Templates As Porous Carbon Application Of Porous Carbon Materials With Metal Organic Framework Compounds As Templates In Electrocatalysis And Zinc-air Batteries

The growing demand for clean energy has led to in-depth research on efficient,cheap and non-toxic energy conversion and storage equipment.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）are important electrochemical processes for fuel cells,water decomposition and various rechargeable batteries.However,developing practical electrocatalysts with enhanced electrochemical performance remains a challenge.Platinum-based electrocatalysts are by far the most effective ORR catalysts.For OER,electrocatalysts based on oxides of iridium and ruthenium are considered to be the most effective catalysts.However,these materials are expensive,have poor stability and are not easily reacted with inert intermediates,which limits their large-scale application.Therefore,it is very meaningful to develop electrocatalysts with high activity,high stability and low cost.Based on this,this paper mainly uses metal-organic framework compounds as templates to synthesize a series of nitrogen-doped porous carbon materials by regulating metal doping.The excellent performance of the synthesized electrocatalyst and the source of such performance are studied in detail application.（1）Using the self-made ZIF-8 as a template,metal hydroxides are loaded on the template surface by hydrolyzing metal salts（Fe（NO₃）₃·9H₂O,Co（NO₃）₂.6H₂O and Ni（NO₃）₃.9H₂O）.One-step pyrolysis produces porous carbon materials（FeNC,CoNC and NiNC）doped with different metals.Scanning electron microscope（SEM）was used to observe the morphological changes of the materials during hydrolysis and pyrolysis in detail,and the effects of metal types and doping levels on the electrochemical performance of the materials were studied.Among them,CoNC exhibits OER catalytic performance far superior to IrO₂ and ORR catalytic performance.These materials play a guiding role in the synthesis of bimetallic doped porous carbon materials,and will be used as a comparative sample in the following work to explain the source of excellent electrochemical properties of bimetallic doped porous carbon materials.（2）Using ZIF-8 as a template,ferric nitrate and nickel nitrate as metal sources,a simple chemical deposition and one-step pyrolysis method was used to synthesize Ni₃Fe-doped porous carbon material（Ni₃Fe@NC）,and the bimetallic Ni₃Fe nanoparticles were uniform Dispersed in a nitrogen-doped carbon matrix and connected by carbon nanotubes.The material exhibits bifunctional catalytic activity for ORR and OER.The half-wave potential of ORR was observed to be 0.86 V.For OER,a potential of 1.56 V was achieved at a current density of 10 mA cm^-2.This bifunctional oxygen electrocatalytic activity is superior to most comparable materials reported to date.The excellent bifunctional electrocatalytic active center was proved to be the synergy of Ni₃Fe nanoparticles rather than materials,which is the first report.It is worth noting that using a dual-function catalyst,the zinc-air battery shows a high peak power density of 108.9 mW cm^-2 and excellent stability,and exhibits a small charge-discharge voltage gap,which is better than commercial Pt/C+IrO₂ catalyst.（3）Cobalt iron nitrate and ferric nitrate are uniformly coated on the ZIF-8 template to coat cobalt-iron bimetallic hydroxide（CoFe LDH）and pyrolyzed under an argon atmosphere to obtain CoFe-doped porous carbon material（CoFe@NC）.CoFe nanoparticles are evenly dispersed in a nitrogen-doped carbon matrix.At the same time,the carbon substrates are also connected to each other through carbon nanotubes to form a 3D network.Using the prepared catalyst,1.61 V and 0.89 V were observed for OER(current density of 10 mA cm^-2)and ORR（half wave potential）.Excellent activity comes from the synergy of multiple active sites and the unique three-dimensional structure.The primary zinc-air battery was assembled and showed a small charge-discharge voltage gap(0.70 V at 5 mA cm^-2)and a high peak power density of 136.0mW cm^-2,which outperformed commercial Pt/C catalysts.In addition,the all-solid-state Zn-air battery is assembled to have excellent voltage efficiency,stability,and flexibility.