Controlled synthesis of high metal-loading, Pt-based electrocatalysts with enhanced activity and durability toward oxygen reduction reaction

Abstract

High metal-loading Pt/C electrocatalysts are much sought after for the fabrication of thin-layered membrane electrode assemblies (MEA) suitable for mass transport and balance control of water and heat. However, such electrocatalysts are still limited to commercial Pt/C, comprised of carbon-supported, 2–5 nm Pt particles without size and size uniformity control, causing poor activity and durability toward oxygen reduction reaction (ORR). Herein, we report the controlled synthesis of 59.9 wt% Pt/C by using metallic ion-containing reversed micelles adsorbed on carbon. Combined with a simple surfactant removal method of washing with water, this unique confining approach enables easy control over the size and size uniformity of the resultant Pt/C, leading to significantly improved activity and durability for ORR compared with commercial 60 wt% Pt/C. The ORR activity enhancement arises from a smaller average size of Pt nanoparticles in combination with a narrower size distribution, with more Pt nanoparticles falling in an optimal size range of 2–4 nm with the highest ORR activity. The narrower size distribution of our Pt/C also makes the Pt nanoparticles resistant to the dissolution–re-deposition Ostwald ripening process, in which small Pt nanoparticles gradually shrink until they disappear, while large ones become bigger and bigger.