Zinc‐Tiered Synthesis of 3D Graphene for Monolithic Electrodes

A high‐surface‐area conductive cellular carbon monolith is highly desired as the optimal electrode for achieving high energy, power, and lifetime in electrochemical energy storage. 3D graphene can be regarded as a first‐ranking member of cellular carbons with the pore‐wall thickness down to mono/few‐atomic layers. Current 3D graphenes, derived from either gelation or pyrolysis routes, still suffer from low surface area, conductivity, stability, and/or yield, being subjected to methodological inadequacies including patchy assembly, wet processing, and weak controllability. Herein, a strategy of zinc‐assisted solid‐state pyrolysis to produce a superior 3D graphene is established. Zinc unprecedentedly impregnates and delaminates a solid (“nonhollow”) char into multiple membranes, which eliminates the morphological impurities ever‐present in the previous pyrolyses using solid‐state carbon precursors. Zinc also catalyzes the carbonization and graphitization, and its in situ thermal extraction and recycling enables the scaled‐up production. The created 3D graphene network consists integrally of morphologically and chemically pure graphene membranes. It possesses unrivaled surface area, outstanding stability, and conductivity both in air and electrolyte, exceeding preexisting 3D graphenes. The advanced 3D graphene thus equips a porous monolithic electrode with unparalleled energy density, power density, and lifetime in electric‐double‐layer capacitive devices.     

3D Graphene Fibers Grown by Thermal Chemical Vapor Deposition

3D assembly of graphene sheets (GSs) is important for preserving the merits of the single‐atomic‐layered structure. Simultaneously, vertical growth of GSs has long been a challenge for thermal chemical vapor deposition (CVD). Here, vertical growth of the GSs is achieved in a thermal CVD reactor and a novel 3D graphene structure, 3D graphene fibers (3DGFs), is developed. The 3DGFs are prepared by carbonizing electrospun polyacrylonitrile fibers in NH₃ and subsequently in situ growing the radially oriented GSs using thermal CVD. The GSs on the 3DGFs are densely arranged and interconnected with the edges fully exposed on the surface, resulting in high performances in multiple aspects such as electrical conductivity (3.4 × 10⁴–1.2 × 10⁵ S m^?1), electromagnetic shielding (60 932 dB cm² g^?1), and superhydrophobicity and superoleophilicity, which are far superior to the existing 3D graphene materials. With the extraordinary properties along with the easy scalability of the simple thermal CVD, the novel 3DGFs are highly promising for many applications such as high‐strength and conducting composites, flexible conductors, electromagnetic shielding, energy storage, catalysis, and separation and purification. Furthermore, this strategy can be widely used to grow the vertical GSs on many other substrates by thermal CVD.     

Vertically Formed Graphene Stripe for 3D Field‐Effect Transistor Applications

A 100‐nm wide, vertically formed graphene stripe (GS) is demonstrated for three‐dimensional (3D) electronic applications. The GS forms along the sidewall of a thin nickel film. It is possible to further scale down the GS width by engineering the deposited thickness of the atomic layer deposition (ALD) Ni film. Unlike a conventional GS or graphene nanoribbon (GNR), the vertically formed GS is made without a graphene transfer and etching process. The process integration of the proposed GS FETs resembles that of currently commercialized vertical NAND flash memory with a design rule of less than 20 nm, implying practical usage of this formed GS for 3D advanced FET applications.     

基于石墨烯森林电极的摩擦纳米发电机

本研究提出并制备了一种以石墨烯森林为电极的摩擦纳米发电机。利用等离子体增强化学气相沉积工艺制备了与其它墙形竖直薄片状的石墨烯形貌差异较大的石墨烯森林。此石墨烯森林具有低薄膜电阻((110±5) Ω/□)以及独特的离散“树状”结构, 有利于石墨烯森林与其他电极材料之间的接触和摩擦。根据石墨烯森林的形貌优势, 将聚酰亚胺膜和石墨烯森林膜作为电极组装摩擦纳米发电机, 其开路电压可达20 V, 短路电流可达0.75 μA。此外, 还讨论了基于石墨烯森林的摩擦纳米发电机的工作原理。最后, 利用此纳米发电机点亮了演示电路中三个不同颜色的LED, 证明了石墨烯森林在摩擦纳米发电机中的有效应用。     

