Synthesis Of Transition-metal Compounds-based Electrocatalysts And Their Electrocatalytic Properties

In the context of sustainable energy development,hydrogen energy,a clean and renewable energy carrier,is considered as a potential alternative to future energy supply,which has been received increasing attention.As a method of generating hydrogen from water,water electrolysis is environmentally friendly and sustainable.However,high overpotential of oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?in the two half reactions of water electrolysis severely restricts the industrial application of the method.Noble-metal-based electrocatalysts are widely concerned due to their excellent electrocatalytic properties,but their high price and their scarcity in nature hinder the application greatly in water electrolysis.Therefore,it is extremely important to develop a low-cost electrocatalyst with excellent OER and HER performance.Metal-organic frameworks?MOFs?are widely used to construct electrocatalysts with excellent properties due to their unique physicochemical properties,composition and structural diversity and special morphology.By changing the type of metal ions and post-treatment process in the precursors of MOFs,we can control the morphology and structure of the products,and the types of metal elements,which provides a good platform for the study of HER and OER.In this thesis,several MOF-based transition metal compounds were designed and prepared,and their electrocatalytic performance towards HER and OER were investigated.Co-Co PBA was used as precursor and template to synthesize Fe-doped CoP hollow nanocube by alkaline etching,ion exchange and low temperature phosphorization treatment,and their electrocatalytic properties for oxygen evolution were investigated;Co-Fe PBA was used as precursor.CoP/CoPS₃ hollow nanoboxes were obtained by vulcanization,coating and low-temperature phosphorization process,and used for electrochemical oxygen evolution reaction;Co-Co PBA was used as template to synthesize CoP/MoS₂ hollow nanoboxes by hydrothermal and low-temperature phosphorization,and their electrocatalytic properties for hydrogen evolution were surveyed.The specific works are concluded as follows:?1?Fe-doped CoP hollow nanocubes were obtained by KOH etching,ion exchange process and low-temperature phosphorization process by using Co-Co PBA as template.Scanning electron microscopy?SEM?,transmission elect ron microscopy?TEM?was used to analyze the microstructure and structure of the material;X-ray energy dispersive spectroscopy?EDS?was used to analyze the content of the material;linear sweep voltammetry?LSV?and cycle voltammetry?CV?and electrochemical impedance spectroscopy?EIS?were used to study the electrocatalytic hydrogen evolution performance of Fe-CoP.By optimizing the doping amount of Fe,Fe-CoP-2 exhibited the best electrocatalytic OER activity and stability.It requires only 326 mV current density to reach 10 mA cm^-2,and the Tafel slope is 48.3 mV dec^-1.In addition,there is no significant attenuation of current density after 1000 cycles.?2?The CoP/CoPS₃ hollow nanoboxes were obtained by using Co-Fe PBA as template and precursor,followed by vulcanization,coating and low-temperature phosphorization process.The morphological,surface valence and crystal structure of the materials were analyzed by SEM,TEM,XRD and X-ray photoelectron spectroscopy?XPS?.At the same time,it is investigated by electrochemical techniques such as LSV,CV and EIS.In 1 M KOH,compared to Co₃S₄,Co₃S₄@CoO_x and S-doped CoP?CoP|S?,CoP/CoPS₃ exhibits excellent OER.The overpotential at 10 mA cm^-2is only 335 mV,and the Tafel is 46 mV dec^-1.Also,the electrocatalytic activity has no significant attenuation after 1000 cycles.?3?The CoP/MoS₂ hollow nanoboxes were synthesized by hydrothermal and subsequent phosphorization with a Co-Co PBA precursor.The morphological,surface valence and crystal structure of the materials were analyzed by SEM,TEM,XRD and XPS.At the same time,the electrocatalytic hydrogen evolution performance of CoP/MoS₂ was investigated by electrochemical techniques such as LSV,CV and EIS.The results show that the CoP/MoS₂ hollow nanoboxes exhibits excellent hydrogen evolution ability in alkaline environment.CoP/MoS ₂ has an overpotential of only 169 mV at 10 mA cm^-2and a Tafel slope of 96.8 mV dec^-1.The current density is almost no attenuation after 1000 cycles,which indicat es excellent HER performance.