Carbon Nanofiber Electrodes Research Articles

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate-coated carbon nanofiber electrodes via dip-coating method for supercapacitor applications

Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate-coated carbon nanofiber electrodes via dip-coating method for supercapacitor applications

3D Self-Supported Nitrogen-Doped Carbon Nanofiber Electrodes Incorporated Co/CoOx Nanoparticles: Application to Dyes Degradation by Electro-Fenton-Based Process.

We developed free-standing nitrogen-doped carbon nanofiber (CNF) electrodes incorporating Co/CoOx nanoparticles (NPs) as a new cathode material for removing Acid Orange 7 (AO7; a dye for wool) from wastewater by the heterogeneous electro-Fenton reaction. We produced the free-standing N-doped CNF electrodes by electrospinning a polyacrylonitrile (PAN) and cobalt acetate solution followed by thermal carbonation of the cobalt acetate/PAN nanofibers under a nitrogen atmosphere. We then investigated electro-Fenton-based removal of AO7 from wastewater with the free-standing N-doped-CNFs-Co/CoOx electrodes, in the presence or not of Fe2+ ions as a co-catalyst. The electrochemical analysis showed the high stability of the prepared N-doped-CNF-Co/CoOx electrodes in electrochemical oxidation experiments with excellent degradation of AO7 (20 mM) at acidic to near neutral pH values (3 and 6). Electro-Fenton oxidation at 10 mA/cm2 direct current for 40 min using the N-doped-CNF-Co/CoOx electrodes loaded with 25 wt% of Co/CoOx NPs led to complete AO7 solution decolorization with total organic carbon (TOC) removal values of 92.4% at pH 3 and 93.3% at pH 6. The newly developed N-doped-CNF-Co/CoOx electrodes are an effective alternative technique for wastewater pre-treatment before the biological treatment.

Nanostructured Geometries Strongly Affect Fouling of Carbon Electrodes.

Electrode fouling is a major factor that compromises the performance of biosensors in in vivo usage. It can be roughly classified into (i) electrochemical fouling, caused by the analyte and its reaction products, and (ii) biofouling, caused by proteins and other species in the measurement environment. Here, we examined the effect of electrochemical fouling [in phosphate buffer saline (PBS)], biofouling [in cell-culture media (F12-K) with and without proteins], and their combination on the redox reactions occurring on carbon-based electrodes possessing distinct morphologies and surface chemistry. The effect of biofouling on the electrochemistry of an outer sphere redox probe, [Ru(NH3)6]3+, was negligible. On the other hand, fouling had a marked effect on the electrochemistry of an inner sphere redox probe, dopamine (DA). We observed that the surface geometry played a major role in the extent of fouling. The effect of biofouling on DA electrochemistry was the worst on planar pyrolytic carbon, whereas the multiwalled carbon nanotube/tetrahedral amorphous carbon (MWCNT/ta-C), possessing spaghetti-like morphology, and carbon nanofiber (CNF/ta-C) electrodes were much less seriously affected. The blockage of the adsorption sites for DA by proteins and other components of biological media and electrochemical fouling components (byproducts of DA oxidation) caused rapid surface poisoning. PBS washing for 10 consecutive cycles at 50 mV/s did not improve the electrode performance, except for CNF/ta-C, which performed better after PBS washing. Overall, this study emphasizes the combined effect of biological and electrochemical fouling to be critical for the evaluation of the functionality of a sensor. Thus, electrodes possessing composite nanostructures showed less surface fouling in comparison to those possessing planar geometry.

