Hydrogen sorption and permeability of compacted LiBH4 nanoconfined into activated carbon nanofibers impregnated with TiO2

Abstract

Activated carbon nanofibers impregnated with titanium (IV) oxide (TiO2), denoted as ACNF-Ti are prepared by carbonization and activation of electrospun nanofibers of polyacrylonitrile (PAN)-titanium (IV) isopropoxide composite. Pristine LiBH4 and nanoconfined LiBH4 in ACNF-Ti, denoted as LiBH4-ACNF-Ti are compacted under the pressures of 434 and 868 MPa. Dehydrogenation temperature of compacted LiBH4 increases (up to 485 °C) with compaction pressure due to poor hydrogen permeability. In the case of compacted LiBH4-ACNF-Ti, major dehydrogenation temperature at 352–359 °C and hydrogen content liberated (74–76% of theoretical capacity) are obtained despite enhanced compaction pressure. Mechanical stability during cycling of compacted LiBH4-ACNF-Ti is achieved. Although hydrogen permeability of compacted LiBH4-ACNF-Ti improves with enhanced compaction pressure, detrimental kinetics and reversibility are detected. Since the fibrous structure of ACNF-Ti are brittle, the broken and/or shorten fibers are observed after compaction under high pressure. The latter results in not only inferior nanoconfinement of LiBH4 into ACNF-Ti, but also agglomeration of hydride materials upon cycling.