Jinkai Hao

Study on hydrophobicity loss of the gas diffusion layer in PEMFCs by electrochemical oxidation

The hydrophobicity loss of the gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs) was investigated by an accelerated stress test of electrochemical oxidation at a constant potential. The fresh and oxidized GDLs were characterized by cyclic voltammetry, contact angle measurements and water permeability. Results showed the occurrence of the oxidation of carbon and the decrease of the hydrophobicity of GDL. To discuss the reasons for the hydrophobicity loss, scanning electron microscopy, X-ray photoelectron spectroscopy and thermogravimetry were analyzed. It was found that the hydrophobicity loss was closely associated with the losses of the carbon materials and polytetrafluoroethylene (PTFE) in GDL under test conditions. In addition, the mass loss of carbon materials was more than that of PTFE.

Development of proton-conducting membrane based on incorporating a proton conductor 1,2,4-triazolium methanesulfonate into the Nafion membrane

In this paper, 1,2,4-triazolium methanesulfonate (C2H4N+3CH3SO−3, [Tri][MS]), an ionic conductor, was successfully synthesized. It exhibited high ionic conductivity of 18.60 mS·cm−1 at 140°C and reached up to 36.51 mS·cm−1 at 190°C. [Tri][MS] was first applied to modify Nafion membrane to fabricate [Tri][MS]/Nafion membrane by impregnation method at 150°C. The prepared composite membrane showed high thermal stability with decomposed temperature above 200°C in air atmosphere. In addition, the membrane indicated good ionic conductivity with 3.67 mS·cm−1 at 140°C and reached up to 13.23 mS·cm−1 at 180°C. The structure of the [Tri][MS] and the composite membrane were characterized by FTIR and the compatibility of [Tri][MS] and Pt/C catalyst was studied by a cyclic voltammetry (CV) method. Besides, the [Tri][MS]/Nafion membrane (thickness of 65 µm) was evaluated with single fuel cell at high temperature and without humidification. The highest power density of [Tri][MS]/Nafion membrane was 3.20 mW·cm-2 at 140°C and 4.90 mW·cm-2 at 150°C, which was much higher than that of Nafion membrane.

High performance anion exchange ionomer for anion exchange membrane fuel cells

The anion exchange ionomer incorporated into the electrodes of an anion exchange membrane fuel cell (AEMFC) enhances anion transport in the catalyst layer of the electrode, and thus improves performance and durability of the AEMFC. In this work, a novel ionomer based on a triblock copolymer with high conductivity and good durability is synthesized successfully. The spectroscopy (such as 1H-NMR, FT-IR) results of the ionomer indicate that the functional group is grafted onto the poly(styrene-ethylene/butylene-styrene) (SEBS) successfully and the OH− conductivity of the ionomer is 30 mS cm−1 at 75 °C. Besides, quaternary ammonium SEBS (QASEBS) is used as the ionomer in a H2/O2 AEMFC and exhibits a significant durability of 500 h at a constant current density of 100 mA cm−2, moreover, the degradation rate of voltage is only 0.22 mV h−1 during the 500 h durability test. In addition, the peak power density of the membrane electrode assembly (MEA) with the QASEBS ionomer reaches 375 mW cm−2 at 50 °C, which is 3 times than that of the MEA using the commercially available Acta I2 ionomer (124 mW cm−2) for comparison.

A novel porous sulfonated poly(ether ether ketone)-based multi-layer composite membrane for proton exchange membrane fuel cell application

An advanced sulfonated poly(ether ether ketone) (sPEEK)-based multi-layer composite membrane with high performance and durability is fabricated, which consists of a porous sPEEK base membrane, two transition layers (TLs) and two PFSA outer layers (PLs). These porous sPEEK base membranes with nanoscale pores are prepared first through a vapor induced phase inversion (VIPI) method. Owing to the higher porosity and the denser distribution of sulfonic acid clusters, the cell performance and physical properties of porous sPEEK membranes are superior to those of sPEEK membranes prepared by a solvent casting method. The multi-layer structure of this composite membrane results in reduced swelling and improved water uptake, and eventually brings about a high proton conductivity. Single cell tests indicate that the multi-layer composite membrane has a higher cell performance and more outstanding durability in comparison with sPEEK membranes. The growth rate of hydrogen crossover current density of this composite membrane is much lower than that of sPEEK membranes, proving the effectiveness of PLs in improving the chemical durability of sPEEK-base membranes. After long-term stability tests, the sPEEK multi-layer composite membrane still shows a good cell performance, especially at low relative humidity (RH).

A new microporous layer material to improve the performance and durability of polymer electrolyte membrane fuel cells

Antimony doped tin oxide (ATO), a kind of semiconducting nanocrystalline material, has excellent electrochemical stability but poor electrical conductivity. Herein, ATO nanocomposites with carbon coatings are prepared by immersing ATO nano-material into dopamine solution, and then thermal treatment to improve the electrical conductivity of the ATO material. The morphology and microstructure of ATO@C/N nanocomposites are characterized using a scanning electron microscope and transmission electron microscopy. The GDLs with the MPL prepared from ATO@C/N nanocomposites are characterized by through-plane resistance testing, mercury intrusion porosimetry and surface contact angle measurement. The results of the above show that ATO@C/N nanocomposites with a 2.16 nm thick carbon coating enhance the electrical conductivity of ATO nanocrystals and exhibit higher electrochemical stability. Further, the performance of MEA fabricated with ATO@C/N as the cathode MPL is evaluated. The maximum power density approaches 1000 mW cm−2, and a slight difference in cell performance is observed compared to XC-72.

Fabrication of N1-butyl substituted 4,5-dimethyl-imidazole based crosslinked anion exchange membranes for fuel cells

Novel N1, C4, C5-substituted imidazolium-based crosslinked anion exchange membranes (AEMs) are prepared by the incorporation of polybenzimidazole (PBI) into the poly(vinylbenzyl chloride) (PVBC) matrix. 1-Butyl-4,5-dimethyl-imidazole (BDIm) with methyl substituents at C4, C5 and long side alkyl substituents at N1 is firstly synthesized to enhance the stability of AEMs by steric hindrance and hyperconjugative effects and characterized by 1H NMR. The effects of crosslinking density of AEMs on the hydroxide conductivity, swelling ratio, thermal stability, oxidative and alkaline stability are evaluated in detail for fuel cell applications. The results reveal that the crosslinking structure between PVBC and PBI plays a vital role in achieving both good mechanical properties and low swelling ratio. Notably, the AEM containing 66.7% PVBC has the highest ionic conductivity of 16.1 mS cm−1 at 20 °C with an IEC of 2.1 mmol g−1. Meanwhile, the AEMs also exhibit excellent oxidative stability in Fentons reagent for 200 h and alkaline stability in 1 mol L−1 KOH at 60 °C for 480 h. Furthermore, the peak power density of an H2/O2 single fuel cell is up to 54 mW cm−2.