(135a) Thin-Film Pt And Pt-Ru Glass Composite Catalyst Layers For Micro Direct Methanol Fuel Cells

Recently, state-of-the-art micro DMFCs have been demonstrated by our group with Phosphorus-doped ion-conducting SiO2 (PSG) thin films [1-2], which are believed to have lower permeability to methanol than Nafion®. Though the proposed DMFC showed promising performance, it was noted that both the anode and cathode electrode/electrolyte interfaces suffered from material incompatibility, making their long-term stability a concern.

At the anode, sputtered PtRu was coated by plasma-deposited P-doped SiO2. It is well known that silicate glasses have poor adhesion with most noble metals, meaning that a ?seed? layer of another metal, typically Ti, is needed. Second, at the cathode, a Nafion® ionomer thin film was cast in order to interface the Pt/C electrode with the PSG, introducing a coefficient of thermal expansion mismatch between the two electrolyte phases. Therefore, it is essential that researchers develop an electrode fabrication method that addresses concerns at both electrodes. To that end, novel thin film Pt-PSG and PtRu-PSG composite electrodes have been developed.

In this work, carbon-supported platinum and platinum-ruthenium alloy nanoparticles are incorporated into a porous silicon dioxide glass matrix. The glass is prepared by the sol-gel hydrolysis reaction between TEOS and water in the presence of methanol. During the hydrolysis reaction, the nanoparticles are introduced to the system under vigorous agitation. The sol reaction is allowed to proceed for a specified time (seconds to days) where it is deposited on the cell substrate and imposed to several curing steps where the solvent is evaporated and the reaction completed. The resulting structure is porous, homogeneous and the catalyst is well dispersed. The electrochemical performance of the resulting films for both methanol oxidation and oxygen reduction has been studied by ex-situ cyclic voltammetry in sulfuric acid electrolyte, polarization measurements in a micro DMFC and ac impedance in a two-compartment glass cell. Preliminary results indicate that the electrochemical performance of the DMFC is improved compared to cells prepared with Nafion®-based catalyst layers where a 50 mV increase in the open circuit potential and higher currents are realized for fuel cells prepared with the composite catalyst.

References

1. D. Bhusari, J. Li, P.J. Jayachandran, C. Moore and P.A. Kohl, Electrochem. Solid-State Lett., 8 (2005) A588.

2. J. Li, C.W. Moore, D. Bhusari, S. Prakash and P.A. Kohl, J. Electrochem. Soc., 153 (2006) A343.

Acknowledgement

The authors would like to thank the Test Resource Management Center (TRMC) Test and Evaluation/Science and Technology (T&E/S&T) Program for their support. This work is funded by the T&E/S&T Program through the Naval Undersea Warfare Center, Newport, RI, contract number N66604-06-C-2330.