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Abstract: Part I of this study carried out membrane electrode assembly degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, for 1000h under idle conditions. Through on-line electrochemical measurements it was found that as degradation advanced, cells with thinner membranes experienced much more rapid performance degradation than those with thicker membranes, especially after 800h of operation, due to a dramatic increase in hydrogen crossover. In the present work we investigate the degradation mechanisms of this four-cell stack using several ex situ diagnostic tools, including scanning electron microscopy (SEM), infrared (IR) imaging, ion chromatography (IC), gas permeability measurement, contact angle measurement, and simulation. The results indicate that the drastic increase in hydrogen crossover is due to membrane thickness loss and pinhole formation. [Copyright &y& Elsevier]

Abstract: The durability of polymer exchange membrane (PEM) fuel cells, under a wide range of operational conditions, has been attracting intensive attention, as durability is one of the largest barriers for commercialization of this promising technology. In the present work, membrane electrode assembly (MEA) degradation of a four-cell stack with Nafion membranes of different thicknesses, including N117, N115, NR212, and NR211, was carried out for 1000h under idle conditions. By means of several on-line electrochemical measurements, the performance of the individual cells was analyzed at different times during the degradation process. The results indicate that the cells with thinner membranes have a lower open circuit voltage (OCV) due to the higher fuel crossover. Before degradation, the thickness of the membranes correlates with performance of the cell. However, with the advancement of degradation, the performance of cells with thinner membranes degraded much faster than those with thicker membranes, especially after 800h of operation. The fast performance degradation for thinner membranes is evident by a dramatic increase in hydrogen crossover indicating membrane thinning or pinhole formation. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel strategy to regulate the discharge reservoir of negative electrodes in Ni–MH batteries is introduced by using Ni(OH) x (x =2.10) and γ-CoOOH. The electrochemical measurements of these batteries demonstrate that the use of Ni(OH) x (x =2.10) and γ-CoOOH can not only successfully regulate the discharge reservoir of negative electrodes in Ni–MH batteries to an adequate quantity, but also effectively improve the electrochemical performance of the batteries. Compared with normal batteries, the in-house prepared batteries with a lower discharge reservoir exhibit an enhanced discharge capacity, improved high-rate discharge ability, higher discharge potential plateau and superior cycle stability. The effect of Ni(OH) x (x =2.10) and γ-CoOOH on the electrochemical performance of nickel electrode is also investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results suggest that the new method is simple and effective for cost reduction of Ni–MH batteries with improved electrochemical performance. [Copyright &y& Elsevier]

Abstract: In this paper we compare the behavior of non-spherical and spherical β-Ni(OH)2 as cathode materials for Ni–MH batteries in an attempt to explore the effect of microstructure and surface properties of β-Ni(OH)2 on their electrochemical performances. Non-spherical β-Ni(OH)2 powders with a high-density are synthesized using a simple polyacrylamide (PAM) assisted two-step drying method. X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), thermogravimetric/differential thermal analysis (TG–DTA), Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, and tap-density testing are used to characterize the physical properties of the synthesized products. Electrochemical characterization, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge/discharge test, is also performed. The results show that the non-spherical β-Ni(OH)2 materials exhibit an irregular tabular shape and a dense solid structure, which contains many overlapped sheet nano crystalline grains, and have a high density of structural disorder and a large specific surface area. Compared with the spherical β-Ni(OH)2, the non-spherical β-Ni(OH)2 materials have an enhanced discharge capacity, higher discharge potential plateau and superior cycle stability. This performance improvement can be attributable to a higher proton diffusion coefficient (4.26×10−9 cm2 s−1), better reaction reversibility, and lower electrochemical impedance of the synthesized material. [Copyright &y& Elsevier]

Abstract: Past studies have shown that both the substrate and microporous layer of the gas diffusion layer (GDL) significantly affect water balance and performance of a proton exchange membrane (PEM) fuel cell. However, little effort has been made to investigate the importance of GDL properties on the durability of PEM fuel cells. In this study, the in situ degradation behaviour of a commercial GDL carbon fiber paper with MPL was investigated under a combination of elevated temperature and elevated flow rate conditions. To avoid the possible impact of the catalyst layer during degradation test, different barriers without catalyst were utilized individually to isolate the anode and cathode GDLs. Three different barriers were evaluated on their ability to isolate GDL degradation and their similarity to a fuel cell environment, and finally a novel Nafion/MPL/polyimide barrier was chosen. Characterization of the degraded GDL samples was conducted through the use of various diagnostic methods, including through-plane electrical resistivity measurements, mercury porosimetry, relative humidity sensitivity, and single-cell performance curves. Noticeable decreases in electrical resistivity and the hydrophobic properties were detected for the degraded GDL samples. The experimental results suggested that material loss plays an important role in GDL degradation mechanisms, while excessive mechanical stress prior to degradation weakens the GDL structure and changes its physical property, which consequently accelerates the material loss of the GDL during aging. [Copyright &y& Elsevier]

Abstract: Spherical Li(Ni1/3Co1/3Mn1/3)O2 with a layered structure has been successfully prepared using the spherical precursor Ni1/3Mn1/3Co1/3OOH at temperature of 600°C. This synthesis temperature is remarkably lower than those of the spherical Li(Ni1/3Co1/3Mn1/3)O2 powders synthesized using Ni1/3Mn1/3Co1/3(OH)2 or Ni1/3Mn1/3Co1/3CO3. The compounds were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD analysis shows that the Ni1/3Mn1/3Co1/3OOH powder has a P3 structure and the Ni1/3Mn1/3Co1/3(OH)2 powder has a T1 structure. Charge and discharge tests show that the Li(Ni1/3Co1/3Mn1/3)O2 cathode prepared at 600°C for 24h has an initial discharge capacity as high as 148mAhg−1. The synthesized powder shows a reversible capacity of 142mAhg−1 a specific current of 0.2C rate in the range of 3.0V to 4.3V up to 50 cycles with no noticeable capacity-fading. [Copyright &y& Elsevier]