Conductive Carbon Fiber Paper Research Articles

Thickness-controlled porous hexagonal NiO nanodiscs electrodes for use in supercapacitors: How nanodiscs thickness influences electrochemical performance

Two-dimensional (2D) nickel oxide (NiO) hexagonal nanodiscs were synthesized via a hydrothermal route, followed by successive calcination. The decisive roles of the [OH−]/[Ni2+] molar ratios, as well as the calcination temperatures, were found in controlling the nanodiscs morphology of the NiO nanostructures. The increase in the concentration of OH− ions in the precursor solution influenced the crystal growth that directed to the formation of the hexagonal nanodisc morphology with increased edge thickness and beyond certain limits transformation from the nanodiscs to complete 3D morphology. The nanodiscs grew with increasing exposed surface size with a high BET area and varied thicknesses from 4 to 20 nm. The increase in calcination temperature improved crystallinity by eliminating crystal defects and voids, while crystals grew along the (200) plane. However, a reduction in the BET area and pore volume occurred at higher calcination temperature because of the collapse in micro-mesopores. The electrochemical performances of NiO electrodes show dependence on the thickness of the nanodiscs, the calcination temperature, and the type of current collector used. A distinct electrochemical feature was observed for NiO nanodiscs over planar conductive carbon fiber paper and 3D porous Ni foam substrates. The hydrothermal approach reported here to produce thickness-controlled NiO nanodiscs with high intrinsic surface area has great potential for developing next-generation battery-type faradic electrodes in conjunction with carbon allotropes and other metal oxide materials for high power and energy density throughput.

In situ growing catalytic sites on 3D carbon fiber paper as self-standing bifunctional air electrodes for air-based flow batteries

Noble metal-free bifunctional catalysts are highly desirable for both oxygen reduction and evolution reactions in air-based flow batteries, but remain a big challenge. Herein, micropores dominated nitrogen and sulfur codoped carbon (NSC) film is directly growing on conductive carbon fiber paper (CFP) as self-standing air electrode through the electropolymerization of 2-amino-5-mercapto-1,3,4-thiadiazole and followed pyrolysis process. NSC film provides abundant active sites, while conductive CFP with 3D macro-networks offers affluent channels for electron and mass transfer. Benefit from the strong interaction between NSC and CFP, the resultant CFP@NSC displays highly catalytic activity for both oxygen reduction (comparable half-wave potential to commercial Pt/C) and oxygen evolution (lower overpotential than commercial IrO2), along with robust stability. As a proof of practical usage, zinc air flow battery with CFP@NSC displays lower charge voltage and higher discharge voltage, compared with commercial Pt/C and IrO2 coated CFP electrode. Importantly, zinc air flow battery also exhibits excellent cycling stability including nearly 100% retention of coulombic efficiency and energy efficiency over 3400 min, representing the most efficient bifunctional oxygen electrode reported so far.

A Janus Nickel Cobalt Phosphide Catalyst for High-Efficiency Neutral-pH Water Splitting.

Transition-metal phosphides have stimulated great interest as catalysts to drive the hydrogen evolution reaction (HER), but their use as bifunctional catalytic electrodes that enable efficient neutral-pH water splitting has rarely been achieved. Herein, we report the synthesis of ternary Ni0.1 Co0.9 P porous nanosheets onto conductive carbon fiber paper that can efficiently and robustly catalyze both the HER and water oxidation in 1 m phosphate buffer (PBS; pH 7) electrolyte under ambient conditions. A water electrolysis cell comprising the Ni0.1 Co0.9 P electrodes demonstrates remarkable activity and stability for the electrochemical splitting of neutral-pH water. We attribute this performance to the new ternary Ni0.1 Co0.9 P structure with porous surfaces and favorable electronic states resulting from the synergistic interplay between nickel and cobalt. Ternary metal phosphides hold promise as efficient and low-cost catalysts for neutral-pH water splitting devices.

