Abstract
An MgO-templated mesoporous carbon, CNovel®, was employed as a catalyst support for the cathode of polymer electrolyte fuel cells (PEFCs) after modifying its dimensional, crystalline, surface and porous structures and the electrochemical oxygen reduction reaction (ORR) activities were examined by the thin-film rotating disk electrode (RDE) method and as well as the membrane electrode assembly (MEA) method. Although the catalytic activity of Pt on CNovel® was comparable with that on a non-porous carbon, Vulcan®, in the RDE configuration without Nafion®, Pt/CNovel showed a considerably higher activity than Pt/Vulcan in the MEA condition with Nafion®. The mechanism inducing this difference was discussed from the results of electrochemical surface area and sulfonic coverage measurements which suggested that Pt particles on inside pores of CNovel® are not covered with Nafion® ionomer while protons can still reach those Pt particles through water network. The MEA performance in the middle and high current-density regions was drastically improved by heat-treatment in air, which modified the pore structure to through-pored ones.
Highlights
Catalyst layers of polymer electrolyte fuel cells (PEFCs) normally consist of an electron conducting solid which supporting catalysts, an ionic conducting polymer and pores for gas transport [1,2,3,4]
Catalysts 2018, 8, 230 compared catalytic activities of Pt/Ketjenblack and Pt/Vulcan with and without Nafion® in an rotating disk electrode (RDE) environment [16] and concluded that Pt/Ketjenblack suffers oxygen reduction reaction (ORR) activities loss by Nafion® ionomer poisoning less significantly than Pt/Vulcan does because Pt particles on inside pores are not covered with the ionomer but still usable for ORR
Considering a significant part of Pt particles are not covered with the ionomer but are reachable by proton with water, these high activities of Pt/CNovels in membrane electrode assembly (MEA) can be attributed to high activity of non-covered and non-poisoned Pt surface
Summary
Catalyst layers of polymer electrolyte fuel cells (PEFCs) normally consist of an electron conducting solid (like carbon) which supporting catalysts (like platinum), an ionic conducting polymer (ionomer) and pores for gas transport [1,2,3,4]. A possible approach tackling these unfavorable effects of ionomers is to modify the molecular structure of ionomers to less-adsorptive ones [13] Another approach is to change the morphology of the substrate, carbon. Catalysts 2018, 8, 230 compared catalytic activities of Pt/Ketjenblack and Pt/Vulcan with and without Nafion® in an rotating disk electrode (RDE) environment [16] and concluded that Pt/Ketjenblack suffers ORR activities loss by Nafion® ionomer poisoning less significantly than Pt/Vulcan does because Pt particles on inside pores are not covered with the ionomer but still usable for ORR. After conducting various treatments for the material to modify the properties, platinum was deposited on the carbon and their properties as a support including ORR activities by the Rotating Disk Electrode (RDE) thin film method as well as by the Membrane Electrode Assembly testing (MEA method) and overall performance as a fuel cell were examined
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