Facile Multiscale Patterning by Creep-Assisted Sequential Imprinting and Fuel Cell Application

The capability of fabricating multiscale structures with desired morphology and incorporating them into engineering applications is key to realizing technological breakthroughs by employing the benefits from both microscale and nanoscale morphology simultaneously. Here, we developed a facile patterning method to fabricate multiscale hierarchical structures by a novel approach called creep-assisted sequential imprinting. In this work, nanopatterning was first carried out by thermal imprint lithography above the glass transition temperature (<i>T</i>_g) of a polymer film, and then followed by creep-assisted imprinting with micropatterns based on the mechanical deformation of the polymer film under the relatively long-term exposure to mechanical stress at temperatures below the <i>T</i>_g of the polymer. The fabricated multiscale arrays exhibited excellent pattern uniformity over large areas. To demonstrate the usage of multiscale architectures, we incorporated the multiscale Nafion films into polymer electrolyte membrane fuel cell, and this device showed more than 10% higher performance than the conventional one. The enhancement was attributed to the decrease in mass transport resistance because of unique cone-shape morphology by creep-recovery effects and the increase in interfacial surface area between Nafion film and electrocatalyst layer

High-Performance Hybrid Catalyst with Selectively Functionalized Carbon by Temperature-Directed Switchable Polymer

Carbon-supported Pt (Pt/C) catalyst was selectively functionalized with thermally responsive poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) to improve water transport in the cathode of proton exchange membrane fuel cell (PEMFC). Amine-terminated PNIPAM selectively reacted with the functional group of −COOH on carbon surfaces of Pt/C via the amide reaction by 1-ethyl-3-(3-dimethylaminopropyl)­carbodiimide (EDC) as a catalyst. Pt surfaces of Pt/C were intact throughout the carbon surface functionalization, and the carbon surface property could be thermally changed. The PNIPAM-functionalized Pt/C was well-dispersed, because of its hydrophilic surface property at room temperature during the catalyst ink preparation. In sharp contrast, when PEMFC was operated at 70 °C, PNIPAM-coated carbon surface of Pt/C became hydrophobic, which resulted in a decrease in water flooding in the cathode electrode. Because of the switched wetting property of the carbon surface, PEMFC with PNIPAM-functionalized Pt/C catalyst in the cathode showed high performance in the high current density region. To explain the enhanced water transport, we proposed a simple index as the ratio of systematic pressure (driving force) and retention force. The synthetic method presented here will provide a new insight into various energy device applications using organic and inorganic composite materials and functional polymers

Understanding the Bifunctional Effect for Removal of CO Poisoning: Blend of a Platinum Nanocatalyst and Hydrous Ruthenium Oxide as a Model System

CO poisoning of Pt catalysts is one of the most critical problems that deteriorate the electrocatalytic oxidation and reduction reactions taking place in fuel cells. In general, enhancing CO oxidation properties of catalysts by tailoring the electronic structure of Pt (electronic effect) or increasing the amount of supplied oxygen species (bifunctional effect), which is the typical reactant for CO oxidation, has been performed to remove CO from the Pt surface. However, though there have been a few reports about the understanding of the electronic effect for rapid CO oxidation, a separate understanding of bifunctional modification is yet to be achieved. Herein, we report experimental investigations of CO oxidation in the absence of electronic effect and an extended concept of the bifunctional effect. A model system was prepared by blending conventional Pt/C catalysts with hydrous ruthenium oxide particles, and the CO oxidation behaviors were investigated by various electrochemical measurements, including CO stripping and bulk oxidation. In addition, this system allowed the observation of CO removal by the Eley–Rideal mechanism at high CO coverages, which facilitates further CO oxidation by triggering the CO removal by the Langmuir–Hinshelwood mechanism. Furthermore, effective CO management by this approach in practical applications was also verified by single-cell analysis