Observation of kinetic isotope effect in electrocatalysis with fully deuterated ultrapure electrolytes

Abstract

Kinetic isotope effect (KIE) is a common physicochemical effect to elucidate complicated microscopic reaction mechanism in biological, chemical and physical systems. In particular, the exchange of hydrogen to deuterium is a standard approach to investigate kinetics and pathways of a wide spectrum of key reactions involving proton transfer. However, KIE in electrocatalysis is still challenge. One main reason is because of high sensitivities of electrochemical systems to impurities. Aiming to establish an appropriate approach to observe KIE in electrocatalysis, we investigated KIE in oxygen reduction reaction with platinum electrodes, which is well-known to be sensitive to impurity, by comparing electrochemical properties in fully deuterated ultrapure electrolytes and high purity but not ultrapure grade solutions. This experimental plan is based on the fact that D2O is usually used in electrochemical systems without additional purifications to reach an ultrapure grade. In the conclusion, the KIE in electrode processes in these systems can be strongly influenced by a purity of a deuterated electrolyte, especially in the case of alkaline conditions. Therefore, additional purifications of D2O is indispensable to study KIE in electrocatalysis. This work shows a method to observe a reliable KIE in electrocatalysis, and therefore, provides a general approach to investigate complicated electrode processes.