Improvement of the Hydrogen-Storage Properties of Mg by Adding a Polymer CMC via Transformation-Involving Milling

Abstract

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydrogen uptake-release properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may make the milled samples be in the good states to absorb and release hydrogen rapidly. Samples with compositions of 95 w/o Mg + 5 w/o CMC (named Mg-5CMC) were made through transformation-involving milling. Mg-5CMC was activated in about 3 hydrogen uptake-release cycles. After activation, Mg-5CMC had a higher beginning hydrogen uptake rate and a larger amount of hydrogen absorbed in 60 min, U (60 min), than milled Mg. At the third cycle (CN = 3), Mg-5CMC had a very high beginning hydrogen uptake rate (1.45 w/o H/min) and a very large U (60 min) (7.18 w/o H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.2 w/o at 593 K in hydrogen of 12 bar at CN = 3. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of β-MgH₂ and MgO, with no evidence of the phases related to CMC. The milling in hydrogen of Mg with CMC is believed to fabricate defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first one in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydrogen uptake-release properties of Mg.