Nakamori, Yuko Miwa, Kazutoshi Ninomiya, Akihito Li, Haiwen Ohba, Nobuko Towata, Shin-ichi Züttel, Andreas Orimo, Shin-ichi 2006-07-28 The thermodynamical stabilities for the series of metal borohydrides <i>M</i>(BH₄)_<i>n</i> (<i>M</i>=Li, Na, K, Cu, Mg, Zn, Sc, Zr, and Hf; <i>n</i>=1–4) have been systematically investigated by first-principles calculations. The results indicated that an ionic bonding between <i>M</i>ⁿ⁺ cations and [BH₄]⁻ anions exists in <i>M</i>(BH₄)_<i>n</i>, and the charge transfer from <i>M</i>ⁿ⁺ cations to [BH₄]⁻ anions is a key feature for the stability of <i>M</i>(BH₄)_<i>n</i>. A good correlation between the heat of formation Δ<i>H</i>_boro of <i>M</i>(BH₄)_<i>n</i> and the Pauling electronegativity of the cation ϰ_<i>P</i> can be found, which is represented by the linear relation, Δ<i>H</i>_boro=248.7ϰ_<i>P</i>–390.8 in the unit of kJ/mol BH₄. In order to confirm the predicted correlation experimentally, the hydrogen desorption reactions were studied for <i>M</i>(BH₄)_<i>n</i> (<i>M</i>=Li, Na, K, Mg, Zn, Sc, Zr, and Hf), where the samples of the later five borohydrides were mechanochemically synthesized. The thermal desorption analyses indicate that LiBH₄, NaBH₄, and KBH₄ desorb hydrogen to hydride phases. Mg(BH₄)₂, Sc(BH₄)₃, and Zr(BH₄)₄ show multistep desorption reactions through the intermediate phases of hydrides and/or borides. On the other hand, Zn(BH₄)₂ desorbs hydrogen and borane to elemental Zn due to instabilities of Zn hydride and boride. A correlation between the desorption temperature <i>T</i>_<i>d</i> and the Pauling electronegativity ϰ_<i>P</i> is observed experimentally and so ϰ_<i>P</i> is an indicator to approximately estimate the stability of <i>M</i>(BH₄)_<i>n</i>. The enthalpy change for the desorption reaction, Δ<i>H</i>_des, is estimated using the predicted Δ<i>H</i>_boro and the reported data for decomposed product, Δ<i>H</i>_hyd/boride. The estimated Δ<i>H</i>_des show a good correlation with the observed <i>T</i>_<i>d</i>, indicating that the predicted stability of borohydride is experimentally supported. These results are useful for exploring <i>M</i>(BH₄)_<i>n</i> with appropriate stability as hydrogen storage materials. application/pdf https://folia.unifr.ch/global/documents/299997 https://folia.unifr.ch/documents/299997/files/zuettel_cbt.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1103/PhysRevB.74.045126 info:eu-repo/semantics/openAccess License undefined Physical Review B. - 2006, vol. 74, p. 045126 info:eu-repo/classification/udc/53 Correlation between thermodynamical stabilities of metal borohydrides and cation electronegativites: First-principles calculations and experiments http://purl.org/coar/resource_type/c_6501