Kinetics and modeling studies of the CaH2/LiBH4, MgH2/LiBH4, Ca(BH4)2 and Mg(BH4)2 systems

► Desorption rates were in the order: Mg(BH4)2>Ca(BH4)2>LiBH4/MgH2>LiBH4/CaH2. ► Diffusion was found to be the rate-controlling process in Mg(BH4)2. ► Reaction at the phase boundary controlled desorption rates from Ca(BH4)2. ► In destabilized LiBH4 mixtures rates were initially phase bounda...

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Veröffentlicht in:Journal of alloys and compounds 2013-04, Vol.556, p.45-50
Hauptverfasser: Ibikunle, A.A., Sabitu, S.T., Goudy, A.J.
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Goudy, A.J.
description ► Desorption rates were in the order: Mg(BH4)2>Ca(BH4)2>LiBH4/MgH2>LiBH4/CaH2. ► Diffusion was found to be the rate-controlling process in Mg(BH4)2. ► Reaction at the phase boundary controlled desorption rates from Ca(BH4)2. ► In destabilized LiBH4 mixtures rates were initially phase boundary controlled. ► Diffusion controlled desorption rates from destabilized LiBH4’s in latter stages. Borohydrides of alkali and alkaline-earth elements are of interest because of their high hydrogen holding capacities. However, their usefulness for hydrogen storage applications is often limited by high thermodynamic stabilities and slow kinetics. In this study comparisons have been made of the physical and chemical characteristics of Mg(BH4)2, Ca(BH4)2, and mixtures of LiBH4/MgH2 and LiBH4/CaH2. Temperature programmed desorption, TPD, analyses showed that samples containing Mg generally had lower onset temperatures than the corresponding samples containing Ca. Pressure Composition Temperature, PCT, isotherms showed that these materials displayed well defined two phase plateau regions. Therefore, kinetics measurements were done to determine the hydrogen desorption rates in the two phase plateau region. All kinetics determinations were done using constant pressure thermodynamic forces in which the ratios of the plateau pressure to the applied hydrogen pressure were kept the same for all samples. In all these measurements the pressure ratio was set at 3 and the temperature was 450°C. Under these conditions the reaction rates were in the order: Mg(BH4)2>Ca(BH4)2>LiBH4/MgH2>LiBH4/CaH2. An attempt was also made to determine the rate-controlling process in these samples by doing kinetic modeling. The results showed that diffusion was the rate-controlling process in Mg(BH4)2 whereas reaction at the phase boundary controlled reaction rates in Ca(BH4)2. In LiBH4/MgH2 and LiBH4/CaH2, reaction at the phase boundary controlled reaction rates initially whereas diffusion controlled rates in the latter stages.
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Borohydrides of alkali and alkaline-earth elements are of interest because of their high hydrogen holding capacities. However, their usefulness for hydrogen storage applications is often limited by high thermodynamic stabilities and slow kinetics. In this study comparisons have been made of the physical and chemical characteristics of Mg(BH4)2, Ca(BH4)2, and mixtures of LiBH4/MgH2 and LiBH4/CaH2. Temperature programmed desorption, TPD, analyses showed that samples containing Mg generally had lower onset temperatures than the corresponding samples containing Ca. Pressure Composition Temperature, PCT, isotherms showed that these materials displayed well defined two phase plateau regions. Therefore, kinetics measurements were done to determine the hydrogen desorption rates in the two phase plateau region. All kinetics determinations were done using constant pressure thermodynamic forces in which the ratios of the plateau pressure to the applied hydrogen pressure were kept the same for all samples. In all these measurements the pressure ratio was set at 3 and the temperature was 450°C. Under these conditions the reaction rates were in the order: Mg(BH4)2&gt;Ca(BH4)2&gt;LiBH4/MgH2&gt;LiBH4/CaH2. An attempt was also made to determine the rate-controlling process in these samples by doing kinetic modeling. The results showed that diffusion was the rate-controlling process in Mg(BH4)2 whereas reaction at the phase boundary controlled reaction rates in Ca(BH4)2. In LiBH4/MgH2 and LiBH4/CaH2, reaction at the phase boundary controlled reaction rates initially whereas diffusion controlled rates in the latter stages.