Strategies to Hierarchical Porosity in Carbon Nanofiber Webs for Electrochemical Applications

A Recent Review of Electrospun Porous Carbon Nanofiber Mats for Energy Storage and Generation Applications

Electrospun porous carbon nanofiber mats have excellent properties, such as a large surface area, tunable porosity, and excellent electrical conductivity, and have attracted great attention in energy storage and power generation applications. Moreover, due to their exceptional properties, they can be used in dye-sensitized solar cells (DSSCs), membrane electrodes for fuel cells, catalytic applications such as oxygen reduction reactions (ORRs), hydrogen evolution reactions (HERs), and oxygen evolution reactions (OERs), and sensing applications such as biosensors, electrochemical sensors, and chemical sensors, providing a comprehensive insight into energy storage development and applications. This study focuses on the role of electrospun porous carbon nanofiber mats in improving energy storage and generation and contributes to a better understanding of the fabrication process of electrospun porous carbon nanofiber mats. In addition, a comprehensive review of various alternative preparation methods covering a wide range from natural polymers to synthetic carbon-rich materials is provided, along with insights into the current literature.

Electrospun Carbon Nanofibers and Their Applications in Several Areas

Carbon nanofibers (CNFs) have a broad spectrum of applications, including sensor manufacturing, electrochemical catalysis, and energy storage. Among different manufacturing methods, electrospinning, due to its simplicity and efficiency, has emerged as one of the most powerful commercial large-scale production techniques. Numerous researchers have been attracted to improving the performance of CNFs and exploring new potential applications. This paper first discusses the working theory of manufacturing electrospun CNFs. Next, the current efforts in upgrading the properties of CNFs, such as pore architecture, anisotropy, electrochemistry, and hydrophilicity, are discussed. The corresponding applications due to the superior performances of CNFs are subsequently elaborated. Finally, the future development of CNFs is discussed.

Enhancement of Room Temperature Ethanol Sensing by Optimizing the Density of Vertically Aligned Carbon Nanofibers Decorated with Gold Nanoparticles

An ethanol gas sensor based on carbon nanofibers (CNFs) with various densities and nanoparticle functionalization was investigated. The CNFs were grown by means of a Plasma-Enhanced Chemical Vapor Deposition (PECVD), and the synthesis conditions were varied to obtain different number of fibers per unit area. The devices with a larger density of CNFs lead to higher responses, with a maximal responsivity of 10%. Furthermore, to simultaneously improve the sensitivity and selectivity, CNFs were decorated with gold nanoparticles by an impaction printing method. After metal decoration, the devices showed a response 300% higher than pristine devices toward 5 ppm of ethanol gas. The morphology and structure of the different samples deposited on a silicon substrate were characterized by TEM, EDX, SEM, and Raman spectroscopy, and the results confirmed the presence of CNF decorated with gold. The influence of operating temperature (OT) and humidity were studied on the sensing devices. In the case of decorated samples with a high density of nanofibers, a less-strong cross-sensitivity was observed toward a variation in humidity and temperature.

Flexible free-standing Ni-Mn oxide antenna decorated CNT/nanofiber membrane for high-volumetric capacitance supercapacitors

There is growing demand for lightweight flexible supercapacitors with high electrochemical performance for wearable and portable electronics. Here, we spun nanoparticles of nickel-manganese oxides along with carbon nanotubes into carbon nanofibers and engineered a 3D networked Ni-Mn oxides/CNT@CNF free-standing membrane for flexible supercapacitor applications. The electrospinning process controlled the nanoparticle aggregation while subsequent heat treatment generates nanochannels in the fibres, resulting in a very porous tubular nanocomposite structure. The preparation process also enabled good interfacial contact between the nanoparticles and the conductive carbon network. The resulting Ni-Mn oxides/CNT@CNF membrane displays high mass loading (Ni-Mn oxides) of 855 mg cm^-3 and low CNT incorporation of ∼0.4%. The outstanding porous structure, synergy of the carbon with Ni-Mn oxides, and fast and facile faradaic reactions on the electrode were responsible for the superior volumetric capacitance of 250 F cm^-3 at 1 A cm^-3, energy density as high as 22 mW h cm^-3 and an excellent power density of 12 W cm^-3. Despite the low CNT loading, the hybrid electrode exhibits excellent cycling performance with capacitance retention of 96.4% after 10 000 cycles evidencing a well-preserved Ni-manganese oxide nanostructure throughout the cycling. The resulting outstanding electrochemical performances of the Ni-Mn oxides/CNT@CNF synergic system offer new insights into effective utilization of transition metal oxides for establishing high-performance flexible supercapacitors within a confined volume.

