ABSTRACT
The development of a novel approach to achieve high-performance and durable fuel cells is imperative for the further commercialization of proton-exchange (or polymer electrolyte) membrane fuel cells (PEMFCs). In this work, multifunctional dendritic Nafion/CeO2 structures were introduced onto the cathode side of the interface between a membrane and a catalyst layer through electrospray deposition. The dendritic structures enlarged the interfacial contact area between the membrane and the catalyst layer and formed microscale voids between the catalyst layer and gas diffusion medium. This improved the PEMFC performance through the effective utilization of the catalyst and enhanced mass transport of the reactant. Especially, under low-humidity conditions, the hygroscopic effect of CeO2 nanoparticles also boosted the power density of PEMFCs. In addition to the beneficial effects on the efficiency of the PEMFC, the incorporation of CeO2, widely known as a radical scavenger, effectively mitigated the free-radical attack on the outer surface of the membrane, where chemical degradation is initiated by radicals formed during PEMFC operation. These multifunctional effects of the dendritic Nafion/CeO2 structures on PEMFC performance and durability were investigated using various in situ and ex situ measurement techniques.
ABSTRACT
We have achieved performance enhancement of polymer electrolyte membrane fuel cell (PEMFC) though crack generation on its electrodes. It is the first attempt to enhance the performance of PEMFC by using cracks which are generally considered as defects. The pre-defined, cracked electrode was generated by stretching a catalyst-coated Nafion membrane. With the strain-stress property of the membrane that is unique in the aspect of plastic deformation, membrane electrolyte assembly (MEA) was successfully incorporated into the fuel cell. Cracked electrodes with the variation of strain were investigated and electrochemically evaluated. Remarkably, mechanical stretching of catalyst-coated Nafion membrane led to a decrease in membrane resistance and an improvement in mass transport, which resulted in enhanced device performance.
ABSTRACT
The purpose of this study was to evaluate the healing process of collagen-apatite composite (CAC) at the titanium-bone interface in animal model. Small gaps (0.5 or 1.0 mm-sized wells) were prepared in the epoxy-resin block implants coated with pure titanium. The gaps were filled with CAC or demineralized freeze-dried bone (DFDB). The titanium-coated epoxy-resin block implants were inserted in the tibia of rabbit for 4 weeks or 8 weeks. The microscopic features of bony healing process in the grafted gaps were examined and analyzed. In the histomorphometric analysis, CAC group showed higher fraction of newly-formed bone than DFDB group in both 0.5 and 1.0 mm gap subgroup at 4-week specimen (P < 0.05). In the transmission electron microscopic examinations, osteoblasts of the newly-formed bone of CAC group showed more cellular activity than that of DFDB group. From the results, it was expected that CAC had more beneficial property on early bony healing process than DFDB at the titanium-bone interface.
