Sha Zeng

Electrochemical fabrication of carbon nanotube/polyaniline hydrogel film for all-solid-state flexible supercapacitor with high areal capacitance

Carbon nanotube (CNT) film is a favorable kind of substrate in flexible electric devices because of its superior flexibility, favorable mechanical strength and excellent electrical conductivity. Moreover, since the conductive polymer polyaniline (PANI) possesses a high capacitance and is easy to manufacture, it is always a favored material in the field of supercapacitors. In this research, CNT film synthesized via a floating catalyst chemical vapor deposition method could be further activated by its electrochemical re-expansion to achieve better porosity and higher specific area, in order to obtain an all-solid-state flexible supercapacitor with a higher area capacitance. In comparison with the pristine CNT film decorated with PANI, electrochemically fabricated CNT hydrogel film with PANI deposition had a higher specific area capacitance of 680 mF cm−2 at 1 mA cm−2. The all-solid-state supercapacitor that was synthesized from this composite film exhibited a high specific area capacitance of 184.6 mF cm−2 at 1 mA cm−2, which was higher than many similar supercapacitors. The rolling test showed that this supercapacitor maintained its high capacitance even under conditions of rolling. After 500 charge–discharge cycles, it also retained its high coulombic efficiency and specific area capacitance. This all-solid-state supercapacitor shows great potential in the field of energy storage devices.

Facile Assembly of Ni-Co Hydroxide Nanoflakes on Carbon Nanotube Network with Highly Electrochemical Capacitive Performance

Herein, we demonstrate the high-density assembly of Ni-Co hydroxide nanoflakes on conductive carbon nanotube (CNT) network through a simple and rapid chemical precipitation method, presenting a low-cost and high-performance scaffold for pseudosupercapacitor. It is found that the Ni-Co layered double hydroxide (LDH) nanoflakes prefer to proliferate around large-diameter CNTs (diameter>50 nm), with conductive CNT network well-maintained. Such hierarchical nanostructures show greatly improved specific surface areas compared with bare CNT network and are freestanding without other organic binder, which can be directly employed as a binder-free compact electrode assembly. By optimizing the chemical composition of as-precipitated LDH nanoflakes, the resultant Co0.4Ni0.6(OH)2 LDH/CNT composite nanostructures exhibit the largest specific electrochemical capacitance and the best rate performance, with their capacitance up to 1843 F/g under a low current density of 0.5 A/g and maintained at 1231 F/g when the current density is increased 20 times to 10 A/g. Importantly, such hierarchical nanostructures tend to prevent the electrode from severe structural damage and capacity loss during hundreds of charge/discharge under a high rate (2 A/g), ensuring the electrode with high-energy density (51 W h/kg) at power density of 3.3 kW/kg.

Oxygen Evolution Assisted Fabrication of Highly Loaded Carbon Nanotube/MnO2 Hybrid Films for High-Performance Flexible Pseudosupercapacitors.

To date, it has been a great challenge to design high-performance flexible energy storage devices for sufficient loading of redox species in the electrode assemblies, with well-maintained mechanical robustness and enhanced electron/ionic transport during charge/discharge cycles. An electrochemical activation strategy is demonstrated for the facile regeneration of carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition strategy into a flexible, robust, and highly conductive hydrogel-like film, which is promising as electrode matrix for efficient loading of redox species and the fabrication of high-performance flexible pseudosupercapacitors. The strong and conductive CNT films can be effectively expanded and activated by electrochemical anodic oxygen evolution reaction, presenting greatly enhanced internal space and surface wettability with well-maintained strength, flexibility, and conductivity. The as-formed hydrogel-like film is quite favorable for electrochemical deposition of manganese dioxide (MnO2 ) with loading mass up to 93 wt% and electrode capacitance kept around 300 F g(-1) (areal capacitance of 1.2 F cm(-2) ). This hybrid film was further used to assemble a flexible symmetric pseudosupercapacitor without using any other current collectors and conductive additives. The assembled flexible supercapacitors exhibited good rate performance, with the areal capacitance of more than 300 mF cm(-2) , much superior to other reported MnO2 based flexible thin-film supercapacitors.

Electrochemical conversion of Ni2(OH)2CO3 into Ni(OH)2 hierarchical nanostructures loaded on a carbon nanotube paper with high electrochemical energy storage performance

Large-diameter carbon nanotube (CNT) paper was used as a porous and conductive template to obtain vertically aligned Ni2(OH)2CO3 nanowire array shells, which could be further converted into highly active Ni(OH)2 nanosheets by a cyclic voltammetry strategy. The as-prepared hierarchical nanostructure showed superior electrochemical performance for the electrodes of supercapacitors.

