NSF-DFG Echem: Mechanistic interrogation of electrocatalytic hydrogen evolution by an artificial hydrogenase

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The development of catalysts that can efficiently convert electrochemical energy into sustainable fuels such as H2 represents a critical obstacle that must be overcome in order to replace fossil fuels with environmentally friendly alternatives. Nature’s catalysts for hydrogen conversion, enzymes known as hydrogenases, exhibit an unparalleled degree of activity; despite global efforts, no sustainable synthetic catalyst has yet been developed that is comparable in rate and efficiency to the natural hydrogenases. Unfortunately, H2 evolution by microorganisms hinges not only on the hydrogenases, but the downstream interactions of these enzymes with other cellular components, limiting practical application of the natural systems. However, decades of study on hydrogenases have provided substantial understanding of the enzyme properties as well as the catalytic mechanism, revealing key features that are necessary for function. We are now well-positioned to build from this solid foundation and apply these general design principles to construct an optimized catalytic system for effective electrochemical energy conversion.Our approach to catalyst design focuses on the development of a robust, artificial hydrogenase enzyme that is integrated within an electrochemical architecture. Using a model metalloenzyme as a well-defined scaffold, we will incorporate select molecular complexes as intramolecular electron relays to functionally model the native redox-active cofactors and establish their role in electrocatalysis. The hybrid enzyme will be anchored onto an electrode surface, which acts as the electron transfer partner, and system variables that impact interfacial charge transfer will be probed. The specific objectives of the research program are to 1) design and implement strategies for integration of the individual components; 2) apply novel in situ spectroelectrochemical studies to interrogate the mechanism of H2 evolution by the hybrid contructs; 3) optimize the systems by tuning secondary and outer sphere properties to enhance catalytic efficiencies. By identifying the role that each component plays in catalysis, sluggish steps will be improved upon and unproductive or degradative pathways can be eradicated to systematically improve the catalytic system. While initially applied to the study of H2 production, the design principles obtained from these fundamental studies will be broadly applicable to the generation of scalable materials for electrochemical energy storage, including water oxidation, nitrogen fixation, and CO2 reduction.