High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt

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Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 443-447
DOI: 10.1126/science.1200832

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  1. Fig. 1

    Schematic diagram of the synthesis of PANI-M-C catalysts. (A) Mixing of high–surface area carbon with aniline oligomers and transition-metal precursor (M: Fe and/or Co). (B) Oxidative polymerization of aniline by addition of APS. (C) First heat treatment in N2 atmosphere. (D) Acid leaching. The second heat treatment after acid leach is not shown.

  2. Fig. 2

    (A) Steady-state ORR polarization plots (bottom) and H2O2 yield plots (top) measured with different PANI-derived catalysts and reference materials: 1, as-received carbon black (Ketjenblack EC-300J); 2, heat-treated carbon black; 3, heat-treated PANI-C; 4, PANI-Co-C; 5, PANI-FeCo-C(1); 6: PANI-FeCo-C(2); 7, PANI-Fe-C; 8, E-TEK Pt/C (20 μgPt cm−2). Electrolyte: O2-saturated 0.5 M H2SO4 [0.1 M HClO4 in experiment involving Pt catalysts (dashed lines)]; temperature, 25°C. RRDE experiments were carried out at a constant ring potential of 1.2 V versus RHE. RDE/RRDE rotating speed, 900 rpm; non–precious metal catalyst loading, 0.6 mg cm−2. (B) Steady-state ORR polarization plots (bottom) and H2O2 yield plots (top) measured with a PANI-Fe-C catalyst in 0.5 M H2SO4 electrolyte as a function of the heat treatment temperature: 1, 400°C; 2, 600°C; 3, 850°C; 4, 900°C; 5, 950°C; 6, 1000°C.

  3. Fig. 3

    Fuel cell and performance durability testing. (A) H2-O2 fuel cell polarization plots recorded with various PANI-derived cathode catalysts at a loading of ~4 mg cm−2: 1, PANI-C; 2, PANI-Co-C; 3, PANI-FeCo-C(1); 4, PANI-FeCo-C(2) (SDs from three independent measurements marked for all data points); 5, PANI-Fe-C. Performance of an H2-air fuel cell with a Pt cathode (0.2 mgPt cm−2) is shown for comparison (dashed line). All tests used a Pt/C catalyst at a loading of 0.25 mgPt cm−2 at the anode; anode and cathode gas pressure, 2.8 bar. (B) Long-term stability test of a PANI-FeCo-C(1) catalyst at a constant fuel cell voltage of 0.40 V (2.8 bar H2/2.8 bar air; 0.25 mgPt cm−2 anode; cell temperature 80°C). (C) PANI-Fe-C catalyst RDE performance at various potentials after potential cycling in nitrogen between 0.6 and 1.0 V in 0.5 M H2SO4 (catalyst loading, 0.6 mg cm−2). (D) PANI-Fe-C catalyst H2-O2 fuel cell performance at various voltages after voltage cycling in nitrogen between 0.6 and 1.0 V (cathode catalyst loading, 2.0 mg cm−2, Pt/C anode catalyst loading, 0.25 mgPt cm−2; anode and cathode gas pressure, 1.0 bar).

  4. Fig. 4

    Micrographs of a PANI-FeCo-C(1) catalyst. (A) HRTEM image of a typical non–precious metal catalyst nanostructure involving carbon nanofibers and metal-aggregates incorporated in graphitic nanoshells. (B) HRTEM image of hollow nanoshells. (C) HRTEM image of onion-like nanoshells. (D to F) HRTEM, HAADF-STEM, and SEM images of the same localized region in an area exhibiting a graphene sheet–like structure, where the green arrows designate the layered graphene sheet in each image and the red arrows designate the same FeCo-containing nanoparticle (technique used is noted in each micrograph).