Analyses of dispersive effects and the distributed capacitance in the time and frequency domains of activated carbon nanofiber electrodes as symmetric supercapacitors

A novel and scalable method is reported to produce flexible and freestanding fabrics composed of high surface area activated carbon nanofibers (aCNF) for applications in supercapacitors. The electrochemical behavior of a symmetric supercapacitor using the aCNF electrodes and the operando Raman spectra study accomplished under polarization conditions are reported. The evolution of Raman spectra during polarization supported the aCNF stability and suggested the insertion of the HSO4− ions in carbon micropores. These findings evidenced a new symmetry at the aCNF/electrolyte interface, where electronic and ionic charges accumulate. The distributed capacitance in the time domain was studied by numeric differentiation of galvanostatic charge-discharge findings. The impedance behavior of the solid and liquid phases composing the aCNF/solution interface was modeled using a macro homogeneous description of two closely mixed phases represented by a single-channel transmission line incorporating the anomalous transport of the ionic charges in the disordered structure of aCNF. Electrochemical findings revealed outstanding charge-storage properties in neutral aqueous electrolyte resulting in long lifespan, low equivalent series resistance (12 mΩ g), high coulombic efficiency (∼99.8 %), a maximum distributed capacitance of 82 F g−1 (0.25 A g−1-1.1 V), maximum specific energy and power of 2.98 W h kg−1 and 72,672 W kg−1, respectively.

Self-supporting porous carbon nanofibers with opposite surface charges for high-performance inverted capacitive deionization

Capacitive deionization (CDI) has attracted much attention as a novel desalination technology. However, the oxidation of carbon anode and co-ion repulsion during charging are key issues which limit the CDI development. Inverted capacitive deionization (i-CDI) can attenuate these effects. Here, a simple method was presented to get the self-supporting carbon nanofibers electrodes with opposite surface charges to improve the deionization performance of i-CDI device. The electrospun polyacrylonitrile/polymethyl methacrylate (PAN/PMMA)-derived flexible carbon nanofiber was found to be negatively charged (N-CNF). The positively charged porous carbon nanofiber (P-CNF) was obtained by further heat treatment of N-CNF in the presence of ZnCl2. The P-CNF possesses much low negative potential of zero charge (PZC = −0.68 V), opposite to N-CNF (+0.32 V), measured by differential capacitance tests. With P-CNF as cathode and N-CNF as anode, the asymmetric capacitor device realized high performance i-CDI, and delivered a super high deionization capacity of 30.4 mg/g and very fast deionization rate (1.0 mg/g/min) with low specific energy consumption. The adsorption-desorption process in i-CDI was analyzed. The device exhibits superior cycling stability and regenerability over 70 cycles. These flexible carbon nanofibers with substantial surface charge difference render it favorable for i-CDI application.

Aligned microfibers interweaved with highly porous carbon nanofibers: A Novel electrode for high-power vanadium redox flow batteries

In this work, we propose and develop a novel electrode made of aligned microscale carbon fibers interweaved with highly porous carbon nanofibers for vanadium redox flow batteries. Such a unique combination not only endows the electrode with a high permeability due to the reduced tortuosity and large macropores, but also an ultra-large specific surface area for redox reactions. As a result, a vanadium redox flow battery equipped with the newly-developed electrode is able to achieve an energy efficiency of 79.3% at the current density of 400 mA cm−2, which is 9.9% higher than that with pure porous carbon nanofiber electrodes, and 14.1% higher than that with pure aligned fiber electrodes. More remarkably, the battery is capable of delivering a peak power density of as high as ∼1.9 W cm−2 and a limiting current density of ∼5000 mA cm−2. These results demonstrate that our strategy of interweaving porous carbon nanofibers between aligned microfibers effectively addresses the contradiction between permeability and surface area of porous electrodes, opening a new platform to fabricate high-performance electrodes for vanadium redox flow batteries.

Photoelectrocatalysis of paracetamol on Pd–ZnO/ N-doped carbon nanofibers electrode

