The synthesis, characterization, and electrocatalytic properties of mesoporous carbon materials doped with nitrogen atoms and iron are reported and compared for the catalyzed reduction of oxygen gas at fuel cell cathodes. Mixtures of common and inexpensive organic precursors, melamine, and formaldehyde were pyrolyzed in the presence of transition-metal salts (e.g., nitrates) within a mesoporous silica template to yield mesoporous carbon materials with greater extents of graphitization than those of others prepared from small-molecule precursors. In particular, Fe,N-doped carbon materials possessed high surface areas (∼800 m2/g) and high electrical conductivities (∼19 S/cm), which make them attractive for electrocatalyst applications. The surface compositions of the mesoporous Fe,N-doped carbon materials were postsynthetically modified by acid washing and followed by high-temperature thermal treatments, which were shown by X-ray photoelectron spectroscopy to favor the formation of graphitic and pyridinic nitrogen moieties. Such surface-modified materials exhibited high electrocatalytic oxygen reduction activities under alkaline conditions, as established by their high onset and half-wave potentials (1.04 and 0.87 V, respectively vs reversible hydrogen electrode) and low Tafel slope (53 mV/decade). These values are superior to many similar transition-metal- and N-doped carbon materials and compare favorably with commercially available precious-metal catalysts, e.g., 20 wt % Pt supported on activated carbon. The analyses indicate that inexpensive mesoporous Fe,N-doped carbon materials are promising alternatives to precious metal-containing catalysts for electrochemical reduction of oxygen in polymer electrolyte fuel cells. ©
Bibliographical noteFunding Information:
This work was supported in part by the Institute for Collaborative Biotechnologies through grant W911NF-09-0001 from the U.S. Army Research Office and by the Institute for Multiscale Materials Studies at Los Alamos National Laboratory (UC Santa Barbara Contract No. 113144). The content of the information does not necessarily reflect the position or the policy of the U.S. Government, and no official endorsement should be inferred. Material characterization measurements were made with the Central Facilities of the UCSB Materials Research Laboratory, which are supported by the MRSEC Program of the NSF under Award No. DMR 1720256; a member of the NSF-funded Materials Research Facilities Network.
- graphitic carbon
- iron, nitrogen-doped carbon
- mesoporous carbon
- nonprecious metal catalyst