Porous Carbon Aerogels Research Articles

Novel Hydrogel-Derived Bifunctional Oxygen Electrocatalyst for Rechargeable Air Cathodes.

The commercialization of Zn-air batteries has been impeded by the lack of low-cost, highly active, and durable catalysts that act independently for oxygen electrochemical reduction and evolution. Here, we demonstrate excellent performance of NiCo nanoparticles anchored on porous fibrous carbon aerogels (NiCo/PFC aerogels) as bifunctional catalysts toward the Zn-air battery. This material is designed and synthesized by a novel K2Ni(CN)4/K3Co(CN)6-chitosan hydrogel-derived method. The outstanding performance of NiCo/PFC aerogels is confirmed as a superior air-cathode catalyst for a rechargeable Zn-air battery. At a discharge-charge current density of 10 mA cm-2, the NiCo/PFC aerogels enable a Zn-air battery to cycle steadily up to 300 cycles for 600 h with only a small increase in the round-trip overpotential, notably outperforming the more costly Pt/C+IrO2 mixture catalysts (60 cycles for 120 h). With the simplicity of the synthetic method and the outstanding electrocatalytic performance, the NiCo/PFC aerogels are promising electrocatalysts for Zn-air batteries.

Self-assembly-template engineering nitrogen-doped carbon aerogels for high-rate supercapacitors

Three-dimensional (3D) interconnected porous nitrogen-doped carbon aerogels (CAs) have been successfully prepared with polyvinyl alcohol and nitrogen-containing N-phenylethanolamine as carbon and in-situ nitrogen sources, and boric acid as both crosslinking agent and 3D self-template. After drying, carbonization and KOH-activation treatment, the as-obtained CAs exhibit large specific surface area, hierarchically porous structure, heteroatom doping and superhydrophilicity. The optimal sample shows a high surface area up to 2016m2g−1 with a total pore volume of 1.179cm3g−1. The synergistic effect of the reasonably hierarchical porosity, high effective surface area utilization, superhydrophilicity, and heteroatom pseudocapacitance are in favor of high specific capacitance of 467Fg−1 in three-electrode system and considerable cycle performance of 85.7%, 90.9% retention over 10,000 cycles at 20Ag−1 and 30Ag−1. Moreover, the symmetric supercapacitor configuration delivers an energy density of 22.75Whkg−1 at power density of 262.5Wkg−1 and 7.6Whkg−1 at power density of 9572Wkg−1. Here, we pioneer an in-situ self-template approach for fabricating hierarchically porous aerogels with a potential application in supplying a peak power for hybrid electric vehicles, memory backup systems, cold-starting assistants and especially electrochromic devices as demonstrated in our case.

Hierarchical Porous Carbon Aerogels with VN Modification as Cathode Matrix for High Performance Lithium-Sulfur Batteries

The hierarchical porous carbon aerogel (CA) with vanadium nitride (VN) was effectively prepared via a facile in-situ method with organic acid catalyzing and non-supercritical drying. The surface morphology and structure of the VN/CA (VCA) composites, and the electrochemical performance of these composites based sulfur cathodes were investigated systematically. This mono-dispersed microsphere composite presents hierarchical pore and uniform dispersion of vanadium nitride, and effectively immobilizes the polysulfides due to the synergistic effects between the VN and CA matrix. Moreover, the VN on the CA has catalytic effect on the electrode reaction, displaying high discharge voltages. In particular, a higher initial discharge capacity of 1279mAhg−1 can be obtained at 0.2C, and it retains 1001mAhg−1 after 100 cycles. Even at a higher rate of 1C, the capacity still delivers 802mAhg−1 after 100 cycles.

