MASS-TRANSPORT IN ELECTROCHEMILUMINESCENT SOLUTIONS - CONVECTIVE MASS-TRANSFER IN ELECTROCHEMILUMINESCENCE CELLS

A theoretical study is presented of the electrochemiluminescence (ECL) occurring in pseudomono-molecular electron-transfer reactions in cell s with electrolyte convection effected by a rotating-disc electrode or by pumping the active medium for potentiodynamic electrolysis. Solvin g the convective mass-transport equations with appropriate initial and boundary conditions yields the relationships that describe the coordi nate and time distribution of the concentration of electrogenerated ra dical cations A(+) of electrochemiluminophor (depolarizer) and, theref ore, the concentration of ECL emitter (singlet-excited electrochemilum inophor molecules) in terms of a unique relation between the two quant ities. It was shown that fast subsequent chemical reactions of the ele ctron transfer from electrochemically inactive species B (nucleophile) to electrophilic species A(+), which are accompanied by emission of E CL photons, occur within the kinetic reaction layer where the distribu tion of species A(+) is virtually unaffected by convection. The transi ent time required for attaining the steady-state state distribution of the A(+) concentration was derived, and conditions under which diffus ion and convective mass transfer become comparable were determined. Th e relationship between the ECL intensity and the electrode rotation sp eed (or the speed of pumped liquid) obtained in our model was noted to be at odds with the relationships that were obtained earlier by Maloy et al. A qualitative interpretation of the ECL experiments in cells w ith convective mass transfer is presented.