Fe and N Functionalized-Ordered Mesoporous Carbon with Different Morphologies: Role of Fe on Surface Properties and Electrocatalytic Activity

Because of their high energy conversion efficiency, low pollution, low operating temperature, high power density, and wide range of applications, fuel cells have received a plethora of attention. Oxygen reduction reaction (ORR) takes place usually on Pt loaded on different carbon supports, but their large-scale commercial application has been precluded mainly by the high cost of the requisite noble metal. To overcome all the drawbacks of Pt or Pt-based catalysts, various efforts have been devoted to find its proper substitute. Heteroatom-doped carbon catalysts, due to their high stability, excellent electrocatalytic performance, and economic viability over costly Pt-based catalysts are being pioneered as a suitable alternative.

Although heteroatom-doped porous carbon materials have evolved as one of best possible solutions in this regard, the probable synergy of heteroatom doping and textural properties has not been well investigated yet in details. In this work, a detailed investigation is carried out on Fe and N-functionalized ordered mesoporous carbon (FeN-OMC) as electrocatalyst ORR in both alkaline and acidic media. The FeN-OMCs with different morphology are synthesized by pyrolysis of iron phthalocyanine-infiltrated corresponding SBA-15 silica templates. The as-synthesized FeN-OMC materials show excellent electrocatalytic ORR activity with nearly four electron transfer process. While the activity in alkaline media is nearly equal to or better than commercial Pt catalyst in terms of onset potential and diffusion-limited current density, it closely follows in acidic media, which is a tremendous achievement for non-precious metal catalysts developed till date. The most interesting observation is that not only heteroatom, but textural properties also affect catalytic activity profoundly. The physical presence of Fe species may be necessary in the synthesis of active heteroatom-doped carbon for high ORR activity, but may be not necessary any more for the as-prepared doped carbon to play as electrocatalyst for ORR.  Despite of being prepared with similar Fe and N content, the catalytic ability of FeN-OMC materials is gradually increased with decrease in mesopore channel length with maximum activity in thin platelet FeN-OMC. These observations demonstrate that structural morphology in addition to heteroatom and other textural properties, has significant synergistic influence on ORR catalysis in heteroatom-doped carbon materials.