The Design And Synthesis Of Metal Oxide-based Two Dimensional Nanosheets For Energy Storage And Conversion

The depletion of fossil fuels resources as well as the desire for a clean environment means that exploiting sustainable energy is becoming more and more important than ever.High performance energy storage and conversion systems such as supercapacitor and oxygen evolution reaction(OER)play a key role in these applications.The supercapacitor can not only store intermittent power(wind/solar power),but also supply power to myriad applications from portable consumer electronic devices to electrical vehicles.OER is a vital step in sustainable energy systems such as water splitting,metal-air batteries and fuel cells.Therefore,developing high performance materials for supercapacitor and OER has an important scientific significance.This work rational designed the transition metal oxides-based two dimensional nanosheets for electrochemical process through the restraining factor in above applications.The excellent performance of supercapacitor and OER are achieved by defects engineering,elements doping and fabricating hydroxysulfide,which improves the electrical conductivity and stability.The main contents are summarized as four parts:(1)The preparation of oxygen-vacancy-rich Co3O4 nanosheets with excellent supercapacitor performances.The superiorities for Co3O4 are high theoretical specific capacitance and multiple valences.However,the major bottlenecks of Co3O4 are intrinsic poor electrical conductivity and low utilization efficiency of electroactive materials.Based on it,we fabricate the oxygen-vacancy-rich Co3O4 nanosheets with thickness of 20 nm to improve the utilization.The oxygen vacancies create new defect states located in the band gap of Co3O4 and thus leading to enhancement of the conductivity.Remarkably,the oxygen-vacancies-rich Co3O4 nanosheets achieve ultrahigh specific capacitance of 2195 F g-1 at a current density of 1 A g-1 which is 3.6 times as high as that of pristine Co3O4 nanosheets.Furthermore,OVR-Co3O4 NSs show enhanced 3000 cycling stability.(2)The preparation of oxygen-vacancy-rich NiCo2O4 nanosheets for supercapacitor.The mixed transition-metal oxides are promising electrode materials for supercapacitor due to the complex chemical compositions and their synergetic effects.The oxygen-vacancy-rich NiCo2O4 nanosheets are prepared by hydrothermal,calcination and liquid reduction.In a typical three-electrode systems,the oxygen-vacancies-rich NiCo2O4 nanosheets achieve specific capacitance of 1980 F g-1 at a current density of 1 A g-1,which is 2.3 times as high as that of pristine NiCo2O4 nanosheets.Furthermore,the specific capacitance can retain 91.5%when the current density increased to 20 A g-1 exhibiting excellent rate capability performance.(3)The preparation of oxygen-vacancy-rich ZnCo2O4 nanosheets for supercapacitor and OER.We report the design of a facile liquid reduction treatment to achieve delicate control of electrolyte penetration and fresh accessible active sites through uniformly creating oxygen vacancies and leaching invalid Zn2+ from the surface of ZnCo2O4 without affecting structural integrity.The oxygen vacancies confined in the surface of electrocatalysts provide greater electronic conductivity,a beneficial ionic and electron diffusion environment.The catalyst exhibits a small overpotential of 324 mV at 10 mA cm-2 for 30 hours,associated with a low Tafel slope of 56.9 mV dec-1,which are superior to the pristine ZnCo2O4 nanosheets.(4)The fabricating of NiCo layered doable hydroxide@NiCo-hydroxysulfide for electrocatalytic OER.NiCo layered double hydroxides in OER is mainly limited by two tough obstacles:the relatively low electrical conductivity and poor stability.Herein,the NiCo layered double hydroxide@NiCo-hydroxysulfide(NiCo-LDH@HOS)nanosheet arrays are prepared by a rapid room-temperature sulfurization of the surface of NiCo-LDH grown on Ni foam.The resulting material,possessing an improved electrical conductivity of5.15×10-4S m-1.This novel electrocatalysts can afford a stable current density of 10.0 mA cm-2 with an overpotential of 293 mV in 0.1 M KOH solution for at least 62 h.The achieved excellent oxygen evolution activity and strong durability,with superior performance in comparison to the pristine hydroxide,originate from high conductive and anti-corrosive hydroxysulfide armor on the surface,which lead to the large active surface area,enhanced mass/charge transport capability,and strong structural stability...