| The design and development of efficient,cheap,and stable bifunctional electrocatalysts is one of the important keys to solve current energy and environmental problems.In this thesis,we have designed and synthesised novel High-entropy Oxides(HEO),whose multi-component nature provides great design scope for the modulation of composition,electronic structure,and catalytic performance.Although high-entropy materials have good catalytic activity and excellent stability,research on the application of high-entropy materials in the direction of bifunctional water electrolysis is still emerging,and the related catalytic mechanisms still need to be further strengthened.Therefore,in this thesis,HEO materials were prepared by hydrothermal method and the effects of changes in structure,composition,and morphology on their electrochemical properties,etc.were systematically investigated and the following results were obtained:(1)(Cr0.2Fe0.2Co0.2Ni0.2Zn0.2)3O4 HEO high entropy oxide was synthesized by hydrothermal method.They were characterised by XRD,SEM and TEM.The results show that the synthesised HEO materials have an AB2O4-type spinel structure with a uniform distribution of each metal element;the morphology of the high-entropy materials is that of nanoparticles with a particle size of about 50 nm.electrochemical tests show that the OER performance of the HEO catalysts is enhanced by 54 mV and the HER performance by 21 mV compared to the corresponding monometallic oxides.this is mainly attributed to the synergistic effect between the HEO This is mainly due to the synergistic effect of the metal elements in HEO,which not only facilitates the charge transfer but also contributes to the reactivity of the surface sites.(2)Although(Cr0.2Fe0.2Co0.2Ni0.2Zn0.2)3O4 materials have been successfully prepared and can be used as bifunctional catalysts for HER and OER,their structure and morphology have not been effectively controlled and their electrochemical properties still have much room for improvement.In addition,elemental changes can also alter the valence state of the metal,resulting in a corresponding change in the catalyst performance.To address these issues,in this thesis,high entropy oxides such as HEO-F-X(X=7.5,15,30 and 45)were successfully prepared by introducing nonequivalent fluorine anions(F-)as dopants based on the above-mentioned high entropy oxides.Relevant experimental results showed that the introduction of F-not only effectively improved the microscopic morphology of the material,but also formed a series of hierarchical structures of 3D nanoflowers assembled by nanosheets,which increased the specific surface area of the catalyst from 0.7 m2 g-1 to 14.81 m2 g-1,which provided more active sites for HER and OER,thus facilitating the overall hydrolysis performance.The electrochemical test results show a significant improvement in the HER and OER performance of the catalysts,mainly due to the unique synergistic effect between the multiple metal ions.The non-equilibrium F-dopants results in a charge redistributions of the active metal sites,which are not fixed at a specific oxidation state but adaptable at(2±δ)+ or(3±δ)+.The HEO-F-30 sample exhibit the overpotentials of 67 mV and 245 mV respectively for the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)under alkaline environment,respectively,while the prepared electrodes are able to work stably for 48 hours.Even at a current density of 50 mA cm2,the sample maintained good HER(overpotential of 157 mV)and OER(overpotential of 286 mV)performance and the electrode is still able to operate stably for 20 hours.In addition,the bi-functional electrode made by HEO-F-30 catalyst can realized the overall water decomposition at 1.65 V at 10 mA cm-2. |
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