A Janus Nickel Cobalt Phosphide Catalyst for High‐Efficiency Neutral‐pH Water Splitting

AbstractTransition‐metal phosphides have stimulated great interest as catalysts to drive the hydrogen evolution reaction (HER), but their use as bifunctional catalytic electrodes that enable efficient neutral‐pH water splitting has rarely been achieved. Herein, we report the synthesis of ternary Ni0.1Co0.9P porous nanosheets onto conductive carbon fiber paper that can efficiently and robustly catalyze both the HER and water oxidation in 1 m phosphate buffer (PBS; pH 7) electrolyte under ambient conditions. A water electrolysis cell comprising the Ni0.1Co0.9P electrodes demonstrates remarkable activity and stability for the electrochemical splitting of neutral‐pH water. We attribute this performance to the new ternary Ni0.1Co0.9P structure with porous surfaces and favorable electronic states resulting from the synergistic interplay between nickel and cobalt. Ternary metal phosphides hold promise as efficient and low‐cost catalysts for neutral‐pH water splitting devices.

Tip-welded ferric-cobalt sulfide hollow nanoneedles on highly conductive carbon fibers for advanced asymmetric supercapacitors

The ever-increasing concerns about global environmental problems and depletion of fossil resources have stimulated intensive research on low-cost and high-performance energy storage materials. Here, we introduce the two-step sulfidation of hierarchical ferric-cobalt sulfide hollow nanoneedles on electrical conductive carbon fiber paper (CFP) for high-performance supercapacitor electrodes. Under the growth regulation of macroporous CFP substrate, prepared free-standing composite paper with tip-welded ferric-cobalt sulfide hollow nanoneedles can offer substantial exposed electroactive sites for Faradaic redox reaction and effectively buffer the drastic volume change during long-term charge-discharge, and also provide fast charge transfer paths through the carbon skeleton for efficient energy storage. Due to these unique features, obtained composite paper electrode delivers a higher specific capacitance (2282 F g−1 at current density of 1 A g−1) than those of the previously reported MCo2S4 based electrodes. Asymmetric supercapacitor assembled using the composite paper as the binder-free positive electrode also shows a high energy density of 86.8 Wh kg−1 at a power density of 800 W kg−1, and an impressive 82.3% capacitance retention after 5000 cycles, demonstrating the great potential of this low-cost and free-standing electrodes towards high-performance energy storage.

Polypyrrole-Decorated Hierarchical NiCo2O4 Nanoneedles/Carbon Fiber Papers for Flexible High-Performance Supercapacitor Applications

A novel polyprrole (PPy)-decorated hierarchical NiCo2O4 nanoneedles was grown on highly conductive carbon fiber paper (CFP) for high performance asymmetric supercapacitor applications. The PPy-decorated hierarchical NiCo2O4 nanoneedle on CFP (PPy-NiCo2O4@CPF) was grown by two steps. At first, NiCo2O4 nanoneedle was grown by hydrothermal process and followed by the deposition of PPy through electrochemical method. The fabricated PPy-NiCo2O4@CPF electrode displayed the higher electrochemical performance. The specific capacitance was ∼910F g-1 at a current density of 1Ag−1 and cyclic stability was ∼88% after 10,000 cycles. To explore real performance of the electrode, we have fabricated solid state asymmetric supercapacitor using PPy-NiCo2O4@CFP as positive and nitrogen doped reduced graphene oxide (N-rGO) as negative electrodes. The fabricated asymmetric device delivered a specific capacitance of 118.6F g-1 at a current density of 1.0Ag−1 with a maximum energy density of 40.81WhKg−1 (at a power density of 738.27WKg−1) and maximum power density of 3746.77WKg−1 (at an energy density of 13.53WhKg−1). The impressive results suggest that flexible PPy-NiCo2O4@CFPs can be a promising electrode material for supercapacitor applications.

Morphology-Controllable Synthesis of Zn-Co-Mixed Sulfide Nanostructures on Carbon Fiber Paper Toward Efficient Rechargeable Zinc-Air Batteries and Water Electrolysis.

