*2.2. Characterization*

For the purpose of determining the phase compositions, the sections of casted ingots were polished and then studied by an X-ray di ffractometer (XRD) employing a DX-2700 X-ray di ffractometer (Dandong Fangyuan, China) with monochromatic CuKα radiation (λKα<sup>1</sup> = 0.154056 nm). The detection angle (2θ) were collected from 30◦ to 80◦ at a scanning speed of 0.03◦/step. The morphology and element analysis were characterized by a cold field scanning electron microscope (SEM, HITACHI SU8020) equipped with an Energy Dispersed X-ray (EDS, Bruker QUANTAX 200) system. In order to minimize the oxidation of fracture surface, the specimens were put into the chamber at once after they were made. The melting behaviors of samples were detected by di fferential scanning calorimeter (DSC, PERKIN-ELMER DSC 7). Indium was used as a reference substance to calibrate the apparatus by testing its melting point. Each sample of 40 mg or so was put into Al pan under a flowing nitrogen atmosphere. In order to observe low-temperature phase transitions in the sample, the related data were collected from −20 to 225 ◦C at an invariable rate of 10 ◦C/min.

#### *2.3. Measurement of Hydrogen Production*

The apparatus was used for hydrogen yield measurement has been illustrated in detail in our previous research [29]. Each sample was cut into a cylindrical sheet with a diameter of about 15 mm and a weight of 0.5 g. A 250 mL glass container was placed in a thermostatic water bath. When 100 mL deionized water reached the predetermined temperature, the plug was closed immediately as soon as a pre-prepared sample was placed into water. Considering that water vapor may cause errors in experimental results, as an improvement, a condensation tube was installed on the outlet side of the Pyrex glass reactor, and the time taken by the reaction for every 10 mL of hydrogen produced was recorded. In the meantime, the height of the calibration bottle was continuously adjusted to ensure that its water level was consistent with the glass burette. The data of hydrogen release rate and reaction time were recorded automatically by the mass flow meter (Alicat Scientific) and stored in a computer. According to the instrument operating procedures, a dryer was directly connected between the mass flow meter and the reactor. In the experiments, theoretical hydrogen production volume was calculated

according to an ideal gas formula (PV = nRT). Under standard conditions (273 K, 10<sup>5</sup> Pa), 1 g Al can generate 1.244 L of hydrogen.
