Collaborative Research: SusChEM: Engineering Charge Transport through Directed Orientation of Transition Metal Dichalcogenide Catalysts

该项目将研究用于有效光催化和光电催化化学反应的新材料和催化剂结构，这些化学反应对从太阳和其他可再生或可持续资源中生产清洁能源具有重要意义。该研究还将适用于一些对国家经济竞争力和资源利用具有重要意义的技术，包括储能、光伏和光电子技术。此外，还将纳入教育和推广活动，包括研究生和本科生培训，K-12相互作用光催化能量转换讲习班，以及高中生夏季研究机会。该项目研究了过渡金属二硫化物（TMDC）催化剂二硫化钨（WS2）用于电催化析氢反应和光催化还原水以产生氢气作为燃料和化学品的可再生成分。具体来说，纳米级WS2催化剂颗粒相对于其负载电荷转移材料的独特的边朝取向将被研究，以实现比传统的扁平颗粒取向催化剂更高的反应速率。已知二硫族化合物是有活性的，这是由于它们的边缘位点在半导体、金属或碳材料上支撑时具有很高的催化活性。在这些应用程序中，性能的最大化需要跨TMDC/支持接口的快速电荷传输。然而，对于大多数电和光催化剂中典型的TMDC取向，界面电荷转移特别缓慢，因为它必须发生在惰性TMDC基面上。该研究将验证这样一个假设，即由于界面键合，WS2层的边向取向将增加WS2支持界面上的电荷转移速率，并且可以通过控制WS2层的边终止来调节该速率。该研究将建立在研究人员初步结果的基础上，该结果显示WS2纳米管阵列具有良好的光催化活性，其中WS2层处于边缘方向。这些WS2纳米管将被用作设计和合成含有定制界面的新型janus型光电极和光催化剂颗粒的平台。为了获得对这些界面的基本理解并指导它们的设计，研究人员准备了由基面或边向WS2单晶组成的模型系统。他们将通过在模型WS2系统上沉积这些材料来创建WS2半导体、金属或碳界面，并将测量WS2取向、缺陷和边缘终止对界面上电荷转移和重组速率的影响。他们还将进行测量和建模，以了解这些速率的潜在因素，包括界面键和分离距离，界面悬垂键及其电子能量，以及界面电势能和局部电场的阶跃变化。

The project will investigate new materials and catalyst structures for the efficient photocatalysis and photoelectrocatalysis of chemical reactions of importance for the production of clean energy from the sun and other renewable or sustainable resources. The research will also have applicability to a number of technologies of importance to the Nation's economic competitiveness and resource utilization, including energy storage, photovoltaics, and optoelectronics. In addition, educational and outreach activities will be incorporated, including both graduate and undergraduate student training, a K-12 workshop on interactive photocatalytic energy conversion, and summer research opportunities for high-school students. The project investigates the transition metal dichalcogenide (TMDC) catalyst tungsten disulfide (WS2) for the electrocatalytic hydrogen evolution reaction and the photocatalytic reduction of water to produce hydrogen as a renewable component of fuels and chemicals. Specifically, a unique edge-on orientation of the nanoscale WS2 catalyst particles with respect to their supporting charge transfer material will be investigated to achieve dramatically higher reaction rates than obtainable with conventional flat particle oriented catalysts. The dichalcogenides are known to be active due to the high catalytic activity of their edge sites when supported on a semiconductor, metal, or carbon material. Maximization of performance in these applications requires rapid charge transfer across the TMDC/support interface. However, for the typical orientations of TMDCs in most electro- and photocatalysts, the interfacial charge transfer is especially slow, since it must occur across the inert TMDC basal plane. The research will test the hypothesis that the rates of charge transfer across the WS2-support interface will be increased by an edge-on orientation of the WS2 layers due to interfacial bonding, and that this rate can be tuned by controlling the edge termination of the WS2 layers. The study will build upon the investigators' preliminary results showing promising photocatalytic activity of WS2 nanotube-arrays, in which the WS2 layers are in an edge-on orientation. These WS2 nanotubes will be used as a platform to design and synthesize novel Janus-type photoelectrodes and photocatalyst particles containing tailored interfaces. To gain fundamental understanding of these interfaces and guide their design, the investigators have prepared model systems consisting of WS2 single-crystals in either a basal plane or edge-on orientation. They will create WS2-semiconductor, metal or carbon interfaces by depositing these materials on top of the model WS2 systems and will measure the influence of WS2 orientation, defects, and edge termination on charge transfer and recombination rates at the interface. They will also perform measurements and modeling to understand these rates in terms of underlying factors including interfacial bonding and separation distance, interfacial dangling bonds and their electronic energies, and step changes in electrical potential energy and local electric field at the interface.