Preparation Of Non-precious Metal ORR Catalysts And Development Of Bio-inspired Air Cathodes For Metal-air Batteries

Metal-air batteries have been regarded as promising power supply technologies for new energy vehicles,wearable electronic devices and smart equipments owing to their high theoretical energy density,convenience of operation and fast response.Yet,the air-cathodes in such batteries still remain the bottleneck constraining their practical applications due to poor energy output and long-term stability.This bottleneck is mainly attributable to the low catalytic activity,limited catalytic sites and instability of the oxygen reduction reaction?ORR?catalysts used in these devices.Meanwhile,the structural defects in air cathodes may reduce mass transfer efficiency,whereas the polymer binder used could block some catalytic sites.Thus,it is of great significance to design a cost-effective air-cathode with high efficiency of O2 utilization as well as ORR catalytic activity for practical applications in metal-air batteries.In this thesis,two ORR electrocatalysts based on non-precious metals have been prepared:one derived from the biomass of corn stover and the other by in situ growth of N-doped carbon nanotubes?CNTs?with encapsulated FeCo nanoparticles on carbon cloth.Then bio-inspired multichannel cathodes have also been fabricated and investigated.The specific work and results are as follows:1.A corn-stover-derived,nitrogen and cobalt co-doped porous biocarbon material has been prepared and utilized as ORR catalysts?NCAC-Co?in aluminum-air batteries.The resultant product exhibits an interconnected hierarchical porous structure with a high specific surface area(1877.3 m² g^-1).The electrocatalytic characterization of NCAC-Co reveals a half-wave potential?0.743V vs.RHE?only slightly lower than that of commercial Pt/C?0.793 V vs.RHE?in alkaline medium.Moreover,NCAC-Co also demonstrates the mechanism of 4-electron oxygen reduction?n=3.87?and outstanding durability.The excellent ORR performance of NCAC-Co can be attributed to the presence of pyridinic N,graphitic N and Co nanoparticles as well as the interconnected hierarchical porous structure.More importantly,NCAC-Co also delivers a good behavior when applied in aluminum-air batteries.2.In-situ grown N-doped carbon nanotubes?CNTs?with encapsulated FeCo nanoparticles?FeCo/N-CNTs?have been prepared and used as the ORR catalyst for flexible batteries.This FeCo/N-CNTs with gill-filament-like catalytic layers obtained by chemical vapor deposition?CVD?demonstrates excellent ORR catalytic property and good flexibility.According to Koutecky-Lecich plots,the electron transfer number of this air-cathode is close to 3.89,indicating first-order kinetics with respect to dissolved O2 and a dominant four-electron transfer pathway in ORR.Furthermore,the flexible battery assembled with the air-cathode exhibits high power density(127.0 mW cm^-2)and stable long-term charging-discharging performance.3.A wood-inspired multichannel air-cathode has been prepared via the method of direct metal laser sintering?DMLS?3D printing.Owing to its bio-mimic structure,the mass transfer efficiency in the air-cathode has been effectively improved.The power density of the metal-air battery assembled with the multichannel air-cathode is superior than those of batteries assembled with carbon cloth and steel mesh.In addition,it is found that the grid with 400?m interval shows higher power density(96.0 mW cm^-2)in zinc-air batteries than the grids of other sizes.The work presented herein affords a novel bionic approach to the development of ORR catalysts and air-cathodes for various metal-air batteries.