Oxygen electrocatalysis study on carbon-based single atomic catalysts for zinc-air batteries

Zinc-air batteries (ZABs) are regarded as one of the most promising candidates for the next-generation green and sustainable energy storage solutions, due to their eco-friendliness, safety and low-cost. Despite of the high energy density, the overall battery performance is restricted and governed by kinetically-sluggish oxygen electrocatalysis, thus requiring adequate catalysts to ensure sufficient reaction rate. The thesis starts with the design of ultra-low loaded platinum (Pt) catalysts, aiming to substantially reduce the Pt content. Therefore, atomic distributed Pt (~0.026 wt.%) material with nitrogen (N)-coordination and co-doped phosphorus (P) electronic modulation in porous carbon substrate was fabricated, which consequently showed an excellent and stable activity towards oxygen reduction reaction (ORR) and good performance of primary ZABs with a highly selective 4-electron pathway. The results of X-ray absorption spectroscopy (XAS), electron microscopy, electron energy loss spectroscopy and computational simulations attributed the activity to the synergy between the Pt-Nx motif and nearby P species. Subsequently, to totally replace the precious metals, manganese (Mn) was introduced into N and P co-doped mesoporous carbon, forming MnNxPy complex. The composite afforded a high ORR activity in alkaline media, overwhelming the commercial Pt benchmark. To further improve ORR performance, atomic iron (Fe) with N and P co-coordination embedded carbon hollow spheres was also synthesized, presenting excellent bifunctional oxygen electrocatalytic activity for ZABs. XAS revealed the tuned electronic structure of Mn and Fe by the heteroatom-coordination, leading to the high activities. Following these findings, iron-nickel (Fe-Ni) dual-metal pairs with N-coordination in porous carbon were designed and prepared to enhance the insufficient oxygen evolution (OER) performance of the above catalysts. The Fe-Ni dimers thus synergistically and effectively conducted respective ORR and OER on Fe and Ni sites as unveiled by XAS and computational simulations, breaking the limitation of Scaling Relations and offering exceptional rechargeable ZAB performance. Finally, the last section outlined future perspectives of the carbon-based single atomic catalysts. It is encouraged to conduct research on addressing the conflicts between high power density and large energy density. Also, scalable production of carbon based single atomic catalysts for ORR/OER would be of great values for the wider application of ZABs. Last but not least, the in-depth understanding on the oxygen electrocatalysis mechanism is highly plausible