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1. Minimizing the Diameter of Electrospun Polyacrylonitrile (PAN) Nanofibers by Design of Experiments for Electrochemical Application

   https://doi.org/10.1002/elan.201800368  

   Yu, Sooyoun; Myung, Nosang V (October 2018, Electroanalysis)

   Abstract An effective method to study and predict the complex mechanism of electrospinning is needed. A combination of design of experiments (DOEs) and finer tuning of the experimental parameters were used to investigate the effect of individual and interactions of solution, electrospinning, and environmental conditions on the dimensions and morphology of polyacrylonitrile (PAN) nanofibers. Analyses on DOEs determined that solution viscosity, controlled by the concentration of polymer precursor, was the predominant factor in manipulating the PAN nanofiber diameter. Similarly, reduced surface tension controlled by the addition of surfactant contributed to smoother nanofibers. An appropriate applied voltage for stable formation of Taylor cone was established. DOE on environmental conditions revealed the absolute moisture content played a significant role in causing beads. A minimum polyacrylonitrile (PAN)‐based fiber diameter of 42±7 nm was achieved with solution containing 3.25 wt. % PAN, 0.1 wt. % BYK® surfactant in N,N‐dimethylformamide (DMF). PAN nanofibers were subsequently stabilized then carbonized. BET analysis of the carbonized nanofibers showed the specific surface area increased as a function of nanofiber diameter, reaching 684 m²/g at 407 nm. Preliminary results from the electrochemical characterization of the carbon nanofibers showed the double‐layer capacitance increased with decreasing fiber diameter, showing suitable potential for electrode applications. 

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2. Electrospun Nanofibrous Membranes for Controlling Airborne Viruses: Present Status, Standardization of Aerosol Filtration Tests, and Future Development

   https://doi.org/10.1021/acsenvironau.1c00047  

   Shen, Hongchen; Han, Minghao; Shen, Yun; Shuai, Danmeng (March 2022, ACS Environmental Au)

   NA (Ed.)

   The global COVID-19 pandemic has raised great public concern about the airborne transmission of viral pathogens. Virus-laden aerosols with small size could be suspended in the air for a long duration and remain infectious. Among a series of measures implemented to mitigate the airborne spread of infectious diseases, filtration by face masks, respirators, and air filters is a potent nonpharmacologic intervention. Compared with conventional air filtration media, nanofibrous membranes fabricated via electrospinning are promising candidates for controlling airborne viruses due to their desired characteristics, i.e., a reduced pore size (submicrometers to several micrometers), a larger specific surface area and porosity, and retained surface and volume charges. So far, a wide variety of electrospun nanofibrous membranes have been developed for aerosol filtration, and they have shown excellent filtration performance. However, current studies using electrospinning for controlling airborne viruses vary significantly in the practice of aerosol filtration tests, including setup configurations and operations. The discrepancy among various studies makes it difficult, if not impossible, to compare filtration performance. Therefore, there is a pressing need to establish a standardized protocol for evaluating the electrospun nanofibrous membranes’ performance for removing viral aerosols. In this perspective, we first reviewed the properties and performance of diverse filter media, including electrospun nanofibrous membranes, for removing viral aerosols. Next, aerosol filtration protocols for electrospun nanofibrous membranes were discussed with respect to the aerosol generation, filtration, collection, and detection. Thereafter, standardizing the aerosol filtration test system for electrospun nanofibrous membranes was proposed. In the end, the future advancement of electrospun nanofibrous membranes for enhanced air filtration was discussed. This perspective provides a comprehensive understanding of status and challenges of electrospinning for air filtration, and it sheds light on future nanomaterial and protocol development for controlling airborne viruses, preventing the spread of infectious diseases, and beyond. 