Biomass-derived dendritic-like porous carbon aerogels for supercapacitors

Three-dimensional (3D) dendritic-like hierarchical porous carbon areogels (PCAs) have been fabricated via a simple and efficient solvent exchange method followed by an activation process. The natural and renewable biomass material, leonardite fulvic acid (LFA) is used as the carbon source. The hierarchical porous structures are composed of numerous nanospheres with interconnected 3D carbon architectures which are in favor of enhancing the electrical conductivity and facilitating ion transport by providing small resistances and short diffusion pathways. The resultant PCAs are advantageous as electrodes for electrochemical energy storage. For example, the PCAs2 sample exhibits a superior high specific capacitance of 368Fg−1 at a current density of 0.05Ag−1 in 6M KOH electrolyte, which can still remain 228Fg−1 when the current density increases to 100Ag−1. The sample also has outstanding cycling stability with capacitance retention of 98.4% after 10,000 cycles. Remarkably, it is shown that the PCAs2 sample exhibits outstanding electrochemical performance in an organic electrolyte as well. It has an energy density of 43.50Whkg−1 at a power density of 33.85Wkg−1 and still maintains 23.25Whkg−1 at a power density of 5.89kWkg−1. This suggests that the 3D hierarchical PCAs should be a competitive and promising supercapacitor electrode material.

In Situ Growth of Fe2O3 Nanoparticles on Highly Porous Graphene/Polyimide‐Based Carbon Aerogel Nanocomposites for Effectively Selective Detection of Dopamine

It is very important to develop a simple, efficient, and scaleable method for detection of dopamine (DA) with high sensitivity and selectivity to diagnose some serious neurological diseases. Herein, electro‐catalysts for detection of DA are simply prepared based on Fe2O3 nanoparticles (NPs) decorated on highly porous carbon aerogels (CAs), which are derived from KOH activated graphene‐polyimide aerogels. In the hierarchical nanocomposites (NCs), CAs provide large specific surface area, abundant mesopores, and macropores, and many sites for in situ growth of Fe2O3 NPs, thus effectively preventing the aggregation of Fe2O3 NPs. Moreover, CAs with 3D interconnected porous structures are able to shorten the charge transfer pathways through the intimate interaction between CAs and Fe2O3 NPs. Therefore, when applied as electro‐catalysts for detection of DA, the optimized NC exhibits rapid amperometric response and a low detection limit of 0.109 × 10−6 m (S/N = 3), with a wide linear concentration range from 5 to 500 × 10−6 m. In addition, the oxidation peak of DA can be readily distinguished from the interference of uric acid and ascorbic acid. Therefore, the highly porous CAs derived from KOH activated graphene‐polyimide aerogels are excellent substrates for in situ growth of Fe2O3 NPs, exhibiting high electrocatalytic activity for DA detection.

Sustainable hierarchical porous carbon aerogel from cellulose for high-performance supercapacitor and CO2 capture

Fabrication of cost-effective and eco-friendly hierarchical porous carbons from the most abundant and widely available biomass cellulose represents a critical and sustainable way to solve the crisis of fossil resources. In this work, a hierarchical porous carbon aerogel with desirable macropores, mesopores, and micropores was obtained via dissolving-gelling and subsequent carbonizing-activating process. The CO2 activated carbon aerogel had a high specific surface area of 1364m2/g and a high specific capacitance of 328Fg−1 (0.5Ag−1, 1.0M H2SO4) as well as an outstanding cycling stability with 96% of the capacitance retention after 5000 charge/discharge cycles. More importantly, for the first time, we demonstrated that the cellulose-derived hierarchical porous carbon aerogel showed a good CO2 adsorption capacity of 3.42mmol/g (at 1atm and 298K), which indicates the possibility of using this carbon aerogel for CO2 capture.

Liquid-phase methylene blue adsorption of a novel hierarchical porous carbon aerogel

A novel hierarchical porous carbon aerogel (HPCA) was fabricated and its nanostructure was investigated by SEM and N2 adsorption. The methylene blue (MB) adsorption properties of the HPCA in water were studied. It is found that the HPCA has a hierarchical micro-, meso- and macropore structure. Its BET and micropore surface areas are 512 and 359 m2·g-1, respectively. The MB adsorption capacity increases with adsorption time, speed of stirring, temperature and pH value, and the MB removal efficiency can reach 99.8% under optimized conditions. The adsorption kinetics can be well described by a pseudo-second-order equation and the adsorption is controlled by liquid film diffusion in the initial stages and intraparticle diffusion later.

