Spontaneous hydrolysis of sodium borohydride in harsh conditions

✍ Scribed by Jérôme Andrieux; Umit Bilge Demirci; Julien Hannauer; Christel Gervais; Christelle Goutaudier; Philippe Miele

• Publisher: Elsevier Science
• Year: 2011
• Tongue: English
• Weight: 987 KB
• Volume: 36
• Category: Article
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2010.10.055

✦ Synopsis

The present study reports fundamental results about the spontaneous hydrolysis of sodium borohydride NaBH 4 , which is a potential hydrogen storage material for small, portable applications. The reaction (without stabilizing agent or catalyst) was carried out at temperatures of 30e80 C, initial NaBH 4 concentrations of 0.63e6.19 mol L À1 (2.3e18.9 wt%), and for unbuffered solutions, which are harsher experimental conditions than those reported so far. The H 2 evolution and the subsequent pH variation were observed to determine the reaction kinetic parameters and characterize the hydrolysis intermediates, i.e. the hydroxyborates BH 4Àz (OH) z À , by XRD, IR and 11 B NMR. It was found that: (i) the apparent activation energy of the reaction was 98 AE 10 kJ mol À1 and the reaction order versus the initial NaBH 4 concentration was 0; (ii) all of the reactions BH 4 À / BH 3 (OH) À , BH 3 (OH) À / BH 2 (OH) 2

À

, BH 2 (OH) 2 À / BH(OH) 3 À and BH(OH) 3 À / B(OH) 4 À took place simultaneously; (iii) only 25 mol% of B(OH) 4 À and 75 mol% of BH 4 À were found at 25% of conversion;

(iii) the hydroxyborates are very short-lived intermediates and only traces of BH 3 (OH) À were detected.