Electrochemical Exfoliation of Graphite to Fluorographene: An Effect of Degree of Functionalization on 2Br⁻/Br₂ Redox Reaction

Abstract

In this work, we employed the electrochemical exfoliation (EE) to synthesize and tune the degree of functionalization in fluorinated graphene (FG) and studied its (degree of functionalization) effect on bromine redox reaction. The degree of functionalization was tuned by varying the concentration of the electrolyte. Physical characterization of as‐synthesized FG reveals that fluorine and oxygen content varies from 2.32 to 3.92 atomic % and from 10.46 to 21.16 atomic % respectively. The concentration of fluoride to hydroxide ion ratio should be at an optimum level in the electrolyte to get maximum degree of fluorination, which shows a sizeable effect on bromine redox reaction. The bromine redox reaction is more reversible on highly FG and less reversible on less FG and Oxygen functionalities has no effect on the reaction. The kinetic parameters such as rate constant (k) (varying from 1.45 x 10−3 to 52.43 x 10−3 mA/cm2) and exchange current density (io) (varying from 2.61 x 10−4 to 9.92 x 10−4 cm/s) suggest that nature and degree of functionalization play a vital role to improve the kinetics of redox reaction of bromine. This investigation can pave paths to design new and sustainable electrode materials for bromine‐based redox flow batteries.

Electrochemically derived functionalized graphene for bulk production of hydrogen peroxide

“…The surface area varies from 46 ± 2 m 2 /g (G-M1) to 11 ± 2 m 2 /g (G-M4). The change in the surface area can be attributed to the rate of exfoliation of the graphite rod which in turn depends upon the availability of fluoride and hydroxide ions at the anode (i.e., the higher the hydroxide ions the faster the exfoliation), which is in line with our recent report [43].…”

“…As described earlier, transmission electron microscopy (TEM) images of EEG samples indicate that the average lateral size is about 3-5 µm (more images in Supporting Information File 1) and scanning electron microscopy (SEM) images indicate the formation of randomly oriented exfoliated graphene nanosheets [43]. However, the TEM images show that the thickness of the graphene increases from G-M1 to G-M4, where the G-M4 is found to block the electron beam despite its layered nature (Supporting Information File 1, Figure S2).…”

“…The detailed physical characterization of electrochemically exfoliated graphene (EEG) was given in our recent report, where the variation in the oxygen functionalities, amount of fluorine content in exfoliated graphene, etc. were shown [43]. As discussed previously, the surface oxygen functional groups are crucial for the reduction of molecular oxygen to H 2 O 2 and hence high-resolution O 1s X-ray photoelectron spectroscopy (XPS) was carried out.…”

“…The O 1s peaks of different EEG samples are shown in Figure 1a. It can be seen that the intensity of the O 1s peak decreases from G-M1 to G-M4 (where G refers to graphene and M1, M2, M3, and M4 refer to the respective molarity of the electrolyte used for the exfoliation), and the elemental composition calculated from the survey spectrum of the materials revealed that the degree of oxygen functionalization varies from ≈21 to ≈10 atom % from G-M1 to G-M4 (as inferred from the XPS survey spectrum as well as the high-resolution C 1s and O 1s XPS spectra (Supporting Information File 1, Figure S1a)) [43]. The O 1s spectrum can be deconvoluted into two distinct peaks (as shown in Figure S2) centered at 532.2 eV and 533.4 eV, corresponding to alcoholic (C-OH)/ ether type of oxygen in ester functional groups and carbonyl (C=O in -COOH) functional groups, respectively [42,44].…”

“…In one of our previous works, different halogenated graphene materials were developed via a single-step electrochemical exfoliation (EE) method [42]. It was found that such a method can produce graphene with varying degrees of oxygen functionalities [43]. Here we explore the possibility of functional groups to control graphene toward the electrochemical production of H 2 O 2 in alkaline medium, and the amount of peroxide generated is quantified using a spectroscopic technique.…”