Three-Dimensional graphene: Synthesis and application

This study presents the synthesis of vertical graphene arrays (VGA) and related graphene-based materials using plasma-enhanced chemical vapor deposition (PECVD), which are explored as electrodes in sensors and fuel cells/secondary batteries.

Three-dimensional (3D) graphene architecture consists of interconnected graphene that forms porous structures. The 3D graphene-based porous framework serves as both a structural backbone and a conductive pathway in energy storage and conversion systems. Common 3D graphene structures, such as foams and sponges, are typically fabricated using a metal foam template followed by metal removal. In contrast, VGAs can be directly grown on various substrates through PECVD. The VGA comprises a self-supported network of few-layer graphene sheets oriented almost vertically on the substrate, creating a distinct 3D architecture with wall-like structures. This configuration ensures intimate contact with the substrate at the base and maximizes exposed edges and open surfaces, enhancing accessibility. Moreover, PECVD enables the production of porous structures in 3D graphene by modifying plasma conditions. Two prominent morphologies—nanowall and nanoporous structures—exhibit large specific surface areas, making these 3D graphenes particularly suitable for various applications due to their high porosity, extensive surface area, and remarkable electrical conductivity.

The synthesis of 3D graphene with varying morphologies is achieved by manipulating plasma parameters, including pressure, the CH₄/H₂ mixing ratio, and substrate temperature. For example, VGA was successfully synthesized on silicon and metal substrates at 15 mTorr using an rf (13.56 MHz) inductively coupled plasma source. Increasing the pressure causes the vertical graphene to bend and branch, ultimately forming a nanoporous structure at 50 mTorr.

3D graphene-based materials show great promise as electrodes in electrochemical sensors and fuel cells/batteries. Their efficacy arises from the chemically stable graphene's large surface area and the potential for surface modifications with metal nanoparticles (NPs) and biomolecules. In this study, platinum (Pt) NPs were synthesized on graphene surfaces through the reduction of Pt salt precursors and used as electrodes in proton-exchange membrane fuel cells and hydrogen peroxide sensors. Additionally, glucose oxidase (GOD) was immobilized on the hydrophilized graphene surface, serving as electrode materials for glucose fuel cells (GFC). The study also proposes the utilization of 3D graphene as a conductive backbone for sulfur electrodes in lithium-sulfur batteries.

Through these findings, 3D graphene demonstrates significant potential across multiple energy-related applications.

Prof. Mineo Hiramatsu received Ph.D. from Nagoya University and is a Full Professor of Department of Electrical and Electronic Engineering, Meijo University, Japan since 2006. He served as the Director of The Japan Society of Applied Physics in 2013-2015 and 2022-2024. His main fields of research are plasma diagnostics and plasma processing for the synthesis of thin films and nanostructured materials. He was awarded the Japan Society of Applied Physics Fellow in 2017.