I will present an approach to achieving a fast rate of electrocatalytic H2 evolution that does not rely on secondary coordination sphere design to include proton relays. Using [Co13C2(CO)24]4- (14-) H2 is evolved at -0.86 V vs SCE, and an analysis of the reaction rates under various reaction conditions will be presented using foot-of-the-wave analysis (FOWA). We propose that the delocalized electronic structure, the 4- cluster charge, and multiple sites for protonation facilitate the facile formation of the putative hydride intermediate [H-Co13C2(CO)24]4- (H-1)4- and enable the fast reaction rate. Reduction of 14- occurs at -1.06 V vs. SCE under 1 atm of N2, and at -1.06 V under 1 atm of CO. We propose that as additional CO ligands bind to the cluster core, a greater number of terminally bonded CO ligands are engaged which more effectively accept electron density from the core of the cluster to afford the 200 mV anodic shift in the 14-/5- potential. In an analogous fashion, reduction and protonation of the cluster are thought to encourage similar rearrangement of carbonyl ligands to terminal coordination so that catalysis is also observed at -0.86 V: 200 mV positive of the 14-/5- couple under N2. Further mechanistic analysis, including the observation of a kinetic isotope effect, suggests that formation of (H-1)4- from 14- follows a concerted electron transfer proton transfer (CEPT) mechanism, consistent with the fast overall H2 evolution. I will also discuss the limitations on the stability of 14- which preclude longer time-scale experiments.

Electrocatalytic H2 evolution mediated by a concerted electron proton transfer pathway with [Co13C2(CO)24]4-

2019 Spring National Meeting

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