PGM-Free Oxygen Reduction Reaction Electrocatalyst: From the Design to Manufacturing

Abstract

Recently, a significant interess to the development of PGM-free catalysts for both the anode [1] and cathode [2] catalysts for the low temperature fuel cells resulted in increasing of their activity, stability and durability [3]. The activity of transition metal/nitrogen/carbon (M-N-C) materials already achieved ~30% of Pt/C. In order to further advance the research, development and commercialization of these materials Pajarito Powder, LLC utilizes the manufacturing platform under a trade mark VariPore™ which allow to control morphology and hydrophobicity/hydrophilicity, level of graphitization and final activity [4-8]. In a close collaboration with world leaders in MEA manufacturing EWII Fuel Cells these materials were integrated in high performed fuel cell MEAs, which were comprehensively tested in segmented cell at Hawaii Natural Energy Institute, University of Hawaii. All three organization are part of US DOE ElectroCat consortium.The synthetic approach is based forming the M-N-C ORR electrocatalyst from organic molecules (ranged from low molecular weight ones up to polymeric materials), which are combined with precursors of transition metals: M=Fe, Ni, Co, Mn. The main parameter which allow to control mentioned above properties is an addition to hybrid Organic-Transition Metal (TM) mixture the particles and pore forming agents (PFs). In the present work these agents were selected from the family of so called “hard templates”: silica, magnesia and a number of high surface area oxides of transition metal. The fine mixture of Organic-TM-PF was heat treated in an inert atmosphere of nitrogen in order to create the matrix of the catalyst enriched with M-Nx active sites [3]. The catalytically inactive PFs were removed from the heat-treated material by the know-how leaching process developed at Pajarito Powder.The family of Fe-N-C materials prepared at Pajarito Powder by the VariPore™ method at the scale of 200 gram per batch were provided to the EWII Fuel Cell MEA manufacturing Team, where a series of MEAs were fabricated with a variation of catalyst:ionomer ratio, deposition method and other. The electrochemical evaluation of these MEAs at low potentials (OCV-0.85V) were performed at Hawaii Natural Energy Institute using a segmented cell. The main focus of these experiments was the understanding the PGM-free ORR behavior during the MEA activation and revealing the highest intrinsic ORR activity of these catalysts. It should be mentioned that all fuel cell experiments were performed at recommended by DOE ElectroCat consortium conditions and can be compared around the ElectroCat community as well as around research groups adopted these protocols. The details on the materials synthesis and evaluation will be presented.Acknowledgments:We would like to acknowledge the financial support from US DOE EERE under the grant DE-EE0008419 “Active and Durable PGM-free Cathodic Electrocatalysts for Fuel Cell Application” (PI: Alexey Serov).