Z.R. Yue et al. /Carbon 37(1999)1785-1796 means that the overall O/C atomic ratios should have decimal places the precision is certainly less. There is a continually increased with progressive oxidation. This nificant decrease in the relative content of graphitic deduction contrasts sharply with the observed O/C ratios carbon(peak I)and a rise in the relative content of carbon from XPS shown in Fig. 2. Therefore, electrochemical bonded to oxygen-containing functions(peaks Il, Ill, IV oxidations are continually generating micropore/void/slit and V)after electrochemical oxidation. This rise comes structures that penetrate increasingly deeper below the mostly from an increase in peak IV assigned to carboxyl outer fiber surface as oxidation progresses. Since XPS (COOH)or ester ( COoR) type groups. The relative nalysis can only sample the outer 50 A of the fiber, concentration of peak IV increased two-fold after oxida- further increases in -COOH and phenolic -OH group tion, from -6.8%(as-received fiber) to 11-14%(electro- generation by oxidation primarily occur below the 50 A chemically oxidized fibers). This is consistent with the data ampling depth of the XPS experiment. Oxygen functions in Fig. 2, where the o Is/C Is atomic ratio increased mainly exist on the internal pore/slit/void surfaces and not 1.5-18-fold after electrochemical oxidation. within the graphitic sheets. Most likely, lateral planes are ight increase in the amount of carbon- oxidized progressively forming pores and slits which oxygen complexes detected by XPs (30 electron take-off interconnect and link as they move increasingly deeper angle) in the outer fiber surface region(50 A depth) as the into the fiber xtent of oxidation increased from 133 C/g to 10 600 C/g High-resolution XPS spectra of the C ls region( Fig 3)(Fig. 3). This contrasts with the increase in the con- show that carbon-based oxides are present on all the entration of acidic functional groups in the fibers mea- samples. Deconvolution of the C Is spectra [28] gives five sured by Naoh uptake which was proportional to the eaks that represent graphitic carbon(peak 1, 284.6 eV), extent of electrochemical oxidation [20]. Clearly, the carbon present in phenolic, alcohol, ether or C=n groups majority of new oxidized functions occur beyond the XPs (peak ll, 286.1-286.3 ev), carbonyl or quinone groups sampling depth of 50 A as the extent of electrochemical (peak Ill, 287.3-287.6 eV), carboxyl or ester groups(peak oxidation goes from 133 C/g to 10 600 C/ IV, 288.4-288.9 eV) and carbon present in carbonate The slight increase in relative concentration of carbon groups and/or adsorbed CO and CO,(peak V, 290.4- oxygen complexes occurring at oxidation levels above 133 290.8eV) The calculated percentages of graphitic and functional ncreasingly porous(e.g, higher void volume). Thus, the carbon atoms are shown in Fig. 3. While listed to two fraction of carbon atoms in this region which exist on the 2.55% 2.42% 84B% 6868% (5300c/g) %舌7%51 Fig. 3. High-resolution XPS C Is spectra of electrooxidized carbon fibers versus the extent of electrochemical oxidation.Z.R. Yue et al. / Carbon 37 (1999) 1785 –1796 1789 means that the overall O/C atomic ratios should have decimal places the precision is certainly less. There is a continually increased with progressive oxidation. This significant decrease in the relative content of graphitic deduction contrasts sharply with the observed O/C ratios carbon (peak I) and a rise in the relative content of carbon from XPS shown in Fig. 2. Therefore, electrochemical bonded to oxygen-containing functions (peaks II, III, IV oxidations are continually generating micropore/void/slit and V) after electrochemical oxidation. This rise comes structures that penetrate increasingly deeper below the mostly from an increase in peak IV assigned to carboxyl outer fiber surface as oxidation progresses. Since XPS (COOH) or ester (COOR) type groups. The relative ˚ analysis can only sample the outer 50 A of the fiber, concentration of peak IV increased two-fold after oxida￾further increases in -COOH and phenolic -OH group tion, from |6.8% (as-received fiber) to 11–14% (electro￾generation by oxidation primarily occur below the 50 A chemically oxidized fibers). This is consistent with the data ˚ sampling depth of the XPS experiment. Oxygen functions in Fig. 2, where the O 1s/C 1s atomic ratio increased mainly exist on the internal pore/slit/void surfaces and not 1.5–1.8-fold after electrochemical oxidation. within the graphitic sheets. Most likely, lateral planes are There is only a slight increase in the amount of carbon– oxidized progressively forming pores and slits which oxygen complexes detected by XPS (308 electron take-off ˚ interconnect and link as they move increasingly deeper angle) in the outer fiber surface region (50 A depth) as the into the fiber. extent of oxidation increased from 133 C/g to 10 600 C/g High-resolution XPS spectra of the C 1s region (Fig. 3) (Fig. 3). This contrasts with the increase in the con￾show that carbon-based oxides are present on all the centration of acidic functional groups in the fibers mea￾samples. Deconvolution of the C 1s spectra [28] gives five sured by NaOH uptake which was proportional to the peaks: that represent graphitic carbon (peak I, 284.6 eV), extent of electrochemical oxidation [20]. Clearly, the carbon present in phenolic, alcohol, ether or C5N groups majority of new oxidized functions occur beyond the XPS ˚ (peak II, 286.1–286.3 eV), carbonyl or quinone groups sampling depth of 50 A as the extent of electrochemical (peak III, 287.3–287.6 eV), carboxyl or ester groups (peak oxidation goes from 133 C/g to 10 600 C/g. IV, 288.4–288.9 eV) and carbon present in carbonate The slight increase in relative concentration of carbon– groups and/or adsorbed CO and CO (peak V, 290.4– oxygen complexes occurring at oxidation levels above 133 2 290.8 eV). C/g occurs because the outer |50 A of the fiber becomes ˚ The calculated percentages of graphitic and functional increasingly porous (e.g., higher void volume). Thus, the carbon atoms are shown in Fig. 3. While listed to two fraction of carbon atoms in this region which exist on the Fig. 3. High-resolution XPS C 1s spectra of electrooxidized carbon fibers versus the extent of electrochemical oxidation