V 2 O 5 /carbon composites were prepared from a homogeneous suspension in which vanadium pentoxide sol and acetylene black powder were mixed with acetone acting as a surfactant. The composite was loaded on indium-tin oxide ͑ITO͒-coated glass, and then the magnesium intercalation property and the high-rate charge-discharge performance were evaluated in an electrolyte of Mg(ClO 4 ) 2 /acetonitrile at room temperature. In cyclic voltammetry, two main peaks of a reversible redox reaction were observed. It was determined that 1.84 mol of Mg per mol of V 2 O 5 were inserted in the first cycle at a relatively slow sweep rate of 0.1 mV s Ϫ1 , which corresponds to a specific capacity of 540 mAh (g-V 2 O 5 ) Ϫ1 . Galvanostatic charge-discharge tests at various current densities showed a high capacity of about 600 mAh (g-V 2 O 5 ) Ϫ1 at a current density of 1.0 A (g-V 2 O 5 ) Ϫ1 , and about 300 mAh (g-V 2 O 5 ) Ϫ1 was maintained even at 20 A (g-V 2 O 5 ) Ϫ1 .

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The effects of structural changes on electrochemical performances in cathode-active materials have to be understood to improve the durability of lithium-ion batteries. Here, cycle testing was conducted on a commercial lithium-ion cell using a LiNi0.8Co0.15Al0.05O2 cathode. Uncycled cells and those cells that were cycled 400 and 800 times were disassembled to obtain their cathodes, which were analyzed using scanning transmission electron microscopy and single particle measurement. After completing 400 cycles, a NiO-like phase is formed on the outermost surface of the particle. Furthermore, after 800 cycles, a NiO-like structure was also formed inside the particle. The rate performance of each single cathode particle that was obtained from the composite cathode was investigated to evaluate its exchange current density (i 0) and Li+ apparent diffusion coefficient (D). The i 0 decreased from 1.5 × 10–1 mA cm–2 (uncycled) to 0.3 × 10–1 mA cm–2 (cycled 400 times) and 0.01 × 10–1–0.05 × 10–1 mA cm–2 (cycled 800 times). D decreased from 2.0 × 10–10 cm2 s–1 (uncycled) to 1.3 × 10–10 cm2 s–1 (cycled 400 times) and 0.2 × 10–10 cm2 s–1 or less (cycled 800 times). It was clarified both electrochemically and quantitatively that the decomposition phase at the outermost surface, which was formed during the initial 400 cycles, causes a decrease in the exchange current density and that the decomposition phase inside the particle, which was formed in the range of 400 to 800 cycles, causes a decrease in the apparent diffusion coefficient of the particle.

Potential cycle tests that simulate the operation of a fuel cell vehicle are widely adopted as a durability testing method of membrane-electrode assemblies (MEAs). The Fuel Cell Commercialization Conference of Japan (FCCJ) has proposed methodologies for testing MEAs and their materials in 2007, focusing on the evaluation of the durability of electrode materials. The two protocols, start/stop durability test and load cycle durability test, were revised in 2011 based on the up-to-date knowledge concerning fuel cell durability. In this study, we applied the revised protocols to a standard electrocatalyst, and the effect of the revision was verified. We have demonstrated that the revision of the protocols accelerates the evaluation of fuel cell materials and verified that the revised protocols effectively separate the degradation of Pt electrocatalyst from that of carbon support.

The effect of sulfur-containing compounds on polymer electrolyte fuel cells (PEFC) was evaluated. The decrease in PEFC performance caused by the hydrogen sulfide contained in the hydrogen could not be recovered by the supply of pure hydrogen, but it was revealed that by holding the open circuit voltage with supplying pure hydrogen, the sulfur content poisoning the Pt catalyst disassociated as hydrogen sulfide and close to the initial performance was recovered. Holding the open circuit voltage and potential cycles with supplying neat air were also effective against the drop in performance due to the sulfur-containing compounds (sulfur dioxide, hydrogen sulfide) contained in the air, but the recovery in performance was limited. Further, it was revealed that the concentration of fluoride ions in the cathode effluent water increased after supplying sulfur-containing compounds with air. It is believed that when the air contains sulfur-containing compounds, not only are the active sites of the platinum catalyst reduced due to poisoning, but also the electrolyte membrane or ionomers simultaneously decompose and therefore an irreversible drop in performance is caused.

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