Unlocking Mesoscopic Disorder in Graphitic Carbon with Spectroelectrochemistry

Abstract

Intrinsic structural and oxidic defects activate graphitic carbon electrodes towards electrochemical reactions underpinning energy conversion and storage technologies. Yet, these defects can also disrupt the long-range and periodic arrangement of carbon atoms, thus, the characterization of graphitic carbon electrodes necessitates in-situ atomistic differentiation of graphitic regions from mesoscopic bulk disorder. Here, we leverage the combined techniques of in-situ attenuated total reflectance infrared spectroscopy and first-principles calculations to reveal that graphitic carbon electrodes exhibit electric-field dependent infrared activity that is sensitive to the bulk mesoscopic intrinsic disorder. With this platform, we identify graphitic regions from amorphous domains by discovering that they demonstrate opposing electric-field-dependent infrared activity under electrochemical conditions. Our work provides a roadmap for identifying mesoscopic disorder in bulk carbon materials under potential bias.

Keywords: Disordered graphitic carbon electrodes; first-principles calculations; in-situ infrared spectroscopy.

Figure 1

Characterization of reduced graphite oxide (rGO) films prepared via the electrodeposition of GO on Au‐coated Si (Au/Si) surfaces. (a) High‐resolution x‐ray photoelectron spectra of the C1s region. (b) Electron energy‐loss spectra of carbon K‐edges. (c) Raman spectrum. (d) Atomic force microscopy image of the rGO−Au‐Si boundary and (e) the height profile along the dotted white line. (f) Grazing‐incidence XRD (GIXRD). GIXRD was conducted on a 0.3 μm‐thick rGO electrodeposited on Au‐coated aluminosilicate glass (see Supporting Information for details).

Figure 2

(a) Cyclic voltammogram of reduced graphite oxide on Au/Si in 0.1 M HClO₄ under N₂‐saturated conditions. Data were collected at 2 mV s⁻¹ with a negative direction of scan. Blue circles represent potentials where ATR‐IR spectra are reported in the negative‐going scan, and red circles represent potentials where ATR‐IR spectra are reported in the positive‐going scan in Figures 2b and 2 c. (b) Simultaneously collected ATR‐IR spectra during the CV scan are shown in Figure 2a. Background spectra were collected in N₂‐saturated 0.1 M HClO₄ at 1.07 V vs RHE. (c) (top) Potential dependence of the peak position of that observed at 1585 cm⁻¹ at 0.89 V in Figure 2b. (bottom) Potential dependence of the peak position of that observed at 1269 cm⁻¹ at 0.89 V in Figure 2b. Error bars depict the spectral resolution.

Figure 3

(a) Computational model‐1 of bulk reduced graphite oxide with amorphous domains (C₁₁₄O₁₀H₄) and varying oxidic domains shown. Orange and yellow spheres represent sp²‐ and sp‐hybridized C atoms, red spheres represent O atoms, and cyan spheres represent H atoms. (b) Computed IR spectra of C₁₁₄O₁₀H₄ as a function of the applied field. (c) Stark shifts observed for two predominant modes along the z‐axis. (d and e) Vibrational modes (only the lowest (L) layer in Figure 3a is shown) contributing to band I and band II, respectively. Other layers depict C−C displacements (see SI).