Synergistic effects of des tabilization, catalysis and nanoconfinement on dehydrogenation of LiBH4

In this report, Ni and TiO2 are successfully embedded into porous carbon aerogel (CA) (donated as NiTiO2@CA). Meanwhile, the synergistic effect of Ni, TiO2 and CA on the dehydrogenation properties of LiBH4 is systematically studied. Ni@CA, TiO2@CA and CA are also investigated for comparisons. Compared to other three materials, NiTiO2@CA exhibits better performance when used as a carrier to support LiBH4. More than 6.75 wt% H2 is released from LiBH4NiTiO2@CA system in nearly 120 min at 350 °C, exhibiting a higher dehydrogenation capacity than that of LiBH4Ni@CA (3.15 wt %), LiBH4TiO2@CA (5.15 wt%) and LiBH4-CA (2.05 wt %), respectively. Furthermore, the apparent energy (Ea) calculated with Kissinger method is 118.8 kJ/mol, much lower than that of pure LiBH4. Dehydrogenation performance of LiBH4NiTiO2@CA may be due to the synergetic effect of destabilization of TiO2, catalysis of Ni, as well as the nanoconfinement of CA.

3D hierarchical porous N-doped carbon aerogel from renewable cellulose: an attractive carbon for high-performance supercapacitor electrodes and CO2 adsorption

3D hierarchical porous N-doped carbon aerogel from renewable cellulose: an attractive carbon for high-performance supercapacitor electrode and CO2 adsorption.

A facile biomass based approach towards hierarchically porous nitrogen-doped carbon aerogels

Nitrogen-doped carbon aerogels with hierarchically porous architectures (NHCAs) are prepared via the hydrothermal treatment of cantaloupe and the following activation with potassium hydroxide.

1D Ni-Co oxide and sulfide nanoarray/carbon aerogel hybrid nanostructures for asymmetric supercapacitors with high energy density and excellent cycling stability.

The fabrication of supercapacitor electrodes with high energy density and excellent cycling stability is still a great challenge. A carbon aerogel, possessing a hierarchical porous structure, high specific surface area and electrical conductivity, is an ideal backbone to support transition metal oxides and bring hope to prepare electrodes with high energy density and excellent cycling stability. Therefore, NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid supercapacitor electrode materials were synthesized by assembling Ni-Co precursor needle arrays on the surface of the channel walls of hierarchical porous carbon aerogels derived from chitosan in this study. The 1D nanostructures grow on the channel surface of the carbon aerogel vertically and tightly, contributing to the enhanced electrochemical performance with ultrahigh energy density. The energy density of NiCo2S4 nanotube array/carbon aerogel and NiCo2O4 nanoneedle array/carbon aerogel hybrid asymmetric supercapacitors can reach up to 55.3 Wh kg-1 and 47.5 Wh kg-1 at a power density of 400 W kg-1, respectively. These asymmetric devices also displayed excellent cycling stability with a capacitance retention of about 96.6% and 92% over 5000 cycles.

Nanocellulose-derived highly porous carbon aerogels for supercapacitors

High-surface-area carbon aerogels are synthesized by pyrolysis of nanocellulose aerogels that are prepared by dissolving of cellulose microcrystalline in NaOH aqueous solutions followed by gelation, regeneration and freeze drying or supercritical CO2 drying. The obtained carbon aerogels are further treated via a CO2 activation process. The result shows that the nanocellulose aerogels dried by supercritical CO2 exhibit a high specific surface area (299 m2/g) and the obtained carbon aerogels preserve the interconnected 3D nanostructure and have a high specific surface area of 892 m2/g and a high pore volume of 1.80 cm3/g, which increase to 1873 m2/g and 2.65 cm3/g respectively after CO2 activation. The highly porous and interconnected nanostructure provides efficient migration of electrolyte ions and electrons, which makes the resultant activated carbon aerogels exhibit excellent electrochemical performance for supercapacitors. The specific capacitances reach 302 and 205 F/g at a current density of 0.5 and 20 A/g respectively within a potential window of −1.0 to 0 V in 6 M KOH solution. The capacitance retains 92% after 4000 cycles of charge/discharge, implying a good cycling stability.

