(492c) Atomic Layer Deposition of Pt On WC for Fuel Cell Applications

One approach to reduce the amount of Pt needed for fuel cell catalysts is to coat a monolayer of Pt over a more inexpensive bulk material. Experimental and theoretical studies have demonstrated the promise of this approach for the major fuel cell reactions such as oxygen reduction reaction[1] and methanol oxidation[2]. These studies deposited one monolayer of Pt on planar substrates, but since real catalysts are nanoparticles, a synthesis technique must be employed that can coat nanoparticles with Pt in a controlled fashion. Currently, the most common powder synthesis method is incipient wetness impregnation; however, the nucleation of particles is based on thermodynamics, and therefore, the level of control needed to deposit such small quantities is not present. One proposed method is atomic layer deposition (ALD), a technique which is typically used in the semiconductor industry to produce thin films with sub-monolayer control. ALD consists of a series of gas-solid interactions that are cycled repeatedly until a specified quantity has been deposited, and its use as a catalyst synthesis method has only recently been explored to make uniform and well-distributed nanoparticles.[3]

We explore the use of ALD to make Pt-WC catalysts for oxygen reduction reaction. Pt-WC has been demonstrated as a promising electrocatalyst for oxygen reduction reaction.[4] WC is a good bulk material candidate because it serves as a promising support over carbon and also has shown to play a role in the catalysis. Pt ALD on planar WC thin films was first demonstrated, with the intent of later making powder catalysts. Pt-WC film samples of increasing number of ALD cycles were produced and characterized using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) for surface composition and scanning electron microscopy (SEM) to determine the surface morphology and approximate coverage. Cyclic voltammetry (CV) was then utilized to demonstrate that ALD Pt on WC shows promising improvements in oxygen reduction activity over Pt foil.

[1] Zhang, J. L.; Vukmirovic, M. B.; Xu, Y.; Mavrikakis, M.; Adzic, R. R. Angewandte Chemie-International Edition 2005, 44, 2132. [2] Zellner, M. B.; Chen, J. G. G. Journal of the Electrochemical Society 2005, 152, A1483. [3] King, J. S.; Wittstock, A.; Biener, J.; Kucheyev, S. O.; Wang, Y. M.; Baumann, T. F.; Giri, S. K.; Hamza, A. V.; Baeumer, M.; Bent, S. F. Nano Letters 2008, 8, 2405. [4] Nie, M.; Shen, P. K.; Wu, M.; Wei, Z. D.; Meng, H. Journal of Power Sources 2006, 162, 173.