Dehydrogenation Properties and Catalytic Mechanism of the KNiF-Doped NaAlH System

The KNiF catalytic effect on the NaAlH dehydrogenation properties was studied in this work. The desorption temperature was studied using temperature-programmed desorption and exhibited a lower onset hydrogen release after doped with different wt % of KNiF (5, 10, 15 and 20 wt %). It was found that the NaAlH doped with 5 wt % KNiF showed the optimal value that can reduce the onset desorption temperature of about 160 °C compared to 190 °C for the milled NaAlH. The NaAlH + 5 wt % KNiF sample showed faster desorption kinetics where 1.5 wt % of hydrogen was released in 30 min at 150 °C. In contrast, the milled NaAlH only released about 0.2 wt % within the same time and temperature. From the Kissinger analysis, the apparent activation energy was 114.7 kJ/mol for the milled NaAlH and 89.9 kJ/mol for the NaAlH-doped 5 wt % KNiF, indicating that the addition of KNiF reduced the activation energy for hydrogen desorption of NaAlH. It is deduced that the new phases of AlNi, NaF, and KH that were formed in situ during the dehydrogenation process are the key factors for the improvement of dehydrogenation properties of NaAlH.