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.
