In recent years, the use of spectroscopy to directly reveal the mechanisms behind a catalytic reaction has reemerged as experimenters find innovative ways to combine in-situ electrochemical cells with advanced spectroscopic probes. A time-resolved spectroscopy in particular has the potential to decode the causal relationships between sequential steps in the catalytic cycle. Previously, picosecond optical spectroscopy of the oxygen evolution reaction (OER) from water on a model titania surface (SrTiO3) followed the formation kinetics of the meta-stable, electron-deficient oxygen intermediates (grouped as Ti-OH*). In this talk, I will focus on how these time-resolved kinetics can be related to an often-used thermodynamic theoretical descriptor at electrochemical surfaces, the free energy difference (ΔGOH*) involved in this electron-transfer step. In particular, a Langmuir isotherm as a function of electrolyte pH extracts an effective equilibrium constant using a principal component analysis of the optical spectra. The experimental methods employed to obtain the high quality kinetics shown, which minimizes the effect of surface degradation on the measured reflectance change and maintains a near constant current evolution, will also be discussed. The talk will also include a brief description of how to relate the photo-driven reaction steps at the semiconductor surface to the purely potential driven OER mechanism more generally cited.

How time-resolving intermediates of in-situ water oxidation identifies theoretical descriptors of the oxygen evolution reaction

ACS Spring Meeting 2021

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