High oxygen reduction reaction activity of C-N/Ag hybrid composites for Zn-air battery

A novel nitrogen-doped biomass carbon/silver (C-N/Ag) composite has been synthesized by a simple method, wherein the precursor of soymilk simultaneously serves as carbon and nitrogen sources, reductant and substrate. The structure, morphology and valence state of samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectra. Results show the formation of nano-sized Ag homogenously disperses on the surface of mesoporous substrate, and the self-reduction role mainly attributes to the presence of unsaturated carbon bonding. Electrochemical properties were characterized by galvanostatic discharge and impedance spectra techniques. The sample prepared with 1 mmol AgNO3 solution, activated by 0.1 M KOH and annealed at 900 °C shows excellent oxygen reduction reaction activity and good electrochemical durability in alkaline medium. The onset potential, limiting diffusion current density and electron transfer number are 0.93 V, 6.26 mA cm−2 and 4.00, respectively, superior to those of 60 wt.% Ag/C and comparable to 20 wt.% Pt/C catalysts correspondingly. The discharge performance of Zn-air batteries is better than that of 20 wt% Pt/C.