Studies On Carbon-based Oxygen Reduction Electrocatalysts And Electrochemical Zn Mirrors

The sluggish kinetics of oxygen reduction reaction(ORR)greatly limits the development of fuel cells and metal-air batteries.Therefore,catalysts for ORR are in urgent need.As the most widely used practical ORR catalyst,Pt/C is high-cost and then hinders the wide development of batteries.Carbon-based catalysts possess the ability of chemical doping,efficient catalytic performance,heterogeneous porosity,good stability,high conductivity and low cost.Therefore,they exhibit a huge potential to replace Pt/C.Herein,we design the molecular and morphological of tailored precursors,programmedly control carbonization temperatures and choose the appropriate post-treatment for pyrolysis products.Many series of porous carbon-based catalysts doped with heteroatoms are prepared via the pyrolysis of biomass materials,metallic ionic liquids and electrospun fiber films.The application and electrocatalytic performance of these carbon-based electrocatalysts for ORR are studied.Furthermore,zinc mirrors,a kind of energy-storage electrochromic devices,are designed with the base of zinc-organic hybrid batteries.The detailed research contents are as follows:(1)The high efficient catalysts for ORR are synthesized via carbonizing the mixture of Gentiana scabra Bunge and NH4Cl,which are easily available and inexpensive.Gentiana scabra Bunge is a carbon source,while NH4Cl brings catalysts more nitrogen and porosity.Furthermore,synergistically tailoring the NH4Cl/Gentiana scabra Bunge feed ratio and the carbonization temperature makes the chemical and physical properties of the as-prepared carbon materials controllable and thus realizes ORR-performance-oriented design and synthesis of nitrogen doped carbon materials.The electrocatalyst displays a high specific surface area(1440.8 m2 g-1),hierarchical porosity and active materials content.Furthermore,the carbon-based electrocatalyst possesses comparable half-wave potential and onset potential to Pt/C,indicating its good catalytic performance for ORR.(2)We describe a self-doping and additive-free strategy for the synthesis of metal-nitrogen-codoped porous carbon-based catalysts via carbonizing well-tailored precursors,metal-containing ionic liquids,at controllable temperatures.The organic skeletons in metal-containing ionic liquids are carbon and nitrogen sources,while metal ions function as porogen and metallic dopants.High nitrogen content,appropriate content of metallic species and high porosity synergistically make the resultant carbon materials efficient electrocatalysts for ORR.MIBA-Fe-900 possesses a high specific surface area(1567 m2 g-1)and shows a comparable electrocatalytic activity to that of Pt/C.Especially,the electrocatalyst achieves a higher long-term durability.(3)A class of Fe/N co-doped carbon nano fibers is successfully synthesized by pyrolysis of polyacrylonitrile/metal-containing ionic liquid-based electrospun films at different programmed temperatures.The ionic liquid serves as both porogen to provide heterogeneous porosity and an activator to bring carbon nanofibers active sites.The electrocatalyst possesses appropriate active sites and unique 3D porous architecture and exhibits remarkable long-term stability and electrocatalytic activity.Furthermore,the Zn-air battery equipped with the synthesized catalyst exhibits similar discharge voltage(1.20 V)to the battery with Pt/C.It is notable that an all-solid-state Zn-air battery based on the carbon nanofibers exhibits good flexibility,indicating its promising application in wearable devices.(4)We realize the multi-function of energy storage devices via the combination between electrochromism and Zn-organic hydrid batteries.The new device acts as both a battery and a switchable electrochromic device when Zn electrodeposits and dissolves on a transparent electrode.Herein,Zn and viologen are the anode and cathode,respectively.During charging,Zn is electrodepo sited on the transparent electrode to form a mirror and electric energy is stored as chemical energy.When Zn mirror dissolves,stored energy is released as electric energy.Compared with traditional reversible electrochemical metallic mirrors,energy is more sufficiently and sustainably utilized.This device achieves a specific capacity of 65.0 mAh g-1.Also,it displays a high reflectance of 84.9%and ultralong memory effects of Zn mirrors.