Increase in the Dehydrogenation Rate of Mg–CMC (Carboxymethylcellulose, Sodium Salt) by Adding Ni via Hydride-Forming Milling

Abstract

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C₆H₇O₂(OH)_x(C₂H₂O₃Na)_y]_n) (named Mg–5 wt% CMC) were prepared through hydride-forming milling. Mg–5 wt% CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg–5 wt% CMC. In this work, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 w% Ni (Mg–5 wt% CMC–5 wt% Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg–5 wt% CMC–5 wt% Ni was completed at the 3rd hydrogenation–dehydrogenation cycle (N = 3). Mg–5 wt% CMC–5 wt% Ni had an effective hydrogen-storage capacity of 5.83 wt% at 593 K in 12 bar hydrogen at N = 3. Mg–5 wt% CMC–5 wt% Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N = 3. Mg–5 wt% CMC–5 wt% Ni dehydrogenated at N = 4 contained Mg and small amounts of MgO, β-MgH₂, Mg₂Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg₂Ni formed during hydrogenation–dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg–5 wt% CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg.