Effect of cations in chloride solutions on low-temperature hydrolysis performances and mechanisms of Mg–Ca-based hydride

Abstract Hydrogen generation via hydrolysis can provide fuel cell with the on-site and controllable supply. However, the current hydrolysis materials that exhibit poor performances at low temperatures are not suitable for portable devices and military. In this study, influence of different cations (Na+, Ca2+, Mg2+ and NH4+) in chloride solutions on low-temperature (253, 263, 273, 283K) hydrolysis performances of Mg–Ca based hydride (MCH) and mechanisms of interaction are investigated. The results demonstrate that Mg2+ and NH4+ in chloride solutions significantly enhance the rate of hydrolysis reaction between MCH and water. In NH4Cl solution, MCH exhibits the best initial hydrolysis performance and the highest H2 yield, 1198 mL g−1(MCH) of H2 is generated within the first 5 min and the final conversion rate reaches 89% at 273 K. MCH displays the best hydrolysis dynamics in MgCl2 solution, where the activation energy is low, only 3.56 kJ mol−1. This can be attributed to the fact that the types of hydroxide products and the corresponding physical states with respect to the hydrolysis of MCH in various chloride solutions differ with the variations of OH− affinity toward Mn+ cations (i.e. pK/(n+1)) when pH values of chloride solutions are altered. Thus, different low-temperature hydrolysis performances can be observed. Above all, the remarkable low-temperature hydrolysis performances of MCH–MgCl2 and MCH–NH4Cl systems indicate that both systems are promising candidates for supplying H2 for the portable and military fuel cells at various remote locations, especially in areas with low temperatures.