustrates how selective response to mixed redox couples introduced by this diode-like ffect can be put to effective use with conventional metal electrodes. While making ohmic contacts to clean metal electrodes is normally routine, contacting semiconductors is mostly nontrivial (1). A resistive or rectifying characteristic on the back-contact under current flow adds an unknown factor to the measured potential of the electrode of interest. In the extreme, the experiment i self may become contac