Seunghyun Kim

Formation of 3D graphene–Ni foam heterostructures with enhanced performance and durability for bipolar plates in a polymer electrolyte membrane fuel cell

Improving the lifetime and the operational stability of polymer electrolyte membrane fuel cells (PEMFCs) is critical for realizing their implementation as a practical and highly-efficient energy conversion system. However, the corrosion of metal bipolar plates, which are a key component in PEMFCs, leads to decreased efficiency and durability. Here, we prepared poly(methyl methacrylate)-derived multilayer graphene (Gr) coatings with high crystallinity and a continuous three-dimensional (3D) structure using a rapid thermal annealing (RTA) system for short periods (≤5 min). The resulting 3D Gr-coated Ni foam is demonstrated to act as a bipolar plate with long-term operating stability. Electrochemical analysis revealed that the synthesized graphene on Ni foam outperforms bare Ni foam and amorphous-carbon-coated Ni foam by providing a two-order-of-magnitude lower corrosion rate in the operating environment for a PEMFC. In addition, after stability tests in a destructive environment, the 3D Gr-coated Ni foam maintained its outstanding interfacial contact resistance of 9.3 mΩ cm2 at 10.1 kgf cm−2. A H2/air PEMFC fabricated using the Gr-coated Ni foam embedded within the groove of a graphite-based bipolar plate exhibited a substantially enhanced power density of ∼967 mW cm−2 at a cell potential of 0.5 V with further advantages of weight reduction and no additional machinery process for the gas flow channel. This facile coating approach addresses one of the key limitations of current metal bipolar plates in PEMFCs, and paves the way to further enhance energy conversion systems through interface engineering.

Investigation of Flow Accelerated Corrosion Models to Predict the Corrosion Behavior of Coated Carbon Steels in Secondary Piping Systems

To investigate various methods to mitigate flow accelerated corrosion of carbon steels, we have deposited various metallic and composite coatings on the surface of carbon steels and tested their performance by exploiting flow accelerated corrosion (FAC) simulation experiments. From the results, we found that both Ni-P/TiO2 composite coating and Fe-based amorphous metallic coating exhibited outstanding FAC resistance thus they are expected to expand the life-time of secondary systems of nuclear power plants. Furthermore, to investigate their life-time in nuclear power plants, we investigated known mechanistic models and commercial models of FAC and imported the parameters of the coated carbon steels into the models.

PWSCC Initiation of Alloy 600: Effect of Long-Term Thermal Aging and Triaxial Stress

Thermally aged nickel based Alloy 600 was investigated to evaluate the effects of long-term thermal aging and triaxial stress on primary water stress corrosion crack initiation behavior. Long-term thermal aging was simulated by heat treatment at 400 °C, a temperature that does not cause excessive formation of second phases that cannot form in nuclear power plant service conditions. Triaxial stress was applied by a round notch in the gauge length of some test specimen; other specimens were smooth. Slow strain rate tests (SSRT) monitored by the direct current potential drop method were conducted to evaluate stress corrosion crack initiation susceptibility of the thermally aged specimens in the primary water environment. For smooth specimens (which experience uniaxial stress), the susceptibility of those thermally aged for the equivalent of 10-years was the highest, while the susceptibility of the as-received specimens was the lowest. However, for the notched specimens (which experience triaxial stress), the specimens thermally aged for the equivalent of 20-years showed the highest susceptibility, while the as-received specimens showed the lowest.