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3. Electrospinning and post-drawn processing effects on the molecular organization and mechanical properties of polyacrylonitrile (PAN) nanofibers

   https://doi.org/10.1557/mrc.2019.67  

   Brennan, David A.; Shirvani, Khosro; Rhoads, Cailyn D.; Lofland, Samuel E.; Beachley, Vince Z. (May 2019, MRS Communications)

   This paper reports the molecular organization and mechanical properties of electrospun, post-drawn polyacrylonitrile (PAN) nanofibers. Without post-drawing, the polymer chain was kinked and oriented in hexagonal crystalline structures. Immediate post-drawing in the semi-solid state disrupted the crystal structures and chain kink at maximum draw ratio. Structural re-orientation at maximum draw resulted in a 500% increase in Young's modulus and a 100% increase in ultimate tensile strength. By applying post-drawing to electrospinning it may be possible to obtain PAN fibers and PAN-derived carbon fibers with enhanced mechanical properties compared to available fabrication technologies. 

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4. Machine-learning-assisted material discovery of oxygen-rich highly porous carbon active materials for aqueous supercapacitors

   https://doi.org/10.1038/s41467-023-40282-1  

   Wang, Tao; Pan, Runtong; Martins, Murillo L.; Cui, Jinlei; Huang, Zhennan; Thapaliya, Bishnu P.; Do-Thanh, Chi-Linh; Zhou, Musen; Fan, Juntian; Yang, Zhenzhen; et al (December 2023, Nature Communications)

   Abstract Porous carbons are the active materials of choice for supercapacitor applications because of their power capability, long-term cycle stability, and wide operating temperatures. However, the development of carbon active materials with improved physicochemical and electrochemical properties is generally carried out via time-consuming and cost-ineffective experimental processes. In this regard, machine-learning technology provides a data-driven approach to examine previously reported research works to find the critical features for developing ideal carbon materials for supercapacitors. Here, we report the design of a machine-learning-derived activation strategy that uses sodium amide and cross-linked polymer precursors to synthesize highly porous carbons (i.e., with specific surface areas > 4000 m²/g). Tuning the pore size and oxygen content of the carbonaceous materials, we report a highly porous carbon-base electrode with 0.7 mg/cm²of electrode mass loading that exhibits a high specific capacitance of 610 F/g in 1 M H₂SO₄. This result approaches the specific capacitance of a porous carbon electrode predicted by the machine learning approach. We also investigate the charge storage mechanism and electrolyte transport properties via step potential electrochemical spectroscopy and quasielastic neutron scattering measurements. 

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5. Selenium infiltrated hierarchical hollow carbon spheres display rapid kinetics and extended cycling as lithium metal battery (LMB) cathodes

   https://doi.org/10.1039/d1ta04705a  

   Wang, Yixian; Hao, Hongchang; Hwang, Sooyeon; Liu, Pengcheng; Xu, Yixin; Boscoboinik, J. Anibal; Datta, Dibakar; Mitlin, David (August 2021, Journal of Materials Chemistry A)

   null (Ed.)

   Lithium metal–selenium (Li–Se) batteries offer high volumetric energy but are limited in their cycling life and fast charge characteristics. Here a facile approach is demonstrated to synthesize hierarchically porous hollow carbon spheres that host Se (Se@HHCS) and allow for state-of-the-art electrochemical performance in a standard carbonate electrolyte (1 M LiPF 6 in 1 : 1 EC : DEC). The Se@HHCS electrodes display among the most favorable fast charge and cycling behavior reported. For example, they deliver specific capacities of 442 and 357 mA h g −1 after 1500 and 2000 cycles at 5C and 10C, respectively. At 2C, Se@HHCS delivers 558 mA h g −1 after 500 cycles, with cycling coulombic efficiency of 99.9%. Post-mortem microstructural analysis indicates that the structures remain intact during extended cycling. Per GITT analysis, Se@HHCS possesses significantly higher diffusion coefficients in both lithiation and delithiation processes as compared to the baseline. The superior performance of Se@HHCS is directly linked to its macroscopic and nanoscale pore structure: the hollow carbon sphere morphology as well as the remnant open nanoporosity accommodates the 69% volume expansion of the Li to Li 2 Se transformation, with the nanopores also providing a complementary fast ion diffusion path. 

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