By the termchronopotentiometrywe mean an electrochemical technique in which a controlled current, usually a constant current, is caused to flow between two electrodes; the potential of one electrode is monitored as a function of time with respect to a suitable reference electrode. The solution is usually, but not necessarily, unstirred and contains an excess of a supporting electrolyte so that diffusion is the principal mechanism of mass transport. This technique is distinguished fromconstant-current coulometric analysisandcoulometric titrimetry1in that the current in chronopotentiometry is sufficiently large that the current efficiency for the reduction of the species of interest falls below 100%, usually within a few seconds. It is distinguished fromgalvanostatics, a constant-current technique useful for the determination of heterogeneous electron-transfer rates,2, 3in that the chronopotentiometric potential-time trace spans several hundred millivolts whereas the galvanostatic potential-time trace extends less than ten millivolts from the equilibrium potential.