Project description:Multifunctional structural materials are capable of reducing system level mass and increasing efficiency in load-carrying structures. Materials that are capable of harvesting energy from the surrounding environment are advantageous for autonomous electrically powered systems. However, most energy harvesting materials are non-structural and add parasitic mass, reducing structural efficiency. Here, we show a structural energy harvesting composite material consisting of two carbon fiber (CF) layers embedded in a structural battery electrolyte (SBE) with a longitudinal modulus of 100 GPa─almost on par with commercial CF pre-pregs. Energy is harvested through mechanical deformations using the piezo-electrochemical transducer (PECT) effect in lithiated CFs. The PECT effect creates a voltage difference between the two CF layers, driving a current when deformed. A specific power output of 18 nW/g is achieved. The PECT effect in the lithiated CFs is observed in tension and compression and can be used for strain sensing, enabling structural health monitoring with low added mass. The same material has previously been shown capable of shape morphing. The two additional functionalities presented here result in a material capable of four functions, further demonstrating the diverse possibilities for CF/SBE composites in multifunctional applications in the future.
Project description:We present a method to modify carbon-fiber microelectrodes (CFME) with porous carbon nanofibers (PCFs) to improve detection and to investigate the impact of porous geometry for dopamine detection with fast-scan cyclic voltammetry (FSCV). PCFs were fabricated by electrospinning, carbonizing, and pyrolyzing poly(acrylonitrile)-b-poly(methyl methacrylate) (PAN-b-PMMA) block copolymer nanofiber frameworks. Commonly, porous nanofibers are used for energy storage applications, but we present an application of these materials for biosensing which has not been previously studied. This modification impacted the topology and enhanced redox cycling at the surface. PCF modifications increased the oxidative current for dopamine 2.0 ± 0.1-fold (n = 33) with significant increases in detection sensitivity. PCF are known to have more edge plane sites which we speculate lead to the two-fold increase in electroactive surface area. Capacitive current changes were negligible providing evidence that improvements in detection are due to faradaic processes at the electrode. The ΔEp for dopamine decreased significantly at modified CFMEs. Only a 2.2 ± 2.2 % change in dopamine current was observed after repeated measurements and only 10.5 ± 2.8% after 4 hours demonstrating the stability of the modification over time. We show significant improvements in norepinephrine, ascorbic acid, adenosine, serotonin, and hydrogen peroxide detection. Lastly, we demonstrate that the modified electrodes can detect endogenous, unstimulated release of dopamine in living slices of rat striatum. Overall, we provide evidence that porous nanostructures significantly improve neurochemical detection with FSCV and echo the necessity for investigating the extent to which geometry impacts electrochemical detection.
Project description:The nontemplating preparation of porous carbon materials by using specially designed polymer precursors for supercapacitor is attracting considerable research attention because of the more controllable frame structure and easier processes than templating methods. Herein, a deliberately designed cross-linking polyphosphamide resin with defined N and P structure is synthesized and then carbonized to obtain porous carbon material. The as-obtained porous carbon material has a specific surface area of 2,620 m2 g-1, high porosity of 1.49 cm3 g-1, and well-distributed micro/mesoporous carbon structure. Different from activation by post-added NH4H2PO4, the confined N and P in the polymer frame are confirmed to play an important role in pore structure development by forming in situ highly dispersed NH4H2PO4 during carbonization. When evaluated as the electrode material for supercapacitors, the polyphosphamide-resin-based porous carbon material demonstrates excellent capacitance (440 F g-1 under 0.5 A g-1) and high stability (retention of 93% over 10,000 cycles).
Project description:The intensified pursuit for lightweight solutions in the commercial vehicle industry increases the demand for method development of more advanced lightweight materials such as Carbon-Fiber-Reinforced Composites (CFRP). The behavior of these anisotropic materials is challenging to understand and manufacturing defects could dramatically change the mechanical properties. Voids are one of the most common manufacturing defects; they can affect mechanical properties and work as initiation sites for damage. It is essential to know the micromechanical composition of the material to understand the material behavior. Void characterization is commonly conducted using optical microscopy, which is a reliable technique. In the current study, an approach based on optical microscopy, statistically characterizing a CFRP laminate with regard to porosity, is proposed. A neural network is implemented to efficiently segment micrographs and label the constituents: void, matrix, and fiber. A neural network minimizes the manual labor automating the process and shows great potential to be implemented in repetitive tasks in a design process to save time. The constituent fractions are determined and they show that constituent characterization can be performed with high accuracy for a very low number of training images. The extracted data are statistically analyzed. If significant differences are found, they can reveal and explain differences in the material behavior. The global and local void fraction show significant differences for the material used in this study and are good candidates to explain differences in material behavior.
