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与开发。氢是许多燃料和化学品的重要组成部分。催化剂在氢的可持续生产中发挥着核心作用，它通过水分子的电化学分裂促进氢的产生，这一过程被称为析氢反应（HER）。在过去的几年中，使用低成本的碳化钼材料催化析氢取得了快速进展，最近报道的活性可以与最优但珍贵的铂催化剂相媲美。该项目将在先进表征技术的支持下，通过协调的理论和实验方法，继续推进碳化钼催化剂的研究和开发。具体目标包括：1)更深入地了解纯金属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；2)阐明反应条件下催化剂的表面结构和组成；3)鉴定出具有优异稳定性和耐久性的催化剂结构和组成。项目成果将超越析氢反应，揭示更广泛的控制原则，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化。该项目将通过为研究生和本科生——特别是那些来自代表性不足群体的学生——提供参与“绿色”能源研究的机会，促进新一代科学家和工程师的培训。采用微波反应和溶胶-凝胶法制备不同化学计量的碳化钼纳米颗粒（即Mo(y)C）。系统地考察了掺杂和不掺杂金属的电化学性能。透射电子显微镜成像，衍射和光谱-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的反应-结构关系，直到原子尺度。环境透射电镜（ETEM）将使这些结构动力学在相关反应条件下的实时研究成为可能。大气压x射线光电子能谱（AP-XPS）和拉曼光谱将用于建立表面化学和反应性之间的相关性。原位表征将与动力学测量和降低电解反应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输入，该模拟采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机制、活性位点和限速步骤来补充实验，这将指导水电解催化剂的设计。这项研究将通过开发新的课程组成部分和新的教育模块来整合到教育工作中，这些模块强调综合理论和实验工作的重要性，以设计适合燃料和化学品可持续制造的新材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.