Jinlin Lu

HPW/MCM‐41 Phosphotungstic Acid/Mesoporous Silica Composites as Novel Proton‐Exchange Membranes for Elevated‐Temperature Fuel Cells

Proton-exchange membrane and direct methanol fuel cells (PEMFCs and DMFCs) have attracted much attention as clean energy sources for various applications, such as electric vehicles, portable electronics, and domestic power generation, because of their high power density, high efficiency, and low greenhouse gas emission. Especially, the operation of PEMFCs and DMFCs at temperatures above 100 8C is considered to have many advantages, such as the elimination of CO poisoning of the platinum electrocatalyst, faster electrode reaction kinetics, simplified water and heat management, higher energy efficiency, and reduced usage of precious Pt and Pt alloy catalyst. However, the state-of-the-art proton-exchange membranes (PEMs) based on perfluorosulfonic acid (PFSA), such as Nafion, are unstable at elevated temperatures ( 100 8C) and proton conductivity decreases significantly due to the loss of water from the membrane under conditions of high temperatures or low humidities. Therefore, development of PEMs with high proton conductivity and stability at elevated temperatures is a major challenge. Great efforts have been dedicated to developing PEMs for operation at elevated temperatures based on mesoporous or nanoporous inorganic materials. Mesoporous inorganic materials have a pore size range of 2–50 nm and are characterized by high specific surface area, nanometer-sized channels or frameworks with an ordered or disordered interconnected internal structure, and high structural stability, which make feasible potential applications as proton-exchange membranes operating at elevated temperatures. Lu and co-workers reported sol–gel-derived mesostructured zirconium phosphates with proton conductivities of about 10 –10 6 S cm . Colomer et al. synthesized nanoporous anatase thin films with conductivity values from 10 5 to 10 3 S cm 1 in the range of 33%–81% relative humidity (RH) at room temperature. Li and Nogami prepared proton-conducting mesoporous silica films with conductivity ranging from 10 6 to 10 4 S cm 1 under 40%–90% humidity. However, the proton conductivity of the pure mesoporous materials depends significantly on their textural characteristics. For instance, Colomer et al. also reported a proton conductivity of 2.0 10 2 S cm 1 on mesoporous acid-free silica xerogels and 3.78 10 2 S cm 1 on a nanoporous anatase thin film at 80 8C and 81% RH. Yamada et al. reported a TiO2-P2O5 mesoporous nanocomposite with a proton conductivity value of 2 10 2 S cm 1 at 160 8C. Halla et al. synthesized meso-SiO2-C12EO10OH-CF3SO3H as a new protonconducting electrolyte and reported a conductivity of 1 10 3 S cm 1 at room temperature and 90% RH. Although the conductivity values of mesoporous acid-free silica xerogels, meso-SiO2-C12EO10OHCF3SO3H or anatase thin films are adequate for fuel cell applications, their performance as an electrolyte in a PEMFC has not been evaluated yet. Yamada and Honma synthesized a H3PW12O40 (abbreviated as HPW) and polystyrene sulfonic acid (PSS) composite by self-assembly of –SO3H onto the HPW surface, achieving a proton conductivity of 1 10 2 S cm 1 at 180 8C. Nevertheless, the power density of the cell based on a PSS with 10wt% HPW composite membrane is very low, ca. 3mW cm 2 at 160 8C in H2/O2 with no external humidity. Uma and Nogami synthesized an inorganic glass composite membrane consisting of a mixture of phosphotungstic acid (HPW) and phosphomolybdic acid (HPM), and reported very high conductivity values, 1.014 S cm 1 at 30 8C and 85% RH for a mesoporous-structured HPW/HPM-P2O5-SiO2 glass, [24] and 1.01 10 1 S cm 1 at 85 8C under 85% RH for a mesoporousstructured HPW-P2O5-SiO2 glass. [17] The cell performance based on these inorganic PEMs was 35–42mW cm 2 in H2/O2 at ca. 30 8C under 30% RH. However, there is little information on the performance of HPWand HPM-incorporated P2O5-SiO2 glass electrolyte cells at elevated high temperatures or in methanol fuels. Here, we present a novel inorganic PEM based on highly ordered mesoporous MCM-41 silica with assembled HPW nanoparticles by the vacuum-assisted impregnation method (VIM). The proton conductivity of the HPW/MCM-41 mesoporous silica inorganic PEM is 0.018 and 0.045 S cm 1 at 25 and 150 8C, respectively. Most significantly, the PEMFCs based on the HPW/MCM-41 mesoporous-silica membrane showed a very impressive performance, achieving a maximum power density of 95mWcm 2 in H2/O2 at 100 8C and 100% RH, and 90mWcm 2 in methanol/O2 at 150 8C and 0.67% RH of the cathode. Highly orderedmesoporous silica MCM-41 can be synthesized according to the procedure given in the literature. Thus, the key issue is to anchor and assemble HPW into the mesopores or channels of MCM-41 host. We have derived a VIM to assemble HPW molecules into the mesoporous silica. In this process, the impurities or trapped air inside the mesopores are removed under vacuum, and the vacuum-treated mesoporous silica