3D Printed Mechanically Robust Graphene/CNT Electrodes for Highly Efficient Overall Water Splitting

3D printing of graphene electrodes with high mechanical strength has been a growing interest in the development of advanced energy, environment, and electronic systems, yet is extremely challenging. Herein, a 3D printed bioinspired electrode of graphene reinforced with 1D carbon nanotubes (CNTs) (3DP GC) with both high flexural strength and hierarchical porous structure is reported via a 3D printing strategy. Mechanics modeling reveals the critical role of the 1D CNTs in the enhanced flexural strength by increasing the friction and adhesion between the 2D graphene nanosheets. The 3DP GC electrodes hold distinct advantages: i) an intrinsically high flexural strength that enables their large-scale applications; and ii) a hierarchical porous structure that offers large surface area and interconnected channels, endowing fast mass and/or charge and ions transport rate, which is thus beneficial for acting as an ideal catalyst carrier. The 3DP GC electrode integrated with a NiFeP nanosheets array exhibits a voltage of 1.58 V at 30 mA cm⁻² as bifunctional electrode for water splitting, which is much better than most of the reported Ni-, Co-, and Fe-based bifunctional electrocatalysts. Importantly, this study paves the way for the practical applications of 3D printed graphene electrodes in many energy conversion/storage, environmental, and electronic systems where high flexural strength is preferred.     

High Volumetric Energy Density Asymmetric Supercapacitors Based on Well‐Balanced Graphene and Graphene‐MnO2 Electrodes with Densely Stacked Architectures

The well‐matched electrochemical parameters of positive and negative electrodes, such as specific capacitance, rate performance, and cycling stability, are important for obtaining high‐performance asymmetric supercapacitors. Herein, a facile and cost‐effective strategy is demonstrated for the fabrication of 3D densely stacked graphene (DSG) and graphene‐MnO₂ (G‐MnO₂) architectures as the electrode materials for asymmetric supercapacitors (ASCs) by using MnO₂‐intercalated graphite oxide (GO‐MnO₂) as the precursor. DSG has a stacked graphene structure with continuous ion transport network in‐between the sheets, resulting in a high volumetric capacitance of 366 F cm^–3, almost 2.5 times than that of reduced graphene oxide, as well as long cycle life (93% capacitance retention after 10 000 cycles). More importantly, almost similar electrochemical properties, such as specific capacitance, rate performance, and cycling stability, are obtained for DSG as the negative electrode and G‐MnO₂ as the positive electrode. As a result, the assembled ASC delivers both ultrahigh gravimetric and volumetric energy densities of 62.4 Wh kg^–1 and 54.4 Wh L^–1 (based on total volume of two electrodes) in 1 m Na₂SO₄ aqueous electrolyte, respectively, much higher than most of previously reported ASCs in aqueous electrolytes.     

3D Printing of Freestanding MXene Architectures for Current‐Collector‐Free Supercapacitors

Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1–3 nm) 2D Ti₃C₂T_x with large lateral size of about 8 µm possessing ideal viscoelastic properties are formulated for extrusion‐based 3D printing of freestanding, high specific surface area architectures to determine the viability of manufacturing energy storage devices. The 3D‐printed device achieves a high areal capacitance of 2.1 F cm^?2 at 1.7 mA cm^?2 and a gravimetric capacitance of 242.5 F g^?1 at 0.2 A g^?1 with a retention of above 90% capacitance for 10 000 cycles. It also exhibits a high energy density of 0.0244 mWh cm^?2 and a power density of 0.64 mW cm^?2 at 4.3 mA cm^?2. It is anticipated that the sustainable printing and design approach developed in this work can be applied to fabricate high‐performance bespoke multiscale and multidimensional architectures of functional and structural materials for integrated devices in various applications.