Effects of crystallinity and morphology of solution combustion synthesized Co_3O_4 as a catalyst precursor in hydrolysis of sodium borohydride

摘要

Solution combustion synthesized (SCS) cobalt oxide (Co_3O_4) powder has been studied as a catalyst precursor for the hydrolysis of sodium borohydride (NaBH_4). Synthesis is completed in less than two minutes and results indicate SCS is capable of reproducibly synthesizing 98.5-99.5% pure Co_3O_4 nano-foam materials. SCS materials demonstrate an as-synthesized specific surface area of 24 m~2 g~(-1) 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-Co_3O_4 outperforms commercially available Co_3O_4 and elemental cobalt (Co) nano powders when used as a catalyst precursor for NaBH_4 hydrolysis. Hydrogen generation rates (HGR) using 0.6 wt% NaBH_4 in aqueous solution at 20 ℃ were observed to be 1.24 ± 0.2 L min~(-1) g_(cat)~(-1) for SCS nano-foam Co_3O_4 compared to 0.90 ± 0.09 and 0.43 ± 0.04 L min~(-1) g_(cat)~(-1) for commercially available Co_3O_4 and Co, respectively. The high catalytic activity of SCS-Co_3O_4 is attributed to its nano-foam morphology and crystallinity. During the hydrolysis of NaBH_4, the SCS-Co_3O_4 converts in-situ to an amorphous active catalyst with a specific surface area of 92 m~2 g~(-1) and exhibits a honeycomb type morphology.