CAREER: Electronic transport and interfacial effects on electrochemical hydrogen evolution reaction for transition metal dichalcogenides

电化学催化可以用来从水中产生氢气，从而为从天然气或石油中产生氢气的传统工艺提供了一种可持续的替代方案。近年来，一类被称为过渡金属二卤化物(TMDCs)的低成本化学材料被确定为有希望用于为燃料电池提供动力的水基氢气生产材料，以及作为制造化学品的原料。尽管有希望，但还需要更多的科学理解和工程设计，以最大限度地提高二卤化物材料的性能，使其达到可与更昂贵的最先进的铂基催化剂相媲美的水平。为此，该项目将探讨二卤化物材料的基本方面及其利用独特的反应堆系统产生氢气的有效性。这项研究将有助于为可持续能源和化学品的未来铺平道路，同时也为美国在燃料和化学品制造领域的长期竞争力奠定基础。这项研究将与强调任职人数不足群体参与的教育和外联活动结合起来。该项目寻求的答案是电子输运性质和界面效应(而不是氢吸附的自由能)限制了TMDCs上的放氢反应(HER)的总体速度。单晶片状纳米器件将被用作HER微反应器，它允许精确控制催化位置的密度和类型，并准确测量催化剂内的电荷传输以及催化剂/集电器界面的肖特基势垒。为了研究TMDC的电学性质、界面肖特基势垒和氢吸附自由能随以下三个方面的变化：1)TMDDC从半导体2H相到半金属1T‘相的相变；2)TMDDC的应变工程；3)不同的集流器。各种性质的变化将与在硫酸电解液中使用耦合到单个TMDC纳米器件的标准三电极电池测量的HER活性相关联。半导体MoS2和WS2以及半金属MoTe2和WTe2纳米薄片将用于拟议的研究，它们是通过化学气相沉积生长的，或者是通过化学气相传输生长的大块晶体机械剥离的。除了对HER的TMDC材料进行优化外，该纳米设备平台还可以应用于其他电和光催化剂，以将它们的催化性能与关键参数关联起来，如催化位置的能量学、平衡电学性质、界面效应和光子诱导的激发态。该项目将通过三个外展项目将研究与教育和外展活动联系起来，分别针对普通公众(耶鲁大学西校区的周末能源研讨会)、未被充分代表的本科生(由少数族裔教员举办的月度研讨会系列)和当地高中生(基于TMDC薄膜的演示工具包和练习册)。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，被认为值得支持。

Electrochemical catalysis can be used to generate hydrogen from water, thereby offering a sustainable alternative to conventional processes that generate hydrogen from natural gas or petroleum. In recent years, a class of low-cost chemical materials, known as transition metal dichalcogenides (TMDCs), have been identified as promising materials for water-based hydrogen production to power fuel cells and as a raw material for the manufacture of chemicals. Despite their promise, additional scientific understanding and engineering design will be needed to maximize the performance of the dichalcogenide materials to levels rivaling more expensive state-of-the-art platinum-based catalysts. To that end, the project will explore fundamental aspects of the dichalcogenide materials and their effectiveness for hydrogen generation utilizing a unique reactor system. The research will help pave the path to a sustainable energy and chemicals future while also laying ground work for long-term competitiveness of the U.S. in the fuels and chemical manufacturing sectors. The research will be integrated with educational and outreach activities emphasizing participation by under-represented groups. The project seeks answers to the extent that electronic transport properties and interfacial effects (rather than the free energy of hydrogen adsorption) limit the overall rate of the hydrogen evolution reaction (HER) on TMDCs. A single-crystalline flake nanodevice will be employed as a HER micro-reactor, which allows precise control of the density and types of catalytic sites, and accurate measurements of charge transport within the catalyst, as well as the Schottky barrier at the catalyst/current collector interface. Three aims are proposed to study how the TMDC electrical properties, interfacial Schottky barrier, and the hydrogen adsorption free energy change as a function of 1) the phase transition from the semiconducting 2H to the semi-metallic 1T' phase of TMDCs, 2) strain engineering of TMDCs, and 3) different current collectors. The changes in the various properties will be correlated with the measured HER activities using a standard three-electrode cell coupled to the individual TMDC nanodevices in sulfuric acid electrolyte solution. Semiconducting MoS2 and WS2, and semi-metallic MoTe2 and WTe2 nanoflakes will be used for the proposed research, grown by chemical vapor deposition or exfoliated mechanically from bulk crystals grown by chemical vapor transport. Beyond optimization of TMDC materials for HER, the nanodevice platform can be applied to other electro- and photo-catalysts to correlate their catalytic properties to critical parameters such as energetics of catalytic sites, equilibrium electrical properties, interfacial effects, and excited states induced by photons. The project will link the research to education and outreach activities via three outreach programs targeting, respectively, the general public (a weekend Energy symposium at Yale West Campus), under-represented undergraduate students (a monthly seminar series given by minority faculty members), and local high school students (a demonstration HER kit and workbook based on TMDC thin films).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.