De novo-design of highly exposed Co-N-C single-atom catalyst for oxygen reduction reaction
The nitrogen-coordinated metal single-atom catalysts(M-N-C SACs)with an ultra-high metal loading synthetized by direct high-temperature pyrolysis have been widely reported.However,most of metal single atoms in these catalysts were buried in the carbon matrix,resulting in a low metal utilization and inaccessibility for adsorption of reactants during the catalytic process.Herein,we reported a facile synthesis based on the hard-soft acid-base(HSAB)theory to fabricate Co single-atom catalysts with highly exposed metal atoms ligated to the external pyridinic-N sites of a nitrogen-doped carbon support.Benefiting from the highly accessible Co active sites,the prepared Co-N-C SAC exhibited a superior oxygen reduction reactivity comparable to that of the commercial Pt/C catalyst,showing a high turnover frequency(TOF)of 0.93 e-·s-1·site-1 at 0.85 V vs.RHE,far exceeding those of some representative SACs with a ultra-high metal content.This work provides a rational strategy to design and prepare M-N-C single-atom catalysts featured with high site-accessibility and site-density.
hard-soft acid-baseCo-N-Csingle-atom catalysthighly accessible active sitesoxygen reduction reaction
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