Design,synthesis And Electrocatalytic Oxygen Evolution Study Of Nonprecious Metal Oxides

Efficient and durable oxygen evolution electrocatalysts are necessary for a wide range of clean energy technologies,with RuO2 and IrO2 as benchmark catalysts.However,RuO2 and IrO2 catalysts suffer from their high costs and instability,so nonprecious metal oxygen evolution electrocatalysts have been developed,such as Ni-,Fe-or Co-based oxides.It’s important to explore various methods to enhance catalytic performance with Ni-,Fe-and Co-based structures as model.The key to efficient and durable oxygen evolution electrocatalysts is abundant catalytic active sites,superior conductivity and stable catalytic active structure.Based on this design key,this thesis mainly focuses on:1.Efficient and durable amorphous NiFeOx/C oxygen evolution electrocatalysts synthesized by a sonochemical method.Amorphous catalysts are a series of less studied catalysts.However,amorphous materials feature in homegeneously dispersed compositions and abundant defects,which are beneficial as oxygen evolution electrocatalysts.That is to say,compared with crystalline catalysts,amorphous catalysts usually possess more catalytic active sites.It’s reported that amorphous catalysts generally possess superior catalytic performance when compared with their crystalline counterparts.However,amorphous catalysts usually suffer low conductivity and unstable structures,which are unfavourable to electocatalysis.Moreover,preparation methods for amorphous electrocatalysts are rather limited.Herein,we find that the feature of somochemistry enables it a convinient method for preparing amorphous NiFeOx/C hybrid oxygen evolution electrocatalysts with tunable compositions.The products not only exhibit prominent OER performance(including activity and stability),but also circumvent demerits of amorphous catalyst——low conductivity and instability.Synchrotron-based X-ray characterizations reveal that superior activities arise from abundant oxygen vacancies,cooperatively unsaturated metal sites,efficient charge transfer induced by homegeneously dispersed Ni/Fe,inner Ni(0)and simultaneously formed carbon scaffold.2.Unique Co4+-containing layered sodium cobaltatc oxygen evolution elcctrocatalysts.Co4+ is reported to be the real active site for Co-based oxygen evolution elcctrocatalysts.Soime studies revealed that increasing Co4+ contents in electrocatalysts can enhance their calalytic activities.However,pure Co4+ is unstable,and the absorption energy of O-containing intermediates is not optium when bound to a pure Co4+ site.So exploring mixed-valent Co-based electrocatalysts containing more and stable Co4+ should be a better way.Moreover,electronic properties can influence catalytic performance.Herein,a facile oxidation of layered sodium cobaltates,maintaing layered structure and stable Co4+,can synergistically enhance oxygen evolution activities through dual engineering of electronic properties including oxidation state,oxygen vacancies,conductivity,Co-O covalency.Synchrotron-based X-ray characterizations reveal that enhanced Co-O covalency and conductivity are the keys to superior oxygen evolution activities.3.HCl oxidative etching method can tune the size of metal nanocrystals with unchanged shapes and further tune their size-dependent plasmonic and catalytic properties.The effects of HC1 oxidative etching include removing twinned seeds and oxidizing metal atoms back to ions so as to decrease the reduction rate of metal ions,thus tuning the size of metal nanocrystals kinetically.This study provides a versatile,simple and effective method for size control of metal nanocrystals.