Abstract
As potential hydrogen storage media, magnesium based hydrides have been systematically studied in order to improve reversibility, storage capacity, kinetics and thermodynamics. The present article deals with the electrochemical and optical properties of Mg alloy hydrides. Electrochemical hydrogenation, compared to conventional gas phase hydrogen loading, provides precise control with only moderate reaction conditions. Interestingly, the alloy composition determines the crystallographic nature of the metal-hydride: a structural change is induced from rutile to fluorite at 80 at.% of Mg in Mg-TM alloy, with ensuing improved hydrogen mobility and storage capacity. So far, 6 wt.% (equivalent to 1600 mAh/g) of reversibly stored hydrogen in MgyTM(1-y)Hx (TM: Sc, Ti) has been reported. Thin film forms of these metal-hydrides reveal interesting electrochromic properties as a function of hydrogen content. Optical switching occurs during (de)hydrogenation between the reflective metal and the transparent metal hydride states. The chronological sequence of the optical improvements in optically active metal hydrides starts with the rare earth systems (YHx), followed by Mg rare earth alloy hydrides (MgyGd(1-y)Hx) and concludes with Mg transition metal hydrides (MgyTM(1-y)Hx). In-situ optical characterization of gradient thin films during (de)hydrogenation, denoted as hydrogenography, enables the monitoring of alloy composition gradients simultaneously.
Highlights
The depleting fossil fuel resources and altering climate conditions increases the necessity for alternative sustainable energy technologies
The poor kinetics for the hydrogenation has been ascribed to two consecutive facts: the dissociation of the hydrogen molecules is hindered by the oxidation of the Mg surface and the hydrogen diffusion is limited in the rutile structure [9]
Even though the kinetics of the fluorite-structured compounds is faster compared to the MgH2, the thermodynamic properties are not improved by the addition of these transition metals
Summary
The depleting fossil fuel resources and altering climate conditions increases the necessity for alternative sustainable energy technologies. The discovery in the late 1960s at the Dutch Philips Research laboratories showed that the intermetallic compound LaNi5 is able to absorb a significant amount of hydrogen gas reversibly Soon after this discovery it was realized that electrodes made of LaNi5 could serve as new electrochemical storage medium and could become a competitive alternative for the cadmium electrode in conventional Ni-Cd batteries. The poor kinetics for the hydrogenation has been ascribed to two consecutive facts: the dissociation of the hydrogen molecules is hindered by the oxidation of the Mg surface and the hydrogen diffusion is limited in the rutile structure [9] Despite these drawbacks, the lightweight property, high energy density and low cost make Mg-hydride a potentially promising hydrogen storage material for mobile applications. This review will focus on the electrochemical and optical properties of the bulk and thin film Mg-TM alloy hydrides
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
