Experiments on the thermal activation of hydrogen release of NaBH₄-sodalites characterized by IR- and MAS-NMR spectroscopy

verfasst von

Claus Henning Rüscher, Lars Schomborg, Thomas Bredow

Abstract

New results on the reactions of the (BH₄)-anion enclathrated in the cages of sodalites are reported. Hydrothermally synthesized NaBH₄-sodalites (ǀNa₈(BH₄)₂ǀ[SiAlO₄]₆) always contain hydro-sodalite type cages (ǀNa₃(H₂O)₄ǀ[SiAlO₄]₃). With increasing temperature dehydration occurs. Above 250 °C a limited reaction of the residual water is going on with (BH₄)-cage fillings releasing hydrogen and the appearance of certain borate specifications enclosed in the sodalite cages. The effect of a reaction of oxygen with the (BH₄)-anions in the sodalite-cages at temperatures above 400 °C is also shown. The degree of (BH₄)-conversion using wet and dry N₂ stream is further followed by IR and MAS NMR investigations. External supply of water largely enhances the degree of reaction, e.g. at 400 °C from 16% to 44% loss of (BH₄)-absorption intensity. However, ¹¹B MAS NMR shows 8% and 22% of a conversion of (BH₄)-cage fillings into new borate species in dry and wet N₂ stream, respectively. These lower values are explained by a loss of B-ions via formation and evaporation of BH₃ from the sodalite. Further evaluation of the ¹¹B MAS NMR spectra could resolve the formation of (B(OH)₃)^-, (BO(OH)₂)^-, (B(OH)₄)^- along with unreacted (BH₄)-species in the cages. ¹H-MAS NMR shows a −3.8 ppm signal related to cage isolated (OH)^-, which suggests an initial reaction step via (H⁺ + BH₄⁻) to (BH₃ + H₂). The formation of (B(OH)₃), however, also indicated sufficient water for a reaction of BH₃ releasing further hydrogen. The formation of (BH₃) could be observed in temperature dependent IR investigations at temperatures above 400 °C.

Organisationseinheit(en)

Institut für Mineralogie

Externe Organisation(en)

Rheinische Friedrich-Wilhelms-Universität Bonn

Typ

Artikel

Journal

International Journal of Hydrogen Energy

Band

47

Seiten

36175-36189

Anzahl der Seiten

15

ISSN

0360-3199

Publikationsdatum

15.10.2022

Publikationsstatus

Veröffentlicht

Peer-reviewed

Ja

ASJC Scopus Sachgebiete

Erneuerbare Energien, Nachhaltigkeit und Umwelt, Feuerungstechnik, Physik der kondensierten Materie, Energieanlagenbau und Kraftwerkstechnik

Ziele für nachhaltige Entwicklung

SDG 7 – Erschwingliche und saubere Energie

Elektronische Version(en)

https://doi.org/10.1016/j.ijhydene.2022.05.302 (Zugang: Geschlossen)