The performance of pseudocapacitive electrodes at fast charging rates are typically limited by the slow kinetics of Faradaic reactions and sluggish ion diffusion in the bulk structure. This is ...particularly problematic for thick electrodes and electrodes highly loaded with active materials. Here, a surface‐functionalized 3D‐printed graphene aerogel (SF‐3D GA) is presented that achieves not only a benchmark areal capacitance of 2195 mF cm−2 at a high current density of 100 mA cm−2 but also an ultrahigh intrinsic capacitance of 309.1 µF cm−2 even at a high mass loading of 12.8 mg cm−2. Importantly, the kinetic analysis reveals that the capacitance of SF‐3D GA electrode is primarily (93.3%) contributed from fast kinetic processes. This is because the 3D‐printed electrode has an open structure that ensures excellent coverage of functional groups on carbon surface and facilitates the ion accessibility of these surface functional groups even at high current densities and large mass loading/electrode thickness. An asymmetric device assembled with SF‐3D GA as anode and 3D‐printed GA decorated with MnO2 as cathode achieves a remarkable energy density of 0.65 mWh cm−2 at an ultrahigh power density of 164.5 mW cm−2, outperforming carbon‐based supercapacitors operated at the same power density.
A surface‐functionalized 3D‐printed graphene aerogel achieves a benchmark areal capacitance of 2195 mF cm−2 and an ultrahigh intrinsic capacitance of 309.1 µF cm−2. This work demonstrates the essential role of 3D‐printed porous structure for simultaneously boosting the kinetics and intrinsic capacitance of thick carbon electrodes with high mass loadings.
Graphene is a two-dimensional material that offers a unique combination of low density, exceptional mechanical properties, large surface area and excellent electrical conductivity. Recent progress ...has produced bulk 3D assemblies of graphene, such as graphene aerogels, but they possess purely stochastic porous networks, which limit their performance compared with the potential of an engineered architecture. Here we report the fabrication of periodic graphene aerogel microlattices, possessing an engineered architecture via a 3D printing technique known as direct ink writing. The 3D printed graphene aerogels are lightweight, highly conductive and exhibit supercompressibility (up to 90% compressive strain). Moreover, the Young's moduli of the 3D printed graphene aerogels show an order of magnitude improvement over bulk graphene materials with comparable geometric density and possess large surface areas. Adapting the 3D printing technique to graphene aerogels realizes the possibility of fabricating a myriad of complex aerogel architectures for a broad range of applications.
Maintaining fast charging capability at low temperatures represents a significant challenge for supercapacitors. The performance of conventional porous carbon electrodes often deteriorates quickly ...with the decrease of temperature due to sluggish ion and charge transport. Here we fabricate a 3D-printed multiscale porous carbon aerogel (3D-MCA) via a unique combination of chemical methods and the direct ink writing technique. 3D-MCA has an open porous structure with a large surface area of ∼1750 m2 g–1. At −70 °C, the symmetric device achieves outstanding capacitance of 148.6 F g–1 at 5 mV s–1. Significantly, it retains a capacitance of 71.4 F g–1 at a high scan rate of 200 mV s–1, which is 6.5 times higher than the non-3D printed MCA. These values rank among the best results reported for low temperature supercapacitors. These impressive results highlight the essential role of open porous structures for preserving capacitive performance at ultralow temperatures.
We describe the synthesis and characterization of monolithic, ultralow density WS2 and MoS2 aerogels, as well as a high surface area MoS2/graphene hybrid aerogel. The monolithic WS2 and MoS2 aerogels ...are prepared via thermal decomposition of freeze-dried ammonium thio-molybdate (ATM) and ammonium thio-tungstate (ATT) solutions, respectively. The densities of the pure dichalcogenide aerogels represent 0.4% and 0.5% of full density MoS2 and WS2, respectively, and can be tailored by simply changing the initial ATM or ATT concentrations. Similar processing in the presence of the graphene aerogel results in a hybrid structure with MoS2 sheets conformally coating the graphene scaffold. This layered motif produces a ∼50 wt % MoS2 aerogel with BET surface area of ∼700 m2/g and an electrical conductivity of 112 S/m. The MoS2/graphene aerogel shows promising results as a hydrogen evolution reaction catalyst with low onset potential (∼100 mV) and high current density (100 mA/cm2 at 260 mV).
