(623d) Electrochemical Steady State Isotopic Transient Kinetic Analysis (eSSITKA)

The intrinsic activity of an electrocatalyst is determined by the ratio of the coverage of reaction intermediates to their surface lifetimes at steady state. Unfortunately, no technique exists for measuring either of these critical activity parameters for electrocatalytic systems. However, they have both been measured for thermal heterogenous catalysts using steady state isotopic transient kinetic analysis (SSITKA). During SSITKA, the isotopic composition of the reactant is rapidly switched while the isotopic composition of the resulting products is monitored using a mass spectrometer. The observed product isotopic transients are directly related to the coverage and lifetime of the corresponding reaction intermediates. Differential electrochemical mass spectrometry (DEMS) is an analytical technique that interfaces an electrochemical reactor to a mass spectrometer using a pervaporation membrane. This configuration enables volatile electrochemical reaction products to be continuously sampled, identified, and quantified in real time. This presentation will demonstrate electrochemical SSITKA for the first time using DEMS and methanol (MeOH) oxidation over platinized Pt as a test reaction. The SSITKA measurements have been utilized to understand the rise and decline of the MeOH oxidation activity in the low overpotential regime. The observed data suggests that the surface is populated by two distinct pools of reaction intermediates, in agreement with the contemporary understanding of the reaction mechanism. A direct correlation between the intrinsic activity calculated using the activity parameters measured via the isotopic transients and the CO₂ partial current density was observed, which validates the accuracy of the approach. The electrochemical SSITKA approach is general and can be applied to investigate any reaction that produces a volatile product. Thus, this analytical method will significantly accelerate our understanding of a variety of different electrocatalytic phenomena.