Diffusion of molecular hydrogen in carbon aerogel

The diffusion of hydrogen molecules adsorbed in a highly porous carbon aerogel has been studied with quasi-elastic neutron scattering. Hydrogen diffusion in this carbon substrate followed an activated jump process with a single activation barrier. The temperature dependence of the diffusion rate agrees well with previous results from activated carbons and other highly porous carbons. The carbon aerogel sample showed a strongly enhanced conversion between the ortho- and para-hydrogen spin states. The ortho-para conversion process, however, was inhibited for a fraction of the hydrogen molecules. This inhibition process is attributed to a rotational confinement of the hydrogen molecules at the nanometre scale.

In-Situ Growth of Few-Layered MoS2 Nanosheets on Highly Porous Carbon Aerogel as Advanced Electrocatalysts for Hydrogen Evolution Reaction

Molybdenum disulfide-based hybrids, acting as cost-effective and acid-stable electrocatalysts for hydrogen evolution reaction (HER), have been developed fast for providing sustainable hydrogen energy in recent years. Herein, few-layered molybdenum disulfide (MoS2) nanosheets/carbon aerogel (CA) hybrids were successfully obtained through the combination of sol–gel process, aging, freeze-drying, high temperature carbonization, and solvothermal reaction. CA with highly continuous porosity and high specific surface area is used as a matrix material for construction of hierarchical MoS2/CA hybrids where few-layered MoS2 nanosheets are uniformly covered on a CA surface. In this heterostructured system, CAs not only provide three-dimensional (3D) conductive pathway for fast transportation of electrons and ions, but also offer highly active regions for the growth of MoS2, greatly preventing the aggregation of MoS2 nanosheets. Due to the rationally designed hybrids with 3D porous nanostructures, the as-prepared Mo...

Soy protein directed hydrothermal synthesis of porous carbon aerogels for electrocatalytic oxygen reduction

Herein we presented, for the first time, facile fabrication of nitrogen doped (0.5–4 wt.%) porous carbon aerogels using biomass derivatives (i.e. glucose or cellulose) as the carbon precursor and soy protein as both the nitrogen precursor and the structure directing agent. Through post thermal treatment to improve the electrical conductivity and porosity, the obtained materials showed excellent oxygen reduction reaction (ORR) catalytic activity. The electrochemical performance was further enhanced after platinum impregnation, combining the advantages of small over-potential from platinum catalyst and high limiting current density from the carbon substrate. Therefore, we demonstrated here not only a novel and low cost hydrothermal synthesis route to achieve high-performing metal-free ORR catalyst or carbon substrate for additional metal catalyst, but also a general principle on how to develop metal nanoparticles/carbon hybrids for ORR.

Green and facile fabrication of carbon aerogels from cellulose-based waste newspaper for solving organic pollution

Carbon-based aerogel fabricated from waste biomass is a potential absorbent material for solving organic pollution. Herein, the lightweight, hydrophobic and porous carbon aerogels (CAs) have been synthesized through freezing–drying and post-pyrolysis by using waste newspaper as the only raw materials. The as-prepared CAs exhibited a low density of 18.5mgcm−3 and excellent hydrophobicity with a water contact angle of 132° and selective absorption for organic reagents. The absorption capacity of CA for organic compounds can be 29–51 times its own weight. Moreover, three methods (e.g., squeezing, combustion, and distillation) can be employed to recycle CA and harvest organic pollutants. Combined with waste biomass as raw materials, green and facile fabrication process, excellent hydrophobicity and oleophilicity, CA used as an absorbent material has great potential in application of organic pollutant solvents absorption and environmental protection.

Biomass-Derived Heteroatom-Doped Carbon Aerogels from a Salt Melt Sol-Gel Synthesis and their Performance in Li-S Batteries.

