TY - JOUR

T1 - Experiments on the thermal activation of hydrogen release of NaBH4-sodalites characterized by IR- and MAS-NMR spectroscopy

AU - Rüscher, Claus Henning

AU - Schomborg, Lars

AU - Bredow, Thomas

N1 - Funding Information: The authors gratefully acknowledge helpful comments by the editor (JS) and an unknown referee. Experimental and theoretical investigations were financially supported in part by Deutsche Forschungsgemeischaft ( DFG) ( RU764/6-1 , BR1768/8-1 ). We thank Dr M. Fechtelkord for the NMR measurements at the “Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum”, Germany. Funding Information: The authors gratefully acknowledge helpful comments by the editor (JS) and an unknown referee. Experimental and theoretical investigations were financially supported in part by Deutsche Forschungsgemeischaft (DFG) (RU764/6-1, BR1768/8-1). We thank Dr M. Fechtelkord for the NMR measurements at the “Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum”, Germany.

PY - 2022/10/15

Y1 - 2022/10/15

N2 - 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.

AB - 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.

KW - Hydro-sodalite

KW - Inter cage reactions

KW - NaBH-Sodalite

UR - http://www.scopus.com/inward/record.url?scp=85128619217&partnerID=8YFLogxK

U2 - 10.1016/j.ijhydene.2022.05.302

DO - 10.1016/j.ijhydene.2022.05.302

M3 - Article

AN - SCOPUS:85128619217

VL - 47

SP - 36175

EP - 36189

JO - International Journal of Hydrogen Energy

JF - International Journal of Hydrogen Energy

SN - 0360-3199

IS - 85

ER -