Nitrogen-doped carbon (CNx) nanotubes were synthesized by thermal decomposition of ferrocene/ethylenediamine mixture at 600-900°C. The effect of the temperature on the growth and structure of CNx nanotubes was studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. With increasing growth temperature, the total nitrogen content of CNx nanotubes was decreased from 8.93 to 6.01 at.%. The N configurations were changed from pyrrolic-N to quaternary-N when increasing the temperature. Examination of the catalytic activities of the nanotubes for oxygen reduction reaction by rotating disk electrode measurements and single-cell tests shows that the onset potential for oxygen reduction in 0.5 M H 2 SO 4 of the most effective catalyst (CNx nanotubes synthesized at 900°C) was 0.83 V versus the normal hydrogen electrode. A current density of 0.07 A cm -2 at 0.6 V was obtained in an H 2 /O 2 proton-exchange membrane fuel cell at a cathode catalyst loading of 2 mg cm -2 .

The vanadium redox flow battery (VRB) is an attractive energy storage technology due to its great advantages such as high energy efficiency and long life cycle. A carbon electrode has been commonly used as the electrode material for the VRB system. In this study, the effects of microwave treatment on the carbon electrode for the VRB are investigated under different microwave powers (0, 500, and 650 W). The microwave‐treated carbon electrode is about twice as large as the pristine carbon electrode in specific surface area, showing about 2.72, 4.46, and 4.63 m2 g−1 at 0, 500, and 650 W, respectively. The oxygen‐containing functional groups such as CO, CO, and OCO, which can promote the redox reactions in the VRB system, are also increased by the microwave treatment. When the microwave‐treated carbon electrode is applied as the positive electrode for the VRB system, the coulomb, voltage, and energy efficiencies are enhanced. Thus, the microwave treatment can be a simple and effective method to prepare the carbon electrode for the VRB system.

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Abstrast High temperature fuel cell has been highlighted for its use in the wide range of the applications because of its simplified system due to easier integration and high energy efficiency.[1-2] There are several fascinating reasons for operating PEMFC at high temperature and low related humidity such as electrochemical kinetics, CO poisoning of Pt/C catalyst and water management. Also, the lifetime targets (5000 h stated objective by DOE) must be achieved while the costs of the fuel cell systems must be reduced concurrently.[1] In order to ameliorate the durability and lifetime of PEMFCs, a better analyzing of failure tools and corresponding mitigation methods are urgently required.[2] In the development of membranes that can effectively operate under higher temperature and lower humidity conditions, researchers have suggested organic-inorganic composite membranes with inorganic particulate additives.[3] Some of the composite membranes with particulate additives have shown improved fuel cell performance at high temperature and low humidity because of improved hydroscopic and thermal stability. Nevertheless, in practice, composite film casting by solvent evaporation or extrusion is often challenging due to particle agglutination. Recently, ceramic nanofibers have been prepared via electrospinning.[4] The uniformly dispersed 3-dimensional foam-like inorganic nanofibrous web completely resolved the agglomeration issue of particulate additives. The aspect ratio of the fibers was extremely high thereby providing additional mechanical strength to the composite membrane that could not be achieved by particulate additives. In this study, we prepared inorganic nanofibrous web supported polymer electrolyte membrane to increase operating temperature of the pristine polymer electrolyte membrane. Accelerated life-time tests (ALT) by changing the voltage sweep were developed to have better understanding of the degradation mechanisms in the fuel cell system. Further, factors of degradation were studied by conducting the electrochemical methods and characterizations. Gravimetric swelling by water of the Aquivion-impregnated inorganic nanofibrous webs as a membrane was higher than Aquivion cast film (32.8% vs. 17.5%) but more importantly, no length change in x- and y-axis was observed in wet state due to the presence of rigid inorganic nanofibrous webs uniformly distributed in the membrane. Therefore, no areal expansion of membrane is expected in the actual fuel cell test that would be beneficial to mechanically stable operation. A single cell with Aquivion/phosphate modified inorganic nanofiber composite membrane showed the best performance at partially humidified condition of 120 °C / 40% RH. It was expected that the higher water retention of the Aquivion/ phosphate modified inorganic nanofiber composite membrane played a beneficial role that the phosphate functionality enhanced proton conductivity by enhancing proton transfer through the Grotthus mechanism at higher temperature and the lower humidity conditions. References [1] B. Wahdame et al., Journal of Power Sources 182 (2008) 429–440 [2] S. Zhanga, et al., International journal of hydrogen energy 34 (2009) 388–404 [3] P. Costamagna, et al., Electrochimica Acta 47 (2002) 1023-1033. [4] Yao, Y et al.. Electrochemistry Communications 13 (2011) 1005-1008.