Oxygen Reduction Electrocatalysis at Chalcogen-modified Ruthenium Cathodes J.-H. Choi, 1,* C. M. Johnston, 1 P. K. Babu, 2 A. Wieckowski, 2 N. Alonso-Vante, 3 and P. Zelenay 1 1 Materials Science & Technology Division Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 2 Department of Chemistry University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA 3 Laboratory of Electrocatalysis University of Poitiers 86022 Poitiers, Cedex, France Polymer electrolyte fuel cells (PEFCs) have long been viewed as a highly promising power source for the automotive, portable and stationary applications. However, in order to become commercially viable, polymer electrolyte fuel cells need to address two major barriers of (i) cost and (ii) performance durability. While overcoming the cost barrier is the key to the success of high-power fuel cell systems for the automotive and stationary power applications, the durability barrier is relevant to all three fuel cell systems, including those for portable applications. In all these applications, the cost of platinum used in electrodes is a major contributor to the high total fuel cell cost. Consequently, the development of well-performing inexpensive and easily accessible non- noble catalysts has become a major challenge for polymer electrolyte fuel cells. In the specific case of the direct methanol fuel cell (DMFCs), under development for portable electronics (laptop computers, cell-phones, etc.), two-wheel propulsion (power-assisted bicycles, scooters, etc.) and military applications (e.g. soldier power), platinum-based cathode catalysts have an additional disadvantage of being methanol-intolerant, which leads to the performance and efficiency losses due to the formation of a mixed potential. Unlike Pt, alternative ORR catalysts promise to be either fully or partially methanol tolerant, thus providing additional benefit for DMFCs. In an effort predominantly aimed at lowering the cost of hydrogen-air fuel cells and developing a methanol- tolerant cathode catalyst for various types of direct methanol fuel cells, including the mixed-reactant feed DMFCs, we have synthesized several typed of electrocatalysts potentially capable of replacing platinum at PEFC cathodes. An important part of this effort has been the selection and optimization of “non-catalytic” components of the membrane-electrode assembly (MEA) for successful introduction of non-platinum metal catalyst(s) to fuel cells without an additional “MEA” performance penalty. As a result of a collaborative research between the University of Illinois Urbana-Champaign, University of Poitiers and Los Alamos National Laboratory, we have recently developed a method for obtaining chalcogenide catalysts, which is based on surface modification of ruthenium black particles rather than the synthesis of a bulk metal-chalcogen compound [1]. Electrochemical, non-electrochemical and fuel cell testing have revealed high ORR activity and very good methanol tolerance of such “surface chalcogenide” catalysts [2,3]. Uniquely for Pt-free cathode catalysts, such surface chalcogenides also exhibit very good performance durability under fuel cell operating conditions at 70°C (Figure 1). In this presentation, we will focus on hydrogen-air and direct methanol fuel cell performance of chalcogen- modified Ru blacks as well as on the mechanism of oxygen reduction on such catalysts, as determined in rotating ring disk-electrode (RRDE) studies. Further, we will introduce methods for potentially reducing ruthenium content (loading) in surface chalcogenide catalysts, required for making these catalysts viable not only for DMFC use but also for high-power fuel cell applications, in automotive transportation in particular. Time (h) 0 200 400 600 800 1000 Current Density (A/cm 2 ) 0.0 0.1 0.2 0.3 0.4 0.5 H 2 -air, 70°C, 0.4 V Figure 1. Long-term performance test of a Se/Ru catalyst in a hydrogen-air polymer-electrolyte fuel cell. Cell voltage 0.4 V; cell temperature 70°C; H 2 flow 75 sccm; anode backpressure: 30 psig; air flow 100 sccm; cathode backpressure 30 psig. References 1. D. Cao, A. Wieckowski, J. Inukai, and N. Alonso- Vante, J. Electrochem. Soc., 153, A869-A874 (2006). 2. J.-H. Choi, D. Cao, A. Wieckowski, N. Alonso-Vante, P. Zelenay, 209 th Meeting of the Electrochemical Society, Denver, CO, May 7-11, 2006; Abstract 1113. 3. P. Zelenay, Hydrogen, Fuel Cells & Infrastructure Technologies Program, 2006 Merit Review and Peer Evaluation Meeting, U.S. Department of Energy, Energy Efficiency and Renewable Energy, Arlington, Virginia, May 16-19, 2006. Title: "Non-Platinum Cathode Catalysts". ____________________ * On leave from the Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, Gwangju, 500-712, South Korea. ECS 210th Meeting, Abstract 0467.pdf