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Mechanisms of partial hydrogen sorption reversibility in a 3NaBH4/ScF3 composite

机译:3NaBH4 / ScF3复合材料中部分氢吸附可逆性的机理

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A new hydrogen storage composite containing NaBH _(4) and a 3d transition metal fluoride, 3NaBH _(4) /ScF _(3) , was synthesized via ball milling. The composite shows no reaction during milling and its dehydriding process can be divided into three steps upon heating: (i) partial substitution of H ~(?) by F ~(?) in NaBH _(4) to form NaBH _( x ) F _(4? x ) at the early stage, releasing about 0.19 wt% of hydrogen; (ii) formations of Na _(3) ScF _(6) , NaBF _(4) and ScB _(2) through the reaction between NaBH _(4) and ScF _(3) , with 2.52 wt% of hydrogen release and a dehydriding activation energy of 162.67 kJ mol ~(?1) H _(2) ; (iii) further reaction of residual NaBH _(4) and Na _(3) ScF _(6) to form NaF, B and ScB _(2) , with a dehydriding activation energy of 169.37 kJ mol ~(?1) H _(2) . The total hydrogen release of the composite reaches 5.54 wt% at 530 °C. The complete dehydrided composite cannot be rehydrogenated while the products after the second dehydriding step can be hydrogenated with an absorption activation energy of 44.58 kJ mol ~(?1) H _(2) . These results demonstrate that by adding 3d transition metal fluorides into NaBH _(4) , a partial reversibility in NaBH _(4) can be achieved.
机译:通过球磨合成了一种新的储氢复合材料,其中含有NaBH_(4)和3d过渡金属氟化物3NaBH_(4)/ ScF_(3)。该复合物在研磨过程中没有反应,加热后其脱水过程可分为三个步骤:(i)在NaBH _(4)中用F〜(?)部分取代H〜(?)以形成NaBH_(x) F _(4?x)在早期,释放出约0.19 wt%的氢; (ii)通过NaBH _(4)和ScF _(3)之间的反应形成Na _(3)ScF _(6),NaBF _(4)和ScB _(2),释放出2.52 wt%的氢脱水活化能为162.67 kJ mol〜(?1)H _(2); (iii)残留的NaBH_(4)和Na_(3)ScF_(6)进一步反应形成NaF,B和ScB_(2),脱水活化能为169.37 kJ mol〜(?1)H _(2)。复合材料的总氢释放在530°C时达到5.54 wt%。完全脱水的复合材料不能再氢化,而第二个脱水步骤之后的产物可以以44.58 kJ mol〜(?1)H _(2)的吸收活化能氢化。这些结果表明,通过将3d过渡金属氟化物添加到NaBH_(4)中,可以实现NaBH_(4)的部分可逆性。

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