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The electrocatalysis of heat-treated Co-TPP/carbon for O 2 reduction and H 2 O 2 formation using a fuel cell reactor with an H 2 SO 4 aqueous electrolyte was studied (TPP: 5,10,15,20-tetrakis(phenyl)-21 H ,23 H -porphyrin). Carbon supports, including vapor grown carbon fiber (VGCF), activated carbon (AC), carbon black XC-72 (XC72), and carbon black Black-Pearl-2000/3500 (BP2000/3500), strongly affected the electrocatalysis of the Co-TPP/carbon. The Co-TPP/VGCF heat-treated at 1023 K, abbreviated as Co-TPP/VGCF(1073), showed a good electrocatalytic activity for H 2 O 2 formation (1.0 mol dm −3 with 40% current efficiency (CE)); however, other carbon supports were unfavorable. Electrocatalytic activities were Co-TPP/VGCF(1073) >> Co-TPP/XC72(1073) > Co-TPP/AC(1073) > Co-TPP/BP2000(1073). Their electrocatalysis were studied by rotating ring-disk electrode voltammetry and kinetic studies of the decomposition of H 2 O 2 and the electroreduction of H 2 O 2 to water. These studies indicated that the electrocatalytic activities for the successive reduction of H 2 O 2 to water determined the final H 2 O 2 concentrations and CEs. An active site of heat-treated Co-TPP/VGCF was characterized by X-ray photoelectron spectroscopy, and X-ray absorption near-edge fine structure spectroscopy. Partial pyrolysis of Co-TPP on the carbon surface was essential to generate the active site for the H 2 O 2 formation. A model of the Co active site, CoN 2 –carbon, was proposed. |
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