A study of ordered mesoporous carbon doped with Co and Ni as a catalyst of oxygen reduction reaction in both alkaline and acidic media

Abstract

The incorporation of trace amounts (<0.2%) of Co and Ni noticeably enhanced the catalytic activity of nitrogen-free ordered mesoporous carbon (OMC) towards oxygen reduction reaction (ORR). (Co,Ni)-doped OMCs were characterized by N2-adsorption measurements, X-ray powder diffraction, field emission scanning electron microscopy and Raman spectroscopy methods, and their ORR activity was estimated by voltammetry on rotating disk electrode in acidic and alkaline media. (Co,Ni)-doped OMCs show modest activities in acidic media, while the catalytic activity in alkaline media is rather high. The measured activities are compared to the Pt-based and Pt-free ORR catalysts reported in the literature. The number of electrons consumed per O2 in metal-doped OMCs was found to vary between 2 and 4, which is advantageous in comparison to metal-free OMC. Also, the mass activities of metal-doped OMCs were found to be up to 2.5 times higher compared to that of metal-free OMC. We suggest that the ORR activity is governed by a balance between (i) textural properties, which determine the electrochemically accessible surface of the catalyst and which are influenced by the addition of a metal precursor, and (ii) novel active sites formed upon the introduction of metals into the carbon structure. In particular, our Density Functional Theory calculations suggest that Co and Ni atoms embedded into the single vacancies of graphene can activate the O2 molecule and contribute to the decomposition of peroxide.