Poly(vinylidene fluoride) and Carbon Derivative Structures from Eco-Friendly MOF-5 for Supercapacitor Electrode Preparation with Improved Electrochemical Performance

Abstract

Electrodes from carbonized Zn₄O(1,4-benzodicarboxylic acid) (MOF-5) structures were prepared successfully via evaporating the solvent with a poly(vinylidene fluoride) (PVDF) binder. The solvent used for a nanocomposite cast was easily removed. Such an elegant method for preparing electrodes provides a facile, cost-effective, and void/cracking-free nanocomposite distribution on the current collector. The highly porous nanoparticles containing pure carbon attach well to the PVDF membrane which results in an increased active surface area of the electrode to 847 m²/g. The electrochemical analysis shows that the best weight ratio of CMOF-5 to PVDF equals 85:15, 80:20, and 75:25, respectively. The specific capacitance of these samples is 218 F/g, 210 F/g, and 180 F/g, correspondingly. An additional advantage of the electrode prepared from the carbonized MOF-5 is the possibility to synthesis MOF structures from recovered substrates used in its synthesis (distilled N,N-Dimethylformamide DMF and terephthalic acid recovered from polyethylene terephthalate waste). We will demonstrate this in this contribution as well. Furthermore, the carbonized MOF-5 can be recovered from the spent electrode and reused again in the electrochemical device.

Keywords: MOF-5 carbonization; MOF-5 synthesis; MOF-5 synthesis from recycled DMF; electrode preparation; supercapacitors.

Figure 1

The SEM images of MOF-5 before (A) and after (B) carbonization with X-ray diffraction patterns.

Figure 2

The structure of supercapacitor (A) and electrode preparation (B) with the SEM image of the electrode on the surface of the current collector (C).

Figure 3

The SEM images of the surface area and cross-section of the MOF-5 pellet (A,D); PVDF layer (B,E) and nanocomposite of PVDF and carbonized MOF-5 (C,F).

Figure 4

The Nyquist plots, CV, and GCD curves of the electrodes prepared by evaporation (A–C) and pellet formation (D–F) along with the measured specific capacitance (calculated from the GCD curves) for the electrodes prepared by evaporation and pellet formation (G).

Figure 5

The scheme (A) of the electrolyte penetration of electrode and the SEM images of the electrode cross-section before (B,C) and after electrolyte penetration (D,E and F,G). The image in Figure 5D,F show the SEM images with a merge signal from potassium (green) and copper (pink) (To interpret the colors in this figure, the reader is referred to the web version of this article). The experiment scheme shows the spots of elemental mapping presented in Figure 5D,F, marked with (*) and (+) respectively.

Figure 6

The GCD curves of the electrodes prepared by evaporation with different ratios of CMOF-5:PVDF.

Figure 7

The specific capacitance curves (A) and Nyquist plots (B) of the electrodes prepared by evaporation with different ratios MOF:PVDF.

Figure 8

The CV curves of the electrodes prepared by evaporation with different ratios of CMOF-5:PVDF.

Figure 9

The SEM images of the electrodes prepared by evaporation with different ratios of CMOF-5:PVDF (scale bar 20 nm).

Figure 10

The cross-section of the electrodes corresponding to the CMOF-5:PVDF ratios: from 95:5 to 80:20 (A), 75:25 (B), 70:30 (C) and 60:40 (D). The scale bar corresponds to 20 µm.

Figure 11

The CV (A) and GCD (B) curves, correlation of the CV curves at 200 mV/s (C) and the GCD capacitance (D) of supercapacitors from recycled and pristine carbonized MOF-5 (ratio 60:40).

Figure 12

The SEM images of the electrodes from the recycled CMOF-5 and electrodes prepared with ratio 70:30 and 60:40 (scale bar 10 nm).

Figure 13

The comparison of the GCD (A) and CV (B) curves at a 200 mV/s scan rate of supercapacitors made of recovered MOF (additionally purified MOF: r2-CMOF-5) and pristine carbonized MOF (at a ratio of 75:25 and 70:30).

Figure 14

The SEM (A–D) and TEM (F) images of carbonized MOF-5 after recycling and purification. The FT-IR spectrum of carbonized MOF-5 before electrode preparation and after CMOF-5 recovery (E).

Figure 15

The SEM images of MOF-5 synthesized from fresh substrates (A,B), recycled DMF and terephthalic acid (C,D). The XRD spectrum of the terephthalic acid and depolymerized PET (E), and MOF-5 from unreacted and recycled substrates (F).