Evaluation of Electrospun Self-Supporting Paper-Like Fibrous Membranes as Oil Sorbents

Presently, adsorption/absorption is one of the most efficient and cost-effective methods to clean oil spill up. In this work, self-supporting paper-like fibrous membranes were prepared via electrospinning and carbonisation at different temperatures (500, 650 or 800 °C) by using polyacrylonitrile/polymethylmethacrylate blends with a different mass ratio of the two polymers (1:0, 6:1 or 2:1). After morphological and microstructural characterisation, the as-produced membranes were evaluated as sorbents by immersion in vegetable (sunflower seed or olive) and mineral (motor) oil or in 1:4 (v:v) oil/water mixture. Nitrogen-rich membrane carbonised at the lowest temperature behaves differently from the others, whose sorption capacity by immersion in oil, despite the great number of sorbent and oil properties involved, is mainly controlled by the fraction of micropores. The encapsulation of water nanodroplets by the oil occurring during the immersion in oil/water mixture causes the oil-from-water separation ability to show an opposite behaviour compared to the sorption capacity. Overall, among the investigated membranes, the support produced with 2:1 mass ratio of the polymers and carbonisation at 650 °C exhibits the best performance both in terms of sorption capacity (73.5, 54.8 and 12.5 g g-1 for olive, sunflower seed and motor oil, respectively) and oil-from-water separation ability (74, 69 and 16 for olive, sunflower seed and motor oil, respectively).

Amorphous cobalt boride nanosheets anchored surface-functionalized carbon nanofiber: An bifunctional and efficient catalyst for electrochemical sensing and oxygen evolution reaction

Development of new metal boride with carbon composite is an emerging class of catalyst and it brings enormous curiosity in the material community because of their potential intriguing properties. Here, we describe a new type of amorphous cobalt boride (A-CoB) nanosheet anchored on the surface of functionalized carbon nanofiber (A-CoB/ƒ-CNF) by a simple method. The emerged A-CoB/ƒ-CNF composite was demonstrated to possess great bifunctional electrocatalytic activity for the electrochemical sensing of antibiotic drug nitrofurantoin (NFT) and oxygen evolution reaction (OER). The prepared A-CoB/ƒ-CNF composite was characterized by various analytical and spectroscopic techniques such as XRD, FE-SEM, HR-TEM, Raman, and XPS analysis. The result from the electrochemical impedance spectroscopy confirms that the A-CoB/ƒ-CNF composite shows high electrical conductivity and the number of electron transferability for the NFT sensor and OER which is due to the presence of abundant active sites/large surface area in A-CoB, and synergistic effect between the A-CoB and ƒ-CNF. As an electrochemical sensor, the A-CoB/ƒ-CNF modified electrode shows substantial sensitivity (3.13 μA μM^-1 cm^-2), wider linear response range (0.01- 527 μM), and lower detection limit (0.003 μM) as-compared to the previously reported noble and non-noble metal-based electrocatalyst for NFT sensor. As well, the A-CoB/ƒ-CNF composite demonstrates superior OER activity with low overpotential and small Tafel slope value of 0.35 V and 173 mV/dec, respectively, which shows advanced kinetics than noble metal catalysts. Based on the results, we believed that the present work gives clear evidence for the preparation of transition metal boride anchored carbon material with an outstanding catalytic activity, and hence, it can be also extended to further electrochemical applications.