The rechargeable zinc-air battery has attracted increasing research interest due to its the high energy density, environmental benignity of aqueous electrolytes, and abundance of zinc. However, the extremely high cost of electrocatalysts (such as Pt and Ir) hinders its practical application. The development of low-cost bifunctional oxygen catalysts for the zinc-air battery is of great significance.

In this thesis, a Fe, Ni-containing carbon-based bifunctional catalyst is developed, with single atoms doped on graphene and compound nanoparticles supported on hollow carbon spheres. The synthetic parameters of this material are systematically studied. The optimised catalyst delivers an overpotential of 0.73 V between oxygen evolution and oxygen reduction reactions, which is compara...[ Read more ]

The rechargeable zinc-air battery has attracted increasing research interest due to its the high energy density, environmental benignity of aqueous electrolytes, and abundance of zinc. However, the extremely high cost of electrocatalysts (such as Pt and Ir) hinders its practical application. The development of low-cost bifunctional oxygen catalysts for the zinc-air battery is of great significance.

In this thesis, a Fe, Ni-containing carbon-based bifunctional catalyst is developed, with single atoms doped on graphene and compound nanoparticles supported on hollow carbon spheres. The synthetic parameters of this material are systematically studied. The optimised catalyst delivers an overpotential of 0.73 V between oxygen evolution and oxygen reduction reactions, which is comparable to that of the commercial Pt/C-IrO₂ catalyst (ca. 0.72 V). The synthesis of the composite materials involves a co-polymerisation of aniline and pyrrole under 0 ℃ for 24 h with Triton X-100 and phytic acid. The polymer nanospheres and graphene oxide are mixed at the mass ratio of 1.5:1, in the metal nitrates solution with a 1:3 relative concentration of Fe to Ni. The precursors are pyrolysed in Ar at 950 ℃ for 5 h. This work provides useful principles on the rational design of more advanced bifunctional electrocatalysts.

Furthermore, the as-synthesised bifunctional catalyst is applied in air electrodes of zinc-air batteries. The PTFE (polytetrafluoroethylene) is selected as the binding material and the catalyst ink is airbrushed on a gas diffusion electrode. The corresponding cell exhibits higher voltage at large-current (up to 60 mA/cm²) during discharge and higher durability during cycling compared to commercial Pt/C-IrO₂ catalyst. The results demonstrate that the Fe, Ni-containing carbon-based bifunctional catalyst can be a good candidate for the rechargeable zinc-air batteries.