Electrocatalysis of heat-treated cobalt-porphyrin/carbon for hydrogen peroxide formation

The electrocatalysis of heat-treated Co-TPP/carbon for O2 reduction and H2O2 formation using a fuel cell reactor with an H2SO4 aqueous electrolyte was studied (TPP: 5,10,15,20-tetrakis(phenyl)-21H,23H-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 H2O2 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 H2O2 and the electroreduction of H2O2 to water. These studies indicated that the electrocatalytic activities for the successive reduction of H2O2 to water determined the final H2O2 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 H2O2 formation. A model of the Co active site, CoN2–carbon, was proposed.