Catalyze hydrolysis reaction for hydrogen generation by Mg/Mg2Ca nanolamellar structure in Mg–Ca alloys

The hydrogen generating characteristics of Mg–Ca alloys with Mg/Mg2Ca nanolamellar structures in the hydrolysis reaction with artificial seawater—a 3.5-wt% NaCl aqueous solution—were investigated for a new hydrogen supply source application. The concept of this study was to fabricate a complete hydrolysis reaction alloy using nanolamellar structure of Mg and Mg2Ca having an electrochemically less noble product than Mg. The hydrolysis reaction properties of Mg-10Ca, Mg-15Ca, Mg-16.2Ca, Mg-20Ca, and Mg2Ca were compared with respect to microstructure, which is the volume fraction of the primary phase and its nanolamellar width, and reaction temperatures at 10 °C, 20 °C, 30 °C, 40 °C, 50 °C, and 60 °C. Mg-16.2Ca and Mg-20Ca reacted completely even at room temperature and became white powders comprising Mg(OH)2, Ca(OH)2, and CaCO3 after 9–14 days without changing the solvent. The hydrolysis reaction rates of the Mg–Ca alloys in the temperature range of 10–40 °C were fast in the order of Mg-16.2Ca ≥ Mg-20Ca ≥ Mg-10Ca ≥ Mg-15Ca. From the results of the hydrolysis reaction rate dependency on temperature, the activation energies of Mg-10Ca, Mg-15Ca, Mg-16.2Ca, Mg-20Ca, and Mg2Ca were estimated to be 41.27, 43.39, 22.07, 15.46, and 29.27 kJ mol−1, respectively. This study revealed that the eutectic structure with several nanogalvanic cells of Mg/Mg2Ca in the alloys accelerated the hydrolysis reaction and completely reacted with artificial seawater for hydrogen generation.