Designing,synthesis And Performance Of Highly Active Zinc-air Battery Air Electrode Catalyst

Oxygen evolution and reduction reactions（ORR and OER）are key procedures in the air electrode of zinc-air batteries（ZAB）.Thus,developing high-performance,stable and low-cost OER and ORR catalysts is key to enhancing ZABs’performances and expanding their applications scenarios.In this thesis,a series OER and ORR catalysts are designed and fabricated by using nitrotriacetic acid,cobalt chrolide,carbon powder,phthalocyanine iron and etc.as the raw materials.The electrochemical performance and physicochemical property are also studied.The structure-function relationships,potential active sites and corresponding catalytic reaction mechanism are also studied based on the electrochemical measurements and characterization results.The achievement in this thesis includes:（1）Nanofibers composed by cobalt nanoparticles coated with N-doped carbon are prepared by using nitrotriacetic acid and cobalt chrolide as the precursors.The obtained catalyst（C-NTACo-500）exhibits high performance towards both ORR and OER,with a half-wave potential of 0.84 V（vs.RHE）for ORR and an OER potential of 1.55 V at 10 m A cm^-2.Specially,it can deliver a ZAB a power density of 203 m W cm^-2and a specific capacity of 822.4 m Ah_Zn^-1,as well as high cycling stability.Based on the characterization results,the higher surface areas,higher pyridinic N contents are proposed to be responsible for the catalyst’s high performance.（2）Co₃O₄nanofibers are prepared by using nitrotriacetic acid cobalt chrolide as the precursors.The obtained catalyst is highly active towards OER,with OER potentials of 1.53and 1.59 V（vs.RHE）at 10 and 100 m A cm^-2,respectively.When used as the air electrode catalyst combining with Pt/C,it can deliver the ZAB a high charging performance,with a current density of 148.4 m A cm^-2at 2.2 V.as well as high cyclic charging-discharging stability.Combined with the physicochemical characterization results,the higher ECSA and higher Co（III）content in NTACO-450 are considered as the important reasons for its outstanding OER performance.（3）Ag-decorated cobalt hydroxide catalysts were in-situ synthesized during the OER process with cobalt-nitrotriacetic complexes and Ag NO₃as the raw material.The obtained catalyst（NTACo-50Ag）has excellent OER performance,with OER potentials of 1.46 V and1.54 V under the current densities of 10 and 100 m A cm^-2in 1 M KOH solution,respectively.When used as the air electrode catalyst combining with Pt/C,it can make the ZAB exhibit excellent charging and discharging performances,as well as outstanding cyclic charging-discharging stability.After 1000 charging-discharging cycles,no obvious performance decay was observed.At the same time,it is also found that the introduction of Ag facilitated the formation of Co³⁺in the catalyst during the OER procedures.The higher Co³⁺content induced by Ag should be responsible for the catalysts’excellent OER performance.（4）A Fe-N-C single atom catalyst is prepared through a low-temperature heat-treatment by using carbon powder and phthalocyanine iron as the precursors.The Fe-N4O1 structures are confirmed based on the characterization results.The obtained catalyst exhibit rather high ORR performance,with a half-wave potential of 0.93 V（vs.RHE）.When used as the air electrode catalyst,it can deliver a ZAB a high power density of 225.2 m W cm^-2.After combining with NTACo-50Ag,the mixed catalyst can make the ZAB highly stable.After1000 discharging-charging cycles,no obvious performance decay is observed.Based on the characterization results,the as-formed Fe-N4O1 structure is confirmed to be the active sites for ORR.Innovation:1.A series high-performance catalyst is designed and synthesize towards OER and ORR.2.The in-situ formation and composition of Ag and Co（OH）_xis achieved by a spontaneous oxide-reduction reaction between Ag₂O and Co（OH）₂,with a cobalt-based complex and Ag NO₃as the raw materials.The catalyst exhibits high OER performance.Also,the key role of Ag for the enhanced OER performance is confirmed.3.A highly active ORR catalyst is obtained through a low-temperature heat-treatment.The Fe-N4O1 center and its key role in enhancing catalysts’ORR performance are also confirmed.