Converting between chemical and electrical energy requires catalysts that can overcome the high activation barriers inherent to multi-electron transfer. These catalysts can be either molecular or heterogeneous. Molecular catalysts are straightforward to tune synthetically and characterize spectroscopically, allowing for unparalleled insight into their mechanisms of action. Similar molecular-level insight into metallic heterogeneous catalysts would be valuable not only on a fundamental level, but also on a practical level since these catalysts are commonplace in nearly all contemporary energy conversion devices, including fuel cells and electrolyzers. However, it is difficult, if not impossible, to obtain this level of understanding for most heterogeneous catalysts because surface active sites are inherently dynamic, difficult to modify at the molecular level, and hard to identify, much less characterize. Here, we report a new class of materials that feature a conjugated aromatic linkage that gives rise to an unprecedented level of electronic coupling between a molecular species and a graphitic electrode. Electrochemical and spectroscopic data indicate that these graphite-conjugated catalysts do not behave like their molecular analogues, but rather as metallic active sites with molecular definition, providing a unique bridge between the traditionally disparate fields of molecular and heterogeneous electrocatalysis. We further use this platform to investigate the thermodynamics and kinetics of interfacial proton-coupled electron transfer in the context of both elementary steps and hydrogen evolution catalysis.

Molecular control of interfacial inner-sphere electron transfer through graphite conjugation

ACS Spring Meeting 2021

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