Thermal properties of alkaline sodium borohydride solutions

Alkaline sodium borohydride solutions are potential hydrogen sources for fuel cells. Thermal properties of the NaBH4–NaOH–H2O ternary system were measured by DSC and temperature-rise calorimetry. Liquidus temperatures showed that it is possible to store and use the solutions well below 0 °C if NaOH concentration is less than 20 wt%. The solubility of sodium borohydride was found to be large in these solutions, but decreased with increasing NaOH concentration. The optimum composition for alkaline borohydride solutions seems to be 15 wt% NaBH4 in 10 wt% NaOH considering both the liquidus temperature and hydrogen storage density.