Layer-by-layer self-assembly of PDDA/PWA-Nafion composite membranes for direct methanol fuel cells

A novel PDDA/PWA-Nafion composite electrolyte membrane with enhanced proton conductivity (sigma) to methanol permeability (P) ratio, sigma/P, was fabricated by layer-by-layer self-assembly of negatively charged water soluble PWA and positively charged polyelectrolyte PDDA.

Nanoparticle self-assembled hollow TiO2 spheres with well matching visible light scattering for high performance dye-sensitized solar cells

Submicrometer-sized hollow TiO(2) spheres are directly self-assembled from TiO(2) nanoparticles without using any template or surfactant as a scattering layer for dye-sensitized solar cells, showing good visible light scattering match to significantly improve the photoconversion efficiency.

Template-free bottom-up synthesis of yolk–shell vanadium oxide as high performance cathode for lithium ion batteries

A template-free strategy is exploited to bottom-up synthesize yolk-shell vanadium oxide through a two-step spontaneous assembly of hydrolytically formed subunits in a one-pot process. The unique structured vanadium pentoxide exhibits excellent cathode performance for lithium ion batteries.

Layer-by-layer assembled sulfonated-graphene/polyaniline nanocomposite films: enhanced electrical and ionic conductivities, and electrochromic properties

In this article, we report the facile synthesis of sulfonic acid-grafted reduced graphene oxide (S-rGO) using a one-pot method under mild conditions, and layer-by-layer (LbL) assembly and electrochromic properties of S-rGO/polyaniline (S-rGO/PANI) nanocomposite thin films. It was found that the multilayer films of S-rGO/PANI exhibit much faster electrochromic switching kinetics than that of corresponding spin-coated PANI thin films. The enhancement can be attributed to the drastically increased electrical and ionic conductivities of the S-rGO/PANI films brought by the graphitic structure of the S-rGO sheets and the sulfonic acid groups attached to S-rGO, which lead to non-diffusion-controlled redox processes of PANI.

A novel inorganic proton exchange membrane based on self-assembled HPW-meso-silica for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) based on high-temperature (100–300 °C) proton exchange membranes (HT-PEMs) offer significant advantages over the current low-temperature DMFCs based on perfluorosulfonic acid (e.g., Nafion™), such as reduction in CO poisoning via faster reaction kinetics, thus increasing the energy efficiency and reducing precious metal loading. This paper reports a novel inorganic proton exchange membrane based on 12-tungstophosphoric acid mesoporous silica (HPW-meso-silica) nanocomposites. The HPW-meso-silica was synthesized via a one-step self-assembly route assisted by a triblock copolymer, Pluronic P123, as the structure-directing surfactant. The threshold of the HPW content in the nanocomposites for the conductivity of mesoporous silica is 5 wt%. The best results were obtained at 25 wt% HPW-meso-silica, delivering a high proton conductivity of 0.091 S cm−1 at 100 °C under 100% relative humidity (RH) and 0.034 S cm−1 at 200 °C under 3% RH and a low activation energy of 14.0 kJ mol−1. The maximum power density of a cell with a 25 wt% HPW-meso-silica membrane is 19 mW cm−2 at 25 °C and increased to 235 mW cm−2 at 150 °C in methanol fuel.

