| Water electrolysis is a promising way to supply and store clean and sustainable sources of energy,the development of which is driven by the dwindling energy supplies and environmental pollution.Unfortunately,its efficiency and commercial implementation are severely restricted due to sluggish oxygen evolution reaction(OER)kinetics at the anode,which is of the thermodynamic uphill reaction that involves complex four-electron transfer process,and the formation of O-O bond needs to overcome high energy barrier,thus requires a high overpotential to drive the reaction.Traditional precious metals and their oxides catalysts have been known to exhibit the best OER catalytic performance.,such as RuO2 and IrO2.Unfortunately,their commercial applications are grealy hindered by their scarcity and high cost as well as poor stability.Rencently,much efforts have been devoted to exploring effercient and inexpensive electrocatalysts.Spinel cobalt oxide Co3O4 is developed as a replacement for noble metal-based catalysts,due to its low-cost,abundant resources and high chemical stability.Meanwhile,the rise of two dimensional materials brings new opportunities for catalysis.The highly unsaturated atoms and large specific surface area provide abundant active sites.Furthermore,the binding between adjacent layer atoms become weak due to the atom level thickness.And dramatic distortion of the crystal structure reduce the reaction barrier.On the other hand,ultrathin nanosheets with large surface are ideal support,and the highly exposed surface atoms are more favorable for the electronic interaction between loading and nanosheets.The electronic structure of nanosheets could be regulated by surface modification.Furthermore,the combination between electronic structure and catalytic performance could be studied in atomic level.Focusing on developing OER catalyst with high efficiency and stability,this thesis is summarized as follows:Chapter 1:This chapter introduces the research progress of ultrathin materials including the classification and synthesis methods.We also illustrate the unique advantages of ultrathin materials and regulatory strategies in the field of electrocatalysis.Chapter 2:The ultrathin porous Co3O4 nanosheets with a thickness of three unit-cell dimension were synthesized successfully by solvothermal treatment and subsequently air heat treatment.The ultrathin porous Co3O4 nanosheets show much better OER performance than bulk samples.The current density of Co3O4 nanosheets is 9.97 mA cm-2 at an overpotential of 0.5 V,which is almost 13 times than bulk sample(0.73 mA cm-2),and also obtain good stability.Chapter 3:To further enhance the OER performance of Co3O4 to meet the industry ’demand,ultrathin porous Co3O4 nanosheets are decorated with Au nanoparticles.Different preparation methods for Co3O4/Au nanocomposites are introduced including impregnation method and physically mixing.The OER performance of ultrathin porous Co3O4 nanosheets with different Au loading show significantly enhancement,in which Co3O4/Au(15 mg/25 mL)sample gives the best OER activity.With the loading of Au nanoparticles,the current density of ultrathin porous Co3O4 nanosheets is enhanced from 9.97 to 14.76 mA cm-2 at an overpotential of 0.5 V.XPS,Raman and XANES demonstrate the strong electron interaction between Au and ultrathin Co3O4 nanosheets.Optimized electronic structure is favorable to the OER reaction.The enhanced OER performance and electronic interaction between Co3O4 and Au is firstly reported in Co3O4 ultrathin porous nanosheets by physically mixing with Au nanoparticles.The possible reason is that ultrathin nanosheets possess more low-coordinated surface atoms compared with bulk materialsChapter 4:The whole works are summarized.And our own opinions based on the previous research are also presented. |
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