(Invited) Development of Highly Active and Durable Hybrid Compressive Platinum Lattice Cathode Catalyst for Polymer Electrolyte Membrane (PEM) Fuel Cells at USC
Authors: Popov Branko N , Kim Taekeun , Jung Won Suk 
Published: February 2020

The overall objective of this work was development proton exchange membrane (PEM) fuel cell catalysts for the oxygen reduction reaction (ORR) having ultra-low Pt loading with low cost, high performance and durability. The approach was based on development of a catalyst bridging the current platinum group metal (PGM) catalyst technology and the non-platinum cathode catalyst developed at USC. To balance the cost and the limited supply of platinum, the ultra-low platinum alloy project at (USC) developed highly stable and kinetically-activated carbon composite supports (A-CCS) as well as highly-active and stable hybrid cathode catalyst (HCC), Pt*/A-CCS (Pt* = Compressive Pt-lattice catalyst) that retain their activity after accelerated testing to simulate startup/shutdown and drive cycle potential cycling thus accomplishing the DOE 2017 targets. The HCC technology is based on a two-step patented process.
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In order to develop a hybrid catalysts, in the first step, the following major constraints in the PEM fuel cells interfaces were addressed : (a) chemical and electrochemical stability of the support at high potentials, low pH and high temperature and (b) the support onset potential and kinetic activity for oxygen reduction reaction to be similar to that of a platinum catalyst. To accomplish these requirements, the A-CCS was synthesized with optimized: (i) BET surface area, porosity, pore-size and distribution and active sties for ORR (ii) hydrophilic/hydrophobic ratio, (iii) structural properties (amorphous/crystalline ratio). In the second step, compressive Pt-lattice catalyst (Pt*) was synthesized through a USC-developed annealing procedure that controls the particle size during annealing and forms monolayers of Pt* by diffusing Co atoms present in the support into Pt which is deposited on A-CCS support. In this step, Pt/Pt*-support interaction was optimized through inclusion of active surface functional groups, and through optimization of transition metal content in the alloy necessary for the formation of compressive Pt-lattice catalyst. The Pt*/A-CCS shows high mass activity (0.41 A/mg Pt), excellent support stability, and enhanced catalyst durability under accelerated stress test (AST) conditions. Initial mass activity, mass activity and ECSA loss after 30K cycles (0.6 -1.0 V- catalyst durability), potential loss after 30 K cycles (0.6-1.0-catalyst durability), potential loss after 5 K cycles (1.0-1.5V-support stability) and mass activity and ECSA loss after 5 k cycles (1.0-1.5V-support stability) will be compared in the presentation with 2020 DOE Technical targets for PEM catalyst and supports.
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