Crosslinked Carbon Nanotube Aerogel Films Decorated with Cobalt Oxides for Flexible Rechargeable Zn–Air Batteries

Air electrodes with high catalytic activity are of great importance for rechargeable zinc-air batteries. Herein, a flexible, binder-free composite air electrode for zinc-air batteries is reported, which utilizes a lightweight, conductive, and crosslinked aerogel film of carbon nanotubes (CNTs) functioned as a 3D catalyst-supporting scaffold for bifunctional cobalt (II/III) oxides and as a current collector. The composite electrode shows high catalytic activities for both oxygen reduction reaction and oxygen evolution reaction, resulting from the synergistic effect of nitrogen-doped CNTs and spinel Co3 O4 nanoparticles. Solid-state Zn-air batteries assembled using such free-standing air electrodes (without the need of additional current collectors) are bendable and show low resistances, low charge/discharge overpotentials, and a high cyclic stability.

A new insight into the rechargeable mechanism of manganese dioxide based symmetric supercapacitors

Pseudocapacitive symmetric supercapacitors, where both the cathode and the anode have the same pseudocapacitive material, have been widely investigated for developing high-performance supercapacitors. However, being different from electrochemical double-layer (EDL) capacitive electrodes, the charge storage of pseudocapacitive materials relies on reversible redox reactions that change the ion valence status, which is not the case for EDL capacitors (EDLCs). In this research, as a typical inorganic pseudocapacitive material for supercapacitors, a manganese dioxide (MnO2) based symmetric supercapacitor was carefully investigated by using a flexible and ultra-light carbon nanotube (CNT) film as the current collector and substrate for MnO2 electrodeposition. The results indicated that the pristine active material on the positive electrode showed no change after cyclic charging/discharging, but only served as a stable counter electrode and reference electrode. The main redox reaction for the energy storage of the supercapacitor occurred on the negative electrode. Furthermore, the dissolved Mn2+ ions on the negative electrode were deposited onto the positive electrode, which induced an increase in mass of the positive electrode and a decrease in mass of the negative electrode. This research could give new insight into the working mechanism of MnO2 electrodes and other pseudocapacitive materials in symmetric supercapacitors.

Large‐Stroke Electrochemical Carbon Nanotube/Graphene Hybrid Yarn Muscles

Artificial muscles are reported in which reduced graphene oxide (rGO) is trapped in the helical corridors of a carbon nanotube (CNT) yarn. When electrochemically driven in aqueous electrolytes, these coiled CNT/rGO yarn muscles can contract by 8.1%, which is over six times that of the previous results for CNT yarn muscles driven in an inorganic electrolyte (1.3%). They can contract to provide a final stress of over 14 MPa, which is about 40 times that of natural muscles. The hybrid yarn muscle shows a unique catch state, in which 95% of the contraction is retained for 1000 s following charging and subsequent disconnection from the power supply. Hence, they are unlike thermal muscles and natural muscles, which need to consume energy to maintain contraction. Additionally, these muscles can be reversibly cycled while lifting heavy loads.

An adaptive and stable bio-electrolyte for rechargeable Zn-ion batteries

Sulfate solutions with high safety, low cost and wide electrochemical windows are widely used as electrolytes for aqueous batteries. However, the practical application of such batteries, especially for wearable devices, is still limited by the lack of a stable polymer electrolyte, due to the strong ability of the favorably selected sulfate electrolytes to precipitate polymers. Herein, we report a very stable sulfate-tolerant gum bio-electrolyte prepared by readily mixing the xanthan bio-polymer with aqueous sulfate solutions. The gum electrolyte is highly conductive (1.46 × 10−2 S cm−1), hydrating, adhesive, and adaptive. Zn-ion batteries assembled using such gum electrolytes show competitive performance in aqueous batteries, which include high capacities (about 260 mA h g−1 for MnO2 at 1C), high rate capability, good cyclability (about 90% capacity retention and about 100% coulombic efficiency over 330 cycles at 1C, and about 127 mA h g−1 capacity over 1000 cycles at 5C), and high durability to bending and twisting. Moreover, the use of the gum electrolyte could prohibit the growth of zinc dendrites. Considering the wide suitability of aqueous sulfate electrolytes for rechargeable aqueous metal-ion batteries, our gum electrolyte would also be applicable for boosting the practical application of such batteries.

Hierarchical carbon nanotube hybrid films for high-performance all-solid-state supercapacitors

Electrodes that have high electrical conductivity, large ion-accessible area and good mechanical robustness are highly needed for developing high-performance flexible supercapacitors. Herein, we report the preparation of a carbon nanotube (CNT) hybrid film consisting of large-diameter multi-walled carbon nanotubes (MWCNTs) and small-diameter single-walled carbon nanotubes (SWCNTs) and its application as an electrode for flexible supercapacitors. In the hybrid film, MWCNTs provide a macroporous and robust scaffold while SWCNTs bridge MWCNTs and improve the films strength and electrical conductivity. Resulting from such a hierarchical structure that could facilitate ion transportation inside of the electrode, the specific capacitance of SWCNTs loaded in hybrid films was increased by about 273% when compared with that of SWCNT films. A thin layer of polyaniline was electrochemically deposited on the hybrid film, forming a composite film with good structural flexibility and high capacitance. Solid-state symmetric supercapacitors assembled using such a composite film electrode showed good rate performance and high cycling stability.