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

该项目将研究高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能和其他可再生或可持续资源生产清洁能源具有重要意义。这项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。此外，还将纳入教育和外联活动，包括研究生和本科生培训、关于互动光催化能源转化的K-12讲习班，以及为高中生提供的暑期研究机会。该项目研究了过渡金属二卤化物(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制氢，作为燃料和化学品的可再生成分。具体地说，将研究纳米WS2催化剂颗粒相对于其支持电荷转移材料的独特的边向取向，以获得比传统的平板颗粒取向催化剂显著更高的反应速率。已知二卤代化合物的活性是因为它们的边缘位置在半导体、金属或碳材料上具有很高的催化活性。要最大限度地提高这些应用的性能，需要通过TMDC/Support接口快速转移电荷。然而，对于大多数电催化剂和光催化剂中的TMDDC的典型取向，界面电荷转移尤其缓慢，因为它必须发生在惰性TMDC基面上。这项研究将检验这样一种假设，即由于界面结合，WS2层的边缘取向将增加WS2-载体界面上的电荷转移速率，并且可以通过控制WS2层的边缘终止来调节这一速率。这项研究将建立在研究人员的初步结果基础上，这些结果表明WS2纳米管阵列具有良好的光催化活性，其中WS2层处于边向取向。这些WS2纳米管将被用作设计和合成新型Janus型光电极和包含定制界面的光催化剂颗粒的平台。为了从根本上了解这些界面并指导它们的设计，研究人员准备了由基面或边缘取向的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、金属或碳的界面，并将测量WS2取向、缺陷和边缘终止对界面处电荷转移和复合速率的影响。他们还将进行测量和建模，以了解这些速率的潜在因素，包括界面键合和分离距离，界面悬挂键及其电子能量，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.