Micropores regulating enables advanced carbon sphere catalyst for Zn-air batteries

Energy conversion technologies like fuel cells and metal-air batteries require oxygen reduction reaction (ORR) electrocatalysts with low cost and high catalytic activity. Herein, N-doped carbon spheres (N-CS) with rich micropore structure have been synthesized by a facile two-step method, which includes the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process. During the preparation, zinc chloride (ZnCl2) was utilized as a catalyst to promote polymerization and provide a hypersaline environment. In addition, the morphology, defect content and activity area of the resultant N-CS catalysts could be regulated by controlling the content of ZnCl2. The optimum N-CS-1 catalyst demonstrated much better catalytic activity and durability towards ORR in alkaline conditions than commercial 20 wt% Pt/C catalysts, of which the half-wave potential reached 0.844 V vs. RHE. When applied in the Zn-air batteries as cathode catalysts, N-CS-1 showed a maximum power density of 175 mW cm−2 and long-term discharging stability of over 150 h at 10 mA cm−2, which outperformed 20 wt% Pt/C. The excellent performance could be due to its ultrahigh specific surface area of 1757 m2 g−1 and rich micropore channels structure. Meanwhile, this work provides an efficient method to synthesize an ultrahigh surface porous carbon material, especially for catalyst application. N-doped carbon spherical material (N-CS) with abundant microporous structure have been fabricated by the polymerization of pyrrole and formaldehyde and followed by a facile pyrolysis process. The resultant N-CS demonstrated more excellent catalytic activity and durability than commercial 20wt% Pt/C catalyst in alkaline media and the home-made Zn-air batteries. [Display omitted] •The N-doped carbon spheres (N-CS) with abundant micropores and defects were prepared by a facile polymerization of pyrrole and formaldehyde and following pyrolysis.•Hypersaline environment of ZnCl2 was found to change the morphology, porosity structure and defects of N-CS and further improve its ORR performance.•N-CS exhibited excellent performance towards ORR in Zn-air battery, due to its ultrahigh specific surface area and rich micropore structure..