Sensitivity of nanocrystalline MgH2-V hydride composite to the carbon monoxide during a long-term cycling

In this work, we present the results of the investigation of the effect of prolonged cycling on the hydriding/dehydriding properties and on the structure of nanocrystalline MgH2-V Composite under hydrogen containing 110 ppm of carbon monoxide. The hydrogen charge and discharge kinetics of the nanocomposite hydride were examined at 300 degreesC using up to 1000 cycles. Pressure composition isotherm measurements at 300 degreesC were also carried out. The measured kinetics curves show a significant and systematic slowing down of the absorption and desorption rates and, consequently, a decreased amplitude and delayed heat transfer signals in the reaction temperature curves. Associated with this effect, we observe an enlargement of the pressure hysteresis and a gradual enhancement of the plateau slopes. The results also show some loss in the hydrogen storage capacity of the composite during cycling. The X-ray crystal structure analysis after 1000 cycles reveals that the degradation of the hydriding and dehydriding properties of the sample is related to the crystal growth and the formation of MgOx phases.