Speaker
Description
The recycling of waste products from human activities is a cornerstone of sustainable production and energy systems. In this context, the electrochemical production of basic chemical feedstocks such as hydrogen, ethanol or ammonia using green electricity plays a key role. To make such processes more active, selective and scalable, we need better catalysts than those available today. The latter requires fundamental understanding of the dynamic structure of the catalytic materials while they are performing their function, i.e. “operando”.
My talk will illustrate that morphologically and chemically well-defined pre-catalysts experience drastic modifications under operation, and that such evolving nanoscale surface structure governs the selectivity and kinetics of the reactions. Examples will be drawn from the study of the electrochemical CO$_2$ reduction (CO$_2$RR), nitrate reduction to ammonia, and the oxygen evolution reaction (OER). The model pre-catalysts studied here will range from size and shape-controlled nanoparticles (Cu$_2$O cubes and octahedra, CoOx NPs, Ni(OH)$_2$, Co(OH)$_2$ and Co$_2$FeO$_4$ nanoplatelets) to epitaxial thin films (Co$_3$O$_4$, Co$_1$$_+$$_δ$ Fe$_2$$_-$$_δ$O$_4$, NiO). The need of a synergistic multi-technique operando microscopy (EC-TEM, EC-AFM, LEEM), spectroscopy (XAS, Raman, XPEEM) and diffraction (HE-SXRD) approach will be evidenced in order to follow the active state formation, its deactivation, or regeneration pathways. Correlations between the dynamic structure and composition of the catalysts and their activity, selectivity and durability will be featured. Moreover, special attention will be given to unveiling the role of impurities (Fe) on the catalyst activation in OER, as well as of electrolyte cations (K, Na, Li, Cs) in the kinetics of the formation of different active “frustrated” oxy-hydroxide phases during OER or in the catalyst surface restructuring during CO$_2$RR.