Preparation Of Metal-Organic Framework Derived Electrocatalysts And Their Performance Of Aluminum-Air Battery

The development and utilization of new energy is a hot trend in today’s era,among which aluminum-air batteries are considered to have a good application prospect because of its ultra-high specific energy（8100 Wh/kg）,ultra-light weight,pollution-free and recyclable charateristics.However,the low power density and slow oxygen reduction reaction of aluminum-air batteries make them unable to be widely promoted.In this work,based on the study of oxygen reduction catalysts,a series of derived catalysts were prepared by combining MOFs with conductive carbon materials to improve the performance of aluminum-air battery.The contents are as follows.Ketjen black was compounded with MOFs and layered bimetallic hydroxide was formed by etching,and Pt nanoparticles（d≈2.38 nm）were loaded on the surface to obtain Pt@Co Ni-LDH/KB catalyst.It was found that the prepared MOF has extremely small particle size（≈60 nm）,high specific surface area,hollow and high porosity,and has excellent performance in electrochemical tests.The electrochemical active area and mass activity are 4.4 and 4.3 times higher than those of 20 wt%Pt/C catalyst,respectively.As a low Pt catalyst（4.76 wt%）,it also shows better open circuit voltage（1.60 V:1.54 V）,power density（167.7 m W/cm²:150.4 m W/cm²）and discharge capacity（947 m Ah/g:884 m Ah/g）than 20 wt%Pt/C catalyst in the application of aluminum-air batteries.In order to further strengthen the catalytic activity of the catalyst,carbon nanotubes were used instead of ketjen black to obtain a special composite structure of carbon nanotubes in series MOFs,and Pt-free catalysts（Ag@Co Ni Fe/MWNTs）were prepared by bimetallic etching to form layered trimetallic hydroxides and supported Ag nanoparticles（d≈75 nm）.Layered trimetal hydroxides provide more active sites for Ag nanoparticles,and the three-dimensional structure of carbon nanotubes in series enhances the transport pathway of electrons,showing lower kinetic slope（94m V/dec:107 m V/dec）and higher current stability（91.2%:83.5%）than 20 wt%Pt/C catalysts in electrochemical tests,and also has the discharge capacity of 1065 m Ah/g when acting on aluminum-air batteries.The Ag Co₃O₄@NC/MWNTs catalyst was prepared by two-step annealing,which enhanced the stability of the catalyst on the basis of maintaining the catalytic activity.Combining the original structural advantages of MOFs with the catalytic advantages of Co₃O₄,the catalytic activity and stability of oxygen reduction of the catalyst were significantly improved.The half-wave potential is positive 12 m V than the 20 wt%Pt/C catalyst,and shows a very high current retention rate（92.9%）.In the test of aluminum-air battery,the open-circuit voltage（1.61 V）,discharge capacity（1161 m Ah/g）and power density（185.2 m W/cm²）were higher than those of 20 wt%Pt/C catalyst,and showed excellent discharge stability.