Large-Area Chemically Modified Graphene Films: Electrophoretic Deposition and Characterization by Soft X-ray Absorption Spectroscopy

Abstract

A facile, rapid, and scalable electrophoretic deposition approach is developed for the fabrication of large-area chemically derived graphene films on conductive substrates based on the electrophoretic deposition of graphene oxide and reduced graphene oxide components. Two distinctive approaches for fabricating conformal graphene films are developed. In the first approach, graphene oxide sheets are electrophoretically deposited from an aqueous solution after the oxidation of graphite to graphite oxide and the subsequent exfoliation of graphite oxide to graphene oxide. Next, the graphene oxide films are reduced via dip-coating in an aqueous solution of hydrazine. In the second approach, graphene oxide is reduced to graphene nanosheets in a strongly alkaline solution and the reduced graphene sheets are directly electrophoretically deposited onto conductive substrates. The film thickness can be modified by the deposition time and the obtained films span several square millimeters in area. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to study the surface chemistry, electronic band structure, and degree of alignment of the electrophoretically deposited films. Polarized NEXAFS measurements verify the presence of epoxide surface functionalities on the graphene basal planes and indicate significant recovery of extended π-bonded networks upon defunctionalization by hydrazine treatment. These measurements further indicate significantly improved alignment of the graphene sheet components of the films parallel to the substrate surface when defunctionalization is performed prior to electrophoretic deposition.

Electrochemical Intercalation of Sodium Ions into Thermally Reduced Graphite Oxide

“…In the OK region, three peaks due to O*(C=O), Q*(O-H) and Q*(C-O) were observed at 531.2, 535.8, 540.1 eV, respectively for GO. 18,19,[22][23][24] After heating, the latter peak slightly shifted to higher energy and the relative intensity of the peaks at lower energies greatly decreased. The peak at 540.1 eV is usually assigned to hydroxyl groups, however, the contribution of the other oxygen functionalities, such as carbonyl, carboxylic and epoxides is also suggested.…”

X-ray absorption spectra of graphene and graphene oxide by full-potential multiple scattering calculations with self-consistent charge density

“…In a considerable number of experiments [37,[50][51][52][53], near 288 eV, we can observe a very pronounced and sharp peak at a higher energy and one or two broader peaks at lower energies. The broader peaks can be attributed to COC and COH bondings on the basal plane, while the sharp one is normally attributed to the carboxylic acid group (-COOH) on the edge or near vacancies.…”

Electrophoretic deposition of graphene-related materials: A review of the fundamentals

“…Upon reduction, a stable suspension of rGO is produced due to the strongly bound K + ions. However, it is important to note that the rGO suspensions prepared by this method contain high concentrations of K + ions, which increase the ionic conductivity of the suspension and may be incorporated within electrophoretic deposited films [73,74]. Interestingly, highly alkaline solutions have also been applied, without using hydrazine, to produce partially stable reduced GO suspensions, with a retained negative charge through conjugate base formation (see section 2.1ii), suitable for anodic EPD [75].…”

“…Due to its hydrophilic nature, unreduced GO can be suspended relatively easily in aqueous media with zeta potential values reported between -2 to -70 mV, as a function of pH [15,34,74,[76][77][78]. For both acidic and basic conditions, GO exhibits net negative surface charge when suspended in water.…”

“…and Figure 17) [8]. Nonuniformity of deposits at high voltages may also originate from the anisotropy of the electric field on the substrate, leading to preferential deposition at the electrode edges [153], the possible formation of aggregates in suspension, or Joule heating effects on relatively insulating deposits [74]. On the other hand, too low a voltage (see Section 3.i.)…”