A review of 3D graphene materials for energy storage and conversion

Abstract

Three-dimensional (3D) graphene monoliths are a new carbon material, that has tremendous potential in the fields of energy conversion and storage. They can solve the limitations of two-dimensional (2D) graphene sheets, including interlayer restacking, high contact resistance, and insufficient pore accessibility. By constructing interconnected porous networks, 3D graphenes not only retain the intrinsic advantages of 2D graphene sheets, such as high specific surface area, excellent electrical and thermal conductivities, good mechanical properties, and outstanding chemical stability, but also enable efficient mass transport of external fluid species. We summarize the fabrication methods for 3D graphenes, with a particular focus on their applications in energy-related systems. Techniques including chemical reduction assembly, chemical vapor deposition, 3D printing, chemical blowing, and zinc-tiered pyrolysis have been developed to change their pore structure and elemental composition, and ways in which they can be integrated with functional components. In terms of energy conversion and storage, they have found broad use in buffering mechanical impacts, suppressing noise, photothermal conversion, electromagnetic shielding and absorption. They have also been used in electrochemical energy systems such as supercapacitors, secondary batteries, and electrocatalysis. By reviewing recent progress in structural design and new applications, we also discuss the problems these materials face, including scalable fabrication and precise pore structure control, and possible new applications.

1. Introduction

Carbon is one of the basic elements in the world, its versatility is indispensable for the mass circle in nature as well as the progress of modern technology. The groundbreaking isolation of graphene-a 2D honeycomb lattice of sp2-bonded carbon atoms-by Geim and Novoselov's team in 2004 marked a milestone in materials science[1]. This material theoretically has unparalleled characteristics: ultrahigh surface area (～2630 m2 g−1), exceptional charge mobility (>200 000 cm2 V−1 s−1)[2–3], superior thermal conductivity (～5000 W m−1 K−1)[4], strong mechanical strength (with a Young's modulus of ～1 TPa)[5], and remarkable chemical stability. Graphene continues to revolutionize materials research through its unique 2D quantum behavior, including phenomena like the ambipolar field effect[1], quantum Hall effect[6–8], giant intrinsic carrier mobility, high sensitivity to external charge[9], among others. Furthermore, recent advances in synthesis methodologies have significantly enhanced production efficiency, enabling cost-effective fabrication and industrial-scale implementation of graphene-based technologies[10,13]. Endowed with a diverse array of attributes, graphene materials have found broadened applications, particularly in advancing energy storage and environmental conservation technologies[14–16]. Nonetheless, the robust π-π stacking and van der Waals forces inherent between graphene sheets instigate significant aggregation, thereby drastically diminishing its key properties. As a consequence, vital characteristics such as its accessible specific surface area and catalytic active sites are substantially diminished, leading to a dearth of contiguous channels imperative for ion mobility. Meanwhile, the 2D stance of graphene has met challenges in energy storage and conversion devices, especially in large-scale 3D devices[17–19].

Given this context, researchers have begun to explore another dimension of graphene: 3D graphene. It is actualized by formulating a 3D porous configuration, which mitigates the re-stacking of graphene sheets and enhances mass transport, thereby unlocking new possibilities for energy applications.