TABLE 1.

Physical-chemical properties of carbon nanomaterials

Carbon nanomaterial (without Nafion)	O/C ratio	Curve-fitting result of C(1s) spectraa				Main dimensionsb
		C=C, C—C, or C—H	C—O	C=O	O=C—O
CNT	0.004	1.000	N/Dc	N/D	N/D	1D; D = 15 nm; L = 100 μmd
O-CNT	0.092	0.882	N/D	N/D	0.118e	D is similar to that of CNT; L is as short as 1 μm
OA-CNT	0.054	0.956	0.044	N/D	N/D	D and L are similar to those of O-CNT
CB	0.015	1.000	N/D	N/D	N/D	3D; spherical; D = 60 nm
rGO	0.404	0.531	N/D	0.399	0.070	2D; flake; L/W is 1 μm and thickness is 1.5 nmf

^aValues are proportions of C with each type of bond. There are some discrepancies between the O/C analysis and the deconvolution of the C(1s) spectra, and the difference was within 30% for O-CNT, OA-CNT, and rGO. For reference to the two methods used, the XPS files for the rGO sample can be found in Fig. S3 in the supplemental material. Since the former data are directly from measurement and the latter are based on curve fitting, the former O/C ratio should be more reliable and have higher accuracy.

^bD, diameter; L, length; W, width.

^cN/D, none detected (<0.001) from the curve-fitting result of the C(1s) spectra.

^dAccording to supplier specifications.

^eA proportion of the carbon atoms (0.055) is fitted at the peak of 290.9 eV (C—F bond), likely from contamination on the sample surface by the fluorinated tubing in the oxidization system, and is not listed in this table.

^fSee reference 30.