Nanjun Chen

Layered double hydroxide–polyphosphazene-based ionomer hybrid membranes with electric field-aligned domains for hydroxide transport

With the aim to improve the conductivity of anion exchange membranes (AEMs), the layered double hydroxide (LDH) was added to the polyphosphazene-based ionomer, and an external AC electric field was applied to the LDH–polyphosphazene-based ionomer hybrid casting solution during solvent evaporation. The introduction of LDH nanoplatelets in AEMs significantly improved the conductivity, ion exchange capacity, water uptake, and mechanical properties of hybrid AEMs, but sacrificed lower dimensional stability. And, most importantly, the present technique is a potentially useful method for fabricating AEMs with oriented LDH nanoplatelets taking full advantage of the bulk conductivity of the LDH nanoplatelets and resulting in a 39% increase in conductivity in the trans-plane direction compared to that of normal methods. In addition, the novel polyphosphazene-based ionomer was designed not only to balance the hydroxide ions but also to improve interfacial adhesion with LDH nanoplatelets for improving the distribution of LDH nanoplatelets in hybrid AEMs.

Cobaltocenium-containing polybenzimidazole polymers for alkaline anion exchange membrane applications

A polybenzimidazole, containing cobaltocenium on its backbones, was used for anion exchange membranes (AEMs) for the first time. The polymer was synthesized by polymerizing 1,1′-dicarboxycobaltocenium and 3,3′,4,4′-biphenyltetramine in a microwave reactor. Before the polymer fabrication, we studied the alkaline stability of three different cobaltocenium cations—cobaltocenium, 1,1′-dimethylcobaltocenium and 1,1′-dicarboxycobaltocenium—by 1HNMR and 13CNMR spectroscopy and investigated the degradation mechanisms of these cations under alkaline conditions. Then the three corresponding cobaltocenium-containing polybenzimidazole membranes were synthesized, and the relationship between the structure and performance of these cobaltocenium-containing polybenzimidazole membranes was investigated by 1HNMR spectroscopy, FTIR spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and AC impedance spectrascopy. These AEMs, based on cobaltocenium-containing polybenzimidazole backbones, show high thermal stabilities, good chemical stabilities, comparable hydroxide conductivities, low swelling ratios and good mechanical properties. The 1,1′-cobaltocenium-5,5′-(2,2′-dimethyl)-bibenzimidazole (MCp2Co+OH−-PBI) membrane shows the best comprehensive performance in this study. The hydroxide conductivity of the MCp2Co+OH−-PBI membrane at 90 °C can reach 37.5 mS cm−1 with a low swelling ratio. Furthermore, the degradation mechanism of the MCp2Co+OH−-PBI membrane under alkaline conditions was investigated by 1HNMR spectroscopy. In summary, our work investigates the degradation mechanisms of the cobaltocenium cations and cobaltocenium-containing polybenzimidazole under alkaline conditions and presents a novel polymer structure for AEM applications.

A new method for improving the ion conductivity of anion exchange membranes by using TiO2 nanoparticles coated with ionic liquid

Recently a new method for increasing the ion conductivity of anion exchange membranes (AEM) was developed based on the novel materials ionic liquids (ILs). We mixed the ILs into the membrane directly instead of immobilizing onto the polymer backbone as in the traditional way. Nano-TiO2 was introduced to stabilize the ILs in the membrane. The ILs were immobilized by the nano-TiO2, acting as the “active sites” in the membrane, to enhance the mobility of the hydroxyl groups so as to increase the ion conductivity. Both pure ILs composite membranes and ILs–TiO2 composite membranes were synthesized, and their properties were compared. 1H nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy were used to analyze the structures of the composite membranes. The mechanical properties, thermal stabilities, ion conductivities, water uptakes, swelling ratios, and ion exchange capacities of the membranes were investigated. The interaction between the TiO2 and ionic liquids was confirmed by X-ray diffraction. The stability of the ILs in the membrane was measured comprehensively. All these results show that this novel method is effective and promising for AEM applications.

Montmorillonite Modified by Cationic and Nonionic Surfactants as High-Performance Fluid-Loss-Control Additive in Oil-Based Drilling Fluids

This work reports the modification of montmorillonite (MMT) by nonionic surfactant sorbitan monooleate (Span 80) and cationic surfactant cetyltrimethylammonium bromide (CTAB), which can be used as fluid-loss-control additive for preventing the fluid invasion into the porous pristine formation and avoiding the collapse of borehole wall in oil-drilling excavation. Transmission electron microscopy imaging revealed modified MMT with small particle size display high dispersibility compared with that of pristine MMT in white oil. Experimental results of small-angle x-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy showed that a bilayer of CTAB and Span 80 was intercalated into the interlayer space of the MMT. The synthesized organo-clays as a fluid-loss-control additive performed well in oil phase. The organo-clays modified with 2.0 cation-exchange capacity (CEC) CTAB and 2.0 CEC Span 80 yielded 100% colloid fraction in colloid fraction tests, showed low filtration loss of 5.7 mL, and left a filter cake approximately 68 µm thick in American Petroleum Institute filtration tests, showing that the synthesized organo-clays can be potentially used as fluid-loss-control additive in oil-drilling excavation. GRAPHICAL ABSTRACT

Ultrastable and High Ion-Conducting Polyelectrolyte Based on Six-Membered N-Spirocyclic Ammonium for Hydroxide Exchange Membrane Fuel Cell Applications

In response to prepare high-stable and ion-conducting polyelectrolyte for hydroxide exchange membrane (HEM) applications, we present an ultrastable polyelectrolyte based on six-membered heterocyclic 6-azonia-spiro[5.5]undecane (ASU) and polyphenyl ether (PPO). A series of ASU-functionalized PPO polyelectrolytes (ASU-PPO), which can be easily dissolved in low-boiling pointing solvent, have been successfully synthesized by a remote-grafting method. The ASU precursor is stable in 1 M NaOH/D2O at 80 °C for 2500 h as well as in 5 M NaOH/D2O at 80 °C for 2000 h, and the predicted half-life of the ASU precursor would exceed 10 000 h, even higher in the future. Besides, these remote-grafting ASU-PPO polyelectrolytes are stable in 1 M NaOH(aq) at 80 °C for 1500 h. Robust and pellucid segmented ASU and triple-ammonium-functionalized PPO-based HEMs attach OH- conductivity of 96 mS/cm at 80 °C and realize maximal power density of 178 mW/cm2 under current density of 401 mA/cm2.

