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Page 6 of 17 Zhang et al. Soft Sci. 2026, 6, 16

Figure 2. FESEM images of (A) SS substrate, (B) C-0, (C) C-1, (D) C-2, and (E) C-3; (F and G) HRTEM images of C-3; EDS elemental
mapping of C-3: (H) HAADF image, (I) C, (J) O, and (K) Fe. FESEM: Field emission scanning electron microscope; SS: stainless steel;
HRTEM: high-resolution transmission electron microscopy; EDS: energy dispersive X-ray spectrometer; HAADF: high-angle annular
dark-field.

C-3 samples are analyzed in Figure 3D and Table 1. Both spectra can be fitted with two peaks at 530.5 and
532.1 eV, corresponding to crystal oxygen and adsorbed oxygen, respectively . Since O is the most
[24]
2
common reactive gas in contact with carbon films, the amount of adsorbed oxygen in coated electrodes is
significantly higher than in the uncoated sample . It was reported that adsorbed oxygen can provide
[25]
unsaturated oxygen coordination, thereby enhancing the electrochemical performance [26,27] ; thus, C-1, C-2,
and C-3 electrodes could benefit from carbon film deposition. The slightly lower adsorbed oxygen in C-3
compared to C-2 and C-1 may be attributed to the lower adsorption energy of molecular oxygen on sp2
carbon . Figure 3E shows the Fe 2p spectrum of electrode C-3. The peaks at 710.8 eV (Fe 2p ) and
[28]
3/2
724.4 eV (Fe 2p ) could be further divided into four subpeaks: 713.2 and 727.0 eV assigned to Fe , and 710.6
3+
1/2
and 724.2 eV corresponding to Fe in Fe O . Raman spectroscopy results are shown in Figure 3F, where all
[29]
2+
4
3
three samples exhibit typical carbon features, including the D and G bands at about 1,340 and 1,570 cm ,
-1
respectively . In particular, the C-3 sample exhibited distinct D and G bands, unlike the overlapping bands
[30]
observed in C-2 and C-1. A slight, broad 2D band is also observed between 2,500 and 3,000 cm , indicating
-1