Enhancing hydrogen storage properties of MgH2 using TiO2@V2O5 hollow nanospheres
The importance of hydrogen energy in the global energy landscape has been growing owing to its several advantages,such as high energy density,sustainability,renewability,and minimal pollution.The effective utilization of hydrogen energy pivots on hydrogen production,storage,and application.Although hydrogen energy offers several advantages,its widespread adoption is hindered by challenges in developing economical,efficient,and safe hydrogen storage technologies.Magnesium-based solid-state storage materials have emerged as a leading contender for hydrogen storage owing to their high storage density and affordability.Magnesium,with its abundant reserves and cost-effectiveness,offers promising potential for solid hydrogen storage owing to its large hydrogen capacity(volumetric capacity:110 kg/m3 and gravimetric capacity:7.6 wt％),excellent reversibility,and non-toxicity,attracting considerable research attention in the last few decades.However,a big challenge in case of magnesium is its strong affinity for hydrogen,which leads to the formation of stable Mg-H bonds with a high decomposition enthalpy for magnesium hydride(MgH2)at 76 kJ/mol H2,necessitating desorption at considerably high temperatures(at least 300-400℃)and resulting in slow dehydrogenation kinetics.Thus,developing effective Mg-based hydrogen storage materials is imperative for realizing efficient and economical hydrogen storage.Recent studies have focused on enhancing the performance of Mg/MgH2 storage systems through alloying,catalyzing,nanosizing,and integrating with complex hydrides.Among these strategies,the incorporation of catalyst additives into ball-milled Mg/MgH2 has garnered substantial attention because it enhances hydrogenation/dehydrogenation kinetics and reduces hydrogen sorption temperatures.It is well known that the addition of transition metals as catalysts considerably improves the hydrogen sorption kinetics of MgH2.While metal oxides,easily reducible to lower-valent metals by reacting with MgH2,are deemed effective for achieving efficient hydrogenation/dehydrogenation of Mg/MgH2.Notably,the charge transfer facilitated by mutual reversible changes in polyvalent Ti and V ions is beneficial for promoting Mg/MgH2 formation.Therefore,incorporating various transition metals as catalysts in MgH2 systems can thus provide synergistic effects,boosting catalytic activity and enhancing hydrogen storage performance.In this context,a novel approach involving the synthesis of TiO2@V2O5 hollow nanospheres,used as catalytic additives to MgH2 is presented.It is demonstrated that these microspheres create a multivalent and multielement catalytic environment through ball milling and dehydrogenation,thereby improving the hydrogen storage kinetics of MgH2.Experimental findings from temperature-programmed desorption and isothermal dehydrogenation analyses indicate that the MgH2+12 wt％TiO2@V2O5 system exhibits excellent dehydrogenation characteristics,releasing H2 at around 204℃ and6.18wt％H2 within 15 minat300℃,while absorbing 4.21 wt％H2 in 15 min at a relative lower temperature of 100℃.The dehydrogenation activation energy for the MgH2+12 wt％TiO2@V2O5 system(86.47 kJ/mol)is considerably lower than that for pure MgH2(142.78 kJ/mol H2).Mechanistic analysis indicates that these improvements are due to the reversible change in titanium valence and the catalytic effect of reduced vanadium,which collectively improve the hydrogen absorption and desorption kinetics of magnesium.Moreover,the bimetallic oxide catalysts synergistically prevent Mg/MgH2 particle aggregation,maintaining the cyclic stability of the MgH2-TiO2@V2O5 system.This study paves the way for rational design of catalysts containing polyvalent metal species and novel hetero-nanostructures for highly efficient and cost-effective hydrogen storage of Mg/MgH2 systems.
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