Guibin Li

Novel side-chain-type sulfonated diphenyl-based poly(arylene ether sulfone)s with a hydrogen-bonded network as proton exchange membranes

A new bisphenol monomer, 3,3′,5,5′-tetramethoxy-4,4′-dihydroxybiphenyl, was synthesized and copolymerized to prepare diphenyl-based poly(arylene ether sulfone) copolymers containing tetra-methoxy groups (MOPAES). After converting the methoxy group to the reactive hydroxyl group, the resulting side-chain-type sulfonated copolymers (SOPAES) with a hydrogen bonded network were obtained by a sulfobutylation reaction. The copolymers were characterized and confirmed by 1H NMR, FT-IR, thermogravimetric analysis (TGA) and small-angle X-ray scattering. The water uptake, proton and methanol transport properties of the resulting membranes were also determined for fuel cell applications. These SOPAES series membranes showed high proton conductivity in the range of 0.032–0.054 and 0.084–0.142 S cm−1 at 25 and 80 °C under hydrated conditions, respectively. SOPAES-40 (IEC = 1.38 mequiv. g−1) showed comparable proton conductivity with Nafion 117 in the hydrated state. The methanol permeability of these membranes was in the range of 1.58–4.29 × 10−7 cm2 s−1, which is much lower than Nafion (1.55 × 10−6 cm2 s−1). It should be noted that the intra/inter hydrogen bonds formed between sulfonic acid and hydroxyl groups or between hydroxyl and hydroxyl groups improved the mechanical properties and reduced the methanol permeability of the membranes effectively. A combination of suitable proton conductivity, low water uptake, and low methanol crossover for selected SOPAES indicates that they are good candidates as proton exchange membrane materials for fuel cells.

Structural, optical and electrical characterization of gadolinium and indium doped cadmium oxide/p-silicon heterojunctions for solar cell applications

Gadolinium and indium co-doped CdO thin films were prepared by a pulsed laser deposition method. The XRD and XPS results indicated that Gd3+ and In3+ ions occupied locations in the interstitial positions and/or Cd2+-ion vacancies in the CdO lattice. The FESEM images showed that the films were homogeneous and consisted of nanograins with a size range of 23–40 nm. The optical band gap of the CdO thin films can be engineered over a wide range of 2.72–3.56 eV by introducing Gd and In dopants. Such transparent semiconducting Gd and In co-doped CdO films were then grown on p-type Si substrates to fabricate n-CdO/p-Si heterojunction devices. The important junction parameters such as the series resistance (Rs), ideality factor (n) and Schottky barrier height (Φb) were determined by analysing different plots from the current density–voltage (J–V) characteristics. The obtained results indicated that the electrical properties of the heterojunction diodes were controlled by the dopant concentration. The p-Si/n-Cd1−x−yGdxInyO heterojunction diode showed the best values of open circuit voltage, Voc = 1.04 V and short circuit current density, Jsc = 11.4 mA cm−2 under an illumination intensity of 100 mW cm−2, which was suitable for solar cell applications.

Intermolecular ionic cross-linked sulfonated poly(ether ether ketone) membranes with excellent mechanical properties and selectivity for direct methanol fuel cells

Amino-substituted poly(ether ether ketone) (APEEK) and sulfonated poly(ether ether ketone) (SPEEK, IEC = 2.07 mequiv. g−1) have been synthesized via nucleophilic aromatic substitution reaction. The structures of APEEK and SPEEK were characterized by 1H NMR spectra. The composite membranes based on APEEK and SPEEK were confirmed by their FTIR spectra, indicating the formation of intermolecular ionic cross-linking networks between amino and sulfonic groups. The water uptake, proton and methanol transport properties of composite membranes were also determined for fuel cell applications. The results showed that the composite membranes exhibit high selectivity, appropriate proton conductivities as well as reduced water uptake and methanol permeability when compared with the pristine SPEEK membrane. Furthermore, it should be noted that the intermolecular ionic cross-linking effectively improved the tensile strength, breaking elongation, and thermal stabilities of the membranes. In particular, the SPEEK-10 membrane (the weight ratio of APEEK is 10%) showed a tensile strength of 121.2 MPa and breaking elongation of 93.5%, which were 1.5 times and 2.5 times higher than those of pristine SPEEK, respectively. The high selectivity, thermal and mechanical properties indicate that the composite membranes are promising to be used as proton exchange membranes for direct methanol fuel cells.

Novel in situ-foaming materials derived from a naphthalene-based poly(arylene ether ketone) containing thermally labile groups

A novel in situ-foaming material was successfully prepared by a naphthalene-based hydroxyl-containing poly(arylene ether ketone) (PAEK) modified with thermally labile tert-butyloxycarbonyl which can decompose and in situ generate CO2 and isobutene as the foaming agents. The structure and thermal properties of the polymers were characterized by using 1H NMR spectra and thermogravimetry coupled time-resolved mass spectrogram (TG/MS). The resulting polymers exhibited relatively high Tg because of the existence of a rigid naphthalene moiety. Then closed microcellular porous membranes with a wide range of expansion ratio (ER) were obtained by a simple thermal treatment from 140 °C to 280 °C for 60 seconds, without using any other physical or chemical foaming agents. The highest ER was 53.98%. This method has never been reported before on high-performance poly(aryl ether) materials. Furthermore, we investigated the relationship between the foaming temperature and the morphology of membranes in detail by using density measurement and scanning electron microscopy (SEM).