Cobalt-polypyrrole-carbon black (Co-PPY-CB) Electrocatalysts for the Oxygen Reduction Reaction (ORR) in Fuel Cells: Composition and Kinetic Activity

Journal Article · Sat Dec 31 00:00:00 EST 2011 · Applied Catalysis B: Environmental

DOI:https://doi.org/10.1016/j.apcatb.2011.03.034· OSTI ID:1041806

Nguyen-Thanh, D; Frenkel, A; Wang, J; OBrien, S; Akins, D

Electrocatalysts consisting of polypyrrole (PPY) and Co deposited on carbon black (CB) at several compositions were prepared and tested for the oxygen reduction reaction (ORR) in a HClO4 buffer (pH = 1) using a rotating ring-disk electrode (RRDE). It was determined that the most favorable catalyst composition (prior to calcination) had a CB:PPY weight ratio of 2 and a pyrrole:Co (i.e., PY:Co) molar ratio of 4. This catalyst had an onset potential of 0.785 V (vs. RHE) and a mass activity of ca. 1 A/g{sub cata} at the fuel cell relevant voltage of 0.65 V. Furthermore, it was found that the number of electrons exchanged during the ORR with the catalyst was ca. 3.5 and resulted in 28% yield of H{sub 2}O{sub 2} at 0.65 V, which hints to an indirect 4e{sup -} reduction of O{sub 2} to H{sub 2}O, with H{sub 2}O{sub 2} as an intermdiate. From energy dispersive spectroscopy (EDS) and extended X-ray absorption fine structure (EXAFS) analysis, it is proposed that a PY:Co ratio of 4 favors the formation, prior to calcination, in the catalyst precursor of Co-N complexes in which Co is coordinated to 3 or 4 N atoms, resulting in strong Co-N interactions that limit the formation upon calcination of low ORR activity Co nanoparticles. These Co-N complexes give rise upon calcination to CoN{sub x-2} sites in which the coordination of Co could favor the adsorption on them of O{sub 2}, which would make those sites particularly active and selective. At the same mass acitivity of 1 A/g{sub cata}, the voltage yielded by the catalyst was 200 mV lower than that for a state-of-the-art Pt (10 wt.%) catalyst, whoch H{sub 2}O{sub 2} output at 0.85 V was 39% and involves the exchange of 3.2 e{sup -}, overall making our material an attractive substitute to noble metal ORR electrocatalysts.

• Research Organization: Brookhaven National Lab. (BNL), Upton, NY (United States)
• Sponsoring Organization: USDOE SC OFFICE OF SCIENCE (SC)
• DOE Contract Number: DE-AC02-98CH10886
• OSTI ID: 1041806
• Report Number(s): BNL-97484-2012-JA; TRN: US201212%%218
• Journal Information: Applied Catalysis B: Environmental, Vol. 105, Issue 1/2; ISSN 0926-3373
• Country of Publication: United States
• Language: English

Related Subjects

04 OIL SHALES AND TAR SANDS
30 DIRECT ENERGY CONVERSION
ABSORPTION
ADSORPTION
ATOMS
BUFFERS
CALCINATION
CARBON BLACK
CATALYSTS
COMPLEXES
ELECTRIC POTENTIAL
ELECTROCATALYSTS
ELECTRODES
ELECTRONS
ENERGY
FINE STRUCTURE
FUEL CELLS
INTERACTIONS
KINETICS
MASS
MATERIALS
METALS
OXYGEN
POTENTIALS
PRECURSOR
PRODUCTION
REDUCTION
RISE
SPECTROSCOPY
WEIGHT
YIELDS