Fe,N-Doped Graphitic Mesoporous Carbon Materials As Oxygen Reduction Catalysts

Fe,N-doped  graphitic mesoporous carbon materials
as oxygen reduction catalysts

Donghun Kim,¹ Niels Zussblatt,¹ Payam Minoofar,² Piotr Zelenay,³ Bradley F. Chmelka¹

¹Department of Chemical Engineering, University of California, Santa Barbara, California, USA

²Teledyne Scientific & Imaging, Thousand Oaks, California, USA

³Materials Physics and Applications Division, Los Alamos National Laboratory, New Mexico, USA

Transition-metal and nitrogen-containing carbon materials exhibit high oxygen reduction electrocatalytic activities and therefore are candidates to replace expensive conventional activated-carbon-supported platinum (Pt/C) catalysts in polymer-electrolyte fuel cells (PEFCs). High loadings of costly Pt catalysts are required to enable oxygen reduction reactions (ORR) that are characterized by intrinsically slow reaction kinetics at conventional operating temperatures (<100 °C). By comparison, iron- and nitrogen-doped carbon materials also exhibit high ORR activities and selectivities, but at significantly lower material costs.  We report here syntheses of highly graphitic Fe,N-doped mesoporous carbon materials as oxygen reduction electrocatalysts, based on pyrolysis of inexpensive industrial organic precursors with high N-contents. The resultant materials exhibit high surface areas (~800 m²/g), relatively high nitrogen contents (~4 atomic %), and graphitic properties, which yield improved activities for ORR and are more stable under alkaline conditions. In addition, these electrocatalysts exhibit high ORR selectivities as established by their stabilities in the presence of ethanol.  In particular, the high ORR selectivities overcome detrimental crossover effects that otherwise limit the performance of Pt/C catalysts in direct ethanol fuel cells (DEFCs).  The highly graphitic properties of Fe,N-containing carbon materials manifest superior chemical and thermal stabilities, increased electrical conductivities, and improved ORR reaction properties.  As cathodic platinum represents one of the largest components of overall fuel cell cost and exhibits significant reduction of activity due to fuel crossover, the synthesis of a non-precious metal alternative with equivalent or superior ORR activity under a variety of conditions will potentially overcome major obstacles to fuel cell commercialization.