Yong Du

Facile Preparation and Thermoelectric Properties of Bi2Te3 Based Alloy Nanosheet/PEDOT:PSS Composite Films

Bi2Te3 based alloy nanosheet (NS)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) composite films were prepared separately by spin coating and drop casting techniques. The drop cast composite film containing 4.10 wt % Bi2Te3 based alloy NSs showed electrical conductivity as high as 1295.21 S/cm, which is higher than that (753.8 S/cm) of a dimethyl sulfoxide doped PEDOT:PSS film prepared under the same condition and that (850-1250 S/cm) of the Bi2Te3 based alloy bulk material. The composite film also showed a very high power factor value, ∼32.26 μWm(-1) K(-2). With the content of Bi2Te3 based alloy NSs increasing from 0 to 4.10 wt %, the electrical conductivity and Seebeck coefficient of the composite films increase simultaneously.

High-Performance Supercapacitor Electrode Materials from Cellulose-Derived Carbon Nanofibers

Nitrogen-functionalized carbon nanofibers (N-CNFs) were prepared by carbonizing polypyrrole (PPy)-coated cellulose NFs, which were obtained by electrospinning, deacetylation of electrospun cellulose acetate NFs, and PPy polymerization. Supercapacitor electrodes prepared from N-CNFs and a mixture of N-CNFs and Ni(OH)2 showed specific capacitances of ∼236 and ∼1045 F g(-1), respectively. An asymmetric supercapacitor was further fabricated using N-CNFs/Ni(OH)2 and N-CNFs as positive and negative electrodes. The supercapacitor device had a working voltage of 1.6 V in aqueous KOH solution (6.0 M) with an energy density as high as ∼51 (W h) kg(-1) and a maximum power density of ∼117 kW kg(-1). The device had excellent cycle lifetime, which retained ∼84% specific capacitance after 5000 cycles of cyclic voltammetry scans. N-CNFs derived from electrospun cellulose may be useful as an electrode material for development of high-performance supercapacitors and other energy storage devices.

A self-supported, flexible, binder-free pseudo-supercapacitor electrode material with high capacitance and cycling stability from hollow, capsular polypyrrole fibers

Flexible energy devices with high performance and long-term stability are highly promising for applications in portable electronics, but remain challenging to develop. As an electrode material for pseudo-supercapacitors, conducting polymers typically show higher energy storage ability over carbon materials and larger conductivity than transition-metal oxides. However, conducting polymer-based supercapacitors often have poor cycling stability, attributable to the structural rupture caused by the large volume contrast between doping and de-doping states, which has been the main obstacle to their practical applications. Herein, we report a simple method to prepare a flexible, binder-free, self-supported polypyrrole (PPy) supercapacitor electrode with high cycling stability through using novel, hollow PPy nanofibers with porous capsular walls as a film-forming material. The unique fiber structure and capsular walls provide the PPy film with enough free-space to adapt to volume variation during doping/de-doping, leading to super-high cycling stability (capacitance retention > 90% after 11 000 charge–discharge cycles at a high current density of 10 A g−1) and high rate capability (capacitance retention ∼ 82.1% at a current density in the range of 0.25–10 A g−1).

Thermoelectric Properties of Flexible PEDOT:PSS/Polypyrrole/Paper Nanocomposite Films

Flexible poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/polypyrrole/paper (PEDOT:PSS/PPy/paper) thermoelectric (TE) nanocomposite films were prepared by a two-step method: first, PPy/paper nanocomposite films were prepared by an in situ chemical polymerization process, and second, PEDOT:PSS/PPy/paper TE composite films were fabricated by coating the as-prepared PPy/paper nanocomposite films using a dimethyl sulfoxide-doped PEDOT:PSS solution. Both the electrical conductivity and the Seebeck coefficient of the PEDOT:PSS/PPy/paper TE nanocomposite films were greatly enhanced from 0.06 S/cm to ~0.365 S/cm, and from 5.44 μV/K to ~16.0 μV/K at ~300 K, respectively, when compared to the PPy/paper TE nanocomposite films. The thermal conductivity of the PEDOT:PSS/PPy/paper composite film (0.1522 Wm−1K−1 at ~300 K) was, however, only slightly higher than that of the PPy/paper composite film (0.1142 Wm−1K−1 at ~300 K). As a result, the ZT value of the PEDOT:PSS/PPy/paper composite film (~1.85 × 10−5 at ~300 K) was significantly enhanced when compared to that of the PPy/paper composite film (~4.73 × 10−7 at ~300 K). The as-prepared nanocomposite films have great potential for application in flexible TE devices.

Multifold enhancement of the output power of flexible thermoelectric generators made from cotton fabrics coated with conducting polymer

Thermoelectric (TE) conversion of human body heat is highly desirable for powering microelectronic devices. However, most of the existing TE generators are not practical because they contain toxic substances, are difficult to process, are rigid and impermeable, or are unable to be produced on a large scale. Previously, we have demonstrated a flexible, air-permeable TE power generator fabricated from polyester fabric coated with a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate), and fine silver wires [Y. Du, et al., Sci. Rep., 2015, 5, 06411]. Here, we show a multifold enhancement of the output power of this type of flexible thermoelectric generator using poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) coated cotton fabric, and fine Constantan wires. A fabric device consisting of 5 TE units was found to generate a voltage output (V) of 18.7 mV and maximum output electrical power of 212.6 nW at a temperature difference (ΔT) of 74.3 K. The fabric generators can be rolled up and remain operational after being bent at different bending radii and in different directions. Furthermore, a TE generator has been shown to be stable even after 10 days of continuous operation at a ΔT up to ∼78 K. This fabric-based TE generator is seen to be useful for the development of self-powered, wearable electronic devices.

Morphologies Tuning of Polypyrrole and Thermoelectric Properties of Polypyrrole Nanowire/Graphene Composites

Polypyrrole (PPy) with different morphologies (e.g., particles, nanotubes, and nanowires) were successfully prepared by adding or without adding different kinds of surfactants through a chemical oxidative polymerization method, respectively. The results show that the morphologies of PPy can be effectively controlled and have a significantly effects on their thermoelectric properties. The PPy nanowires exhibit the highest electrical conductivity and Seebeck coefficient among the various PPy morphologies, such as particles, nanotubes, and nanowires, so PPy nanowires were chosen to prepare PPy nanowire/graphene thermoelectric composites via a soft template polymerization method using cetyltrimethyl ammonium bromide as the template. Both electrical conductivity and Seebeck coefficient of the PPy nanowire/graphene composites increased as the content of graphene increases from 0 to 20 wt %, and as the measured temperature increases from 300 K to 380 K, which leds to the same trend for the power factor. A highest power factor of 1.01 μWm−1K−2 at ~380 K was obtained for the PPy nanowire/graphene composites with 20 wt % PPy nanowire, which is about 3.3 times higher than that of the pure PPy nanowire.

Single-walled Carbon Nanotube / Polypyrrole Thermoelectric Composite Materials

A single-walled carbon nanotube/polypyrene (SWCNT/PPy) thermoelectric composites were prepared by an in situ oxidative polymerization method. The effect of SWCNT composition on the microstructure of the SWCNT/PPy nanocomposites was investigated. The thermoelectric properties of the composites were measured at different temperatures between 298 K and 398 K. Both of the electrical conductivity and the See beck coefficient of the SWCNT/PPy nanocomposites with 40% SWCNT loading increased simultaneously in the measured temperature. A maximum power factor of 5.46 μWm-1K-2 was obtained at 398 K for the SWCNT/PPy nanocomposite with 40 wt% SWCNT loading.