The presence of pharmaceuticals in water bodies has become a major concern in recent years. An efficient and innovative way of eliminating these pollutants is through photoelectrocatalytic (PEC) degradation owing to its environmental sustainability and its ability to remove recalcitrant pollutants. In this study, palladium loaded zinc oxide/carbon nanofibers (CZnO–Pd) were employed as a novel photoanode for PEC degradation of paracetamol. The CZnO–Pd composite was prepared through electrospinning and atomic layer deposition (ALD). The obtained materials were characterized. Photoelectrochemical studies were carried out with linear sweep voltammetry and chronoamperometry. The removal efficiency was recorded using high-performance liquid chromatography coupled to a mass spectrometer detector (HPLC-MS), while the mineralization was assessed through total organic carbon (TOC) removal. The composite electrode of CZnO–Pd nanofiber showed higher photoelectrochemical activity than ZnO carbon nanofiber, which was evident in the higher photocurrent response recorded. Upon application of the material in photoelectrocatalysis, the total removal of paracetamol was achieved within 3 h with an applied current density of 10 mAcm−2. The percentage of TOC removal was 71.20 ± 0.31% after 4 h, which indicated significant mineralization. The results obtained in the present work reveal that Pd–ZnO/C has great potential for photoelectrocatalytic removal of organic micropollutants.

A feasible strategy to enhance mass transfer property of carbon nanofibers electrode in vanadium redox flow battery

Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the V3+/V2+ and VO2+/VO2+ redox couples in vanadium redox flow battery (VRFB), while its inferior mass transfer property limits the cell power density seriously due to the lower porosity and poorer permeability. In order to improve the mass transfer property, starch based carbon microsphere (SCMS) of a few micrometers is synthesized by a green hydrothermal method and introduced into the electrospun precursor solution. Subsequently, a novel spherical-filament binary carbon nanofibers electrode (ECNFs-SCMS) is constructed by the controllable electrospining technique along with the subsequent heat treatment processes. The novel binary carbon nanofibers exhibits more loose structure, improved hydrophilia, increased oxygen contents and more defects, which result in the simultaneous improvement of electrochemical reaction area, electrocatalytic activity and mass transfer kinetics. The single VRFB cell with ECNFs-SCMS as electrodes shows higher energy efficiency and maximun power density as compared to the one with pure ECNFs electrodes. The results in this work suggest that improving permeability is a feasible strategy to enhance the mass transfer property of carbon nanofibers electrode.

In Situ Pore-Making and Heteroatom Doping of Carbon Nanofibers Electrode for High Performance Vanadium Redox Flow Battery

Electrochemical performance of the electrospun carbon nanofibers (ECNFs) electrode for all vanadium redox flow battery (VRFB) is significantly enhanced by introducing urea into the precursor solution and the subsequent thermal treatment. A novel N, O dual-doped carbon nanofibers with a series of micronanometer multiscale pores on the surface can be easily obtained by the in situ thermolysis processes of urea, which endows the electrode larger surface area, better wettability and improved electroactive sites. The electrochemical results demonstrate that the N, O co-doping ECNFs with multiscale pores shows reduced charge transfer resistance and diffusion resistance for vanadium ions redox reactions, which should be attributed to the synergy of the larger effective surface area and better electrocatalytic activity. The VRFB equipped with the novel carbon nanofibers electrode delivers a 84.6% increase of the discharge capacity and 17% amplification of the energy efficiency compared with the pristine ECNFs at 150 mA cm−2. This simple method to construct electrodes with N, O dual-doped and micronanometer multiscale pores also paves the way to finely regulating the internal microstructure and composition of the electrodes in a variety of energy storage systems.

Anti-Fouling Effects of Carbon Nanofiber in Electrochemical Sensing of Phenolic Compounds

Electrode fouling has been a major problem in the analysis of phenolic compounds. This work synthesized carbon nanofiber (CNF) by electrospinning and demonstrated the anti-fouling properties of the material. The synthesized CNF was characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, infrared spectroscopy, electrochemical impedance spectroscopy, and cyclic voltammetry. Three electrode preparation methods were then tested including as-spun sheet, screen printing and dropcasting. The electrochemical behaviors of CNF towards a wide range of systems were demonstrated, including reversible redox processes [e.g. K4Fe(CN)6 and catechol], the deposition and stripping of metal ions [e.g. Ag(I) and Cu(II)], and irreversible redox processes [e.g. resorcinol and bisphenol-A]. To highlight the advantages of the anti-fouling properties of CNF, we then used resorcinol which is an environmental contaminant as a model system and explored the analytical performances of CNF electrodes. The linear range of resorcinol detection was 10–250 μM. The sensitivity and limit of detection (3sB m−1) were determined to be 0.021 μA μM−1 and 7.27 μM, respectively.

