Fabricate Holey Structure to Improve Capacitive Performance of GrapheneYan Dou, Materials Science and Engineering

Mentor: Qiong Nian, Assistant ProfessorSchool for Engineering of Matter, Transport and Energy

What is the electrochemical difference between graphene and holy graphene?

Abstract:Drilling nanosized holes on the graphene basal plane can improve its capacitance and create efficient ion transport pathways. To take advantage of this effect, the holey graphene-based electrode was fabricated successfully by microwave-assisted chemical etching(MACE) and the microstructure of nanosized holes was observed by SEM. Using the cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) test, it was found that the nanosized holes can improve the gravimetriccapacitance from 24.35Fg-1 to 48.12Fg-1 in sodiumsulfate solution. This positive result has a potential toopen up more opportunities for mobile power supply.

Background:According to MACE method, holy graphene can befabricated by follow steps:1) Pretreatment: The graphene oxide(GO) solution is

pretreated by irradiating in a microwave reactor toform defected graphene oxide(dGO).

2) MACE process: The dGO is mixed with hydrogenperoxide in a reaction tube and irradiated in themicrowave reactor to further etch and extend thedGO to holy graphene oxide(hGO).

3) reduction:The hGO isreduced to holygraphene (rhGO),which can provideabundant iontransport channelsand achievecharge transfer.

Results:

• The CV(Fig. 2a) and GCD(Fig. 2b) indicate that rhGO-ECs shows a significantly improved electrochemical performance beyond the rGO-ECs. The approximate rectangular part of CV curves and the triangular GCD curves reveal an almost electrical-double-layer capacitive behavior as well as efficient electrolyte ion transport throughout the rhGO-ECs.

• The GCD curves also can derive the specific capacitance values(Fig. 2c). A good gravimetric capacitance of 48.12 F g-1 at a current density of 1 A g-1 is exhibited by rhGO-ECs. On thecontrary, the gravimetric capacitance of rGO(24.35 F g-1 ) electrodes is about half of the rhGO.

• Increasing the current density up to 100 A/g, the rhGO displays a 66.73% capacitance retention(32.11 F g-1 ), the GO only retained about 55.77% of its initial capacitance (13.58 F g-1).

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Figure 2 | Electrochemical characterization of rGO-EC and rhGO-EC in 1 M Na2SO4 .(a) CV curves of rGO-EC and rhGO-EC at a scan rateof 100mVs-1 . (b) Galvanostatic charge/discharge curves of rGO-EC and rhGO-EC at a current density of 5 Ag-1 . (c) Comparison of specificcapacitances versus different current densities for rGO-EC and rhGO-EC.

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The surface morphology of rhGOwas investigated using SEM at different magnification as shown in figure 1. It can be clearly seen wrinkled surfaces and which are smooth with folding and wrinkles at edges(Fig. 1a, b). As shown in Fig.1b, the 10~20 nanosized holes were found like nearly spherical on the smooth surface, but they are not well dispersed.

Figure 1 | Structural characterization of rhGOs by SEM.(a) SEM image ofinterior microstructures of rhGO. Scale bar, 500nm. (b) SEM image of nanosizedholes on rhGO. Scale bar, 100nm.

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Conclusion:The holey graphene fabricated successfully via MACEmethod exhibits a better electrochemical performancewhen in comparison with graphene. Moreover,through SEM, the diameter of spherical nanoholes arefound in a range of 10nm to 20nm, but the distributionand quantity of nanoholes are not ideal. Fromelectrochemical measurements, the nanoholes ongraphene create efficient ion transport pathway andminimize the impact of graphene re-stackingsignificantly. In the future, more work should focus onthe population and distribution of nanosized holes.

References:1. Wang, Dini, et al. "Scalable and controlled creation of nanoholes in

graphene by microwave-assisted chemical etching for improved electrochemical properties." Carbon 161 (2020): 880-891.

2. Xu, Yuxi, et al. "Holey graphene frameworks for highly efficient capacitive energy storage." Nature communications 5 (2014): 4554.

3. Han, Xiaogang, et al. "Scalable holey graphene synthesis and dense electrode fabrication toward high-performance ultracapacitors." ACS nano 8.8 (2014): 8255-8265.

4. Chen, Yanan, et al. "Electronic detection of bacteria using holey reduced graphene oxide." ACS applied materials & interfaces 6.6 (2014): 3805-3810

5. Shui, Jianglan, et al. "Nitrogen-doped holey graphene for high-performance rechargeable Li–O2 batteries." ACS Energy Letters 1.1 (2016): 260-265.

Acknowledgements:This project is supported by “MORE” program. I thankProfessor Nian for insightful discussions and advice. Alsothis project was partly guided by Dini Wang, who taughtand helped me with electrochemical measurements. RuiDai and Kun Bi helped me complete the SEMcharacterization. In the end, I appreciate Ira A. FultonSchools of engineering for providing this chance.