In-situ growth of CNTs on porous carbon fibers for solar-driven enhanced interfacial evaporation

Large accessible surface area, facile pore engineering, and high electrical conductivity are highly desirable properties of efficient electrode materials. Herein, porous carbon fibers with a graphitic carbon skeleton and amorphous carbon body are successfully synthesized from directly carbonized polyacrylonitrile (PAN)/FeCl3 electrospun fibers via in situ catalytic graphitization and subsequent chemical activation. Due to the graphitic carbon skeleton, which facilitates fast electron transfer, and porous carbon body, which gives a large specific surface area for charge accumulation and fast ion diffusion, optimal porous graphitic carbon fibers are developed that exhibit a fast‐charging electrochemical performance with a capacitance of 165 F g−1 at high current densities of 300 A g−1 in an alkaline electrolyte. These findings can prove to be beneficial for realizing a supercapacitor with rapid charging and discharging ability at high current densities.

As a specific morphology, the porous carbon fiber was prepared through carbonization of polyacrylonitrile/polymethyl methacrylate (PAN/PMMA) blend fiber with the PAN weight of 70%. The morphology and crystalline structure of the obtained porous carbon fibers were investigated by SEM, XRD, and Raman. The obtained porous carbon fiber produced at carbonization temperature of 1000-1400°C as well as the solid carbon fiber were cut into millimeter size and used as fillers to add to epoxy in order to make composite with the weight of 6%. The complex permittivity of these composites was measured using a network analyzer. The results reveal that the cross section of obtained carbon fiber from PAN/PMMA (70/30) is full of pores with size of 0.1-1um. The graphite crystalline degree becomes high with increasing the carbonization temperature. The composite filled by the porous carbon fiber shows better microwave absorption than that filled by the solid carbon fiber, the lowest reflection loss is-24.5dB and the band width with reflection loss below-10dB is 1.9GHz as the porous carbon fiber is the filler. Among three carbonization temperature: 1000°C, 1200°C, 1400°C, the porous carbon fiber prepared at 1200°C gives the best microwave absorbing performance.

Porous carbon fibers from gel-spun polyacrylonitrile and poly(methyl methacrylate)-block-poly(acrylonitrile)

Capacitive deionization (CDI) is energetically favorable for desalinating low-salinity water. The bottlenecks of current carbon-based CDI materials are their limited desalination capacities and time-consuming cycles, caused by insufficient ion-accessible surfaces and retarded electron/ion transport. Here, we demonstrate porous carbon fibers (PCFs) derived from microphase-separated poly(methyl methacrylate)-block-polyacrylonitrile (PMMA-b-PAN) as an effective CDI material. PCF has abundant and uniform mesopores that are interconnected with micropores. This hierarchical porous structure renders PCF a large ion-accessible surface area and a high desalination capacity. In addition, the continuous carbon fibers and interconnected porous network enable fast electron/ion transport, and hence a high desalination rate. PCF shows desalination capacity of 30 mgNaCl g-1 PCF and maximal time-average desalination rate of 38.0 mgNaCl g-1 PCF min-1, which are about 3 and 40 times, respectively, those of typical porous carbons. Our work underlines the promise of block copolymer-based PCF for mutually high-capacity and high-rate CDI.

Lithium-sulfur batteries (LSBs) are deemed to be among the most prospective next-generation advanced high-energy batteries. Advanced cathode materials fabricated from biological carbon are becoming more popular due to their unique properties. Inspired by the fibrous structure of bamboo, herein we put forward a smart strategy to convert bamboo sticks for barbecue into uniform bamboo carbon fibers (BCF) via a simple hydrothermal treatment proceeded in alkaline solution. Then NiCl2 is used to etch the fibers through a heat treatment to achieve Ni-embedded porous graphitic carbon fibers (PGCF/Ni) for LSBs. The designed PGCF/Ni/S electrode exhibits improved electrochemical performances including high initial capacity (1198 mAh g-1 at 0.2 C), prolonged cycling life (1030 mAh g-1 at 0.2 C after 200 cycles), and improved rate capability. The excellent properties are attributed to the synergistic effect of 3D porous graphitic carbon fibers with highly conductive Ni nanoparticles embedded.

Solar evaporation has emerged as an attractive technology to produce freshwater by utilizing renewable solar energy. However, it remains a huge challenge to develop efficient solar steam generators with good flexibility, low cost and remarkable salt resistance. Herein, we prepare flexible, robust solar membranes by filtration of porous carbon and commercial paper pulp fiber. The porous carbon with well-defined structures is prepared through controlled carbonization of biomass/waste plastics by eutectic salts. We prove the synergistic effect of porous carbon and paper pulp fiber in boosting solar evaporation performance. Firstly, the porous carbon displays a high light absorption, while the paper pulp fiber with good hydrophilicity effectively promotes the transport of water. Secondly, the combination between porous carbon and paper pulp fiber reduces the water vaporization enthalpy by 20%, which is important to significantly improve the evaporation performance. As a proof of concept, the porous carbon/paper pulp fiber membrane possesses a high evaporation rate of 1.8 kg m−2 h−1 under 1 kW m−2 irradiation. Thirdly, the good flexibility and mechanical property of paper pulp fiber enable the solar membrane to work well under extreme conditions (e.g., after 20 cycles of folding/stretching/recovery). Lastly, due to the super-hydrophilicity and superwetting, the hybrid membrane exhibits the exceptional salt resistance and long-term stability in continuous seawater desalination, e.g., for 50 h. Importantly, a large-scale solar desalination device for outdoor experiments is developed to produce freshwater. Consequently, this work provides a new insight into developing advanced flexible solar evaporators with superb performance in seawater desalination.