Flexible All-Solid-State Supercapacitor Fabricated with Nitrogen-Doped Carbon Nanofiber Electrode Material Derived from Polyacrylonitrile Copolymer

Flexible All-Solid-State Supercapacitor Fabricated with Nitrogen-Doped Carbon Nanofiber Electrode Material Derived from Polyacrylonitrile Copolymer

Facile Fabrication of Flexible Carbon Nanofiber Electrodes with Both High Packing Density and Capacity for Li‐Ion Batteries

Freestanding carbon nanofiber (CNF) films are promising flexible battery electrodes because of their rich functionalities and the avoidance of the unnecessary usage of conductive additives and binders, which introduce additional interfacial resistance. However, most reported freestanding CNF electrodes have lower energy density than the metrics of practical usage. Herein, an in situ welding strategy is proposed to fabricate flexible CNF electrodes with both high packing density (0.343 g cm−3) and capacity (832.4 mA h g−1 @0.1 C) by electrospinning of a polyacrylonitrile (PAN) and poly(vinyl‐butyral) (PVB) sol followed by pyrolysis. The addition of 20 wt% of low‐thermal‐stability PVB into PAN carbon precursors endows the CNFs with mixed amorphous/graphitic carbon domains and welded structures. The former enhances the capacity and long‐cycling stability, and the latter improves the flexibility and packing density of the anodes. As a result, these flexible anodes display stable reversible capacities of 430 mA h g−1 @1 C over 1000 cycles and excellent rate performance from 0.1 to 5 C. The successful fabrication of high‐capacity CNF anodes at commercial‐level density opens a new avenue for their practical application.

Improvement of the Electronic-Neuronal Interface by Natural Deposition of ECM.

The foreign body reaction to neuronal electrode implants limits potential applications as well as the therapeutic period. Developments in the basic electrode design might improve the tissue compatibility and thereby reduce the foreign body reaction. In this work, the approach of embedding 3D carbon nanofiber electrodes in extracellular matrix (ECM) synthesized by human fibroblasts for a compatible connection to neuronal cells was investigated. Porous electrode material was manufactured by solution coelectrospinning of polyacrylonitrile and polyamide as a fibrous porogen. Moreover, NaCl represented an additional particulate porogen. To achieve the required conductivity for an electrical interface, meshes were carbonized. Through the application of two different porogens, the electrodes’ flexibility and porosity was improved. Human dermal fibroblasts were cultured on the electrode surface for ECM generation and removed afterwards. Scanning electron microscopy imaging revealed a nano fibrous ECM network covering the carbon fibers. The collagen amount of the ECM coating was quantified by hydroxyproline-assays. The modification with the natural protein coating on the electrode functionality resulted in a minor increase of the electrical capacity, which slightly improved the already outstanding electrical interface properties. Increased cell numbers of SH-SY5Y cell line on ECM-modified electrodes demonstrated an improved cell adhesion. During cell differentiation, the natural ECM enhanced the formation of neurites regarding length and branching. The conducted experiments indicated the prevention of direct cell-electrode contacts by the modification, which might help to shield temporary the electrode from immunological cells to reduce the foreign body reaction and improve the electrodes’ tissue integration.

Polyelemental Nanoparticles as Catalysts for a Li-O2 Battery.

