Hydrogen evolution reaction of microwave-synthesized pristine and metal-doped molybdenum carbides: Insights from electrochemical modeling and in situ visualization

不断增长的能源需求，加上减少温室气体排放的紧迫性，刺激了可持续化学和燃料技术的研究和开发。氢是许多燃料和化学品的基本成分。催化剂在可持续生产氢气中发挥着核心作用，它通过一种称为析氢反应(HER)的过程促进了水分子的电化学分解产生氢气。在过去的几年里，使用低成本的碳化钼材料催化析氢取得了快速进展，最近报道的活性可与最好的但珍贵的铂催化剂相媲美。该项目将继续通过先进的表征技术支持的协调的理论和实验方法来推动碳化钼催化剂的研究和开发。具体目标包括1)加深对纯金属碳化物材料和金属掺杂金属碳化物材料促进的表面催化析氢反应的机理的了解，2)阐明反应条件下催化剂的表面结构和组成，以及3)鉴定表现出卓越的稳定性和耐用性的催化剂结构和组成。项目成果将超越析氢反应，揭示可用于理解与电池技术和燃料电池等应用相关的各种电化学转换的更广泛的管理原则。该项目将促进对新一代科学家和工程师的培训，为研究生和本科生--特别是那些来自代表人数不足的群体--提供参与“绿色”能源研究的机会。将利用微波反应和溶胶凝胶法合成各种化学计量比(即Mo(Y)C)的碳化钼纳米颗粒。系统地研究了金属掺杂前后的电化学性能。透射式电子显微镜成像、衍射和光谱分析--能量色散X射线(EDS)和电子能量损失(EELS)--将被用来阐明催化剂在原子尺度上的反应性-结构关系。环境透射电子显微镜(ETEM)可以在相应的反应条件下实时研究这些结构动力学。常压X射线光电子能谱(APXPS)和拉曼光谱将被用来建立表面化学和反应性之间的关联。现场表征将与动力学测量和降低水电解反应的阳极过电位的实验条件密切配合。这将为密度泛函理论(DFT)电化学模拟提供关键的输入，该模拟使用约束热力学来确定HER条件下催化剂的表面组成/结构，包括热力学/动力学限制。此外，该理论将通过阐明HER的机理、活性中心和限速步骤来补充实验，从而指导水电解催化剂的设计。这项研究将通过开发新的课程内容和新的教育模块来整合到教育工作中，强调整合理论和实验努力的重要性，以设计为燃料和化学品的可持续制造量身定做的新材料。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，认为值得支持。

Increasing energy demands, combined with urgency to decrease greenhouse gas emissions, has spurred research and development of sustainable chemical and fuels technologies. Hydrogen is an essential component of many fuels and chemicals. Catalysts play a central role in the sustainable production of hydrogen by facilitating hydrogen generation via electrochemical splitting of water molecules, by a process known as the Hydrogen Evolution Reaction (HER). Over the past few years, rapid progress has been made in catalyzing hydrogen evolution using low-cost molybdenum carbide materials, with recently reported activities rivaling those of the optimum, but precious, platinum catalysts. The project will continue to advance research and development of molybdenum carbide catalysts through a coordinated theoretical and experimental approach supported by advanced characterization techniques. Specific goals include 1) deeper mechanistic understanding of the surface-catalyzed hydrogen evolution reaction as promoted by both pure and metal-doped metal carbide materials, 2) elucidation of catalyst surface structure and composition under reaction conditions, and 3) identification of catalyst structures and compositions that demonstrate exceptional stability and durability with time-in-service. Project outcomes will extend beyond the hydrogen evolution reaction to uncover broader governing principles that can be used to understand a wide variety of electrochemical transformations related to applications such as battery technology and fuel cells. The project will promote training of new generations of scientists and engineers by offering opportunities for both graduate and undergraduate students - particularly for those from underrepresented groups - to participate in “green” energy research.Molybdenum carbide nanoparticles of various stoichiometry (i.e., Mo(y)C) will be synthesized using a microwave reaction and sol-gel process. The electrochemical performance with and without metal dopants will be systematically examined. Transmission electron microscopy imaging, diffraction, and spectroscopy - energy-dispersive X-ray (EDS) and electron energy-loss (EELS) - will be employed to elucidate the reactivity-structure relationships of the catalysts down to the atomic scale. Environmental transmission electron microscopy (ETEM) will enable these structural dynamics to be studied in real-time under relevant reaction conditions. Ambient-pressure X-ray photoelectron spectroscopy (AP­XPS) and Raman spectroscopy will be utilized to establish a correlation between surface chemistry and reactivity. In situ characterization will be closely coordinated with kinetic measurements, and experimental conditions for lowering the anodic overpotential of the water electrolysis reaction. This will provide critical input for density functional theory (DFT) electrochemical simulations employing constrained thermodynamics to determine the surface composition/structure of the catalyst under the HER conditions including thermodynamic/kinetic limitations. Furthermore, the theory will complement the experiments by elucidating the HER mechanisms, active sites, and rate-limiting steps, which will guide the design of catalysts for water electrolysis. The research will be integrated into educational efforts via development of new course components and novel education modules that emphasize the importance of integrated theoretical and experimental efforts to design new materials tailored for the sustainable manufacturing of fuels and chemicals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.