Chloride substitution in sodium borohydride

The dissolution of sodium chloride and sodium borohydride into each other resulting in formation of solid solutions of composition Na(BH4)1−xClx is studied. The dissolution reaction is facilitated by two methods: ball milling or combination of ball milling and annealing at 300 °C for three days of NaBH4–NaCl samples in molar ratios of 0.5:0.5 and 0.75:0.25. The degree of dissolution is studied by Rietveld refinement of synchrotron radiation powder X-ray diffraction (SR-PXD) data. The results show that dissolution of 10 mol% NaCl into NaBH4, forming Na(BH4)0.9Cl0.1, takes place during ball milling. A higher degree of dissolution of NaCl in NaBH4 is obtained by annealing resulting in solid solutions containing up to 57 mol% NaCl, i.e. Na(BH4)0.43Cl0.57. In addition, annealing results in dissolution of 10–20 mol% NaBH4 into NaCl. The mechanism of the dissolution during annealing and the decomposition pathway of the solid solutions are studied by in situ SR-PXD. Furthermore, the stability upon hydrogen release and uptake were studied by Sieverts measurements.

Graphical AbstractDissolution of sodium chloride and sodium borohydride into each other resulting in formation of solid solutions of composition Na(BH4)1−xClx is studied. Dissolution is facilitated by two methods: ball milling or annealing at 300 °C for three days of NaBH4–NaCl samples. Sample compositions and dissolution mechanism are studied by Rietveld refinement of synchrotron radiation powder X-ray diffraction data.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Studies of dissolution of sodium chloride and sodium borohydride into each other. ► Solid state diffusion facilitated by mechanical and thermal treatments. ► Dissolution is more efficiently induced by heating than by mechanical treatment. ► Mechanism for dissolution studied by Rietveld refinement of in situ SR-PXD data.