It remains an ongoing challenge to develop cheap, highly active, and stable electrocatalysts to promote the sluggish electrocatalytic oxygen evolution, oxygen reduction, and hydrogen evolution reactions for rechargeable metal-air batteries and water-splitting systems. In this work, we report the morphology-controllable synthesis of zinc cobalt mixed sulfide (Zn-Co-S) nanoarchitectures, including nanosheets, nanoplates, and nanoneedles, grown on conductive carbon fiber paper (CFP) and the micronanostructure dependent electrochemical efficacy for catalyzing hydrogen and oxygen in zinc-air batteries and water electrolysis. The formation of different Zn-Co-S morphologies was attributed to the synergistic effect of decomposed urea products and the corrosion of NH4F. Among synthesized Zn-Co-S nanostructures, the nanoneedle arrays supported on CFP exhibit superior trifunctional activity for oxygen reduction, oxygen evolution, and hydrogen evolution reactions than its nanosheet and nanoplate counterparts through half reaction testing. It also exhibited better catalytic durability than Pt/C and RuO2. Furthermore, the Zn-Co-S nanoneedle/CFP electrode enables rechargeable Zn-air batteries with low overpotential (0.85 V), high efficiency (58.1%), and long cycling lifetimes (200 cycles) at 10 mA cm-2 as well as considerable performance for water splitting. The superior performance is contributed to the integrated nanoneedle/CFP nanostructure, which not only provides enhanced electrochemical active area, but also facilitates ion and gas transfer between the catalyst surface and electrolyte, thus maintaining an effective solid-liquid-gas interface necessary for electrocatalysis. These results indicate that the Zn-Co-S nanoneedle/CFP system is a low cost, highly active, and durable electrode for highly efficient rechargeable zinc-air batteries and water electrolysis in alkaline solution.

Carbonized cellulose paper as an effective interlayer in lithium-sulfur batteries

One of the several challenging problems hampering lithium-sulfur (Li-S) battery development is the so-called shuttling effect of the highly soluble intermediates (Li2S8–Li2S6). Using an interlayer inserted between the sulfur cathode and the separator to capture and trap these soluble intermediates has been found effective in diminishing this effect. Previously, most reported interlayer membranes were synthesized in a complex and expensive process, and might not be suitable for practical cheap batteries. Herein, a facile method is reported to pyrolyze the commonly used cellulose filter paper into highly flexible and conductive carbon fiber paper. When used as an interlayer, such a carbon paper can improve the cell capacity by several folds through trapping the soluble polysulfides. The enhanced electronic conductivity of the cathode, due to the interlayer, also significantly improves the cell rate performance. In addition, it was demonstrated that such an interlayer can also effectively mitigate the self-discharge problem of the Li-S batteries. This study indicates that the cost-effective pyrolyzed cellulose paper has potential as interlayer for practical Li-S batteries.

Synthesis of 3D Cos/CNF Electrode for Efficient Oxygen Evolution

In order to achieve a high efficiency oxygen production, 3D electrode was designed and synthesized by electrodeposition of cobalt sulfides (CoS) onto the conductive carbon fiber paper (CFP) substrate (1×1 cm2) by cyclic voltammetry at different scan rate of 5, 10, 20, 30 mV s-1 in 12.5 mM Co(NO3)2 and 12.5 mM thiourea. The CoS/CFP was directly used as anode to highlight the merits of the novel architecture, showing a rather low Tafel slope (~60 mV dec-1) and low overpotential (~0.3 V). The high electrochemical performance of CoS/CFP electrode will be discussed in detail with the analysis of SEM, XRD and XPS.

Carbon Fiber Paper Cathodes for Lithium Ion Batteries

A lithium ion battery cathode structure was produced which has the potential for excellent capacity retention and good thermal management. In these cathodes, the active cathode material (lithium iron phosphate) was carbon bonded to a thermally and electrically conductive carbon fiber paper (CFP) support. Electrochemical testing was performed on Swagelok cells consisting of CFP cathodes and lithium anodes. High specific energy, near-theoretical capacity, and good cycling performance were demonstrated for 0.11 and thick CFP cathodes.