Designed Synthesis Of Functional Nanomaterials And Application In Energy Storage And Conversion

As the demand of energy is increasing every day in today's society,which cause the energy depletion and environmental pollution.These things become the two major challenges for human people in the 21 st century.As a result,developing efficient,clean and renewable new energy become a major topic in the study of economic sustainable development strategy.In the related fields of new energy,lithium ion battery and electrocatalytic water splitting are two very attractive approaches to energy storage and conversion.Lithium ion battery possesses many advantages,such as high working voltage,high energy density,long cycle life and environment friendly etc.It is considered to be the main energy source for electric cars and hybrid vehicles.Electrocatalytic water splitting has many merits,such as high purity hydrogen production,simple operation,no pollution and recycle utilization.Electrolyzing water to produce hydrogen is one of the most application prospect of development,which can be regarded as the best way to produce hydrogen.Hence,it is critical to design the electrode material and catalyst with unique structure to enhance the property of the energy storage and conversion.In this thesis,we synthesize the unique structure of the octahedral micro/nano hierarchical LiFePO4 cathode material and peapod-like Co(SxSe1-x)2@C catalyst.By the way,we characterize the composition,morphology and structure of the materials.And test the electrochemical performance in their own aspect.Novel Monodispersed single-crystalline LiFePO4 with octahedral micro/nano hierarchical structure has been firstly synthesized using a controllable solvothermal approach and calcinations.In this method,monoclinic phase FeFe2(PO4)2(OH)2 with micro-sized octahedral structure is fabricated via solvothermal approach as precursor.Then through a high-temperature reduction,single-crystalline LiFePO4 with micro/nano hierarchical structure can be obtained.This special micro/nano hierarchical structure is a feasible programme to surmount the inherent problems of LiFePO4.Secondary micro-sized octahedral structure will assure high tap density and cycling stability.Primary LiFePO4 nanoparticles will improve the high-rate performance by shortening the Li+ diffusion pathways and increasing the effective reaction areas.The intersices between primary LiFe PO4 nanoparticles is beneficial for electrolyte penetration,accelerating the insertion/extraction reaction.Therefore octahedral micro/nano hierarchical Li FePO4 cages show excellent discharge capacity at high C-rate and superior tap density as a cathode material,which could promote the development of lithium-ion batteries.The development of efficient electrocatalysts with low cost and earth abundance for overall water-splitting is very important in energy conversion.Although many electrocatalysts based on transition metal dichalcogenides have been developed,rational design and controllable synthesis of fine nanostructures with subtle morphologies and sequential chemical compositions related to these materials remains a challenge.Herein,we report a series of peapod-like composites with component-controllable Co(SxSe1-x)2 nanoparticles encapsulated in carbon fibers,which were obtained by using Co(CO3)0.5(OH)·0.11H2 O nanowires as precursor followed by coating carbon fiber and an adjustable sulfuration/selenylation process.Due to its increased exposure of active sites and improved charge and mass transport capability derived from the unique structure and morphology,the Co(SxSe1-x)2 samples display favorable catalytic activities.We found that Co(S0.71Se0.29)2 exhibits the best HER performance and Co(S0.22Se0.78)2 shows the highest activity for OER.When using Co(S0.71Se0.29)2 as a cathode and Co(S0.22Se0.78)2 as an anode,it demonstrates a durable activity for overall water splitting to deliver 10 mA cm-2 at a cell voltage of 1.63 V,thus offering an attractive cost-effective earth abundant material system toward water splitting.