The effect of different Co phase structure (FCC/HCP) on the catalytic action towards the hydrogen storage performance of MgH2

Abstract High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH2. In this study, Co particles with a face centered cubic (FCC) structure and a hexagonal close packed (HCP) structure were prepared facilely and proved to be good catalysts for magnesium hydride. Co particles with FCC structure presented better catalytic effect on MgH2 than that with HCP structure. Both 7% (mass) Co FCC and HCP particle modified MgH2 decreased the initial dehydrogenation temperature from 301.3 °C to approximately 195.0 °C, but 7% (mass) Co with FCC structure modified MgH2 has a faster desorption rate, and around 6.5% (mass) H2 was desorbed in 10 min at 325 °C. Hydrogen uptake was detected at 70 °C under 32.5 bar hydrogen pressure and 6.0% (mass) H2 was recharged in 40 min at 150 °C. The hydrogen desorption and absorption activation energy for 7% (mass) FCC Co modified MgH2 was significantly decreased to 76.6 (±8.3) kJ·mol−1 and 68.3 (±6.0) kJ·mol−1, respectively. Thermodynamic property was also studied, the plateau pressures of MgH2+7% (mass) FCC Co were determined to be 0.14, 0.28, 0.53 and 0.98 MPa for 300 ℃, 325 ℃, 350 ℃ and 375℃. The decomposition enthalpy of hydrogen (ΔH) for MgH2+7% (mass) FCC Co was 80.6 (±0.1) kJ·mol−1 , 5.8 kJ·mol−1 lower than that of as-prepared MgH2. Moreover, cycling performance for the first 20 cycles revealed that the reaction kinetics and capacity of MgH2-FCC Co composite remained almost unchanged. The result of density functional theory calculation demonstrated that cobalt could extract the Mg-H bond and reduced the decompose energy of magnesium hydride. Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.