Shuiliang Chen

Supercapacitors based on hybrid carbon nanofibers containing multiwalled carbon nanotubes

Hybrid carbon nanofibers containing multiwalled carbon nanotubes (CNTs) were produced by electrospinning CNTs suspended in a solution of polyacrylonitrile in N,N-dimethylformamide, followed by carbonization and activation using a hydroperoxide–water steam mixture at 650 °C. Transmission electron microscopy and scanning electron microscopy were used to observe the morphology of the CNT-embedded carbon nanofibers. The specific surface area of the nanofibers was measured using the Brunauer–Emmett–Teller method. The electrochemical properties of the nanofibers were characterized by cyclic voltammetry and galvanotactic charge/discharge in 1 M H2SO4 electrolyte. The specific capacitance of electric double-layer capacitors containing CNT-embedded carbon nanofibers as electrodes reached 310 F g−1, which is almost double that obtained for capacitors containing virgin carbon nanofibers as electrodes. The CNTs embedded in the carbonized electrospun nanofibers provide improved conductive pathways for charge transfer in the electrodes and therefore lead to a significantly enhanced specific capacitance.

Needle-like polyaniline nanowires on graphite nanofibers: hierarchical micro/nano-architecture for high performance supercapacitors

Long, ordered and needle-like polyaniline (PANI) nanowires were grown on graphitized electrospun carbon fibers (GECFs) to prepare PANI/GECF composite cloths as electrode material for supercapacitors. The flexible PANI/GECF composite cloths showed three-dimensional (3D) hierarchical micro/nano-architecture and were directly made into electrodes without any conductive additives and binders. The results of electrochemical tests indicated that PANI/GECF electrodes not only displayed a high specific capacitance of 976.5 F g−1 at the current density of 0.4 A g−1, with a retention ratio of 89.2% after 1000 cycles at the current density of 10 A g−1, but also retained a specific capacitance of nearly 500 F g−1 and a coulombic efficiency of 95% at a high current density of 50 A g−1. The good performance of PANI/GECF is attributed to the high electrical conductivity of GECFs and 3D hierarchical micro/nano-architecture, which is a combination of 3D macroporosity of GECF cloth with the 3D nanostructure of ordered needle-like PANI nanowires.

Layered corrugated electrode macrostructures boost microbial bioelectrocatalysis

The future success of microbial bioelectrochemical systems like microbial fuel cells inevitably depends on the increase of their performance at decreasing material costs. One of the key elements and a research priority is the biofuel cell anode. Here we propose layered corrugated carbon (LCC) as an inexpensive but high performance electrode material produced from the carbonization of one of the most abundant packing materials of our society: corrugated cardboard. In the base configuration of one corrugated layer the projected current density of LCC already reaches 70 A m−2. Increasing the number of corrugated layers increases the current density linearly. Thus, 200 A m−2 are achieved at three and 390 A m−2 at six corrugated layers. These current density values, which were confirmed by experiments in two independent laboratories, represent a performance increase of above one order of magnitude compared to the current state of research.

A three-dimensionally ordered macroporous carbon derived from a natural resource as anode for microbial bioelectrochemical systems.

Top of the crops: The direct use of a natural three-dimensional (3D) architecture in microbial fuel cells (MFCs) is reported for the first time. Stems from the crop plant kenaf (Hibiscus cannabinus) are carbonized and used as anode material in MFCs. The current density generated by the carbon is comparable to that of other 3D anodes prepared by other methods. The renewable and low-cost characteristics of this material provide an excellent basis for large-scale application in microbial bioelectrochemcial systems.

Reticulated carbon foam derived from a sponge-like natural product as a high-performance anode in microbial fuel cells

In this paper, we report a reticulated carbon foam prepared by direct carbonization of the sponge-like natural product Pomelo peel, and its application as an anode in microbial fuel cells (MFCs). Electrochemical measurements show that the carbon foam anode generates a high projected current density of over 4.0 mA cm−2 and a volumetric current density of 18.7 mA cm−3, which is five times that of commercial Reticulated Vitreous Carbon Foam (RVC) and 2.5 times that of graphite felts with similar electrode size. The high current density could be attributed to the wrinkled electrode surface, large pore size and high porosity of over 97% in the carbon foam.

