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转化为氢气等可持续燃料的催化剂是必须克服的一个关键障碍，以便用环境友好的替代品取代化石燃料。自然界用于氢转化的催化剂，即氢酶，显示出无与伦比的活性；尽管全球做出了努力，但尚未开发出在速度和效率上可与天然氢酶相媲美的可持续合成催化剂。不幸的是，微生物的氢气释放不仅取决于氢酶，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，几十年来对氢酶的研究已经对酶的性质以及催化机理有了实质性的了解，揭示了发挥功能所必需的关键特征。我们现在处于有利地位，可以在这一坚实的基础上构建并应用这些一般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、集成在电化学体系中的人工氢酶。使用模型金属酶作为明确的支架，我们将包括选择的分子络合物作为分子内电子继电器，对天然氧化还原活性辅因子进行功能模拟，并确定它们在电催化中的作用。杂交酶将固定在电极表面，电极表面充当电子转移伙伴，并将探索影响界面电荷转移的系统变量。该研究计划的具体目标是1)设计和实施集成单个组件的策略；2)应用新的原位光谱电化学研究来询问混合结构析氢的机制；3)通过调节二次和外球属性来优化系统，以提高催化效率。通过确定每个组分在催化中的作用，可以改善缓慢的步骤，消除无效或降解的途径，从而系统地改善催化体系。虽然最初应用于制氢研究，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能量存储材料的生成，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.