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D.F. Carrasco, J.I. Paredes, S. Villar-Rodil et al. Carbon 195 (2022) 57e68 Fig. 3. Spectroscopic characterization of different precursors and the holey graphenes derived from them. (a) UVeVis absorption/extinction spectra of electrochemically derived, highly oxidized graphene (black trace) and mildly reduced graphene oxide (orange trace). High resolution C 1s XPS of (b) EOG (red trace) and EOG-H (blue trace); (c) MRGO (orange trace) and MRGO-H (green trace). Raman spectra of (d) EOG (red trace) and EOG-H (blue trace); (e) MRGO (orange trace) and MRGO-H (green trace). TPD profiles for (f) EOG (CO2: red solid trace; CO: red dotted trace) and EOG-H (CO2: blue solid traces; CO: blue dotted traces); (g) MRGO (CO2: orange solid trace; CO: orange dotted trace) and MRGO-H (CO2: green solid trace; CO: green dotted trace). (A colour version of this figure can be viewed online.) the average size of the aromatic domains in EOG and MRGO was essentially the same. Nevertheless, we note that the full width at half maximum (FWHM) values of their respective D and G bands were substantially different, indicating that the two graphenes should be structurally dissimilar. Specifically, the Raman bands of MRGO were broader than those of EOG [FWHM values of 80 ± 1 (G) and138±2(D)cm1 forMRGOvs.72±3(G)and97±5(D)cm1 for EOG], which pointed to a more disordered lattice in the former graphene. Indeed, the FWHM of the G band can be taken as a proxy to discriminate between samples belonging to the nano- crystallization and amorphization regimes, even though they may exhibit the same ID/IG value [28,43]. Along this line, it can be concluded that the structure of EOG belongs to the nano- crystallization regime, while that of MRGO belongs to the amorphization one, and therefore that the aromatic domains are larger in the electrochemically derived graphene. The previous spectroscopic data collectively indicated that the aromatic domains of a highly oxidized graphene obtained by the electrochemical route tend to be larger than those of a counterpart derived from standard graphene oxide, even though both exhibit the same overall degree of oxidation. Such a subtle difference in their microscopic structure can be expected, however, to translate into distinct macroscopic properties for materials prepared from the two graphenes [28]. This should be particularly the case of the electrical conductivity. Because the electrical transport in graphite/ graphene materials is made possible by delocalized p states asso- ciated to their extended aromatic character, an oxidized graphene having larger aromatic domains should be electrically more conductive than another graphene with smaller domains [44,45]. We measured the electrical conductivity of thin paper-like films of EOG and MRGO obtained by vacuum filtration of their respective aqueous dispersions. As expected, the value determined for the EOG film was considerably larger than that of its MRGO counterpart (50 vs. 0.09 mS cm1), which lent further support to the idea of the structural differences discussed above. 3.2. Electrochemically derived holey graphene: role of labile groups To be useful as precursors to holey graphene, oxidized graphe- nes should possess a significant amount of labile oxygen groups that can be easily removed in the form of CO and CO2 molecules by, e.g., chemical or thermal treatment. To probe the presence of such labile groups in EOG, the sample was analyzed by temperature- programmed desorption (TPD) under a flowing argon 62PDF Image | electrochemical route to holey graphene nanosheets
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