The intrinsic activity of an electrocatalyst is determined by the steady state coverage of reaction intermediates and their surface lifetimes. Thus, electrocatalytic activity promotion occurs by either increasing the steady state coverage of reaction intermediates, reducing their surface lifetimes, or some combination of both. The steady state coverage and surface lifetimes of reaction intermediates have been measured for thermal heterogenous catalytic reactions using steady state isotopic transient kinetic analysis (SSITKA). SSITKA is performed by rapidly changing the isotopic composition of the reactant and measuring the transient isotopic composition of the corresponding product using a mass spectrometer. The observed product isotopic transient is then used to calculate the coverage and surface lifetime of the corresponding reaction intermediate. SSITKA measurements have never been performed for any electrocatalytic reaction due to the difficulty of quantifying the transient product distribution on the timescales relevant to SSITKA. In this presentation, electrochemical SSITKA (eSSITKA) will be demonstrated for the first time using methanol (MeOH) oxidation to CO2 over Pt as a test reaction. eSSITKA was performed using a custom differential electrochemical mass spectrometer (DEMS) setup. DEMS is an analytical technique that interfaces an electrochemical reactor to a mass spectrometer using a pervaporation membrane. The insights provided by these eSSITKA measurements are leveraged to explain the origins of the potential-dependent rate of MeOH oxidation within the low overpotential regime. This technique can be used to investigate any electrochemical reaction or electrocatalyst material that produces a volatile reaction product. Applying eSSITKA to reactions such as CO reduction over a Cu is of significant importance to reach the overarching goal of elucidating cation effects and how they influence the characteristic components of electrocatalytic activity. Thus, this analytical method will significantly accelerate the elucidation of a variety of different electrocatalytic phenomena, such as cation-dependent electrocatalytic activity promotion.
