Department of Chemical Engineering , University of California , Santa Barbara , California 93106-5080 , United States.
Materials Physics and Applications Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.
ACS Appl Mater Interfaces. 2018 Aug 1;10(30):25337-25349. doi: 10.1021/acsami.8b06009. Epub 2018 Jul 23.
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 m/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.
报道了氮原子和铁掺杂的中孔碳材料的合成、表征及其在燃料电池阴极中催化还原氧气的电催化性能，并进行了比较。在中孔硅模板中，将常见且廉价的有机前体三聚氰胺和甲醛与过渡金属盐（例如硝酸盐）混合进行热解，得到的中孔碳材料的石墨化程度比用小分子前体制备的其他材料高。特别是，Fe,N 掺杂的碳材料具有高的比表面积（800 m²/g）和高的电导率（19 S/cm），这使其成为有吸引力的电催化剂应用材料。通过酸处理和随后的高温热处理对中孔 Fe,N 掺杂碳材料的表面组成进行了后合成修饰，X 射线光电子能谱表明这有利于形成石墨和吡啶氮基团。这种表面修饰的材料在碱性条件下表现出高的电催化氧气还原活性，其起始电位和半波电位分别为 1.04 和 0.87 V（相对于可逆氢电极），塔菲尔斜率低（53 mV/decade）。这些值优于许多类似的过渡金属和 N 掺杂的碳材料，并与商业上可用的贵金属催化剂（例如负载在活性炭上的 20wt%Pt）相当。分析表明，中孔 Fe,N 掺杂的碳材料是聚合物电解质燃料电池中电化学还原氧气用贵金属催化剂的有前途的替代品。
