Superior catalytic effect of N vs. Ni for improving hydrogen storage kinetics of LiBH 4 @ X-doped-C-MSU-H (X=N or Ni) nanoporous carbon composites

Abstract

Lithium borohydride (LiBH4) is a promising hydrogen storage material releasing 13.8 wt% H2 upon decomposition in lithium hydride and boron, significantly overpassing other complex hydrides. However, sluggish dehydrogenation kinetics still hinder the use for practical applications. The infiltration of LiBH4 into carbon nanoscaffolds proved to be effective in improving the hydrogen absorption / desorption (a/d) kinetics. Further improvement of kinetics can be achieved by modification of the nanocarbon with dopant elements. The present work compares nanoporous carbon (C-MSU-H) and C-MSU-H doped either with 1 at% N or 1 at% Ni as matrix for infiltration of LiBH4. The catalytic effect of nitrogen proved to be superior to nickel (keeping the same doping level) for improving the hydrogen a/d kinetics of LiBH4 infiltrated in doped C-MSU-H. X-ray photoelectron spectroscopy was used to detect the amount and chemical proximity of nitrogen in nanoporous carbon following the thermal treatment in ammonia flow. The morphology and porosity of doped C-MSU-H was investigated by X-ray diffraction, FTIR, TEM, BET. Hydrogen a/d kinetics of LiBH4@C-MSU-H nanocomposites was investigated by volumetric method. The desorption peak temperatures (measured at 2 °C /min rate) are 339 °C for the undoped LiBH4@C-MSU-H, 328 °C for the LiBH4@C-MSU-H doped with 1 at% Ni and 318 °C for the LiBH4@C-MSU-H doped with 1 at% N nanocomposites. The activation energies of hydrogen desorption for the investigated nanocomposites were obtained from Kissinger plots: 142.7 kJ/mol for undoped LiBH4@C-MSU-H, 123.8 kJ/mol for LiBH4@ C-MSU-H 1 at% Ni and 119.5 kJ/mol for LiBH4@ C-MSU-H 1 at% N nanocomposites. The catalytic effect on LiBH4 dehydrogenation due to N-doping of nanocarbon is discussed.