The development of highly efficient catalysts in the cathodes of rechargeable Li-O2 batteries is a considerable challenge. Polyelemental catalysts consisting of two or more kinds of hybridized catalysts are particularly interesting because the combination of the electrochemical properties of each catalyst component can significantly facilitate oxygen evolution and oxygen reduction reactions. Despite the recent advances that have been made in this field, the number of elements in the catalysts has been largely limited to two metals. In this study, we demonstrate the electrochemical behavior of Li-O2 batteries containing a wide range of catalytic element combinations. Fourteen different combinations with single, binary, ternary, and quaternary combinations of Pt, Pd, Au, and Ru were prepared on carbon nanofibers (CNFs) via a joule heating route. Importantly, the Li-O2 battery performance could be significantly improved when using a polyelemental catalyst with four elements. The cathode containing quaternary nanoparticles (Pt-Pd-Au-Ru) exhibited a reduced overpotential (0.45 V) and a high discharge capacity based on total cathode weight at 9130 mAh g-1, which was ∼3 times higher than that of the pristine CNF electrode. This superior electrochemical performance is be attributed to an increased catalytic activity associated with an enhanced O2 adsorbability by the quaternary nanoparticles.

Simples fabrication of hierarchical NiCoSe4 nanorods grown on carbon nanofibers as excellent electrocatalysts for tryptophan oxidation

In this study, a simple approach is established to fabricate NiCoSe4 nanorods grown onto carbon nanofiber (CNF) skeletons by combining electrospinning and a hydrothermal process. We achieved the rapid and ultrasensitive electrocatalytic sensing of tryptophan (Trp) in 0.1 M KOH by using intrinsically metallic NiCoSe4 anchored on CNFs as an alternative working electrode material. Benefiting from the large surface area due to rich defect active sites and the high electrocatalytic behavior of NiCoSe4 with CNF, the fabricated sensor exhibits a lower electron-transfer resistance of Rct 92 Ω with respect to the CNF–NiCo and CNFs electrodes. The results of voltammetric technique confirmed that the CNF–NiCoSe4-GCE showed higher anodic peak intensity and a lower anodic potential for Trp detection than CNFs-GCE and CNF–NiCo-GCE electrodes since the integration of sp2 carbon on the surface of the CNFs and bimetallic selenides improves the sensing performance. The amperometric I-t curve showed a linear response in the Trp concentration range of 5–95 nM and a detection limit of 0.68 nM at low potential of 0.4 V vs. Hg/HgO. The CNF–NiCoSe4-GCE was successfully utilized for the electrocatalytic monitoring of Trp from human serum, milk, and tomato juice samples with a recovery of 95.4–105.5%.

Fabrication of Hierarchically Porous Carbon Nanofibers from Immiscible PAN/PVDF Polymer Blends as Electrode Materials

Most previous work on the preparation of electrode materials has usually used to grind carbon nanofibers and add non-reactive binders, which lead to limited surface area and lower electrochemical performance in electrode materials. In this study, porous carbon nanofibers were prepared from non-miscible PAN/PVDF polymer blends by electrospinning and carbonization to obtain electrode materials with high performance and high specific surface area. In the process of preparing electrode materials, carbon nanofibers can be directly prepared as electrodes with high-performance and flexibility without adding any inactive materials, such as polymer binders or electronic conductors. Results showed that PF-C-50 has the maximum specific surface area of 773 m2 g−1 and the specific capacitance as high as 181 F/g at the current density of 0.4 A/g and 134 F/g at the current density of 1 A/g. PF-C-80 exhibits a specific capacitance as high as 156 F/g at the current density of 0.4 A/g and 117 F/g at the current density of 1 A/g with the smallest IR drop and Rct. The prepared porous carbon nanofiber electrode improves the electrochemical performance and flexibility of the electrode material. These unique structures and characteristic materials can be excellent candidates for high-performance flexible electrodes, laying a good foundation for wearable devices.

Fabrication of Carbon Nanofibers Decorated with Various Kinds of Metal Oxides for Battery Applications

Carbon nanofibers decorated with various metal oxide nanoparticles were fabricated by combining an electrospinning technique of bicomponent polymer mixture and a sol-gel reaction and subsequent carbonization process. Electrospun polymer nanofibers consisting of polyacrylonitrile (PAN) and poly(vinyl pyrrolidone) (PVP) with controllable diameters were fabricated with PAN/PVP core/shell types via phase-separation due to the immiscibility between two polymers. The electrospun nanofibers served as supporting materials with binding sites of PVP to incorporate titanium oxide precursor. Subsequently, the carbonization of the fibers led to the formation of carbon nanofibers@TiO2 for energy application, in which rutile TiO2 nanoparticles were decorated on the surface of carbon nanofiber. Especially, this TiO2 decorated carbon nanofiber electrode exhibited excellent electrochemical property in lithium-ion batteries (≈600 mA h g−1 at C/5 rate for 100 cycles). Furthermore, the carbon nanofibers were also successfully modified with other metal oxides, including NiO, SnO2, and ZrO2 nanoparticles, in a similar manner.

