Xueqiang Gao

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 Ir/CeO2–C nanoparticle electrocatalyst for the hydrogen oxidation reaction of alkaline anion exchange membrane fuel cells

Alkaline anion exchange membrane fuel cells have faster kinetics for the oxygen reduction reaction (ORR) than proton exchange membrane fuel cells; however, the hydrogen oxidation reaction (HOR) at anodes with precious metals is more sluggish under alkaline conditions than that under acidic conditions, which hinders the further development of fuel cells. Herein, a novel catalyst, iridium nanoparticle-supported ceria–carbon black (10% Ir/CeO2–C), was developed for use in the hydrogen oxidation reaction (HOR) under basic conditions. Cyclic voltammetry reveals that the electrochemical surface area of 10% Ir/CeO2–C is 1.5 times that of 10% Ir/C. The RDE measurement suggests that the exchange current density of 10% Ir/CeO2–C is 2.4 times that of 10% Ir/C, and the mass activity and specific activity of 10% Ir/CeO2–C for HOR are greater than those of 10% Ir/C by 2.8 fold and 1.8 fold, respectively. The effective prevention of the agglomeration of the highly dispersed Ir nanoparticles could be ascribed to the strong metal–support interaction between Ir and CeO2, and the promoted electrocatalytic activity would benefit from the oxophilic effect due to the higher oxygen storage-release capacity of ceria. Thus, 10% Ir/CeO2–C would be a good candidate for use at the anode of alkaline anion exchange membrane fuel cells.

Nickel/cobalt oxide as a highly efficient OER electrocatalyst in an alkaline polymer electrolyte water electrolyzer

Water electrolysis by an alkaline solid polymer electrolyte (APE) water electrolyzer is a promising approach for hydrogen production from water. In this work, Ni/Co oxides were prepared by a hydrothermal method, and used as a high-efficiency OER electrocatalyst in an APE water electrolyzer. The APE water electrolyzer assembled with the as-prepared Ni/Co oxides and home-made APE showed a nearly constant operating potential, ∼2.03 V @ 100 mA cm−2 in 1 wt% KHCO3 solution for about 550 h in a durability test, indicating the catalyst with good stability can meet the long-term durability requirements of the water electrolyzer. This result shows the practical application of Ni/Co oxides in an alkaline solid polymer electrolyte electrolyzer.

A novel cathode architecture using Cu nanoneedle arrays as the cathode support for AAEMFC application

A novel cathode architecture using vertically aligned Cu nanoneedle arrays (NNAs) as an ordered support for alkaline anion-exchange membrane fuel cell (AAEMFC) application is developed. Cu NNAs are directly grown on a GDL via three steps of electrochemical reaction. After depositing a Pd layer on the surface of Cu by a pulse electrodeposition method to form Pd/CuNNAs, the cathode catalyst layer is formed. The AAEMFC prepared without alkaline ionomer in the cathode catalyst layer shows an enhanced performance with ultra-low Pd loading down to 47 μg cm−2, which is much higher than that of a conventional cathode electrode with the Pt loading of 100 μg cm−2. This is the first report where three-dimensional Cu NNAs are applied as the cathode support in an AAEMFC, which is able to deliver a higher power density without an alkaline ionomer than conventional MEAs.

3D Pd/Co core–shell nanoneedle arrays as a high-performance cathode catalyst layer for AAEMFCs

A novel cathode architecture using vertically aligned Co nanoneedle arrays as an ordered support for application in alkaline anion-exchange membrane fuel cells (AAEMFCs) has been developed. The Co nanoneedle arrays were directly grown on a stainless steel sheet via a hydrothermal reaction and then a Pd layer was deposited on the surface of the Co nanoneedle arrays using a vacuum sputter-deposition method to form Pd/Co nanoneedle arrays. After transferring the Pd/Co nanoneedle arrays to an AAEM, a cathode catalyst layer was formed. Without the use of an alkaline ionomer, the AAEMFC with the prepared cathode catalyst layer showed an enhanced performance with ultra-low Pd loading of down to 33.5 μg cm−2, which is much higher than the conventionally used cathode electrode with a Pt loading of 100 μg cm−2. This is the first report where three-dimensional Co nanoneedle arrays have been used as the cathode support in an AAEMFC, which is able to deliver a higher power density without an alkaline ionomer than that of conventional membrane electrode assembly (MEA).

Ultrathin IrRu nanowire networks with high performance and durability for the hydrogen oxidation reaction in alkaline anion exchange membrane fuel cells

Developing highly active and stable HOR catalysts still remains a challenging task for alkaline anion exchange membrane fuel cells. A carbon supported IrRu nanowire catalyst with different compositions was prepared by a soft template method, involving the chemical reduction of iridium and ruthenium complexes using sodium borohydride. The Ir1Ru1 ultrathin nanowires exhibit higher hydrogen oxidation activity and better stability under alkaline conditions in comparison with commercial Pt/C. An electrochemical test demonstrates that the mass and specific activities at an over potential of 50 mV of Ir1Ru1 NWs/C are 4.2 and 3.8 times that of commercial Pt/C, respectively. Furthermore, the synthesized Ir1Ru1 NWs display better stability against potential cycling due to their unique interconnected structure. After 2000 potential cycles, the electrochemically active surface area (ECSA) of Ir1Ru1 NWs/C reduces only by 2.27%, and the mass activity@50 mV is reduced by 8.21%. The single cell used the as-prepared Ir1Ru1 NWs/C as the anode catalyst and Pt/C as the cathode catalyst, and the AAEMFC shows a peak power density of more than 485 mW cm−2, which is about 1.66 fold that of the AAEMFC using commercial Pt/C as the anode catalyst (292 mW cm−2). These results suggest that carbon supported ultrathin Ir1Ru1 NW catalysts can be used as substitutes for commercial Pt/C for the HOR in alkaline media for alkaline anion exchange membrane fuel cell application.

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.