Defect-Free Single-Layer Graphene by 10 s Microwave Solid Exfoliation and Its Application for Catalytic Water Splitting.

Mustafa K Bayazit,Lunqiao Xiong,Edward White,Chaoran Jiang,Savio J A Moniz,Junwang Tang,Milo S P Shaffer

doi:10.1021/acsami.1c03906

Abstract

Mass production of defect-free single-layer graphene flakes (SLGFs) by a cost-effective approach is still very challenging. Here, we report such single-layer graphene flakes (SLGFs) (>90%) prepared by a nondestructive, energy-efficient, and easy up-scalable physical approach. These high-quality graphene flakes are attributed to a novel 10 s microwave-modulated solid-state approach, which not only fast exfoliates graphite in air but also self-heals the surface of graphite to remove the impurities. The fabricated high-quality graphene films (∼200 nm) exhibit a sheet resistance of ∼280 Ω/sq without any chemical or physical post-treatment. Furthermore, graphene-incorporated Ni–Fe electrodes represent a remarkable ∼140 mA/cm2 current for the catalytic water oxidation reaction compared with the pristine Ni–Fe electrode (∼10 mA/cm2) and a 120 mV cathodic shift in onset potential under identical experimental conditions, together with a faradic efficiency of >90% for an ideal ratio of H2 and O2 production from water. All these excellent performances are attributed to extremely high conductivity of the defect-free graphene flakes.

Highlights

The graphene-based technologies heavily rely on the availability of mass production of high-quality and low-cost single-layer material in a liquid-processable form,[1,2] which still is a challenge.[3]
Chemical approaches are always believed to be a low-cost technology but the resultant graphene products usually suffer from unavoidable surface defects and low yields.[16−18] A benchmark work using advanced chemical reduction of highly defective graphene oxide successfully improved the quality of graphene flakes with still ∼7 atom % total oxygen and a few milligrams of yield.[19]
We found that the pretreatment in Br2/CHCl3 solution for 2 h produced stable P-graphite

Summary

Introduction

The graphene-based technologies heavily rely on the availability of mass production of high-quality and low-cost single-layer material in a liquid-processable form,[1,2] which still is a challenge.[3] So far, physical approaches have been favored to produce relatively high-quality graphene flakes, the high cost and low product yields could be major obstacles limiting its scale-up.[4] For example, liquid-phase exfoliation of graphite has widely been used to produce graphene flakes; it either produces multilayered products or the yield of the produced mono/bilayer graphene is not satisfactory due to the strong π−π interactions between the highly ordered graphitic layers.[5−10] Increasing the ultrasonication time or intensity or applying a high shear force could improve the graphene production yield by weakening layer−layer interactions These processes tend to create defects on the graphene surface, which significantly disrupt the electronic properties of the material and increases the manufacturing costs.[5,9−13] In addition to the liquid-phase exfoliations, a gasdriven exfoliation of graphite was shown to be effective in preparing monolayer flakes with a yield of 62%.14. Similar phenomena were reported.[20,21]

Methods

Results

Conclusion