Structural changes of a Nafion-coated Pt/C electrocatalyst were observed by in situ transmission electron microscopy. The catalyst sample mounted on a gas-injection specimen-heating holder was exposed to a reaction gas of either dry or wet air, simulating the cathode environment of polymer electrolyte fuel cells. In the dry-air atmosphere, the carbon support was oxidized gradually and shrank with change of higher-order structure. In the wet-air atmosphere, the support was slightly oxidized and shrank without any change of higher-order structure. In both atmospheres, the movement of Pt particles was less active compared with the case of the catalyst Nafion-uncoated. These results suggest that Nafion protects the Pt/C electrocatalyst against degradation such as corrosion of the carbon support and displacement of Pt particles.

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Cycle tests using commercial 18650-type lithium-ion cells were conducted at temperatures of 0°C, 25°C, and 45°C and start charging State-of-Charges (SOCs) of 0%, 40%, and 70%. The current rate was 1/3C, which corresponds to the average C-rate for traveling electric vehicles. The discharge capacity decreased faster at 45°C, and high start charging SOC accelerated capacity fade at 45°C. In contrast, a start charging SOC of 0% accelerated the decrease in capacity and the increase in internal resistance at 0°C, and start charging SOC had almost no effect on degradation at 25°C. Differential voltage analyses revealed that the capacity decrease was ascribed to the mismatch of cathode and anode caused by side reactions.

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