Kinetics of catalyzed sodium borohydride hydrolysis and fuel cell applicability
Abstract
Metal boride catalysts have been developed through reduction of (Ni, Co, and Ru) metal salts with sodium borohydride solutions. The resulting metal borides were determined to be Ni3B, Co3B, and elemental Ru by use of XRD analysis. SEM images give the particle size of the catalyst to be in the range or 65-150nm. Optimum heat treatment for the samples was determined to be 150°C for Ni3B, 200°C for Co3B, and 400°C for Ru. Ruthenium catalysts were found to have the greatest catalytic activity followed by cobalt boride and nickel boride. Hydrolysis testing with nickel boride catalysts has shown that the maximum hydrolysis rate as a function of sodium borohydride occurs at 5-10 wt% NaBH 4 when considered in solution with 5 wt% NaOH. The hydrolysis rate increases for the nickel boride catalyst with increasing NaOH concentration. Tests were performed at elevated pressures and showed that reaction rate could be controlled and even stopped with sufficient hydrogen pressures on the order of 10 MPa. Decreases in system pressure cause the reaction rate to increase, which tends to maintain the system at the equilibrium pressure. Thus, a high pressure hydrogen generator is considered. 210mg of Co3B catalyst in a 30 wt% solution of sodium borohydride can produce 30kW of hydrogen electrical power equivalent if utilized within a fuel cell operating at 40% efficiency. A semi-empirical isotherm model has been developed to accurately calculate the reaction rate for a Co3B catalyzed reaction as a function of temperature (35-80°C) and pressure (0.1-10MPa).
Degree
Ph.D.
Advisors
Revankar, Purdue University.
Subject Area
Nuclear engineering
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