Kraft lignin-derived free-standing carbon nanofibers mat for high-performance all-solid-state supercapacitor

In the present investigation, renewable kraft lignin-based nanofibers were synthesized by facile electrospinning technique and further converted into carbon nanofibers (CNFs) by heat treatment at different temperatures (600, 800 and 1000 °C). These different heat treated carbon nanofiber mats were characterized using SEM, Raman, FTIR, BET and electrochemical workstation. These CNFs were used as a free-standing electrode and characterized for electrochemical performance using a three-electrode system. Among different electrodes, the 800 °C heat treated CNF electrode shows higher specific capacitance (196.63 F/g @ 1 A/g) as compared to the 600 and 1000 °C heat treated CNF electrodes. Based on the electrochemical performance, 800 °C heat treated CNF electrode is selected to assemble two different types of symmetrical supercapacitor devices i.e., aqueous (using 1 M H2SO4) and solid-state electrolyte using PVA-1M H2SO4 polymer gel. The solid-state electrolyte device operating potential window of 0–2 V which is higher than that of an aqueous electrolyte based device. In addition to this, it delivers higher energy and power density as 62.6 Wh/kg and 1.25 kW/kg respectively with an efficiency of 99.5% after 10,000 cycles. These remarkable results of Kraft lignin-derived ribbon type CNF based solid-state symmetrical supercapacitor device opens new paths for the development of futuristic carbon-based free-standing mat as energy storage devices.

Preparation of Porous Carbon Nanofiber Electrodes Derived from 6FDA-Durene/PVDF Blends and Their Electrochemical Properties.

Highly porous carbon electrodes for supercapacitors with high energy storage performance were prepared by using a new precursor blend of aromatic polyimide (PI) and polyvinylidene fluoride (PVDF). Supercapacitor electrodes were prepared through the electrospinning and thermal treatment of the precursor blends of aromatic PI and PVDF. Microstructures of the carbonized PI/PVDF nanofibers were studied using Raman spectroscopy. Nitrogen adsorption/desorption measurements confirmed their high surface area and porosity, which is critical for supercapacitor performance. Energy storage performance was investigated and carbonized PI/PVDF showed a high specific capacitance of 283 F/g at 10 mV/s (37% higher than that of PI) and an energy density of 11.3 Wh/kg at 0.5 A/g (27% higher than that of PI) with high cycling stability.

Integration of RuO2/conductive fiber composites within carbonized micro-electrode array for supercapacitors

Abstract This study employed a carbon microelectromechanical system (C-MEMS) in fabricating a 3D micro-electrode array of conductive carbon cylinders directly on the surface of a graphite substrate. The capacitance of the array was further enhanced by decorating it with a composite material comprising highly-porous carbon nanofibers (CF) and electroactive RuO2 nanoparticles to function as an active electrode. In galvanostatic charge-discharge tests, the specific capacitance of an electrode decorated with RuO2 30 wt%/CF was 219.2 F g−1 at a current density of 0.5 A g−1, which is 2.27 times higher than that of the pristine CF electrode. When the current density was increased from 0.5 A g−1 to 3 A g−1, the capacitance retention of the RuO2 30 wt%/CF electrode was 54.8%. A symmetric supercapacitor based on the RuO2 30 wt%/CF composite electrode exhibited an impressive energy density of 74.2 Wh kg−1 with power density of 4333 W kg−1. It also demonstrated good capacitance retention of 80.2% following 3000 consecutive charge/discharge cycles at a current density of 2 A g−1.