Preparation Of Micro/Nanostructured Bimetallic Oxides And Enhanced Electrocatalytic Performance

Water splitting is a chemical reaction that is necessary to be able to store intermittent energy quantities(such as solar and wind energy)in the form of hydrogen fuel.And water splitting includes anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER).Among them,HER involves two-electron transfer and OER involves four-electron transfer.Therefore,OER requires a higher overpotential to proceed,which is generally considered to be the bottleneck of water splitting.In recent years,transition metal-based materials have attracted wide attention due to their great research value in the fields of photocatalysis,electrocatalysis,gas sensors,and lithium ion batteries.At present,the electrocatalytic performance of general transition metal-based oxides is not outstanding,and their stability needs to be further improved.Therefore,not only do we need to design materials with higher specific surface areas,but their structures also need to be maintained for a long time in the electrocatalytic process without collapse.In this dissertation,from the aspects of morphology and structure,it is necessary to design materials with higher specific surface area,and their structures should be maintained for a long time in the electrocatalytic process without collapse.In this paper,yolk-shell structured ZnFe2O4 microspheres,Ni-doped C03O4 nanoplates and monodispersed hierarchical NiFe2O4 and CoFe2O4 microspheres were prepared.The main research findings are as follows:(1)In this part,yolk-shell structured ZnFe2O4 microspheres assembled by nanoparticles were prepared by a facile solvothermal method with the assistance of sodium dodecyl sulfonate(SDS).Through a series of time-dependent experiments,the formation mechanism of the yolk-shell structured ZnFe2O4 microspheres is attributed to the Ostwald ripening.It exhibits an overpotential of 280 mV at a current density of 10 mA cm-2,the Tafel slope is of 70 mV dec-1 and the structure of yolk-shell ZnFe2O4 has only changed a little after 12 h test.The excellent electrocatalytic oxygen evolution performance of the yolk-shell ZnFe2O4 may attributed to one of the most important factors:namely the mesopores/macropores structure with high surface area and unique yolk-shell morphology assembled by nanoparticles,which can provide more active sites and enhance the contact of reactant and active sites to help the transfer of the electrons,thus improving the catalytic activity(2)In this part,Ni-doped Co3O4(Ni:2 wt%,4 wt%,6 wt%and 8 wt%)porous nanoplates are synthesized by hydrothermal method and annealing treatment Electrochemical measurements indicate that Co3O4 with low amount of Ni doping possesses remarkably enhanced activity for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)in alkaline media.And especially,4 wt%Ni-doped Co3O4 possesses the most efficient activity with an overpotential of 240 mV at the current density of 10 mA cm-2 for OER and 120 mV for HER in 1 M KOH than the pure Co3O4 and other Ni-doped Co3O4 samples(3)In this part,a series of monodispersed hierarchical CoFe2O4,Co0.75Ni0.25Fe2O4,Co0.5Ni0.5Fe2O4,Co0.25Ni0.75Fe2O4 and NiFe2O4 microspheres assembled by nanoparticles and nano sheets were also prepared by a facile solvothermal method.What is interesting is that these materials have almost the same morphology and size under the same conditions.With the increased content of Ni,the OER performance has been enhanced.The great performance of the hierarchical NiFe2O4 microspheres is attributed to the obtained unique microsphere structure with the assistance of sodium dodecyl sulfonate,the large specific surface area and the better adsorption strength of oxygenated intermediates.