</description><identifier>ISSN: 0925-8388</identifier><identifier>EISSN: 1873-4669</identifier><identifier>DOI: 10.1016/j.jallcom.2012.12.144</identifier><language>eng</language><publisher>Kidlington: Elsevier B.V</publisher><subject>Alternative fuels. 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Borohydrides of alkali and alkaline-earth elements are of interest because of their high hydrogen holding capacities. However, their usefulness for hydrogen storage applications is often limited by high thermodynamic stabilities and slow kinetics. In this study comparisons have been made of the physical and chemical characteristics of Mg(BH4)2, Ca(BH4)2, and mixtures of LiBH4/MgH2 and LiBH4/CaH2. Temperature programmed desorption, TPD, analyses showed that samples containing Mg generally had lower onset temperatures than the corresponding samples containing Ca. Pressure Composition Temperature, PCT, isotherms showed that these materials displayed well defined two phase plateau regions. Therefore, kinetics measurements were done to determine the hydrogen desorption rates in the two phase plateau region. All kinetics determinations were done using constant pressure thermodynamic forces in which the ratios of the plateau pressure to the applied hydrogen pressure were kept the same for all samples. In all these measurements the pressure ratio was set at 3 and the temperature was 450°C. Under these conditions the reaction rates were in the order: Mg(BH4)2&gt;Ca(BH4)2&gt;LiBH4/MgH2&gt;LiBH4/CaH2. An attempt was also made to determine the rate-controlling process in these samples by doing kinetic modeling. The results showed that diffusion was the rate-controlling process in Mg(BH4)2 whereas reaction at the phase boundary controlled reaction rates in Ca(BH4)2. In LiBH4/MgH2 and LiBH4/CaH2, reaction at the phase boundary controlled reaction rates initially whereas diffusion controlled rates in the latter stages.</description><subject>Alternative fuels. Production and utilization</subject><subject>Applied sciences</subject><subject>Borohydrides</subject><subject>Diffusion</subject><subject>Diffusion rate</subject><subject>Energy</subject><subject>Exact sciences and technology</subject><subject>Fuels</subject><subject>Hydrogen</subject><subject>Hydrogen storage</subject><subject>Kinetics</subject><subject>Modeling</subject><subject>Phase boundaries</subject><subject>Pressure ratio</subject><subject>Reaction kinetics</subject><subject>Thermodynamics</subject><subject>Two phase</subject><issn>0925-8388</issn><issn>1873-4669</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2013</creationdate><recordtype>article</recordtype><recordid>eNqFUE1LK0EQHOQJ5qk_QdiLoOAm07OzM7Mn0aBGjHjRi5dhMtMbJ-yHbm8E_71ZE3zHBwXVDVVddDF2AnwMHNRkNV65qvJtPRYcxHiAlHtsBEZnqVSq-MNGvBB5ajJjDthfohXnHIoMRuz1ITbYR0-Ja0JStwGr2CwT6tchIiVtmfRvmEzdTEzm8XomL5LH5b956s42fC5-zI_L3UJf1GNNR2y_dBXh8Y4P2cvtzfN0ls6f7u6nV_PUC6P7tDBBg8IFNz5H8KoQxcKBy7WUJXCnF1wVSiAICGUIuRJKm4VGL7JcC-lkdsjOtnffu_ZjjdTbOpLHqnINtmuykKkcwHA9SPOt1HctUYelfe9i7bovC9wOXdqV3XVphy7tADn4TncRjryrys41PtKvWWiAjBd6o7vc6nDz72fEzpKP2HgMsUPf29DG_yR9A4BWh1s</recordid><startdate>20130415</startdate><enddate>20130415</enddate><creator>Ibikunle, A.A.</creator><creator>Sabitu, S.T.</creator><creator>Goudy, A.J.</creator><general>Elsevier B.V</general><general>Elsevier</general><scope>IQODW</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>8BQ</scope><scope>8FD</scope><scope>JG9</scope></search><sort><creationdate>20130415</creationdate><title>Kinetics and modeling studies of the CaH2/LiBH4, MgH2/LiBH4, Ca(BH4)2 and Mg(BH4)2 systems</title><author>Ibikunle, A.A. ; Sabitu, S.T. ; Goudy, A.J.