GOALI: Collaborative Research: Phase Behavior and Reactivity of a Hygroscopic System

CBET-0755253Johnson该项目是对硼氢化钠与水的水解反应机制的基础研究。反应的最简单形式为NaBH 4 + H2O = 2 H2 + NaBO 2。实际上，NaBH 4水解是用于燃料电池的氢存储的一种选择。由于吸湿NaBH 4表面的复杂性和水吸附对反应动力学的作用，该反应具有重要的科学意义。尽管研究和开发的历史很长，但这些步骤的基本机制并没有在分子基础上得到理解。特别是，南卡罗来纳州大学最近的实验表明，当反应通过使水蒸气与氢化物接触进行时，可获得定量的氢产率。与水溶液水解相关的动力学限制不存在于气相反应途径中。然而，反应产率对温度和气相组成非常敏感。这一证据导致了这样的假设，即反应途径中的第一步是将水蒸气吸附到表面上;随后，只有当足够的水被吸附形成薄的液体层时，反应才进行。本项目的目标是通过发展对水解反应的基本分子水平的理解来探索这一假设。具体目标是（1）量化反应包络（温度、压力和水蒸气组成的空间），其允许水吸附和水解反应发生;（2）在反应过程中获得实时原位拉曼光谱，以揭示与吸附和反应相关的分子事件，（3）通过NaBH_4表面的分子模拟以及水蒸气与表面的吸附和初始反应来理解和解释实验结果。这是一个合作的GOALI项目，与南卡罗来纳州大学、匹兹堡大学和千禧细胞公司合作。位于新泽西州的伊顿镇。实验研究将在南卡罗来纳州进行，而分子模拟将在皮特进行。千禧细胞公司是一家小型企业，生产基于NaBH4的储氢和发电系统。该项目继续与南卡罗来纳州现有的智力合作，并将其扩展到匹兹堡大学。智力优势：该项目代表了在分子水平上理解这种特定水解反应的尝试，这是一个更大的一类可能的水解反应。PI期望对高吸湿性氢化物表面的结构和反应性以及吸附和反应机制有新的科学见解。在实验和理论上，这是一个具有挑战性的系统，因为水吸附后几乎同时发生反应。吸附现象的实验数据将使用第一原理方法建模。实时拉曼光谱将提供对反应的深入了解，进而为分子模拟提供信息。更广泛的影响：对这种反应的研究对实际储氢系统的开发有直接的影响。GOALI计划将通过让工业科学家和工程师参与进来，加强这两个领先实验室的互动。除了定期交流和传播研究成果外，合作伙伴还将定期进行实地访问。千禧细胞公司每年将举办一个工业实习的研究生，加强该项目的科学和工业信息流。这个基础科学项目是在位于南卡罗来纳州大学的NSF资助的工业/大学燃料电池合作研究中心创造的环境中开发的。

CBET-0755253Johnson This project is a fundamental study of the mechanisms involved in the hydrolysis reaction of sodium borohydride with water. In its simplest form the reaction is written as NaBH4 + H2O = 2 H2 + NaBO2. Practically, NaBH4 hydrolysis is an option for hydrogen storage for fuel cells. The reaction is significant scientifically because of the complexity of the hygroscopic NaBH4 surface and the role of water sorption on the reaction kinetics. Despite a long history of research and development, the basic mechanism of these steps is not understood on a molecular basis. In particular, recent experiments at the University of South Carolina show that quantitative yields of hydrogen are obtained when the reaction is conducted by contacting water vapor with the hydride. The kinetic limitations associated with aqueous solution hydrolysis are not present in the gas phase reaction pathway. However, the reaction yields are very sensitive to temperature and gas phase composition. This evidence leads to the hypothesis that the first step in the reaction pathway is sorption of water vapor onto the surface; subsequently the reaction proceeds only when sufficient water has adsorbed to form a thin liquid layer. The goal of this project is to explore this hypothesis by developing a fundamental, molecular level understanding of the hydrolysis reaction. The specific objectives are (1) to quantify the reaction envelope (space of temperature, pressure, and composition of water vapor) that allows water sorption and the hydrolysis reaction to occur; (2) to obtain real-time, in situ Raman spectra during the course of the reaction to shed insight on the molecular events associated with adsorption and reaction, and (3) to understand and interpret experimental results through molecular simulation of the NaBH4 surface and the adsorption and initial reaction of water vapor with the surface. This is a collaborative, GOALI project that partners the University of South Carolina, the University of Pittsburgh, and Millennium Cell Inc. of Eatontown, NJ. Experimental studies will be conducted at South Carolina, while molecular simulations will be done at Pitt. Millennium Cell, Inc. is a small business that manufactures hydrogen storage and generation systems based on NaBH4. This project continues an existing intellectual collaboration with South Carolina, and extends it to the University of Pittsburgh. Intellectual Merit: This project represents an attempt at molecular level understanding of this particular hydrolysis reaction, which is one of a larger class of possible hydrolysis reactions. The PIs expect new scientific insights into the structure and reactivity of the highly hygroscopic hydride surface, and of the mechanisms of adsorption and reaction. Experimentally and theoretically this is a challenging system because of the near simultaneous reaction that follows water adsorption. Experimental data on the adsorption phenomenon will be modeled using first principles methods. The real-time Raman spectra will provide insight into the reaction that in turn will inform the molecular simulations. Broader Impacts: Study of this reaction has immediate implications for development of practical hydrogen storage systems. The GOALI program will enhance interaction of these two leading laboratories by involving industrial scientists and engineers. In addition to regular communications and dissemination of research results, the partners will engage in periodic site visits. Millennium Cell Inc. will annually host a graduate student on an industrial internship, strengthening the flow of scientific and industrial information for the project. This basic science project has been developed from the environment created by the NSF-funded Industry/University Cooperative Research Center for Fuel Cells, located at the University of South Carolina.