An Investigation of the Inhibition of the Oxygen Reduction Reaction at a Rotating Cylinder Electrode under Isothermal and Controlled Conditions of Heat and Mass Transfer

Abstract

The inhibition of the oxygen reduction reaction on a carbon steel rotatingcylinder electrode in naturally aerated 600 ppm Cl- solution was studied using anoptimum inhibitor blend, i.e., Sodium Nitrite (SN): Sodium Hexametaphosphate(SHMP) = 500:100 obtained via a weight loss technique. Potentiostatic technique, then,was applied at different bulk temperatures and various flow rates using un-inhibited andinhibited solutions under isothermal and controlled conditions of heat transfer.In an un-inhibited solution and under isothermal conditions, with limiting conditions ofconcentration polarization, the limiting current density of oxygen reduction reaction isflow and temperature dependent. The charge transfer of the oxygen reduction reaction isa 4 electron process in the range of bulk temperature employed from 303 to 323 K.Under heat transfer conditions, the charge transfer is still 4 electron process up to 336 Kinterfacial temperature, above which the contribution of the 2 electron process appeared.Moreover, the limiting current density values of the oxygen reduction reaction ininhibited solutions is much lower than those under identical conditions in un-inhibitedsolutions. This confirms the inhibition of the cathodic reaction, i.e., the oxygenreduction reaction under isothermal and heat transfer conditions, due to SHMP.