A Dynamic Surface Metal-Organic Framework Electrocatalyst: Potential-Driven Activation of Atomically Defined Au Sites for the Hydrogen Evolution Reaction.

Surface metal-organic frameworks (SMOFs) are promising platforms for catalysis, yet their structural response to electrochemical bias is often overlooked. We report the potential-driven activation of an N-heterocyclic carbene (NHC)-based SMOF on Au(111) for the hydrogen evolution reaction (HER). Operando electrochemical scanning tunneling microscopy (EC-STM) reveals that the framework, initially "frozen" in a strongly interconnected 1D chain morphology at open circuit potential, transitions into a dynamic phase under cathodic bias. This reconfiguration involves a dynamic cycle of metal abstraction and release, generating a high density of undercoordinated sites. DFT calculations confirm that while internal bridging Au nodes are inert (ΔGH* = 0.99 eV), the potential-induced decoupling of the chains creates terminal Au nodes and lattice vacancies with near-thermoneutral adsorption energies of 0.05 and 0.07 eV, respectively. This study demonstrates that superior HER performance originates from the SMOF's ability to dynamically transform into a fluxional active state, providing a strategy for designing adaptive interfacial catalysts.