The reduction kinetics of Ti-IV species in aqueous H2SO4 and HCl was studied using an amalgamated lead rotating disc electrode. Whereas a one electron Ti-IV reduction mechanism was operative in aqueous HCl, Ti-IV reduction in aqueous H2SO4 appeared to involve a Ti-IV-Ti-III-sulfate intermediate, which absorbed visible light strongly, and probably proceeded via an ECE mechanism. A potentiostatically controlled amalgamated lead plate cathode was used to reduce Ti-IV species in acidic sulfate electrolytes in a membrane-divided reactor operated in batch recycle mode with a continuously stirred tank reservoir. The kinetic behaviour was modelled mathematically as an ECE process, both with a second order irreversible chemical reaction and with a chemical equilibrium between the Ti-IV-Ti-III-sulfate intermediate, Ti-IV and Ti-III. Analysis of the predicted concentration profiles in the cathode diffusion layer showed that the mass transport controlled Ti-IV reduction current density was independent of the rate of the second order chemical reaction, enabling the Ti-IV diffusion coefficient to be extracted from rotating disc electrode data, but precluding derivation of kinetic information. The concentration-time and current density-time behaviour of the ECE reaction in a plug flow reactor operated in batch recycle mode with a continuously stirred tank reservoir was predicted for various values of the chemical reaction rate coefficient. For an irreversible chemical reaction; the concentration of the intermediate was greater, the larger the value of the chemical rate coefficient for formation of the intermediate. Predicted current densities were initially smaller, and at longer times, greater, than predicted for a simple, mass transport controlled process.