Table 1. Morphology and Surface Chemistry Trends of the Electrode Materials^a.

				surface chemistry trends
geometry and electrode type	morphology	fiber dimensions	roughness estimation (PyC as the planar reference)b	sp2	sp3	sp	COOH andketone/aldehyde	Id/Ig ratio	contact angle (hydrophobicity/hydrophilicity)
forest-like (CNF/ta-C)	vertically aligned fibers with Ni particles attachedc	1 μm length, 50–75 nm diameter, and 200–500 nm spacing between fibers	18 X	√			√ (considerable)	1.1	θadv = 86 ± 2° θrec = 32 ± 2° (weakly hydrophilic)
spaghetti-like (MWCNT/ta-C)	porous network of intertwined and curved fibers	10 μM length and 5–10 nm bundle diameter	100 X	√			√	1-highly defective	θadv ≈ 86–120° θrec < 40°d (hydrophobic)
planar (PyC)	flat surface (RMS 1.2 ± 0.6 nm)16		1 X	√	√	√	√ (negligible)	3.17	θadv = 60 ± 1° θrec = 22 ± 2° (moderately hydrophilic)

^aSurface chemistry studies (XAS and Raman spectroscopy) and morphology have been previously reported: CNF/ta-C and MWCNT/ta-C^19−21,23 and PyC.^16,22

^bRoughness estimation was performed by double-layer capacitance studies.

^cSome chunks of fibers and smaller structures between the main fibers are also observed.

^dContact angles were not stable for MWCNT/ta-C due to highly non-uniform surface.