Graphene coated nickel foams for hydrogen storage

Hybrid composites where graphene (Gr) and other 2D materials replicate the meso-and micro-structure of 3D porous substrates have shown innovative functionalities in catalysis and energy-related fields. Concerning hydrogen storage, the high surface-to-volume ratio exhibited by both 2D and 3D components of the hybrid material is expected to increase the efficiency of surface chemisorption and bulk absorption of hydrogen in comparison to the flat counterparts. To explore this possibility, we have grown single layer Gr on porous nickel foams and have investigated the interaction with H atoms as a function of the temperature by using X-ray photoelectron spectroscopy and thermal programmed desorption (TPD) at the SuperESCA beamline of Elettra.

The growth of Gr on the Ni foam was obtained by exposing the sample at 773 K to ethylene. Selected C 1s spectra taken at increasing growth time are shown in Fig.1a. Upon exposure to ethylene, the carbide phases (N1-N4 components) observed in the pristine sample disappear, while new Gr components (labeled C0 and C1) progressively increase in intensity and eventually saturate. The component C0 is attributed to GrS regions grown on the (111) foam grains, where the interaction with the support is as strong as that between Gr and the ordered Ni(111) surface; C1 is attributed to GrW regions that are rotated with respect to (111) grains, or are grown on Ni grains exposing different orientations, and therefore, are interacting weakly with the support.

Figure 1, top-story G. Petrone et al., C 1s and TPD spectra

Figure 1: a) C 1s spectra measured during the Gr growth after 0, 3,10,16 and 44 minutes of exposure to ethylene at 773 K and (bottom) at RT after growth; b) C 1s spectra acquired on the Gr/foam hydrogenated with the same H dose at the indicated temperatures TH and c) TPD curves measured during sample annealing.

Fig. 1b shows the C 1s spectra measured on the Gr/foam exposed to a flux of H atoms at temperatures TH between 78 and 298 K. Starting from TH=98 K, the C 1s line shapes appear broadened on the high binding energy (BE) side, due to the appearance of a component (labeled A) at 285.0 eV, and also on the low BE side, due to another component (labeled B) at 284.1 eV. A and B are ascribed to C atoms directly bonded to H atoms and to their first neighbors, and therefore indicate the occurrence of H chemisorption on Gr. From 198 K, some intensity is transferred from C0 to C1, because at this temperature the H atoms start to intercalate below GrS, which detaches gradually from the substrate. The intercalation under the nearly free-standing GrW remains undetected, because here the penetration of H underneath does not cause any measurable extra-shift of the C1 component.

Fig. 1c shows H2 TPD curves measured while heating the Gr/foam hydrogenated at increasing TH. The desorption of H atoms chemisorbed on Gr originates solely the weak peak G at ~ 650 K.  Hence, all other TPD features correspond to the desorption of H atoms intercalated below Gr and residing at the Ni foam surface or even diffused into the Ni bulk. Hence, differently from GrS, where H atoms intercalate only for TH ~ 198 K, intercalation below GrW occurs at much lower temperatures. The TPD curves up to TH=173 K are dominated by the D peak, due to the desorption of H atoms penetrated in metastable subsurface sites of the Ni foam. The H2 release at higher temperatures is related to the slower desorption of bulk H atoms and to the release of H atoms chemisorbed on the Ni surface. It turns out that the highest quantity of loaded hydrogen is detected for TH= 113 K and amounts to ~ 5 times the quantity which saturates the Ni (111) surface with equivalent macroscopic lateral dimension.

The comparison of the results discussed above with those obtained for the bare Ni foam (not shown here) demonstrates that the presence of the Gr cover does not reduce the effectiveness of H loading. Moreover, it contributes to stabilizing in part the loaded hydrogen, although does not appear effective in increasing significantly the stored amount with respect to the bare support. However, the invaluable advantage anyway provided by the presence of Gr is the protection of the foam surface from the adsorption of contaminants, which might limit H chemisorption and consequently subsurface diffusion and loading in the bulk. Although the fundamental aspects of Gr/foam hydrogenation were here investigated in a regime far below the saturation of the bulk absorption, these measurements can be the starting point for further investigations aimed at establishing the ultimate storage capability of these hybrid nanostructured tanks.

This research was conducted by the following research team:

Gaetana Petrone1, Francesca Zarotti1, Rosanna Larciprete1, Roberto Felici2, Paolo Lacovig3, Daniel Lizzit3, Ezequiel Tosi3, Silvano Lizzit3

1 CNR- Instituto dei Sistemi Complessi, Roma, Italy
2 CNR-SPIN, Roma, Italy
3 Elettra Sincrotrone Trieste S.C.p.A., Trieste, Italy

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G. Petrone, F. Zarotti, P. Lacovig, D. Lizzit, E.  Tosi , R.  Felici, S. Lizzit and R.Larciprete, "The effect of structural disorder on the hydrogen loading into the graphene/nickel interface", Carbon 199, 357 - 366 (2022), DOI: 10.1016/j.carbon.2022.07.050

Last Updated on Friday, 23 December 2022 10:34