Mechanical characterization of single high-strength electrospun polyimide nanofibres

Ultimate tensile strength and axial tensile modulus of single high-strength electrospun polyimide [poly(p-phenylene biphenyltetracarboximide), BPDA/PPA] nanofibres have been characterized by introducing a novel micro tensile testing method. The polyimide nanofibres with diameters of around 300 nm were produced by annealing their precursor (polyamic acid) nanofibres that were fabricated by the electrospinning technique. Experimental results of the micro tension tests show that polyimide nanofibres had an average ultimate tensile strength of 1.7 ± 0.12 GPa, axial tensile modulus of 76 ± 12 GPa and ultimate strain of ∼3%. The ultimate tensile strength and axial tensile modulus of the electrospun polyimide nanofibres in this study are among the highest ones reported in the literature to date. The precursor nanofibres with similar diameters and molecular weights had an average ultimate tensile strength of 766 ± 41 MPa, axial tensile modulus of 13 ± 0.4 GPa and ultimate strain of ∼43%. The experimental stress–strain curves obtained in this study indicate that under axial tension, the precursor (polyamic acid) nanofibres behave as linearly strain-hardening ductile material without obvious softening at final failure, while the polyimide nanofibres behave simply as brittle material with very high tensile strength and axial tensile modulus. Furthermore, by using a transmission electron microscope, detailed fractographical analysis was performed to examine the tensile failure mechanisms of the polyimide nanofibres, which include chain scission, pull-out, chain bundle breakage, etc. X-ray diffraction analysis of the highly aligned polyimide nanofibres shows the high chain alignment along the nanofibre axis that was formed in the electrospinning process and responsible for the high tensile strength and axial tensile stiffness. (Some figures in this article are in colour only in the electronic version)

Stainless steel mesh supported nitrogen-doped carbon nanofibers for binder-free cathode in microbial fuel cells

In this communication, we report a binder-free oxygen reduction cathode for microbial fuel cells. The binder-free cathode is prepared by growth of nitrogen-doped carbon nanofibers (NCNFs) on stainless steel mesh (SSM) via simple pyrolysis of pyridine. The interaction force between NCNFs and SSM surface is very strong which is able to tolerate water flush. The NCNFs/SSM cathode shows high and stable electrocatalytic activity for oxygen reduction reaction, which is comparable to that of Pt/SSM and ferricyanide cathode. This study proposes a promising low-cost binder-free cathode for microbial fuel cells.

Effect of fiber diameter on the behavior of biofilm and anodic performance of fiber electrodes in microbial fuel cells

A series of fiber electrodes with fiber diameters ranging from about 10 to 0.1 μm were tested as anodes in microbial fuel cells to study the effect of fiber diameter on the behavior of biofilm and anodic performance of fiber electrodes. A simple method of biofilm fixation and dehydration was developed for biofilm morphology characterization. Results showed that the current density of fiber anodes increased until the fiber diameter approached 1 μm which was about the length of the dominant microorganisms in biofilm. The highest current density was 3.08 mA cm(-2), which was obtained from fiber anode with high porosity of over 99% and fiber diameter of 0.87 μm. It was believed that the high current density was attributed to the high porosity, as well as proper fiber diameter which ensured formation of thick and continuous solid biofilms.

Highly strong and highly tough electrospun polyimide/polyimide composite nanofibers from binary blend of polyamic acids

Electrospun blend-polyimide (blend-PI) nanofibers with high tensile strength and toughness are highlighted in this article. The blend-PI nanofibers were prepared by electrospinning the binary blend of rigid and flexible polyamic acids, followed by thermal imidization. The method is simple and can be extended to other kinds of polyamic acids. The morphologies and structures of the blend-PI nanofibers were investigated by scanning electron microscopy (SEM) and wide-angle X-ray diffraction (XRD). The mechanical properties, thermal properties and miscibility of the blend-PI nanofibers were studied by a tensile test, thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The mechanical properties of the blend-PI nanofibers, including tensile strength, modulus, elongation at break and toughness, could be well-tuned by modifying the molar ratio of the rigid component (B-PI) and the flexible component (O-PI). The blend-PI nanofibers with B-PI/O-PI molar ratio of 4/6 had an ultra-high strength of 1.3 GPa with an excellent toughness of 82 J g−1. All the blend-PI nanofibers showed thermal stability to above 500 °C. The presence of only one glass transition temperature (Tg) suggested the good miscibility of the binary PIs in the blend-PI nanofibers. This study would provide completely new opportunities for modifying the properties of electrospun PI nanofibers.

Natural source derived carbon paper supported conducting polymer nanowire arrays for high performance supercapacitors

Free-standing electrode materials have shown important application in supercapacitors. In this paper, a low cost and large scale producible carbon paper (CP) was prepared by the carbonization of cellulose paper. Self-supported conducting polymer composites were fabricated by in situ polymerization of aniline on the resulting CP substrate. The morphology and structure of the as-prepared polyaniline/carbon paper (PANI/CP) composites were characterized by scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy and an automatic N2 adsorption instrument. PANI/CP hybrids could be directly built into electrodes without adding polymer binders and conductive agents. The capacitance performance of PANI/CP electrodes was systematically studied with cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. PANI/CP hybrids showed a high specific capacitance of 1090.8 F g−1 along with low resistance and good stability. All the results indicated the prepared PANI/CP hybrids were promising electrode materials for supercapacitors.