Quantitatively Deconvoluting the Influences of Electrolyte and Potential on Atomically Precise Catalysts at Electrified Interfaces

Atomically precise active sites on electrode surfaces promise new chemical transformations that simultaneously exploit both the potent physical handle of applied voltage and the highly-tailored reactivity of well-defined active sites. Often, these catalysts have off-electrode analogs in biology or organometallic chemistry, and effectively leveraging these analogies requires an understanding of how catalysis at the active site is perturbed by the complex interplay of electrolyte species and electric fields at electrode interfaces. In this talk, we will share how cohesive, statistically rigorous kinetic analyses have helped to deconvolute the various roles of electrolyte species and applied potential on atomically precise CO₂ reduction and electrochemical hydroformylation catalysts.

First, we investigate the mechanism of carbon dioxide electroreduction (CO₂RR) on immobilized cobalt phthalocyanine (CoPc) through collecting kinetic data over a wide range of operating conditions, fitting rate models, and quantitatively comparing candidate mechanisms.[1] The proposed reaction mechanism illuminates unexpected roles of both the electrolyte and applied potential. First, the electrolyte anion, bicarbonate, has multiple roles in the reaction – it is a proton donor, pH buffer, and, unexpectedly, can also poison the catalyst. Second, the nature of electron transfer does not follow one of the mechanisms typically assumed for CO₂RR - rather, there is mixed control between concerted and sequential proton-electron transfers, and the relative preference changes depending on reaction conditions.

Second, we investigate the various perturbations of the electrified interface on hydroformylation (HFN) catalysis. HFN is a well-studied thermochemical reaction, typically catalyzed by organometallic catalysts, that appends CO to an olefin in the presence of H₂ gas. We mimic homogeneous HFN catalysts on electrode surfaces using single atom-decorated nanoparticles. We show that electrochemistry can be used to circumvent the need to supply H₂ as a reactant. Instead, protons, electrons, and CO can be used to hydroformylate a model substrate. We again use quantitative analysis of kinetic data collected over a wide range of operating temperatures, pressures, applied potentials, and reactant concentrations to investigate the reaction mechanism and describe the role of applied potential, and electrolyte species in perturbing organometallic catalysis-inspired chemistry at electrified interfaces.

These studies build towards a more rigorous and quantitative understanding of how the many components of an electrode interface interact with and influence catalysis on atomically precise active sites. It is crucial to carve out this complexity if we wish to effectively import catalysts or design principles from other catalytic contexts onto electrified interfaces.

[1] J. Zeng, et al. ACS Catal. 10, 7, 4326-4336 (2020)