Neutron diffraction study of titanium carbide TiC x prepared from hydrogen-containing titanium powder

Diversity of Adsorbed Hydrogen on the TiC(001) Surface at High Coverages

“…The peaks at 370 and 340 K are probably associated with hydrogen bound to ideal terrace sites of TiC(001). For doses under UHV conditions, saturation in the H coverage of 0.6-0.7 ML was seen upon H 2 exposures above 100 L. As we will see below, this saturation coverage for UHV dosing is in good agreement with the corresponding coverage calculated using DFT for H on a perfect TiC(001) surface at 300 K. A higher H coverage of 1.4-1.6 ML was seen upon exposure of the 10 ratio, no significant penetration of hydrogen into the bulk of the sample is expected 8.…”

“…On a TiC(001) substrate with a 1:1 stoichiometric ratio, no significant penetration of hydrogen into the bulk of the sample is expected. 8 Furthermore, the theoretical calculations, to be discussed in the next section, show that hydrogen atoms or molecules are not stable in the interstitial sites of a perfect TiC(001) lattice. However, a reconstruction in the lattice of the carbide could produce sites where hydrogen binds well.…”

“…For a sample with these characteristics, no penetration of H 2 or H into the bulk is to be expected. 8 The experiments were carried out in an ultrahigh-vacuum (UHV) chamber that has a high-pressure cell or a batch reactor attached. 3,4 The sample could be transferred between the reactor and the UHV chamber without exposure to air.…”

“…14,15 It has also been shown that TiC can be useful as a material for hydrogen storage, although the low gravimetric content prevents its technological use. [6][7][8][9] Under electrochemical conditions H is found to be absorbed on defective TiC x compounds. 6,7 As the TiC x composition progressively deviates from a 1:1 stoichiometry, the insertion of H and/or H 2 into the substrate lattice increases linearly, where H/H 2 species occupy carbon vacancies, 7, 8 a point that also occurs in heterogeneous catalysis working conditions.…”

“…6−9 Under electrochemical conditions, H is found to be absorbed on defective TiC x compounds. 6,7 As the TiC x composition progressively deviates from a 1:1 stoichiometry, the insertion of H and/or H 2 into the substrate lattice increases linearly, where H/H 2 species occupy carbon vacancies, 7,8 a situation that also occurs in heterogeneous catalysis working conditions. 16,17 Studies using X-ray diffraction 6,7 have shown that TiC allows the insertion of hydrogen within its structure but only under two conditions.…”