An investigation of the reduction of oxygen at a rotating disc electrode with heat transfer facilities

Abstract

The oxygen reduction reaction on a nickel rotating disc electrode has been examined under isothermal conditions and with heat transfer. The results show that although the limiting rate of oxygen mass transfer increases with an increase in the bulk temperature under isothermal conditions, the rate of charge transfer does not increase correspondingly. It is suggested that as the temperature is increased the oxygen reduction reaction on nickel moves from a predominantly 4 electron process to a predominantly 2 electron process. The effect of heat flux is to stimulate the limiting rate of mass transfer. This effect is attributed to the creation of thermal convection by the production of thermal eddies rather than to an increase in the interfacial temperature. It is shown that, notwithstanding the change from a4 to a2 electron process, as the temperature is raised, the effect of heat flux also gives rise to an increase in charge transfer in the oxygen reduction reaction on nickel since the thermal eddies increase mass transfer faster than the change in interfacial temperature decreases z. It is suggested that similar mass transfer effects produced by heat transfer will occur on other metals but that the charge transfer effect associated with oxygen reduction will depend on the mechanism of the reaction on the particular metal.