Zong-Qiong Lin

Nanostructured Conjugated Polymers for Energy-Related Applications beyond Solar Cells.

To meet the ever-increasing requirements for the next generation of sustainable and versatile energy-related devices, conjugated polymers, which have potential advantages over small molecules and inorganic materials, are among the most promising types of green candidates. The properties of conjugated polymers can be tuned through modification of the structure and incorporation of different functional moieties. In addition, superior performances can be achieved as a result of the advantages of nanostructures, such as their large surface areas and the shortened pathways for charge transfer. Therefore, nanostructured conjugated polymers with different properties can be obtained to be applied in different energy-related organic devices. This review focuses on the application and performance of the recently reported nanostructured conjugated polymers for high-performance devices, including rechargeable lithium batteries, microbial fuel cells (MFCs), thermoelectric generators, and photocatalytic systems. The design strategies, reaction mechanisms, advantages, and limitations of nanostructured conjugated polymers are further discussed in each section. Finally, possible routes to improve the performances of the current systems are also included in the conclusion.

A π-conjugated polymer gelator from polyfluorene-based poly(tertiary alcohol) via the hydrogen-bonded supramolecular functionalization

The supramolecular approach of π-conjugated polymers imparts excellent self-assembly behaviour to construct organogels and simultaneously affords superstructured thin films, which allow for uncovering structure–function relationships. Herein, a polyfluorene-based poly(tertiary alcohol), poly(9-(4-(octyloxy)phenyl)-2,7-fluoren-9-ol) (PPFOH), has been synthesized to investigate the organic solvent effect on the gelation at room temperature. The driving force of hydrogen bonding and π–π stacking interactions in the aggregate processing of PPFOH has been investigated using nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and photoluminescence (PL). Aggregated structures of PPFOH in gelation solvents have been correlated with the characteristic emission peak at 440 nm in PL spectra. Large effects of the number molecular weight (Mn) on critical gel concentration (CGC) and green emissions of the organogels and nanostructured thin films have been observed. Finally, the emission colour of PPFOH from supramolecular thin films can be tuned flexibly from blue to yellow via selecting different types of solvent and Mn, which are promising approaches to control the optoelectronic functionalities of supramolecular π-conjugated polymers with potential applications in organic thin film electronics, optoelectronics and mechano-electronics.

Inkjet-printed porous polyaniline gel as an efficient anode for microbial fuel cells

Future application of microbial fuel cells (MFCs) requires a high-throughput and more convenient pathway to manufacture high-performance anodes. In this research, inkjet-printed PANI gel on carbon paper was first fabricated and then successfully employed as anodes in MFCs. Thanks to the inkjet-printing technology, such anodes can be easily produced in large quantities. Moreover, these anodes possessed good conductivity and a porous structure, as well as the ability to electrostatically interact with bacteria cells, which contributed to a 6.1-fold increase in the output power over that of the unmodified carbon paper. Taken together, our study presents a novel strategy in preparing highly scalable, high-performance MFC anodes, in promoting the practical application of MFC technology.

Living and Conducting: Coating Individual Bacterial Cells with in situ Formed Polypyrrole

Coating individual bacterial cells with conjugated polymers to endow them with more functionalities is highly desirable. Here, we developed an in situ polymerization method to coat polypyrrole on the surface of individual Shewanella oneidensis MR-1, Escherichia coli, Ochrobacterium anthropic or Streptococcus thermophilus. All of these as-coated cells from different bacterial species displayed enhanced conductivities without affecting viability, suggesting the generality of our coating method. Because of their excellent conductivity, we employed polypyrrole-coated Shewanella oneidensis MR-1 as an anode in microbial fuel cells (MFCs) and found that not only direct contact-based extracellular electron transfer is dramatically enhanced, but also the viability of bacterial cells in MFCs is improved. Our results indicate that coating individual bacteria with conjugated polymers could be a promising strategy to enhance their performance or enrich them with more functionalities.

