Numerical Modeling of H2 Absorption Kinetics in Ni-Catalyzed Mg

F. COVA; F. C. GENNARI; P. ARNEODO LAROCHETTE

Rio de Janeiro

Conferencia; International Conference on hydrogen Storage Embrittlement and Applications HySEA 2014; 2014

COPPE/UFRJ, Brazil

Magnesium has been deeply studied as a possible hydrogen storage material for both,  mobile and static applications. However, this material has the disadvantage of its slow  reaction kinetics at temperatures below 300°C. Addition of Ni to the system can result in  reasonable absorption times at temperatures as low as 150°C due to the catalytic effect of  Ni. In this work the aim was to model the hydrogen absorption in the material  50MgH 2 :1Ni. Several absorption measurements were performed in a wide range of  pressures (500 kPa-4500 kPa) and temperatures (150°C-300°C) in a Sieverts-like reactor.  Absorption reaction rates were calculated for different experimental conditions, allowing  to create a surface of the speed dependence with pressure and temperature. Two distinct  regimes were found, one for high temperatures and another one which was present at low  temperatures and intermediate temperatures and low pressures.  For the high temperature range, an experimental model was proposed. This model  considers the independent contribution of three variables: temperature, pressure and  reacted fraction to obtain the hydrogen absorption rate. The model allowed to estimate  the activation energy for the process, and the value obtained (92 kJ/mol) was concordant  with previous values reported in the literature. This model considers an additional  equation that takes into account the variation of temperature produced by the heat  released during the reaction [1].  For low temperature measurements, the model proposed was based in the Ginstling-  Brounshtein equation. The equation was modified to take pressure influence in the  reaction rate into account. The thermal equation utilized in the high temperature model  was also added to the low temperature model in order to include the thermal effects that  occurs during the reaction process [2].  The developed models allowed to simulate the chemical and thermal behaviour of the  system in a wide range of pressure and temperature.