Ji-Hoon Jang

Despite the many advantages of catalyst‐coated membranes (CCMs), there have been few studies of the use of CCMs to construct membrane‐electrode assemblies (MEAs) for high‐temperature polymer‐electrolyte membrane fuel cells (HT‐PEMFCs) using phosphoric acid (PA) doping. In this article, the use of membrane patterning to enable CCM to be utilized for HT‐PEMFCs is reported. A PA‐doped ion‐pair membrane and an electrode containing protonated phosphonic acid ionomers are employed to fabricate CCMs using the direct‐decal‐transfer method. A membrane with an inverted‐pyramid structure, created using solvent‐assisted patterning, further exploits the advantages of CCMs. The resulting CCM exhibits improved decal‐transfer efficiency, increased capillary infiltration of PA, and reduced PA loss during compression. The enlarged, interlocked, 3D structure increases the interfacial adhesion strength and the electrochemically active surface area compared to a conventional MEA with either a catalyst‐coated substrate or a flat CCM. Due to the morphological modification of the electrode, the patterned CCM also exhibits the lowest oxygen‐transport resistance among the MEAs. As a result of these enhancements, the patterned CCM achieves the high performance of 680 mW cm⁻² at 160 °C in dry H₂/air with low total Pt usage of 0.5 mg cm⁻².

We report on the syntheses of core-shell Fe_x@Pt (x = 0.4–1.2) nanoparticles (NPs) with Pt-shell thickness systematically controlled while the overall particle size is constant. The syntheses were achieved via one-pot ultrasound-assisted polyol synthesis (UPS) reactions. Fe_1.2@Pt showed a record-breaking high core-element content (55 at%) of core-shell NPs. Based on observations from a series of control experiments, we propose a mechanism of the NPs' formation that enables control of shell thickness in UPS reactions. Fe_x@Pt NPs showed drastic enhancements in mass and specific activity for oxygen reduction reaction (ORR) and significantly enhanced durability compared to commercial Pt NPs. Fe_x@Pt with a 1 (monolayer) ML Pt shell showed the highest activity. The ab initio density functional theory calculations on the binding energies of oxygen species on the surfaces of Fe_x@Pt NPs showed that the 1 ML case is most favourable for the ORR and in good agreement with the experimental results.

Highly conductive and water-dispersible sheets of reduced graphene oxide (RGO) were produced by rapidly heating graphene oxide (GO) paper at a low temperature (300 °C) for a short processing time of 3 s. The GO paper was thermally treated during the rapid-heating reduction process and, consequently, the oxygen functional groups in the obtained RGO were highly reduced. The RGO film displays good thermal stability, crystallinity, low sheet resistance, and good dispersibility in water, which makes it an ideal candidate to be used in various carbon-based electronic devices. We finally demonstrate the suitability of RGO as an active channel material and as a source-drain electrode for graphene field-effect transistors, which bring the possibility of realizing all-carbon devices a step closer to reality.