Project description:We demonstrate a cross-linked, 3D conductive network structure, porous silicon@carbon nanofiber (P-Si@CNF) anode by magnesium thermal reduction (MR) and the electrospinning methods. The P-Si thermally reduced from silica (SiO2) preserved the monodisperse spheric morphology which can effectively achieve good dispersion in the carbon matrix. The mesoporous structure of P-Si and internal nanopores can effectively relieve the volume expansion to ensure the structure integrity, and its high specific surface area enhances the multi-position electrical contact with the carbon material to improve the conductivity. Additionally, the electrospun CNFs exhibited 3D conductive frameworks that provide pathways for rapid electron/ion diffusion. Through the structural design, key basic scientific problems such as electron/ion transport and the process of lithiation/delithiation can be solved to enhance the cyclic stability. As expected, the P-Si@CNFs showed a high capacity of 907.3 mAh g-1 after 100 cycles at a current density of 100 mA g-1 and excellent cycling performance, with 625.6 mAh g-1 maintained even after 300 cycles. This work develops an alternative approach to solve the key problem of Si nanoparticles' uneven dispersion in a carbon matrix.
Project description:Electrospinning offers a powerful route for building one-dimensional (1D) micro/nanostructures, but a common requirement for toxic or corrosive organic solvents during the preparation of precursor solution has limited their large scale synthesis and broad applications. Here we report a facile and low-cost way to prepare 1D porous carbon microfibers by using an electrospun fiber-like natural product, i.e., silk cocoon, as precursor. We surprisingly found that by utilizing a simple carbonization treatment, the cocoon microfiber can be directly transformed into 1D carbon microfiber of ca. 6 μm diameter with a unique three-dimensional porous network structure composed of interconnected carbon nanoparticles of 10~40 nm diameter. We further showed that the as-prepared carbon product presents superior electrochemical performance as binder-free electrodes of supercapacitors and good adsorption property toward organic vapor.
Project description:Novel hierarchical porous carbon materials (HPCs) were fabricated via a reactive template-induced in situ hypercrosslinking procedure. The effects of carbonization conditions on the microstructure and morphology of HPCs were investigated, and the adsorption of methylene blue (MB) on HPCs was explored. The as-prepared HPCs has a hierarchical micro-, meso- and macropore structure, which results from the overlap of hollow nanospheres possessing microporous shells and macroporous cavities. The carbonization temperature, carbonization time and carbonization heating rate played important roles in tailoring the nanostructures of HPCs. The BET specific surface area and micropore specific surface area can reach 2388 m2 g-1 and 1892 m2 g-1, respectively. Benefitting from the well-developed pore structure, the MB removal efficiency can exceed 99% under optimized conditions. The adsorption kinetics and thermodynamics can be well described by a pseudo-second-order model and Langmuir model, respectively. Furthermore, such adsorption was characterized by a spontaneous endothermic process.
Project description:We have created a new architected material, which is both highly deformable and ultra-resistant to dynamic point loads. The bio-inspired metallic cellular structure (with an internal grid of large ceramic segments) is non-cuttable by an angle grinder and a power drill, and it has only 15% steel density. Our architecture derives its extreme hardness from the local resonance between the embedded ceramics in a flexible cellular matrix and the attacking tool, which produces high-frequency vibrations at the interface. The incomplete consolidation of the ceramic grains during the manufacturing also promoted fragmentation of the ceramic spheres into micron-size particulate matter, which provided an abrasive interface with increasing resistance at higher loading rates. The contrast between the ceramic segments and cellular material was also effective against a waterjet cutter because the convex geometry of the ceramic spheres widened the waterjet and reduced its velocity by two orders of magnitude. Shifting the design paradigm from static resistance to dynamic interactions between the material phases and the applied load could inspire novel, metamorphic materials with pre-programmed mechanisms across different length scales.
Project description:Hierarchical porous activated carbon (HPAC) materials with fascinating porous features are favored for their function as active materials for supercapacitors. However, achieving high mass-loading of the HPAC electrodes remains challenging. Inspired by the concepts of carbon/carbon (C/C) composites and hydrogels, a novel hydrogel-derived HPAC (H-HPAC) encapsulated H-HPAC (H@H) composite material was successfully synthesized in this study. In comparison with the original H-HPAC, it is noticed that the specific surface area and pore parameters of the resulting H@H are observably decreased, while the proportions of nitrogen species are dramatically enhanced. The free-standing and flexible H@H electrodes with a mass-loading of 7.5 mg/cm2 are further prepared for electrochemical measurements. The experiments revealed remarkable reversible capacitance (118.6 F/g at 1 mA/cm2), rate capability (73.9 F/g at 10 mA/cm2), and cycling stability (76.6% of retention after 30,000 cycles at 5 mA) are delivered by the coin-type symmetric cells. The cycling stability is even better than that of the H-HPAC electrode. Consequently, the findings of the present study suggest that the nature of the HPAC surface is a significant factor affecting the corresponding capacitive performances.