Synthesis of a highly efficient bifunctional Co2P@N-doped carbon nanotubes electrocatalyst by GO-Induced assembly strategy for rechargeable Zn-air batteries

Due to the bonding force between the surface Co atom and the adsorbed intermediate are so strong that intermediate cannot desorb from Co atom, the oxygen reduction reaction of Co 2 P based electrocatalyst cannot satisfy the commercialized application of the Zn-air battery. In this work, a GO-induced assembly strategy was designed to construct cobalt phosphide (Co 2 P) nanoparticles encapsulated in N-doped carbon nanotubes (Co 2 P@NCNTs). The experimental results show that adding graphene oxide (GO) content has a significant impact on the formation of well-defined Co 2 P@NCNTs nanotubes structures and the exaltation of the graphitization degree. Benefitting from the synergistic effect between N-doped nanotubes and Co 2 P, the Co 2 P@NCNTs-15 electrocatalysts exhibited better catalytic performance, a more positive onset potential (0.90 V vs RHE) and half-wave potential (0.82 V vs RHE), maximum limiting diffusion current density (5.5 mA cm −2 ) and Tafel slope only 73 mV dec −1 . The potential gap (ΔE) between E j=10 of OER and ORR half-wave potential (E 1/2 ) of Co 2 P@NCNTs-15 is only 0.93 V, which lower than Pt/C electrocatalyst (1.15 V). More importantly, the Co 2 P@NCNTs-15-based rechargeable Zn-air battery performed the highest peak power density (159.7 mW cm −2 ), specific capacity (792.6 mAh g −1 at 10 mA cm −2 ) and remarkable cycle stability. This method also offers a high yield and cost-effective synthesis strategy for preparing the other transition metal phosphide electrocatalysts.