Preparation And Electrochemical Properties Of Metal Oxides Derived From Coordination Polymer

In recent years,the extensive use of fossil energy vehicles has caused a lot of energy consumption and serious environmental pollution.Duing to energy saving and environmental protection,electric cars have become an ideal substitute for traditional cars and become a necessary tool for people to travel in the future.Battery is an important part of electric car,playing the important role of the electric car.Due to the infinite O2 supply and good charging and discharging stability,rechargeable metal-air battery has the advantages of high specific capacity and high energy density.However,due to the relatively low working voltage and power density of zinc-air battery,its wide application is limited.On the contrary,Zn-Co3O4 battery has higher working voltage and power density,which can make up for the deficiency of zinc-air battery.In order to improve the voltage and power density of zinc-air battery,we integrated Zn-Co3O4 and zinc-air battery to assemble a hybrid battery at the battery level.The performance of cathode material plays a crucial role in zinc-air battery or hybrid battery.Cathode materials must have good charging and discharging capacity and excellent ORR and OER activity,and Co3O4 fully meets these requirements.Surprisingly,we found that Co3O4 nanomaterial,as an artificial enzyme,was found to have a peroxidase-like activity,which could be used to detect various analytes and construct colorimetry.In this work,with three different cobalt coordination polymers as precursors,three different Co3O4 nanomaterials has been synthesized successfully and applied to zinc-air battery,hybrid battery and color reaction,etc.In the first part:employing a Co based coordination polymer as a precursor,a composite material built from Co3O4 and Co-N active centres with nitrogen doped mesoporous carbon as a matrix has been synthesized successfully.This composite material possesses outstanding activity and stability in the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)processes.It possesses a small half-wave potential(ORR1/2=0.786 V)and low overpotential(OER10=1.575 V)for the ORR and OER,respectively.With this composite material as an air cathode electrocatalyst,a rechargeable Zn-air battery was assembled successfully.During the discharge process,the maximum power density of this Zn-air battery is 122 mW·cm-2 at 0.76 V.The specific capacity of this battery is 505 mA·h·g-1 at 25 mA·cm-2.The voltage gap between the charge and discharge processes is only 0.744 V at 10 mA·cm-2 and 1.308 V at 100 mA·cm-2.This rechargeable battery also shows promising stability after long-term charge-discharge experiments.Furthermore,the composite material also exhibits outstanding microwave adsorption properties.Its maximum reflection loss(RL)arrives at-13.9 dB with a thickness of only 1.0 mm.Thus,we find that coordination polymers are an ideal precursor for Zn-air battery cathode electrocatalysts and microwave absorbers.In the second part,to enhance the voltage and power density of Zn-air battery,a hybrid battery is assembled through the integration of Zn-Co3O4 and Zn-air batteries at cell level.In this hybrid battery,cathode material is composed by oxygen vacancy rich Co3O4-x and N,S-co-doped carbon derive from Metal-Organic Framework;anode is Zn plate.The specific capacity of cathode material achieves 144 mAh·g-1 at 1 A·g-1.Its oxygen reduction reaction completes through typical four-electron process with half wave potential 0.78 V.In oxygen evolution reaction,η10 potential of this cathode material is merely 365 mV.For this hybrid battery,it shows two discharge platforms at 1.75 and 1.11 V,when discharge at 1 mA·cm-2.Specific capacity and energy density of this hybrid battery achieves 711 mAh·g-1 and 810 Wh·kg-1.It also inherits superior power density of Zn-Co3O4 battery,with peak value 43.6 mW·cm-2.This is much higher than Zn-air battery composed by the same cathode material.The hybrid battery also exhibits excellent stability with capacity and charge-discharge voltage well kept after 600 cycle tests for 600 h.This work develops a hybrid battery by the integration of two distinct batteries together,which combines high voltage,specific capacity and superior power,energy densities in one power source.In the third part,Co based coordination polymer(CoCP)was prepared by hydrothermal method.With this coordination polymer as precursor,a composite material,named as Co3O4@CN was synthesized after calcination.In this study,the obtained Co3O4@CN nanomaterials have peroxide-like activity,and can effectively catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine(TMB)in the presence of H2O2,and the obvious blue product(OxTMB)can be seen in 3 min.Glutathione(GSH)reacts with H2O2 to remove the color of the product of the TMB-H2O2-Co3O4@CN system,and the concentration of GSH can be quantitatively determined based on the change in absorbance at 652 nm.Based on the peroxide-like activity and GSH properties of Co3O4@CN nanomaterials,colorimetric sensors were established for detecting H2O2 and GSH,which have a wide linear range and a low detection limit.Therefore,this paper proposes a simple,sensitive and selective colorimetric sensor for detecting GSH and H2O2.