CAS: Understanding Structural Metamorphosis of Transition Metal Chalcogenide Electrocatalyst Interfaces

在化学系(CHE)的化学催化(CAT)计划和材料研究部(DMR)的固态和材料化学(SSMC)计划的支持下，密苏里科技大学的Manashi Nath和梁新华正在研究过渡金属硫化物基电催化剂的表面化学。这些材料在反应的电化学条件下催化电解水，了解它们的基本活性对于进一步改进它们是很重要的。水电解，也被称为水分解，是一种很有前途的氢气和氧气的生产方法。电化学产生的氢气具有巨大的可再生能源潜力。然而，析氧反应(OER)是电催化水分离中最具挑战性的一个方面。尽管在过去的几年里已经发现了几种高活性的OER电催化剂，但对导致其反应活性的实际催化剂表面物种仍然缺乏了解。在这个项目中，PIS将研究一类有趣的、定义明确的硫化物(硒和碲化物)电催化剂，这些催化剂具有高OER催化活性，以诊断它们的界面行为。除了提供有关活性表面组成的新见解外，PI还将(I)通过组织研讨会和分发演示工具包，为高中生和教育工作者提供科学教育机会；(Ii)为PI研究实验室中代表性不足的群体成员和女性提供机会，并增加工作场所的多样性；(Iii)让从本科生到博士后的学术水平的研究人员参与进来，并指导这些同事提高他们的研究和科学交流技能。通过这一合作研究项目，来自密苏里科技大学的Manashi Nath和梁新华的团队将共同研究过渡金属硫化物基电催化剂的表面化学。尽管过渡金属硫化物以其前所未有的高效率在催化水氧化方面显示出巨大的前景，但对这些催化剂在操作条件下的活性表面组成仍然缺乏正确的了解。在这个项目中，PI将通过对实验创建的表面模型类似物进行详细的原位和非原位表征以及密度泛函理论(DFT)研究，试图通过跟踪活性电化学界面的形态和演变来了解过渡金属硒和碲化物基电催化剂高催化活性的原因，从而弥合这一知识鸿沟。PI假设在碱性介质中催化硫化物表面可以用两种不同的结构模型来描述：一种是硫化物完全化学转化为氧化物表面导致氧化物包裹的硫化物表面，另一种是部分羟化的混合阴离子(羟基)硫化物表面，它保持了硫化物的组成完整性。PI进一步提出了混合阴离子(羟基)硫化物模型来更准确地描述活性表面。这些假设将通过电沉积和原子层沉积合成类似于氧化物涂层硫化物和(羟基)硫化物模型的催化剂表面，并从广泛的体相和表面表征技术的组合中收集实验证据来评估。将进行模拟研究，以破译反应条件下催化活性中心周围的局部配位环境。该项目有可能提供对活性电化学界面性质的结构和功能洞察，以及指导此类重要过渡金属硫化物基功能材料的未来表面工程努力所需的信息。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。

With the support of the Chemical Catalysis (CAT) program in the Chemistry Division (CHE) and the Solid State and Materials Chemistry (SSMC) program in the Division of Materials Research (DMR), Manashi Nath and Xinhua Liang from Missouri University of Science & Technology are studying the surface chemistry of transition metal chalcogenide-based electrocatalysts. The materials catalyze water electrolysis under reactive electrochemical conditions and understanding their fundamental activity is important to further improve them. Water electrolysis, also known as water splitting, is a promising way to produce hydrogen and oxygen. Electrochemically-produced hydrogen has significant potential for renewable energy. However, the oxygen evolution reaction (OER) is the most challenging aspect to overcome in electrocatalytic water splitting. Although several highly active OER electrocatalysts have been discovered over the last few years, there remains a lack of understanding of the actual catalyst surface species responsible for their reactivity. In this project, the PIs will investigate an interesting and well-defined family of chalcogenide (selenide and telluride) electrocatalysts with high OER catalytic activity to diagnose their interfacial behavior. Apart from offering new insight about the active surface composition, the PIs will also (i) provide science education opportunities for high school students and educators by organizing workshops and distribution of demonstration toolkits; (ii) provide opportunities for members of underrepresented groups and women in the PI research laboratories and increase diversity in the workplace; (iii) involve researchers at academic levels from undergraduate to postdoc and mentor these coworkers to sharpen their research and scientific communication skills.Through this collaborative research project, the teams of Manashi Nath and Xinhua Liang from Missouri University of Science & Technology will together studying the surface chemistry of transition metal chalcogenide-based electrocatalysts. Although transition metal chalcogenides have shown tremendous promise for catalytic water oxidation owing to their unprecedented high efficiency, there remains a lack of proper understanding of the active surface composition for these catalysts under operational conditions. In this project, the PIs will focus on bridging this knowledge gap by trying to understand the cause of high catalytic activity of transition metal selenide and telluride based electrocatalysts by following speciation and evolution of the active electrochemical interface through detailed in situ and ex situ characterizations of experimentally created surface model analogues, along with density functional theory (DFT) studies. The PIs hypothesize that the catalytic chalcogenide surface in alkaline medium can potentially be described by two different structural models: one resulting from complete chemical conversion of chalcogenide to oxide surface leading to oxide-coated chalcogenide surface, and the other comprising partially hydroxylated mixed anionic (hydroxy)chalcogenide surface which retains compositional integrity of the chalcogenide. The PIs further propose the mixed anionic (hydroxyl)chalcogenide model to be more accurate description of the active surface. These hypotheses will be evaluated by synthesizing catalyst surfaces analogous to the oxide-coated chalcogenide and (hydroxy)chalcogenide models through electrodeposition and atomic layer deposition and collecting experimental evidence from a combination of extensive bulk and surface characterization techniques. Simulation studies will be performed to decipher local coordination environment around the catalytically active site under reactive conditions. This project has the potential to provide structural and functional insight on the nature of the active electrochemical interface, information needed to guide future efforts at surface engineering of such important transition metal chalcogenide-based functional materials.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.