Robust Carbon-Based Electrodes for Hydrogen Evolution through Site-Selective Covalent Attachment of an Artificial Metalloenzyme

The use of biological systems for electrochemical energy conversion applications is often limited by instability of the protein or protein-electrode system. Here, we present a simple but efficient method for covalent attachment of nickel-substituted rubredoxin (NiRd), a model hydrogenase, to an unmodified graphite electrode based on amide bond formation. The resultant electrodes are shown to be highly active for H-2 evolution over a period of several weeks. The effects of different attachment methods on interfacial electron transfer (ET) rates and catalysis are investigated, with decreased ET rates and increased background reactivity observed for surface-modified electrodes. Electrochemical simulations reveal that reduced protein dynamics of the attached NiRd enzyme are likely responsible for decreased catalytic rates by modulating the intramolecular proton transfer step. Ultimately, this straightforward approach can be broadly applied to diverse redox-active proteins and enzymes and will expand the utility of such systems by conferring increased stability over extended periods of time.