The Sythesis Of Cobalt Oxide On Carbon And The Impact Of Alkali-doping On Their Electrocatalytic Activity

In order to solve the problem that the high cost and poor stability of precious metal electrocatalysts,in this work,the main purpose is to prepare Co3O4/C catalysts through two different methods and enhance the ORR and OER performance of Co3O4/C through doping of alkali metal.Firstly,Co3O4/C catalysts with different crystallinity were parepared through oil bath and hydrothermal reaction with different time.And we find that the crystallinity and particle size increase with the hydrothermal time.The catalyst prepared through 3h hydrothermal reaction have the best morphology,structure,ORR performance and OER performance.Then the carbon-supported Li-Co3O4 solid solution catalysts were prepared through the same method above,and the carbon-supported Li-Co3O4 nanocrystals with average particle size of approximately 4.5nm.Among all synthesized Li-Co3O4/C sample,the ORR performance increase with the increase of Li amount and the catalyst prepared at the Li/Co atomic ratio of 5%displays the most positive half-wave potential,which is 0.865V(vs RHE)and 21 mV higher than the undoped Co3O4/C sample.Moreover,the doping of Li can enhance the ORR performance of Co3O4/C,which derives from the increased content of covalent O-C=O-Co? bond formed at the interfaces between Li-Co3O4 and carbon support.Through the above process,we find that interfacial interaction at the interfaces between oxide and carbon support play a vital role in ORR performance.Therefore,the Co3O4/GCB samples with different interfacial interaction were prepared through oil bath and 2h annealing with different temperature.We find the existence of the preferred orientation along(111)plane in the spherical spinel Co3O4 nanoparticles and the preferred orientation is greatest at 300?.The formation of the preferred orientation along(111)plane may be attributed to the chemical interaction C-O-Co ormed between the Co3O4 nd the graphitized carbon black(GCB)as support.Electrocatalysis experiments in an alkaline environment reveals that the electrocatalytic activity for ORR over the preferred oxide increase as a function of the degree of the crystal lattice orientation,implying a closely intrinsic correlation of the predominant(111)plane and the catalytic activity.The catalyst with greatest preferred orientation displays the most positive half-wave potential,which is 0.83V(vs RHE).And the preferred orientation can reduce the electronic band gap(Eg)of Co3O4,which contributes to improve the ORR activity.Next,the carbon-supported Na-Co3O4 ans K-Co3O4 solid solution catalysts were prepared through oil bath and hydrothermal reaction different with the first method,and find that the doping of Na and K can enhance the ORR performance of Co3O4/C.Among all these synthesized Na(K)-Co3O4/C sample,the sample prepared at the Na(K)/Co atomic ratio of 10%displays the most positive half-wave potential,which is 0.860V(vs RHE)(0.862V vs RHE)and more than 10mV higher than the undoped sample.The doping of Na(K)increases the oxygen vacancy in Co3O4 to enhance ORR performance.Through the OER performance test,we find that all the doping of Li,Na and K can enhance the OER performance of Co3O4/C,and the gap with RuO2 is further reduced.The reason is that the doping of alkali metal ions can change the distribution of cations in Co3O4 to increase the amount of Co3+,which is the active site during OER.