An ionothermal sol-gel strategy to synthesize hierarchically porous carbon aerogels doped with different heteroatoms is presented by using biomass precursors in a scalable process. Morphologically similar but chemically different materials are used to study the influence of heteroatoms in Li-S batteries. The materials show capacities as high as 1290 mAh g(-1) in the first cycle using 50 wt % S loading. Heteroatom doping reduces the capacity fading and the polarization throughout cycling. Zeta potential measurements reveal positive surface charges for heteroatom-doped carbons and indicate attractive interactions with polysulfides causing reduced fading. A polysulfide-selective sorption study reveals strongly different adsorption behavior depending on the carbon's chemical composition. Interestingly, the polysulfide fraction is also crucial. The results indicate that improved adsorption of long-chain polysulfides to doped carbons is related to improved capacity retention.

Investigation of the effect of rice husk derived Si/SiC on the morphology and thermal stability of carbon composite aerogels

Highly porous carbon aerogels were prepared by pyrolyzing the novolac–silica aerogels. The silica phase was extracted from rice husk ash (RHA). The polymer aerogel was synthesized via the novel method of sol–gel polymerization in solvent vapor-saturated atmosphere. This method removes the need for supercritical drying and reduces the shrinkage of aerogels during drying stage and also has much lower process time compared to the conventional sol–gel method. In the next step, polymer composite aerogels become carbon/silica and carbon/silica/silicon carbide composites in pyrolysis (800 °C) and carbothermal reduction (1500 °C) stages, respectively. The characterization of the prepared composite aerogels was performed by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) analyses, respectively. Thermal and mechanical properties of the samples were investigated by differential scanning calorimetry (DSC) and compressive strength analysis. The resultant composite aerogels show a nanostructure with high porosity (above 82%) and low density (below 0.3 g cm− 3). Si mapping images showed the good distribution of silica phase throughout the carbon matrix. Also the rate of oxidation for carbon composites decreased by silica incorporation and oxidation temperature increased about 20% by adding RHA silica. Compressive strength of composite samples increased about 25% by increasing RHA silica phase content.

Graphene-based nitrogen self-doped hierarchical porous carbon aerogels derived from chitosan for high performance supercapacitors

Graphene-based nitrogen self-doped hierarchical porous carbon aerogels were synthesized for supercapacitor electrode application by using chitosan as a raw material through a carefully controlled aerogel formation–carbonization–activation process. The as-synthesized N-doped graphene-based carbon aerogels contained both macropores and mesopores from the aerogel preparation and carbonization process, and micropores from the chemical activation, confirmed by TEM, SEM, BET, etc. Because chitosan is a nitrogen-containing renewable biopolymer, the carbon aerogel derived from chitosan in this work was N-self-doped. The carbonized carbon aerogel was composed of a graphene framework and amorphous carbon, and the ratio between these two components was controlled by the activation temperature. With an increase in activation temperature, the amorphous carbon was etched away gradually, and a stable graphene portion remained to form a framework. Accordingly, the performance of the graphene-based carbon aerogel as a supercapacitor varied with increasing activation temperature. Electrochemical investigation measurements showed that the N-doped graphene-based hierarchical porous carbon aerogel represents a good electrode candidate for construction of a solid symmetric supercapacitor, which displays a high specific capacitance of about 197Fg−1 at a current density of 0.2Ag−1. In addition, the solid state supercapacitor displayed excellent cyclability with a capacitance retention of about 92.1% over 10,000 cycles. The excellent energy storage ability of the chitosan-derived hierarchical graphene-based carbon aerogels is ascribed to the high conductivity of the graphene framework with nitrogen doping and the high storage ability of amorphous carbon with variable pore size and distribution.

β-FeOOH decorated highly porous carbon aerogels composite as a cathode material for rechargeable Li–O2batteries

A β-FeOOH–carbon aerogels composite was applied in Li–O2batteries as an O2electrode material. It exhibits an excellent electrochemical performance and electrocatalytic activity.