Date of Award

2013

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Mechanical Engineering

First Advisor

Timothee L. Pourpoint

Committee Chair

Timothee L. Pourpoint

Committee Co-Chair

Lori J. Groven

Committee Member 1

Steven F. Son

Committee Member 2

Timothy S. Fisher

Abstract

Solution combustion synthesized (SCS) cobalt oxide (Co3O4) powder has been studied as a catalyst precursor for the hydrolysis of sodium borohydride (NaBH4). Synthesis is completed in less than two minutes and results indicate SCS is capable of reproducibly synthesizing 98.5-99.5% pure Co3O4 nano-foam materials. SCS materials demonstrate an as-synthesized specific surface area of 24 m2/g, a crystallite size of 15.5 nm, and fine surface structures on the order of 4 nm. Despite having similar initial surface areas and sample purities, SCS-Co3O4 outperforms commercially available Co3O4 and elemental cobalt (Co) nano powders when used as a catalyst precursor for NaBH4 hydrolysis. Hydrogen generation rates (HGR) using 0.6 wt.% NaBH4 in aqueous solution at 20°C were observed to be 1.24±0.2 L min-1gcat-1 for SCS nano-foam Co3O4 compared to 0.90±0.09 and 0.43±0.04 L min-1gcat-1 for commercially available Co3O4 and Co, respectively. The high catalytic activity of SCS- Co3O4 is attributed to its nanoscale foam-like morphology.

During the hydrolysis of NaBH4, the SCS-Co3O4 converts in-situ to an amorphous active catalyst with a specific surface area of 92 m2/g and exhibits a honeycomb type

morphology. The active catalyst was observed to be magnetic, and as such, a magnetic immobilization method was developed for use in a single-pass tube reactor. While development of the hydrogen generation system is far from optimal, this work has shown the feasibility of this magnetic immobilization method under flow conditions using 12 wt.% NaBH4in NaOH solutions.

Furthermore, a single-use, cartridge type hydrogen generation system was evaluated using solid, pre-catalyzed 40 wt.% NaBH4 mixtures where stoichiometric amounts of water were added as the limiting reagent for reaction. Under these conditions, HGR and gravimetric density were observed to be 4.99 L min-1gcat-1 and 10.4 wt.% (materials only) respectively for this system, which represents a significant increase over the dilute NaBH4 solutions typically used for hydrolysis. Water delivery, thermal management, form factor, and mixing methods were evaluated for this system in terms of HGR performance. Gradual water delivery was identified as being most influential in stabilizing HGR and thermal management in preventing by-product solidification due to reaction self-heating.

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