Characterization of metal hydrides for thermal applications in vehicles below 0 °C

Abstract

Metal hydrides promise great potential for thermal applications in vehicles due to their fast reaction rates even at low temperature. However, almost no detailed data is known in literature about thermochemical equilibria and reaction rates of metal hydrides below 0°C, which, though, is crucial for the low working temperature levels in vehicle applications. Therefore, this work presents a precise experimental set-up to measure characteristics of metal hydrides in the temperature range of -30 to 200 °C and a pressure range of 0.1 mbare100 bar. LaNi4.85Al0.15 and Hydralloy C5 were characterized. The first pressure concentration-isotherms for both materials below 0 °C are published. LaNi4.85Al0.15 shows an equilibrium pressure down to 55 mbar for desorption and 120 mbar for absorption at mid-plateau and -20 °C. C5 reacts between 580 mbar for desorption and 1.6 bar for absorption at -30 °C at mid-plateau. For LaNi4.85Al0.15, additionally reaction rate coefficients down to -20 °C were measured and compared to values of LaNi5 for the effect of Al-substitution. The reaction rate coefficient of LaNi4.85Al0.15 at -20 °C is 0.0018 s^-1. The obtained data is discussed against the background of preheating applications in fuel cell and conventional vehicles.