*(2) Valence-Band Spectra*

Figure 6 shows the variation in the Valence-band (VB) spectrum of the ACC substrate after modification with PAni. The spectrum of the bare carbon cloth (Figure 6a) is characterized by two broad peaks of similar relative intensity corresponding to O2s (25 eV) and C2s (19 eV) levels [40]. This latter peak may also involve a possible contribution from N2s orbitals at its low BE energy side (18–16 eV) [40]. The region below 16 eV is characterized by features resulting from the strong overlap of mixed O2p, C2p and N2p components [40]. In Figure 6a, a sharp peak appears in this region (12.2 eV), serving as a distinctive fingerprint for our base carbon fabric material. This characteristic peak is totally suppressed in the VB spectrum of hybrid PAni-ACC composites formed at prolonged electropolymerization time (Figure 6c, 120 min). The VB lineshape in this material shows three weak consecutive peaks laying in the region 10–20 eV and an asymmetric peak of high intensity at 24.5 eV. Moreover, it should be emphasized that the VB edge is far below the Fermi level in the ACC substrate, but the growth of PAni increases the density of states near the Fermi energy to delineate a small shoulder at ~4 eV. A similar VB pattern has been reported earlier for PAni films, although the relative peak intensity and resolution of the various peaks is highly dependent on the particular intrinsic redox state, the doping and protonation levels, and the nature of the dopant ion [46–48]. Nakajima et al. [46] reported a set of peaks in the region 10–20 eV (17.5 eV, 14 eV and 11.5 eV) due to an overlap of molecular orbitals involving benzenoid C and N in leucoemeraldine salt, while the electron density close to the

Fermi level was found to be characteristic of a conjugated structure of double and single bonds. More recently, Bocchini et al. [48] distinguished a C2s peak at 13 eV, a 9–11 eV feature corresponding to a C–N 2p-σ state, and a group of weak photoemission peaks below 8 eV assigned to C2p-σ and C2p-π bands in polyemeraldine doped with camphorsulphonic or aminosulphonic acids. Hybrid PAni-ACC composites formed at intermediate electropolymerization times (Figure 6b) show mixed features from both the underlying carbon matrix and a polymer thin film. Thus, the lineshape, relative intensity and position of peaks above 15 eV change to become similar to that of PAni, whereas the characteristic sharp peak survives, but is shifted to lower BE. Also, the VB edge lies between that of the untreated ACC and that of the fabric coated with thick PAni layers.

**Figure 6.** Valence-band X-ray photoelectron spectra of (**a**) untreated ACC and hybrid PAni-ACC composites synthesized after (**b**) 20 min and (**c**) 120 min of galvanostatic electropolymerization.
