Graphene restoration bid farewell to “flood irrigation” to open “precision drip irrigation”

Schematic diagram of the rapid repair process for graphene film defects. (Courtesy of Zhao Wenjie)

Recently, the coupling damage and life extension team of harsh environmental materials in the Ocean Laboratory of ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, has designed a method to quickly and accurately repair graphene film defects, which can efficiently repair multiple scales and types of defects on graphene films within 15 minutes, and improve the corrosion protection performance of graphene films without affecting the excellent conductivity of graphene.

The research work was officially published in advanced functional materials, a high-level journal in the field of materials, under the title of “Eliminating the Galvanic Corrosion Effect of Graphene Coatings by Accurate and Rapid Self-Assembling Defect Repair Methods”.

“Born” defects expect precise repairs

Since its inception, graphene, with its excellent chemical stability and impermeability, is considered to be the most promising and known thinnest preservative material. Chemical vapor deposition (CVD) is commonly used to prepare large-area and high-quality graphene films, but the CVD method inevitably introduces different types and sizes of intrinsic defects, such as vacancies, pinholes, cracks and graphene island grain boundaries.

The presence of defects causes the metal matrix to be directly exposed to the corrosive medium, causing galvanic corrosion between the metal matrix and graphene, and accelerating the corrosion rate of the metal matrix. In addition to reducing the corrosion resistance of graphene films, these defects can also reduce the electrical properties, especially after corrosion occurs.

Some existing methods to repair graphene defects, such as depositing passivated zinc oxide, alumina and other oxides on graphene by atomic layer deposition (ALD) method. The oxide covers the entire graphene surface, which can improve the corrosion resistance of the graphene coating.

However, the ALD method takes several hours and lacks high selectivity for defects, and oxides deposited in the defect-free regions of graphene tend to drastically reduce the electrical properties of graphene.

Innovative approach, revealing mechanisms

Zhao Wenjie, the corresponding author of the above article and a researcher at the Ningbo Institute of Materials, told China Science News that the biggest challenge in repairing graphene defects is high efficiency and accuracy, while not affecting its chemical stability and electrical properties.

The research team self-assembled in situ based on 1H, 1H, 2H, 2H-perfluorooctanethiol (PFOT) molecules at the site of graphene defects during the evaporation of the solution, and quickly repaired defects by forming chemical bonds with the copper substrate exposed at the defect site by thiols. The accuracy of PFOT repairing graphene defects was verified by combining atomic force microscopy and Raman spectroscopy, and it was found that PFOT selectively adsorbed on graphene defects of different types and sizes, and no PFOT molecules appeared in the complete region of graphene.

They revealed the formation mechanism of chemical bonds through micro-infrared, XPS and DFT calculations, and the results obtained by experimental characterization and DFT calculations were very consistent. The PFOT molecule forms a very strong covalent bond with the basal copper atom exposed to the defect location and the carbon atom at the edge of the graphene defect, and the PFOT molecule forms a weak van der Waal bond with the intact and defect-free graphene surface, which is easy to remove, which is why PFOT accurately repairs the graphene defect.

In addition, the chemical bonding between the thiol and the basal copper atom and the carbon atom at the edge of the defect causes the Ehrlich-Schwoebel barrier of the PFOT molecule to diffuse to the defect location to decrease. This allows the PFOT molecule to repair graphene defects quickly (in only 15 minutes) and with precision.

Universal restoration methods may affect the industrial sector

Zhao Wenjie said that the method of accurate repair of graphene corrosion-resistant film defects shows universality and has three key elements:

The repair substance must have a strong chemical bond with the metal substrate to ensure long-term chemical stability and make the repair have long-term efficacy; the repair substance will not form a chemical bond with the defect-free graphene to ensure that the repair process does not affect the electrical properties of graphene; the repair substance contains hydrophobic functional groups, reducing the wetting properties of the corrosive medium on the surface, thereby improving the corrosion resistance of the graphene film layer.

Therefore, if the previous restoration method is “flood irrigation”, the achievement of this achievement is “precision drip irrigation” fixed-point repair.

In this regard, the reviewers of “Advanced Functional Materials” believe that the author has repaired the multi-scale and multi-type defects on the surface of the graphene film through systematic experimental characterization and first-principle calculation, eliminated the potential galvanic corrosion between the graphene and the copper substrate, and profoundly revealed the repair mechanism, which can be applied to other repair processes, and this work will stimulate extensive research on the repair of graphene film in the electronics industry, coatings and sensors. (Source: China Science Daily Zhang Nan)

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