Adsorption energy engineering of nickel oxide hybrid nanosheets for high areal capacity flexible lithium-ion batteries

Porous carbon fiber with hollow structure and hydrophilic groups was successfully prepared from cotton. The structures and surface chemical properties of the porous carbon fiber were characterized by nitrogen adsorption isotherms, thermogravimetry, FTIR spectroscopy, and scanning electron microscopy. The morphologies of porous carbons prepared under different conditions were observed and compared. The resulting porous carbons had a microporous structure with a pore size distribution around 0.7-2.0 nm. The pyrolysis and decomposition of cotton to form a condensation cross-linked ring structure took place from 230 to 350 °C. Nitrogen-containing groups could be incorporated into the carbon matrix by urea decomposition during the carbonization process. The porous carbon contained more hydrophilic groups and its fiber structure was kept; the carbon yield was improved in the presence of KOH/urea. The porous carbon fiber showed high adsorption capacities of CO2 as a result of its surface hydrophilic groups and developed pore structure.

Utilizing porous polyacrylonitrile (PAN) fibers as the precursors, porous carbon fibers were obtained by cross-linking of precursor fibers with hydrazine hydrate and subsequent heat treatment. A nitrogen content of more than 14 wt % was achieved in the carbon fibers. The porous carbon fiber that was prepared at low concentration of hydrazine hydrate (5 wt %) showed an optimal BET surface area of 277.4 m2/g with micro-/meso-/macropores. The CO2 adsorbed amount of this porous carbon fiber was 101 mg/g at 25 °C under atmospheric pressure, which was 2.1 times that of the fiber without cross-linking with hydrazine hydrate. In the simulated flue gas environment (10% CO2/90% N2), the adsorption capacity of the above-mentioned porous fiber was 32 mg/g at 25 °C, which was 1.4 times that of the fiber without cross-linking. These CO2 adsorption results demonstrated that the nitrogen functionalities and porous structure of the porous carbon fiber played an equivalent important role in the adsorption of CO2. The porou...

Highly conductive, hierarchical porous ultra-fine carbon fibers derived from polyacrylonitrile/polymethylmethacrylate/needle coke as binder-free electrodes for high-performance supercapacitors

Porous microfibers by the electrospinning of amphiphilic graft copolymer solutions with multi-walled carbon nanotubes

Carbon is an abundant material with remarkable thermal, mechanical, physical, and chemical properties. Each allotrope has unique structures, properties, functionalities, and corresponding applications. Over the past few decades, various types of carbon materials such as graphene, carbon nanotubes, carbon quantum dots, and carbon fibers have been produced, finding applications in energy conversion and storage, water treatment, sensing, polymer composites, and biomedical fields. Among these carbon materials, porous carbons are highly interesting owing to their large surface areas and massive active sites to interact with molecules, ions, and other chemical species. The pore size and pore size distributions can be tunable (micro-, meso-, and macro-pores), providing chemical species with hierarchical structures to transport with low resistances. In this context, designing carbon precursors and preparing porous carbon with desired structures, properties, and functionalities are highly significant. Polymers are versatile carbon precursors. Designing the polymer precursors that facilitate the formation of well-controlled pores is an effective strategy to prepare porous carbons. In particular, porous carbon fibers (PCFs) in a fibrous format offer additional features of hierarchical porosity control, increased surface area, and fast ion transport. The most common approach to synthesizing PCFs is to use sacrificial agents (e.g., homopolymers of polystyrene (PS) and poly(methyl methacrylate) (PMMA), inorganic nanoparticles, and other additives) in a matrix of polyacrylonitrile (PAN) as the carbon fiber precursor. However, the nonuniform mixing of sacrificial agents in the PAN matrix results in PCFs with nonuniform pores and wide pore size distributions. Moreover, complete removal of the inorganic additives is challenging and sometimes requires the use of hazardous chemicals. Therefore, developing innovative methods for synthesizing PCFs is imperative to advance these engineering materials for emerging applications. In this Account, we summarize our efforts on the use of block copolymer precursors to prepare PCFs with tunable pore sizes and pore size distributions for a series of applications. First, we will introduce the synthesis methodologies for preparing PCFs. We have used reversible addition-fragmentation chain transfer (RAFT) polymerization to synthesize block copolymer precursors. Second, we will discuss the effects of preparation conditions on the properties of PCFs. The mechanical and electrical properties highly depend on the composition of the block copolymer, pyrolysis conditions, and humidity level during the fiber spinning process. Lastly, we will discuss the effects of controlled porosity on the surface area, electrical/ionic conductivity, and polymer-matrix interactions, which are crucial for applications including energy storage (e.g., batteries and supercapacitors), fiber-reinforced polymer composites, separation, and filtration.

Nitrogen-doped asphaltene-based porous carbon fibers as supercapacitor electrode material with high specific capacitance

Hierarchical Bi2O3 nanosheets and ZIF-8 derived porous nitrogen-doped carbon fibers as novel assembled nanocomposites for high-performance flexible supercapacitors

Design of free-standing porous carbon fibers anode with high-efficiency potassium-ion storage