The superior catalytic effect of N vs. Ni for improving hydrogen storage kinetics of LiBH4@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 surpassing other complex hydrides. However, sluggish dehydrogenation kinetics still hinder the use for practical applications. The infiltration of LiBH₄ into carbon nanoscaffolds has proved to be effective in improving the hydrogen absorption/desorption (a/d) kinetics. Further improvement of storage 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 the matrix for infiltration of LiBH₄. The catalytic effect of nitrogen proved to be superior to that of 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 were investigated by X-ray diffraction, FTIR, TEM, and BET. Hydrogen a/d kinetics of LiBH₄@C-MSU-H nanocomposites was investigated by a volumetric method. The desorption peak temperatures (measured at 2 °C min⁻¹ 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⁻¹ for undoped LiBH₄@C-MSU-H, 123.8 kJ mol⁻¹ for LiBH₄@C-MSU-H 1 at% Ni and 119.5 kJ mol⁻¹ for LiBH₄@C-MSU-H 1 at% N nanocomposites. The catalytic effect on LiBH₄ dehydrogenation due to N-doping of nanocarbons is discussed.