A bimetallic Pt-Cu catalyst on mesoporous carbon has been designed to improve activities and stabilities for the oxygen reduction reaction, which is of great interest in polymer electrolyte membrane fuel cells (PEMFC). Recently, Koh and Strasser reported Pt-Cu bimetallic catalysts, which showed an activity enhancement of ~4x over commercial catalysts after the copper was electrochemically dealloyed from the nanoparticle surface.¹

An emerging concept in catalyst design is to pre-synthesize metal nanocrystals coated with stabilizing ligands to control their morphology, and then to infuse the particles onto high surface area supports. The decoupling of nanocrystal synthesis and infusion provides exquisite control of the nanocrystal size, composition, morphology, and dispersibility within the porous support. We have designed PtCu catalysts by first synthesizing PtCu nanoparticles with controlled size (< 3nm) and composition via stabilizing, short-chain, hydrocarbon ligands (oleic acid and oleylamine), followed by infusion onto the high surface area mesoporous carbon supports.  XRD spectra shows that the catalyst is predominantly a single phase Cu rich alloy with <5% of a Pt rich phase. The catalysts were electrochemically dealloyed to preferentially leach out copper from the nanoparticle surface. These catalysts show significantly improved specific mass and area activities for ORR at 0.9V (vs. NHE) as measured using rotating disk electrodes.       

The stability of fuel cell catalysts for ORR was investigated by potential cycling up to 1.2V. For automotive applications, catalyst support stability at 1.2V is required for an accumulated life time of the vehicle, with a maximum allowable performance loss of < 30 mV. Typical amorphous carbon supports, for example Vulcan carbon, easily oxidize at potentials of 1.2V, which leads to significant activity losses. Herein we use corrosion resistant graphitic supports to enhance the stability of the catalysts. The strong metal interaction with the ¹ electron support sites was used to enhance the catalyst stability. We have studied the stability of the PtCu catalysts by accelerated durability test (ADT) by potential cycling between 0.5V and 1.2V at 50 mV/s for 1000 cycles. Mesoporous carbon supports with different degree of graphitization have investigated, and high stabilities have been achieved.

(1) Koh, S.; Strasser, P. Electrocatalysis on bimetallic surfaces: modifying catalytic reactivity for oxygen reduction by voltammetric surface dealloying. J Am Chem Soc.  2007, 129, 12624-12625.