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Fig. 5 - Raman spectra for sample C6 at different potentials. Excitation line = 632.8 nm, 6 M KOH.

Figure 5 - Raman spectra for sample C6 at different potentials. Excitation line = 632.8 nm, 6 M KOH.

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Table 2 - Thermal treatment temperature, porous texture, surface chemistry characterization, % wt of hydrogen electrochemically storage and active surface area (ASA) for the different samples The active surface area (ASA) gives a measurement of the number of reactive carbon atoms or active carbon sites of a carbon sample. The ASA of samples C6, B and A was esti- mated by a modification of the Laine et al. method [24]. Firstly, the samples were treated up to 950 °C in helium to remove the surface complexes present as a result of the previous activa- tion process. The ASA was then determined from the amount of surface oxygen complexes formed at 300 °C in synthetic air flow during 7 h (a longer time did not result in an increase the weight of the sample). The number of oxygen complexes can be determined either from the weight uptake of the samples
Table 2 - Thermal treatment temperature, porous texture, surface chemistry characterization, % wt of hydrogen electrochemically storage and active surface area (ASA) for the different samples The active surface area (ASA) gives a measurement of the number of reactive carbon atoms or active carbon sites of a carbon sample. The ASA of samples C6, B and A was esti- mated by a modification of the Laine et al. method [24]. Firstly, the samples were treated up to 950 °C in helium to remove the surface complexes present as a result of the previous activa- tion process. The ASA was then determined from the amount of surface oxygen complexes formed at 300 °C in synthetic air flow during 7 h (a longer time did not result in an increase the weight of the sample). The number of oxygen complexes can be determined either from the weight uptake of the samples
Fig. 1 - Galvanostatic charge/discharge curves for samples C6, B and A. 6 M KOH.
Fig. 1 - Galvanostatic charge/discharge curves for samples C6, B and A. 6 M KOH.
It can be observed that when the amount of surface oxy- gen complexes is low, the hydrogen storage keeps a linear relationship with the porosity of the material. A very similar relationship is found if the wt% of hydrogen stored is plotted against the Vpr(CO,) (not shown). Other researchers have published a linear trend followed by the porosity and the per- centage of hydrogen electrochemically stored [19,20]. Never-
It can be observed that when the amount of surface oxy- gen complexes is low, the hydrogen storage keeps a linear relationship with the porosity of the material. A very similar relationship is found if the wt% of hydrogen stored is plotted against the Vpr(CO,) (not shown). Other researchers have published a linear trend followed by the porosity and the per- centage of hydrogen electrochemically stored [19,20]. Never-
Interestingly, as the potential decreases below —0.672 V, two bands appear simultaneously at about 1110 and 1500 cm *, which reach their maximum intensity at —0.872 V. This fact indicates that a structural change in the carbon material is taking place while the potential decreases. Similar bands have been observed in nano-diamond films formation and have been attributed to the C(sp*)—H (v1) bending vibration and the C=C (v3) stretching vibration, respectively, in amor- phous carbon—hydrogen bonds localized at grain boundary 28,29]. This suggests that the bands observed here are a con- sequence of the hydrogenation of carbon atoms forming C(sp?)-H bonds. Interestingly, the potential at which the bands start to appear is very close to the potential at which The Raman spectrum for the material at approximately —0.172 V, a potential very close to the open circuit one, shows the typical features for carbon materials [27]. Two broad and Fig. 6 - Raman spectra for sample C1 at different potentials. Excitation line = 784.8 nm, 6 M KOH.
Interestingly, as the potential decreases below —0.672 V, two bands appear simultaneously at about 1110 and 1500 cm *, which reach their maximum intensity at —0.872 V. This fact indicates that a structural change in the carbon material is taking place while the potential decreases. Similar bands have been observed in nano-diamond films formation and have been attributed to the C(sp*)—H (v1) bending vibration and the C=C (v3) stretching vibration, respectively, in amor- phous carbon—hydrogen bonds localized at grain boundary 28,29]. This suggests that the bands observed here are a con- sequence of the hydrogenation of carbon atoms forming C(sp?)-H bonds. Interestingly, the potential at which the bands start to appear is very close to the potential at which The Raman spectrum for the material at approximately —0.172 V, a potential very close to the open circuit one, shows the typical features for carbon materials [27]. Two broad and Fig. 6 - Raman spectra for sample C1 at different potentials. Excitation line = 784.8 nm, 6 M KOH.
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