Hydrogen storage in bulk Mg–Ti and Mg–stainless steel multilayer composites synthesized via accumulative roll-bonding (ARB)

We have tested the hydrogen storage cycling behavior of bulk centimeter-scale magnesium – titanium and magnesium – stainless steel multilayer composites synthesized by accumulative roll-bonding (ARB). Roll-bonding of either titanium or stainless steel with magnesium allows the reversible hydrogen sorption of the resulting composite at 350 °C. Identically roll-bonded pure magnesium can hardly be absorbed at this temperature. In the composites, the kinetics of the first cycle of absorption (also called “activation”) improves with increased number of fold and roll (FR) operations. With increasing FR operations the distribution of the Ti phase is progressively refined, and the shape of the absorption curve no longer remains sigmoidal. Increasing the loading amount of the second phase also accelerates the kinetics. This holds true up to a threshold limit. Microscopy analysis performed on 1–2 wt.% hydrogen absorbed composites demonstrates that MgH2 formed exclusively on various heterogeneous nucleation sites. During activation, MgH2 nucleation occurred at the Mg-hard phase interfaces. During the subsequent absorption cycles, heterogeneous nucleation primarily occurred in the vicinity of “internal” free surfaces such as cracks.

Research highlights
► We prepared Mg–Ti & Mg–SS composites by accumulative roll-bonding at room conditions.
► These composites can reversibly absorb hydrogen at 350 °C.
► The hydride forming phase in both cases is MgH2.
► Kinetics of the first absorption cycle is enhanced by addition of both Ti & SS.
► Heterogeneous nucleation of MgH2 during the first cycle occurs close to Ti/SS.