Electrorheological effect induced quaternized poly(2,6-dimethyl phenylene oxide)-layered double hydroxide composite membranes for anion exchange membrane fuel cells

To improve the performance of anion exchange membranes (AEMs), we fabricated quaternized poly(2,6-dimethyl phenylene oxide)-layered double hydroxide composite membranes by combining the advantages of the two components. Also, the electrorheological effect was employed during the casting process to induce the formation of ion conducting channels along the through-plane direction. The membrane with 3% layered double hydroxide (LDH) (QPPO-Im-3% LDH) showed the largest increase in ionic conductivity over that of the pure membrane (QPPO-Im) (15.85 mS cm−1 at 30 °C to 22.52 mS cm−1 at 80 °C vs. 5.93 mS cm−1 at 30 °C to 11.63 mS cm−1 at 80 °C). The ionic conductivity was further improved by applying the electric field treatment, confirming that the addition of LDH and the electric field greatly affect the ionic conductivity of the AEMs. Moreover, the morphology, thermal and mechanical properties, ion-exchange capacity (IEC), water uptake (WU) and swelling ratio (SR) were also studied systematically to determine the effects of LDH and electric field on the membranes.

Three-Decker Strategy Based on Multifunctional Layered Double Hydroxide to Realize High-Performance Hydroxide Exchange Membranes for Fuel Cell Applications

Herein, we present a three-decker layered double hydroxide (LDH)/poly(phenylene oxide) (PPO) for hydroxide exchange membrane (HEM) applications. Hexagonal LDH is functionalized with highly stable 3-hydroxy-6-azaspiro [5.5] undecane (OH-ASU) cations to promote its ion-exchange capacity. The ASU-LDH is combined with triple-cations functionalized PPO (TC-PPO) to fabricate a three-decker ASU-LDH/TC-PPO hybrid membrane by an electrostatic-spraying method. Notably, the ASU-LDH layer with a porous structure shows many valuable properties for the ASU-LDH/TC-PPO hybrid membranes, such as improving hydroxide conductivity, dimensional stability, and alkaline stability. The maximum OH- conductivity of ASU-LDH/TC-PPO hybrid membranes achieves 0.113 S/cm at 80 °C. Only 11.5% drops in OH- conductivity was detected after an alkaline stability test in 1 M NaOH at 80 °C for 588 h, prolonging the lifetime of the TC-PPO membrane. Furthermore, the ASU-LDH/TC-PPO hybrid membrane realizes a maximum power density of 0.209 W/cm2 under a current density of 0.391 A/cm2. In summary, the ASU-LDH/TC-PPO hybrid membranes provide a reliable method for preparing high-performance HEMs.

Pt–Co deposited on polyaniline-modified carbon for the electro-reduction of oxygen: the interaction between Pt–Co nanoparticles and polyaniline

Polyaniline-modified carbon black supported platinum–cobalt alloy nanoparticle (Pt–Co/C-PANI) catalysts were prepared via a microwave-assisted polyol method and subsequent high temperature annealing. X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and derivative thermogravimetric (DTG) analysis were used to characterize the structure of the catalysts. We find that the electron delocalization between the metal d orbitals and PANI is beneficial for improving the ORR performance and the PANI on carbon can prevent the aggregation of Pt–Co nanoparticles during high temperature treatments. Electrochemical evaluations reveal that the obtained Pt–Co/C-PANI catalysts annealed at 500 °C show the highest mass activity of 1.33 A mgPt−1 and a specific activity of 1.29 mA cm−2, which are 7.8 and 5.4 times higher than those of the commercial JM Pt/C catalyst, respectively. X-ray photoelectron spectroscopy (XPS) results show that only part of PANI is decomposed at 500 °C and the metal–nitrogen (M–N) bonds are formed in Pt–Co/C-PANI-500 °C, which are attributed to the impressive ORR activity enhancement in Pt–Co/C-PANI-500 °C.

Chitosan-Modified Poly(2,6-dimethyl-1,4-phenylene Oxide) for Anion-Exchange Membrane in Fuel Cell Technology

ABSTRACT A series of cross-linking chitosan-modified quaternary ammonium poly(2,6-dimethyl-1,4-phenylene oxide)s membranes (CS-QAPPO) were prepared by the Menshutkin reaction. The mechanical property, dimensional stability, and alkaline stability of the CS-QAPPO membrane have been impressively improved by introducing CS into PPO backbone. Even the hydroxide conductivity of CS-QAPPO membranes is higher than that of the pristine QAPPO membrane. The 20% chitosan-modified QAPPO membrane shows the best performance, and the hydroxide conductivity is 32 mS cm−1 at 90°C. The alkaline stability measurements demonstrated excellent chemical stability of the CS-QAPPO membrane in 2 M NaOH solution at room temperature after 2,000 h. GRAPHICAL ABSTRACT