Electrocatalytic activity for proton reduction by a covalent non-metal graphene–fullerene hybrid

A non-metal covalent hybrid of fullerene and graphene was synthesized in one step via fluorographene chemistry. Its electrocatalytic performance for the hydrogen evolution reaction and durability was ascribed to intrahybrid charge-transfer phenomena, exploiting the electron-accepting properties of C60 and the high conductivity and large surface area of graphene.


Synthesis of G-C 60
15 mg (0.48 mmol) of fluorographene (FG), exfoliated from GF (100 mg), were suspended in 5 mL of anhydrous o-DCB with the aid of sonication for 4 h and the mixture was degassed and flushed with nitrogen. In parallel, 50 mg (0.049 mmol) of ammonium-fulleropyrrolidine salt C 60 -pyr-NH 3 + were dissolved in 3 mL of anhydrous o-DCB and afterwards, 50 µL of Et 3 N were added to the solution as a counter-balance agent for the protonated primary amine. Subsequently, o-DCB solution containing the C 60 -pyr-NH 2 was added to the o-DCB suspension of FG and the reaction mixture was heated at 130 °C and stirred under nitrogen for 72 h. Then, the G-C 60 hybrid material was separated using centrifugation and washed consecutively with carbon disulfide, in order to remove any non-covalently bound fullerene moiety, dichloromethane and ethanol.

Control experiment
15 mg of exfoliated FG were mixed with o-DCB solution containing fullerene C 60 and the reaction was carried out according to the above-mentioned process. The reaction did not introduce any functionality onto FG (see Fig. S1).

Instrumentation
FT-IR spectra were recorded on an iS5 FTIR spectrometer (Thermo Nicolet) using the KBr pellet accessory. Spectra were acquired by summing 64 scans. Pellet made by pure KBr was employed for the background acquisition. Baseline correction was applied to the collected spectra. X-ray photoelectron spectroscopy (XPS) was carried S2 out with a PHI VersaProbe II (Physical Electronics) spectrometer using an Al Kα source (15 kV, 50 W). The obtained data were evaluated with the MultiPak (Ulvac -PHI, Inc.) software package. Raman spectra were recorded on a DXR Raman microscope using the 633 nm excitation line of a diode laser. Thermogravimetric analysis (TGA) with evolved gas analysis (EGA) was performed using a Netzsch STA 449C Jupiter thermo-microbalance coupled with a QMS 403C Aëolos quadrupole mass spectrometer. Measurements were carried out in an α-Al 2 O 3 open crucible under N 2 flow. A temperature program from 40 to 950 °C with heating rate of 10 °C min -1 was used. Before each experiment, the crucible was heated to 1300 °C and then cooled to room temperature. Differential pulse voltammograms (DPV) were recorded on an Autolab PGSTAT128 N potentiostat/galvanostat equipped with a dual mode bipotentiostat (BA module) electrochemical analyzer using a three-electrode system.
A platinum cloth served as the counter electrode and a platinum wire was used as the reference electrode. A platinum button electrode was used as the working electrode.
Ferrocene/ferrocenium redox couple was used as an internal standard. All solutions were purged prior to electrochemical measurements using nitrogen gas. 0.1 M TBAPF 6 was used as supporting electrolyte. The potential are vs Fc/Fc + and the scan rate is 100 mV/s. Electron microscopy images were obtained with a High Resolution Transmission Electron Microscope (HRTEM) Titan G2 60-300 (FEI) with image corrector on accelerating voltage 80 kV. Images were taken with BM UltraScan CCD camera (Gatan). AFM images were obtained in the amplitude modulated semicontact mode on an NT-MDT NTegra system equipped with a VIT-P AFM probe with the amplitude set point set to 71% of the free amplitude, a scanning speed of 0.5 Hz per line for all pictures, and using fresh cleaved muscovite mica. The height profile and surface roughness (RMS) was calculated using Gwyddion 2.51 software. All electrochemical measurements were carried out using an Autolab PGSTAT128N potentiostat/galvanostat and were carried out at room temperature in a standard threecompartment electrochemical cell by using a graphite rod as a counter-electrode, an RDE with glassy carbon disk (geometric surface area: 0.0196 cm 2 ) as a working electrode, and Hg/HgSO 4 (0.1 M KOH) as reference electrode. LSV measurements were carried out at room temperature in N 2 -saturated aqueous 0.1 M KOH. The catalyst ink was prepared by dispersing 1.0 mg of the catalytic powder in 250 μL mixture of deionized water, isopropanol and 5% Nafion (v/v/v = 4:1:0.2) and sonicated for 1 h prior use. Before casting the electrocatalytic ink on the electrode's S3 surface, the working electrode was polished with 3 and 1 mm diamond pastes, rinsed with deionized water, and sonicated in double-distilled water. Afterward, 8.5 μL aliquots of the electrocatalyst were casted on the electrode surface and were left to dry at room temperature. EIS measurements were conducted from 10 5 to 10 -1 Hz with an AC amplitude of 0.01 V.     Figure S3. Raman spectra of pristine GF (grey) and G-C 60 (red). Figure S4. TGA graphs of pristine GF (grey), C 60 -pyr-NH 2 (blue) and G-C 60 (red). S6 Figure S5. Differential pulse voltammograms of C 60 -pyr-NH 2 (blue) and G-C 60 (red)

References
in o-DCB with 0.1 M TBAPF 6 as supporting electrolyte. The potential are vs Fc/Fc + and the scan rate is 100 mV/s.  . S8