Preparation And Performance Study Of Carbon Nanotube-based Oxygen Electrode Catalyst

Zinc air battery（ZAB）has attracted great attention due to its high energy density,safety and environmental friendliness.ZAB involves two important reactions:oxygen reduction（ORR）during discharging and oxygen evolution（OER）during charging.However,the slow kinetics and high overpotential of ORR and OER make ZAB with high charge/discharge voltage,low energy conversion efficiency and poor stability.Therefore,it is an urgent need to develop low–cost,highly active and stable ORR/OER catalysts to promote the commercial application of ZAB.In this paper,carbon nanotubes（CNT）based ORR/OER catalysts were constructed using good electrical conductivity and high chemical stability of CNT as the starting point and combining with metal organic framework（MOF）–derived preparation strategy.The catalytic performance of the obtained catalysts and their application prospects of ZABs were investigated.The main research contents are as follows:（1）Two–dimensional MOF–derived nanosheet precursor containing Fe/Co bimetallic centers was synthesized by hydrolysis of particulate MOFs.Based on this precursor,three–dimensional Fe/Co–N co–doped CNT loaded with Fe Co nanoparticles（Fe Co/N–CNT）was prepared.The resulting Fe Co/N–CNT material has a three–dimensional CNT network structure that ensures fast mass transfer and electron transport and Fe Co nanoparticles and Fe/Co–N doping sites that enhance the catalytic kinetic process.Thus,the Fe Co/N–CNT material showed excellent catalytic performance as an oxygen electrode catalyst（OER and ORR potential difference of0.71 V）.The Fe Co/N–CNT catalyst was used to assemble liquid–state ZAB showing a power density and specific capacity of 237.5 m W cm^–2 and 747.4 m Ah g^–1,respectively.More importantly,the battery charge/discharge voltage difference kept almost constant after the 1300^th constant current charge/discharge cycle.This work innovatively proposes a two–dimensional MOF derivation strategy with both bimetallic centers,which opens up a new way for the design and preparation of high–performance catalytic materials.（2）The proposed CNT bridging strategy bridges iron phthalocyanine（Fe Pc）molecules containing Fe–N₄ on the wall of N–doped CNTs to form Fe–N₅ sites with ultra–high ORR activity,while Ni Co nanoparticles supported on carbon particles are linked by CNT.In situ Raman spectroscopy reveals that Ni Co nanoparticles will transform into the corresponding high–performance hydroxides during the OER process.As a result,the resulting catalysts exhibited excellent OER and ORR catalytic performance with an oxygen potential difference of 0.686 V.The resulting catalysts were assembled into liquid–state ZAB showing a power density of 219.5m W cm^–2,a charge/discharge voltage difference of 0.72 V,and excellent cyclic charge/discharge stability performance.In addition,a power density of 113.8 m W cm^–2 was obtained by assembling the resulting catalysts into solid–state ZAB.This work novelly proposes a CNT bridging strategy to realize the simultaneous improvement of ORR and OER performance,and provides scientific guidance for the research and development of oxygen electrode catalysts in ZAB.