“Buckets effect” in the kinetics of electrocatalytic reactions

In this study, we systematically investigated the effect of proton concentration on the kinetics of the oxygen reduction reaction (ORR) on Pt(111) in acidic solutions. Experimental results demonstrate a rectangular hyperbolic relationship, i.e., the ORR current excluding the effect of other variables increases with proton concentration and then tends to a constant value. We consider that this is caused by the limitation of ORR kinetics by the trace oxygen concentration in the solution, which determines the upper limit of ORR kinetics. A model of effective concentration is further proposed for rectangular hyperbolic relationships: when the reactant concentration is high enough to reach a critical saturation concentration, the effective reactant concentration will become a constant value. This could be due to the limited concentration of a certain reactant for reactions involving more than one reactant or the limited number of active sites available on the catalyst. Our study provides new insights into the kinetics of electrocatalytic reactions, and it is important for the proper evaluation of catalyst activity and the study of structure-performance relationships.