Developing an understanding of effective approaches to finetune the syntheses of hydrogen storage materials with optimum properties for hydrogen cycling remains one of the most tantalizing challenges limiting the wide-spread adoption of hydrogen fuel cell technology, for onboard and stationery applications. For instance, magnesium borohydride, Mg(BH₄)₂, stands as one of the few materials with potential for meeting all the on-board hydrogen storage requirements, with inherently high gravimetric capacity (14.8 wt % H₂) and favorable thermodynamics (ΔH = 39 kJ/mol H₂, ΔS = 112 J/K mol H₂) for hydrogen cycling under moderate conditions. However, due to very slow kinetics, direct hydrogenation of bulk MgB₂to Mg(BH₄)₂ has only been accomplished at high temperatures (≥ 300 °C) and high pressures (≥ 700 bar).
In this talk, innovative approaches to modification of metal borides through nanosizing and incorporation of additives in attempts to drastically lower the direct hydrogenation temperature (<300 °C) and pressure (<400 bar) of metal borides to boron hydrides will be discussed. Our work indicates the bulk hydrogenation of modified MgB₂ to Mg(BH₄)₂ at ~400 bar and ~300 ^oC, with surficial Mg(BH₄)₂ formation observed at temperatures and pressures as low as 250 ^oC and 260 bar, using additives such as graphene nanoplatelets. Recent efforts involve finetuning the syntheses of a variety of modified metal borides using a combination of techniques including ultra-sonication, solvothermal or mechanochemistry, resulting in nanosized boride materials for hydrogenation to borohydrides. The as-synthesized and/or hydrogenated materials including borides of calcium, magnesium, zirconium and titanium were characterized by a variety of techniques such as XPS, XAS, (S)TEM, TPD, ¹¹B NMR and XRD. The results of these findings will be presented.

Alexander Baker

Appearances