A direct measurement of the heat evolved during the sodium and potassium borohydride catalytic hydrolysis

Abstract

NaBH 4 and KBH 4 hydrolysis reactions (BH 4 − + 4H 2O → B(OH) 4 − + 4H 2), which can be utilized as a source of high purity hydrogen and be easily controlled catalytically, are exothermic processes. Precise determination of the evolved heat is of outmost importance for the design of the reactor for hydrogen generation. In this work we present an efficient calorimetric method for the direct measurement of the heats evolved during the catalyzed hydrolysis reaction. A modified Setaram Titrys microcalorimeter was used to determine the heat of hydrolysis in a system where water is added to pure solid NaBH 4 or KBH 4 as well as to solid NaBH 4 or KBH 4 mixed with a Co-based solid catalyst. The measured heats of NaBH 4 hydrolysis reaction were: −236 kJ mol −1, −243 kJ mol −1, −235 kJ mol −1, and −236 kJ mol −1, without catalyst and in the presence of Co nanoparticles, CoO and Co 3O 4, respectively. In the case of the KBH 4 hydrolysis reaction, the measured heats were: −220 kJ mol −1, −219 kJ mol −1, −230 kJ mol −1, and −228 kJ mol −1, without catalyst and with Co nanoparticles, CoO and Co 3O 4, respectively. Also, a comparison was made with an aqueous solution of CoCl 2·6H 2O used as catalyst in which case the measured heats were −222 kJ mol −1 and −196 kJ mol −1 for NaBH 4 and KBH 4 hydrolysis, respectively. The influence of solid NaOH or KOH additions on the heat of borohydride hydrolysis has been investigated as well.