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

开发能够有效地将电化学能量转化为可持续燃料（如H2）的催化剂是用环境友好型替代品取代化石燃料必须克服的一个关键障碍。自然界中氢转化的催化剂——被称为氢化酶的酶，表现出无与伦比的活性；尽管全球都在努力，但目前还没有开发出在速度和效率上可与天然氢化酶相媲美的可持续合成催化剂。不幸的是，微生物的H2进化不仅取决于氢化酶，还取决于这些酶与其他细胞成分的下游相互作用，限制了自然系统的实际应用。然而，几十年来对氢化酶的研究已经对酶的性质和催化机制有了实质性的了解，揭示了功能所必需的关键特征。我们现在有能力在这个坚实的基础上，应用这些一般的设计原则来构建一个优化的催化系统，以实现有效的电化学能量转换。我们的催化剂设计方法侧重于开发一种强大的人工氢化酶，该酶集成在电化学结构中。使用金属酶模型作为明确定义的支架，我们将结合选择的分子复合物作为分子内电子继电器，对天然氧化还原活性辅助因子进行功能建模，并确定它们在电催化中的作用。混合酶将被固定在电极表面，作为电子转移伙伴，并将探索影响界面电荷转移的系统变量。研究计划的具体目标是：1)设计和实施整合各个组件的策略；2)应用新的原位光谱电化学研究来探究混合结构中H2的演化机制；3)通过调整二级和外球性质来优化系统，以提高催化效率。通过确定每个组分在催化中所起的作用，可以改进缓慢的步骤，消除非生产性或降解途径，从而系统地改进催化系统。虽然最初应用于氢气生产的研究，但从这些基础研究中获得的设计原则将广泛适用于可扩展的电化学储能材料的产生，包括水氧化、固氮和二氧化碳还原。

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.