Synergistic Effects of Self-Doped Nanostructures as Charge Trapping Elements in Organic Field Effect Transistor Memory

Despite remarkable advances in the development of organic field-effect transistor (OFET) memories over recent years, the charge trapping elements remain confined to the critical electrets of polymers, nanoparticles, or ferroelectrics. Nevertheless, rare reports are available on the complementary advantages of different types of trapping elements integrated in one single OFET memory. To address this issue, we fabricated two kinds of pentacene-based OFET memories with solution-processed amorphous and β-phase poly(9,9-dioctylfluorene) (PFO) films as charge trapping layers, respectively. Compared to the amorphous film, the β-PFO film has self-doped nanostructures (20-120 nm) and could act as natural charge trapping elements, demonstrating the synergistic effects of combining both merits of polymer and nanoparticles into one electret. Consequently, the OFET memory with β-PFO showed nearly 26% increment in the storage capacity and a pronounced memory window of ∼45 V in 20 ms programming time. Besides, the retention time of β-PFO device extended 2 times to maintain an ON/OFF current ratio of 10(3), indicating high bias-stress reliability. Furthermore, the β-PFO device demonstrated good photosensitivity in the 430-700 nm range, which was attributed to the additive effect of smaller bandgap and self-doped nanostructures of β-phase. In this regard, the tuning of molecular conformation and aggregation in a polymer electret is an effective strategy to obtain a high performance OFET memory.

An ambipolar azaacene as a stable photocathode for metal-free light-driven water reduction

Present photoelectrochemical (PEC) cells for water splitting are based on inorganic electrodes. For future large-scale applications, electrodes that are metal-free, of low cost, and with sustainable availability are crucial. Herein, we report a new ambipolar larger azaacene (DQNDN) as a single-active-element-based photocathode in PEC cells with a current density of 0.13 mA cm−2 at −0.13 V versus RHE.

A polyhedral supramolecular system of endocyclic crystalline organic nanostructures: the case of triptycenes

Controlled synthesis of polyhedral crystals has acquired intense attention over the past few years due to their potential electrical and optical properties and special functionalities for integrated devices. In this work, endocyclic molecules of triptycene are self-assembled into pretty uniform polyhedra of quasi-decahedra and well-defined nanosheets via the assistance of P123 and CTAB, respectively. These nanostructures have been clearly investigated by using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) and X-ray diffraction (XRD) patterns. The aromatic multi-plane triptycene molecules exhibit a definite three-dimensional assembly tendency and the assembly process can also be effectively tuned by surfactants. The above results are invaluable to the design of polyhedron supramolecular synthons and go forward through simulation as well as morphology control to certain promising nanoscale structures.

Charge trapping behavior visualization of dumbbell-shaped DSFXPY via electrical force microscopy

The electrons and holes are injected into the sterically hindered organic semiconductor film (DSFXPY, 1,6-di(spiro[fluorene-9,90-xanthene]-2-yl)pyrene) through applying controllable biases on the conductive atomic force microscopy tip. The scanned visualized images of trapped charge spots in films depend on such factors as decay time after injection, injection biases, and scanning biases with the use of electrostatic force microscopy (EFM). Using the quantitative analysis, the total amount of trapped charges and the surface trapped charge density of the DSFXPY films are calculated and the injected charge signs are confirmed. The results exhibit that the injected charge carriers are highly localized in DSFXPY films, and the retention ability of the holes is stronger than that of the electrons. It is proved that the holes have better endurance in DSFXPY films than electrons by the microscopic experiments. Combining with the evolution processes of trapped charge spots in the different thickness DSFXPY films via Kelvin probe force microscopy (KPFM), the diffusion mechanism of trapped charges is discussed. The results show the application potential of DSFXPY in nonvolatile memory devices due to its outstanding charge storage properties.

Nanostructured Polymers and Polymer/Inorganic Nanocomposites for Thermoelectric Applications

Thermoelectric generators (TEGs) are being considered as one of the most promising green technology to convert the waste energy into useful electricity. Conjugated polymers and their nanostructures possess high electrical conductivity, low thermal conductivity, and reasonable Seebeck coefficient, which can meet the requirements for high-efficiency TEGs. This chapter focuses on recent progress in the development of nanostructured polymers and polymer/inorganic nanocomposites with multi-dimensional nanostructures (0D, 1D to 2D) for thermoelectric applications. The challenges and perspectives in the emerging field of nanostructured polymers are also involved.