Graphene is an atomically thin, two-dimensional (2D) carbon material that offers a unique combination of low density, exceptional mechanical properties, thermal stability, large surface area, and ...excellent electrical conductivity. Recent progress has resulted in macro-assemblies of graphene, such as bulk graphene aerogels for a variety of applications. However, these three-dimensional (3D) graphenes exhibit physicochemical property attenuation compared to their 2D building blocks because of one-fold composition and tortuous, stochastic porous networks. These limitations can be offset by developing a graphene composite material with an engineered porous architecture. Here, we report the fabrication of 3D periodic graphene composite aerogel microlattices for supercapacitor applications, via a 3D printing technique known as direct-ink writing. The key factor in developing these novel aerogels is creating an extrudable graphene oxide-based composite ink and modifying the 3D printing method to accommodate aerogel processing. The 3D-printed graphene composite aerogel (3D-GCA) electrodes are lightweight, highly conductive, and exhibit excellent electrochemical properties. In particular, the supercapacitors using these 3D-GCA electrodes with thicknesses on the order of millimeters display exceptional capacitive retention (ca. 90% from 0.5 to 10 A·g–1) and power densities (>4 kW·kg–1) that equal or exceed those of reported devices made with electrodes 10–100 times thinner. This work provides an example of how 3D-printed materials, such as graphene aerogels, can significantly expand the design space for fabricating high-performance and fully integrable energy storage devices optimized for a broad range of applications.
Aerogels are used in a broad range of scientific and industrial applications due to their large surface areas, ultrafine pore sizes, and extremely low densities. Recently, a large number of reports ...have described graphene aerogels based on the reduction of graphene oxide (GO). Though these GO-based aerogels represent a considerable advance relative to traditional carbon aerogels, they remain significantly inferior to individual graphene sheets due to their poor crystallinity. Here, we report a straightforward method to synthesize highly crystalline GO-based graphene aerogels via high-temperature processing common in commercial graphite production. The crystallization of the graphene aerogels versus annealing temperature is characterized using Raman and X-ray absorption spectroscopy, X-ray diffraction, and electron microscopy. Nitrogen porosimetry shows that the highly crystalline graphene macrostructure maintains a high surface area and ultrafine pore size. Because of their enhanced crystallinity, these graphene aerogels exhibit a ∼200 °C improvement in oxidation temperature and an order of magnitude increase in electrical conductivity.
A MoS2/graphene hybrid aerogel synthesized with two‐dimensional MoS2 sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO2 detection. The ...combination of graphene and MoS2 leads to improved sensing properties with the graphene scaffold providing high specific surface area and high electrical and thermal conductivity and the single to few‐layer MoS2 sheets providing high sensitivity and selectivity to NO2. The hybrid aerogel is integrated onto a low‐power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO2. By heating the material to 200 °C, the response and recovery times to reach 90% of the final signal decrease to <1 min, while retaining the low detection limit. The MoS2/graphene hybrid also shows good selectivity for NO2 against H2 and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO2 sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.
Hybrid aerogels made from layered 2D materials can be tuned for high performance. Here, a high surface area graphene scaffold is coated with few‐layer MoS2 sheets to give a hybrid aerogel with good electrical and thermal conductivity. When used for NO2 gas detection, the material is ultrasensitive and selective with fast response and recovery time (<1 min).
Carbon aerogels (CAs) are a unique class of high surface area materials derived by sol–gel chemistry. Their high mass-specific surface area and electrical conductivity, environmental compatibility, ...and chemical inertness make them very promising materials for many applications, such as energy storage, catalysis, sorbents, and desalination. Since the first CAs were made via pyrolysis of resorcinol–formaldehyde (RF)-based organic aerogels in the late 1980s, the field has really grown. Recently, in addition to RF-derived amorphous CAs, several other carbon allotropes have been realized in aerogel form: carbon nanotubes (CNTs), graphene, graphite, and diamond. Furthermore, the popularity of graphene aerogels has inspired research into aerogels made of a host of graphene analog materials (e.g., boron nitride, transition metal dichalcogenides, etc.), with potential for an even wider array of applications. Finally, the development of three-dimensional-printed aerogels provides the potential for CAs to have an even broader impact on energy-related technologies. Here, we will present recent work covering the novel synthesis of RF-derived, CNT, graphene, graphite, diamond, and graphene analog aerogels.
We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are ...prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol−gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm3. In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets. These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude (∼1 × 102 S/m) compared to graphene assemblies with physical cross-links alone (∼5 × 10−1 S/m). The graphene aerogels also possess large surface areas (584 m2/g) and pore volumes (2.96 cm3/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications.
Alkaline water electrolysis at high current densities is plagued by gas bubble generation and trapping in stochastic porous electrodes (e.g., Ni foams), which causes a significant reduction in the ...number of electrolyte accessible catalyst active sites. Here, 3D printed Ni (3DPNi) electrodes with highly controlled, periodic structures are reported that suppress gas bubble coalescence, jamming, and trapping and, hence, result in rapid bubble release. The 3DPNi electrodes decorated with carbon‐doped NiO achieve a high current density of 1000 mA cm−2 in 1.0 m KOH electrolyte at hydrogen evolution reaction and oxygen evolution reaction overpotentials of 245 and 425 mV, respectively. This work demonstrates a new approach to the deterministic design of 3D electrodes to facilitate rapid bubble transport and release to enhance the total electrode catalytic activity at commercially relevant current densities.
This work demonstrates a new approach to the deterministic design of 3D electrodes to minimize the deleterious effects of gas bubbles by carefully engineering porous highways and transport networks that facilitate rapid bubble transport and release to enhance the total electrode catalytic activity at commercially relevant current densities.
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