In this study, the effects of repetition of assembly and disassembly of polymer electrolyte membrane fuel cells on electrochemical performance were systematically investigated. Additionally, the effects of additional activation on polymer electrolyte membrane fuel cells were evaluated. All fuel cells were measured every three days. For the disassembled polymer electrolyte membrane fuel cells, membrane electrode assemblies were stored in a vacuum desiccator. For the maintained assembly, fuel cells were stored at room temperature. The performance and electrochemical characteristics of the fuel cell were analyzed by electrochemical impedance spectroscopy. As a result, the addition of activation to maintained assembly fuel cells showed the best performance among fuel cells with other assembly and activation conditions. Repetition of assembly and disassembly, as well as insufficient activation, caused degradation of the performance of fuel cells.

Polymer electrolyte membrane fuel cells (PEMFC) require activation to maximize their performance. Thus, an appropriate activation process is essential for the performance of the fuel cell. In this study, the performance of the fuel cell was investigated by changing the voltage range during the activation process. There were three voltage ranges: 0.3-0.9 V, 0.3-0.6 V, and 0.6-0.9 V. When the fuel cell was activated in the low voltage region, the highest performance was output. On the other hand, it showed the lowest performance at high voltage. The results suggest that it is advantageous to activate the fuel cell with a high current. On the other hand, if activation is performed while outputting at a low current, the generation of water and the electrochemical reaction are insufficient, resulting in a load on the fuel cell. Through this experiment, it was confirmed that the control method greatly affects fuel cell performance when activated.

In this study, the electrochemical characteristics of fuel cell were evaluated after applying a compressive load to the activation area of membrane electrode assembly (MEA) in polymer electrolyte membrane fuel cells. The effects of the pressed area under the compressive load were systematically investigated using polarization curves and electrochemical impedance spectroscopies (EIS) of the fuel cell. Interestingly, the performance of the fuel cell was improved as the pressed area of the MEA was increased from 25.2% to 100% of the active area. In addition, the increased pressed area led to a decrease in the ohmic resistance and the activation resistance of fuel cells.

The WC-5wt.% TiC compacts, which was fabricated by pulsed current activated sintering process (PCAS), were cryogenically treated to improve the mechanical performance. The densely consolidated specimens were exposed to liquid nitrogen for 6, 12, and 24 h. All cryogenically treated samples exhibited compressive stress in the sintered body compared with the untreated sample. The cryogenically treated samples exhibited significant improvement in mechanical properties, with a 9% increase in Vickers hardness and a 52.6% decrease in the fracture toughness compared with the untreated samples. However, excessive treatment of over 12 h deteriorates the mechanical properties due to tensile stress in the specimens. Therefore, the cryogenic treatment time should be controlled precisely to obtain mechanically enhanced hard materials.