Simultaneous catalyzing and reinforcing effects of imidazole-functionalized graphene in anhydride-cured epoxies

In this study, an imidazole-functionalized graphene (G-IMD) was prepared from graphene oxide by a facile one-pot method. The functionalized graphene not only showed improved organic compatibility but also could simultaneously play the roles of a cure accelerator and reinforcement for anhydride-cured epoxies. Our results showed that G-IMD could successfully catalyze the curing reaction without the addition of any routine accelerator. Thermal and mechanical properties of the epoxy–G-IMD nanocomposites were systematically studied at different filler loadings. Compared with neat epoxy resin, tensile strength and Youngs modulus of the nanocomposites were enhanced by 97% and 12%, respectively, at only 0.4 wt% G-IMD loading. Dynamic mechanical analysis and electron microscopic results revealed that the drastic improvements in mechanical properties could be attributed to the homogeneous dispersion of G-IMD and covalent bonding at the interface, which effectively improved the efficiency of load transfer between the matrix and graphene.

One-pot sequential electrochemical deposition of multilayer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid)/tungsten trioxide hybrid films and their enhanced electrochromic properties

Hybrid thin films composed of multilayer poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonic acid) (PEDOT:PSS) and tungsten trioxide (WO3) were electrochemically deposited on indium tin oxide (ITO) from a one-pot solution using a square-wave galvanostatic method. The morphology of the hybrid thin films could be easily manipulated to optimize their electrochromic properties by adjusting deposition conditions. In the hybrids, both components can be simultaneously switched to coloured or bleached states. The hybrid film obtained with very short deposition times of PEDOT:PSS and WO3 in each cycle exhibits significantly enhanced electrochromic properties. The optical contrast of the hybrid film is higher than that of PEDOT:PSS or WO3 films of the same thickness. Moreover, the stability of the hybrid film is also drastically enhanced. The enhancement may be attributed to the favourable interactions between the two components, i.e., PEDOT:PSS may enter the defect sites in electrodeposited WO3, preventing surface-defect-induced anodic dissolution during cycling, while the surface functional groups of WO3 may act as dopants to inhibit over-oxidation of PEDOT, as well as the large interfacial area created using this unique one-pot multilayer deposition method.

Nafion membranes with ordered mesoporous structure and high water retention properties for fuel cell applications

Ordered mesoporous structures were successfully introduced into Nafion membranesvia a soft micelle templating method, using a non-ionic block copolymer surfactant, PEO127–PPO48–PEO127 (Pluronic F108). Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) analysis show the typical features of the formation of ordered mesopores in the as-prepared Nafion membranes. TGA and FTIR results show that the mesoporous Nafion (meso-Nafion) has a much higher water retention capability as compared to conventional Nafion membranes. The proton conductivities of meso-Nafion are much higher than those of Nafion 115 membranes especially at reduced relative humidity (RH) and elevated temperatures. The results show that the conductivity and water retention ability are sensitive to the surfactant loading. At 80 °C and 40%RH, the conductivity of the best meso-Nafion membrane is 0.07 S cm−1, 5 times better than 0.013 S cm−1 obtained on Nafion 115. At 60%RH and 80 °C, the cell with meso-Nafion reached a stable power output of 0.63 W cm−2, more than 2 times higher than the cell with pristine Nafion 115 under identical experimental conditions. When the RH reduced to 20%, the power output of meso-Nafion membranes is 5.6 times higher than that of Nafion 115. The cells with meso-Nafion membranes also demonstrate much better power output at elevated temperature of 120 °C and reduced humidity.

2D single- or double-layered vanadium oxide nanosheet assembled 3D microflowers: controlled synthesis, growth mechanism, and applications

A facile one-pot solvent-thermal method was developed to synthesize a unique 3D microflower structure assembled from single- or double-layered 2D nanosheets of V4O9 (F-VO). Simply by controlling the precursor concentration, yolk-shelled V4O9 (YS-VO) or bulk V4O9 (B-VO) can be produced instead. The precursor-concentration dependent growth mechanism is proposed. The exceptional catalytic/electrochemical properties and large specific surface area of F-VO promise a wide range of applications. As a proof-of-concept demonstration, we investigate its use in high-performance supercapacitors (~392 F g(-1)), and for sensitive detection of H2O2 (with a low detection limit of ~0.1 μM) and methanol (with a low detection limit of ~60 μM). Furthermore, we show that F-VO greatly outperforms its counterparts (YS-VO and B-VO) presumably owing to its unique structure and crystal plane orientation.