Kefei Han

Synthesis and electrocatalytic performance of MnO2-promoted Ag@Pt/MWCNT electrocatalysts for oxygen reduction reaction

Two forms of crystalline MnO2 were synthesized by a hydrothermal method, and MnO2-doped Ag@Pt/MWCNT composites were prepared by ultrasonic treatment for oxygen reduction reaction in proton exchange membrane fuel cells (PEMFC). The morphology of the electrocatalyst samples was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). We found that the Ag@Pt/MWCNTs catalyst exhibited a core–shell nanostructure and the two forms of MnO2 were α-MnO2 and β-MnO2. The electrochemical properties of the electrocatalyst samples were studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in an acidic medium. The results demonstrated that Ag10%@Pt10%/MWCNTs-α-MnO220% had the largest electrochemical activity area (85.83 m2 g−1) of all electrocatalysts and the oxygen reduction reaction on the electrocatalyst proceeds through a 4e− reduction pathway.

The Preparation of a Polyether Demulsifier Modified by Nano-SiO2 and the Effect on Asphaltenes and Resins

Abstract In order to enlarge the range of applications of nanomaterials and improve the performance of macromolecular polymer demulsifier, nano-SiO2 was integrated with polyether demulsifier TA1031 to form nanomodified demulsifier using an in situ synthesis method. Analysis of the polyether demulsifier modified by nano-SiO2 was performed using transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy. The result showed that applying nanomaterials to crude oil demulsifier greatly improves the performance of the original demulsifier. When the ratio of nano-SiO2 and TA1031 is 1:10, the performance of the nanomodified demulsifier was best, and the ratio of demulsification was improved by about 20%. The time of demulification and dewatering was also greatly shortened by about 30 min. The influence of nanomodified demulsifier on the asphaltenes and resins was studied by FTIR.

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.

Synthesis and electrocatalytic performance of phosphotungstic acid-modified Ag@Pt/MWCNTs catalysts for oxygen reduction reaction

Keggin-structured phosphotungstic acid H3PW12O40 (HPW)-modified Ag@Pt/MWCNTs electrocatalysts were successfully prepared using a chemical impregnation method. Physical characterization by X-ray powder diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy revealed that the HPW molecules were incorporated into the Ag@Pt/MWCNT structure The diameter of the catalyst used was about 4.0xa0nm, and electrochemical investigation results indicated that HPW could ameliorate electrocatalytic activity. The catalyst with HPW content of 25xa0% displayed the best excellent electrocatalytic activity with an electrochemically active area of 83.62xa0m2xa0g−1 and a half-wave potential for the oxygen reduction reaction of 0.851xa0V, all ascribed to the high utilization of Pt and the protective effect of the HPW layer on the catalyst surface. The synergic effect of the HPW and Ag@Pt enhanced the rate of electron transfer and increased the catalytic efficiency of oxygen reduction reaction, influencing 4e− reduction reactions on Ag@Pt/MWCNTs-HPW catalysts.Graphical Abstract Phosphotungstic acid-modified Ag@Pt/MWCNTs catalysts were successfully synthesized by the chemical impregnation method. The morphology and catalytic performance of the prepared catalysts were investigated, leading to the understanding of catalytic mechanism of the catalyst in acidic medium, especially, the importance of HPW in the hybrid catalysts. The investigation indicated that the hybrid catalyst showed excellent activity toward oxygen reduction. Schematic diagram for mechanism of ORR on Ag@Pt/MWCNTs-HPW nanostructure.

Non-planar backbone structure polybenzimidazole membranes with excellent solubility, high proton conductivity, and better anti-oxidative for HT-PEMFCs

As an efficient, inexpensive, readily accessible monomer of the polybenzimidazole (PBI) copolymer, the 4,4′-[(4,4′-bipyridine)-2,6-diyl]dibenzoic acid (BPY) containing bipyridine unit was firstly used to synthesize a series of novel non-planar PBI copolymers (BPY–PBI-x) by regulating the ratio with 2,6-pyridinedicarboxylic acid under microwave-assisted conditions. The copolymers exhibit superior solubility in aprotic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide than general PBI, and the corresponding BPY–PBI-x serial membranes were prepared by a solution casting method. All the membranes have been characterized by thermal stability, a tension test, scanning electron microscopy, PA-doping ability and swelling ratio, proton conductivity, and a Fenton test. The membranes exhibit excellent comprehensive properties containing high proton conductivity and long lifetime. The conductivity of the doping levels of the BPY–PBI-100% membrane with the highest doping level (342.7%) reaches 78.6 mS cm−1 at 160 °C. The high proton conductivity is attributed to the increase in N atoms of the proton acceptor from the bipyridine monomer and the enhancement of free volume from the existence of a bulky stereostructure BPY unit. The long lifetime is due to the fact that the pyridine unit can quench radicals by the formation of pyridine-N-oxide. The unique anti-oxidation mechanism of the BPY–PBI-x serial membranes, which firstly was pointed out for the application of pyridine heterocyclic rings in HT-PEMs, provides new insights for novel anti-oxidation membrane design. In short, 3-fold objectives, namely, (I) soluble PBI, (II) higher proton conductivity PBI, and (III) anti-oxidative PBI, were achieved in this paper.