Nitrogen-Doped\nMesostructured Carbon-Supported Metallic Cobalt Nanoparticles for\nOxygen Evolution Reaction

Abstract

A series\nof metallic cobalt nanoparticles supported on mesostructured nitrogen-doped\ncarbons was successfully synthesized through soft-templating by using\npoly­(ethylene oxide)-<i>b</i>-polystyrene (PEO-<i>b</i>-PS) as a structure directing agent. The formation of metallic cobalt\nnanoparticles and nitrogen-doping into carbon structures were simultaneously\nachieved by ammonia treatment. The physicochemical properties of the\nresulting materials and consequently their performance for the oxygen\nevolution were systematically altered by varying the cobalt loading\n(5–89 wt %), pyrolysis atmosphere (argon or ammonia), and temperature\n(600–800 °C). Thereby, up to 37 wt % of the cobalt nanoparticles\nwere confined in the pores of the mesostructured nitrogen-doped carbon\nmaterials with a high BET surface area. At temperatures above 700 °C,\nthe cobalt additionally catalyzes the graphitization of the carbon\nsupport. The catalyst with a cobalt loading of 37 wt % pyrolyzed at\n700 °C under an ammonia atmosphere shows the highest turnover\nfrequency (TOF) of 311 h^–1 in the oxygen evolution\nreaction due to the improved electronic properties of the carbon support\nfrom the incorporation of nitrogen atoms combined with a large amount\nof accessible cobalt sites. This class of materials shows even higher\nactivity in comparison with ordered mesoporous Co₃O₄.