Water electrolysis and carbon dioxide electroreduction are examples of electrochemical technologies with promise to aid in the energy transition, for example for the seasonal storage of renewable electricity, or carbon sequestration, thereby aiding in the abatement of anthropogenic climate change. Such reactions are often even more difficult to characterize “at work” with spectroscopy than traditional thermo- or heterogeneous catalysis[1-3], as they bring at least one additional complicating variable; the electrolyte which, particularly for reactions in aqueous environments dramatically attenuates the electromagnetic radiation with which we set out to probe the reaction. Ideally, one would be able to speciate the kinetic regime where e.g., charge-transfer, and adsorption/desorption reactions happen, and be able to separate (speciate) these events from for example those which relate to capacitance, e.g., charging and discharging of the electric double layer, and mass transfer phenomena all happening on a different time scale. To fully understand the morphology of the electrode, the effect of local pH gradient, and the resistance of the electrolyte, one should develop a method able to combine the study of both the electrode, and the electrolyte and reactants preferably simultaneously. Through the development of a methodology that includes bespoke reactor and setup design, along with potential-modulated excitation experimentation, operando high time resolution FT-IR and operando sub-second time resolution X-ray absorption spectroscopy (quick-XAS), and supervised regression, we are able to speciate signals from the diffusion, and Helmholtz layers, to the catalyst surface, and reaction intermediates of electrocatalytic reactions in aqueous media. We thereby establish, for example, structure-performance relationships of electrocatalytic oxidation and reduction reactions (e.g., ammonia, and urea oxidation, oxygen evolution reaction and CO₂ reduction) over several different metals and electrode geometries.

This supervised-pulsed-speciation operando spectroscopic approach is a powerful tool to overcome some of the common issues dealt with in operando spectroscopy of electrocatalysis, such as weak reaction intermediate signals which are clouded by electrolyte rearrangement in for example double layer formation, thereby elucidating several details of mechanisms not yet described in literature, such as the contribution of ice-like water layers, and nanoparticle geometry-dependent adsorption events.