Synergetic influence of nitrogen-doped species and hollow microporous structure on surface active sites of carbonaceous catalysts for oxygen reduction reaction of Zn-air battery

The development of metal-free carbon catalysts towards oxygen reduction reaction has focused on their surface active sites multiplied by heteroatom doping and/or pore adjustment. Herein, to coordinate nitrogen doping and pore structure is uncovered to expect highly comparable properties of the carbons to those of commercial Pt/C catalysts. N-doped porous carbons have been fabricated by a ready and collaborative strategy in two-step pyrolysis. The first is to pyrolyze only a raw citrate forming porous carbons with micro-, meso-, or macro-porous structure. Subsequent cyanoguanidine thermolysis induces gaseous nitrogen doping to generate edge defects. Especially, the hollow microporous architecture gives rise to large specific surface area and relatively high catalytic activity of the carbon catalysts (denoted as N-CK). Furthermore, theoretical calculations indicate meta-positional dual-N doped sites with the carbon combining graphitic N and pyridinic N (Gn-C-Py) show a minimum overpotential of 0.39 V. Such a catalyst under the synergistic effect of high-active N-doped species and hollow microporous architecture enables its Zn-air batteries to deliver a superior peak power density of 99.9 mW cm−2 vs. 95.7 mW cm−2 for those using commercial Pt/C. Considering the comprehensive comparability, the N-CK catalysts in a hollow microporous construction possess great feasibility for practical applications.