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c287t-98d716eb08c5e1c6929ba1a5744f10a7b06962e121dfdd562678b7ec235724a43</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2013</creationdate><topic>Alternative fuels. Production and utilization</topic><topic>Applied sciences</topic><topic>Borohydrides</topic><topic>Diffusion</topic><topic>Diffusion rate</topic><topic>Energy</topic><topic>Exact sciences and technology</topic><topic>Fuels</topic><topic>Hydrogen</topic><topic>Hydrogen storage</topic><topic>Kinetics</topic><topic>Modeling</topic><topic>Phase boundaries</topic><topic>Pressure ratio</topic><topic>Reaction kinetics</topic><topic>Thermodynamics</topic><topic>Two phase</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Ibikunle, A.A.</creatorcontrib><creatorcontrib>Sabitu, S.T.</creatorcontrib><creatorcontrib>Goudy, A.J.</creatorcontrib><collection>Pascal-Francis</collection><collection>CrossRef</collection><collection>METADEX</collection><collection>Technology Research Database</collection><collection>Materials Research Database</collection><jtitle>Journal of alloys and compounds</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Ibikunle, A.A.</au><au>Sabitu, S.T.</au><au>Goudy, A.J.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Kinetics and modeling studies of the CaH2/LiBH4, MgH2/LiBH4, Ca(BH4)2 and Mg(BH4)2 systems</atitle><jtitle>Journal of alloys and compounds</jtitle><date>2013-04-15</date><risdate>2013</risdate><volume>556</volume><spage>45</spage><epage>50</epage><pages>45-50</pages><issn>0925-8388</issn><eissn>1873-4669</eissn><abstract>► Desorption rates were in the order: Mg(BH4)2&gt;Ca(BH4)2&gt;LiBH4/MgH2&gt;LiBH4/CaH2. ► Diffusion was found to be the rate-controlling process in Mg(BH4)2. ► Reaction at the phase boundary controlled desorption rates from Ca(BH4)2. ► In destabilized LiBH4 mixtures rates were initially phase boundary controlled. ► Diffusion controlled desorption rates from destabilized LiBH4’s in latter stages. Borohydrides of alkali and alkaline-earth elements are of interest because of their high hydrogen holding capacities. However, their usefulness for hydrogen storage applications is often limited by high thermodynamic stabilities and slow kinetics. In this study comparisons have been made of the physical and chemical characteristics of Mg(BH4)2, Ca(BH4)2, and mixtures of LiBH4/MgH2 and LiBH4/CaH2. Temperature programmed desorption, TPD, analyses showed that samples containing Mg generally had lower onset temperatures than the corresponding samples containing Ca. Pressure Composition Temperature, PCT, isotherms showed that these materials displayed well defined two phase plateau regions. Therefore, kinetics measurements were done to determine the hydrogen desorption rates in the two phase plateau region. All kinetics determinations were done using constant pressure thermodynamic forces in which the ratios of the plateau pressure to the applied hydrogen pressure were kept the same for all samples. In all these measurements the pressure ratio was set at 3 and the temperature was 450°C. Under these conditions the reaction rates were in the order: Mg(BH4)2&gt;Ca(BH4)2&gt;LiBH4/MgH2&gt;LiBH4/CaH2. An attempt was also made to determine the rate-controlling process in these samples by doing kinetic modeling. The results showed that diffusion was the rate-controlling process in Mg(BH4)2 whereas reaction at the phase boundary controlled reaction rates in Ca(BH4)2. In LiBH4/MgH2 and LiBH4/CaH2, reaction at the phase boundary controlled reaction rates initially whereas diffusion controlled rates in the latter stages.</abstract><cop>Kidlington</cop><pub>Elsevier B.V</pub><doi>10.1016/j.jallcom.2012.12.144</doi><tpages>6</tpages></addata></record>
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subjects Alternative fuels. Production and utilization
Applied sciences
Borohydrides
Diffusion
Diffusion rate
Energy
Exact sciences and technology
Fuels
Hydrogen
Hydrogen storage
Kinetics
Modeling
Phase boundaries
Pressure ratio
Reaction kinetics
Thermodynamics
Two phase
title Kinetics and modeling studies of the CaH2/LiBH4, MgH2/LiBH4, Ca(BH4)2 and Mg(BH4)2 systems
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