Study On The Modulation Of Prussian Blue Analogues Nanostructure For Oxygen Evolution Reaction

Nowadays,the energy-related problem has threatened our existence and development.Traditional fossil fuels are drying up,and the burning of fossil fuels could cause a serious of environmental problems.In order to resolve above questions,researchers are paying attention to exploiting hydrogen as clean and renewable energy.High efficient water splitting is one of the most potential technologies for producing hydrogen.There are two important reactions,which are hydrogen evolution reaction（HER）in the cathode and oxygen evolution reaction（OER）in the anode.OER is a 4electrons reaction with more sluggish dynamics than HER,which needs higher overpotential.Therefore,it is an urgent requirement for developing low-cost and efficient electrocatalysts for water splitting.Prussian blue（PB）,which was found in 1704,is the earliest discovered metal-organic framework.It is a kind of classical porous structure by self-assembling with metal sites worked as centres and cyanide groups worked as ligands.Due to the specific structure and convenient synthesis process,Prussian blue and its analogues are widely applied in various fields such as sensor,catalysis,buttery and absorption.However,Prussian blue analogues（PBA）are considered as inactive electrocatalysts because of poor electrical conductivity and small pores size.In this regard,researchers often used PBA as precursors to prepare metal alloys or other metallic compounds by high-temperature treatment for electrochemical catalysis.But the highly dispersed active sites in PBA are almost lost during the annealing process.Hence,the key challenge of developing efficient OER electrocatalysts of PBA is how to retain their primary structures.In this thesis,we synthesized a sort of trimetallic PBA by co-precipitation and then modulate its structure to enhance the performance for OER activity.The material was prepared as following:firstly,we used Na₂S as a delicate digger to widen pores size,regulate the metal ratio of metal elements and modulate valence of metal by using the ion replacement between[Fe（CN）₆]^x-/[Co（CN）₆]^y-and S^2-.Secondly,300°C annealing treatment in Ar atomosphere was conducted to remove a portion of cyanide groups,leading to the structure collapse while maintaining the major structure of PBA.In addition,the existence of the Fe-O bonds in electrocatalysts structure may increase the conductivity.After the treatment with Na₂S etching and then annealing at 300°C,the PBA-based electrocatalysts showed a significant OER activity with a small overpotential of 261 mV at 10 mA cm^-2,and an ideal Tafel slope of 38 mV dec^-1,exceeding not only most of OER electrocatalysts obtained by PBA but also the ideal IrO₂.This method may provide a new reference to synthesize PBA-based and even design MOF-based electrocatalysts in electrochemical water splitting oxygen evolution reaction.