| Today,the rapid development of social economy has accelerated the consumption of energy,and traditional fossil fuels such as coal,oil and natural gas are increasingly depleted,resulting in a series of severe environmental problems(e.g.,the greenhouse effect and global warming).At present,the common clean energy sources mainly include water energy,wind energy and solar energy,all of which come from nature and meet the requirements of green sustainable development.However,due to the intermittency of these energy sources,their low energy density,and their limited use due to geographical and climatic conditions,we urgently need to develop clean,sustainable and efficient energy sources.Hydrogen(H2)has been found to be the most attractive alternative to conventional fossil fuels as a high energy density and clean,pollution-free energy carrier,with a wide range of sources and only water as the combustion product.The electrochemical water splitting can decompose water into hydrogen and oxygen on a large scale,which is green,safe and efficient,and is regarded as the most ideal renewable energy production method.Electrochemical water splitting mainly includes anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER).The OER is a four-electron transfer process reaction with slow kinetics and requires higher overpotentials to overcome kinetic barriers,and the HER is a reaction of two electron transfer process.Due to the lack of hydrogen ions in the alkaline medium,a large amount of water needs to be dissociated to provide protons in the early stage,which may require a higher voltage than the theoretical voltage(1.23 V)to drive the electrochemical water splitting reaction.Based on the above reasons,exploring a highly active and stable OER and HER catalyst for cost-effective water splitting is of great significance for improving the ecological environment.Currently,noble metal-based materials(Ru O2,Ir O2,and Pt/C,etc.)are considered as the most effective catalysts for OER and HER.However,the disadvantages of noble metal-based materials,such as high cost,poor durability,and low earth reserves,limit their wide application.Therefore,it is an important task to explore the catalysts which are low in price,excellent in catalytic performance,abundant in earth content and can be widely used in practical applications.Based on the above analysis,a series of transition metal-based electrocatalysts were designed and synthesized in this dissertation mainly through simple and feasible experimental methods.At the same time,the OER and HER electrocatalytic activities,long-term durability and commercial application prospects of the series of catalysts were investigated in detail by means of various testing and characterization methods,and their catalytic mechanisms were analyzed and elaborated.The specific research contents are as follows:1.Fe2P-WO2.92/NF catalyst:In the preparation process of this catalyst,we first synthesized a series of target catalyst precursors on nickel foam through a controllable hydrothermal reaction,and soaked in a K3[Fe(CN)6]solution at room temperature,and then the target catalyst was prepared by low-temperature phosphating treatment in a tube furnace,and the oxygen evolution reaction activity of the catalyst was explored at the same time.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)test analysis showed that the catalyst exhibited a porous morphology.X-ray powder diffraction(XRD)tests showed that the composites consisted of Fe2P and WO2.92.In addition,the specific surface area,metal valence state and actual metal content of the catalyst were further studied by testing the catalyst for Brunauer-Emmett-Teller(BET),X-ray photoelectron spectroscopy(XPS)and inductively coupled plasma atomic emission spectrometry(ICP).Electrochemical tests show that when the current density reached 10 m A cm-2,the catalyst has a low overpotential of 215 m V and a low Tafel slope of 46.3 m V dec-1,which is far superior to other control catalysts.When tested with a two-electrode electrolyzer composed of Pt/C for overall water splitting,the cell voltages of 1.51 and 1.90 V were needed to achieve current densities of 10 and 400 m A cm-2 with good long-term stability.The electrocatalytic mechanism shows that the abundant oxygen vacancies expose more active sites and provide good electrical conductivity.In addition,the unique porous structure can facilitate electrolyte diffusion and gas release,thus synergistically improving the OER performance of the catalyst.2.1T-Co4S3-WS2/CC catalyst:In the preparation process of the catalyst,we used a continuous two-step synthesis method.First,the target catalyst precursor was grown in situ on the carbon cloth by the hydrothermal method,and then the target catalyst 1T-Co4S3-WS2/CC ultrathin nanosheet arrays was obtained by culcanization in a tube furnace.Through XRD,Raman spectroscopy,BET,SEM,TEM,XPS,ICP and other related characterization tests,the crystal form,chemical composition,morphological characteristics,chemical valence state and actual content of metals of the catalyst were determined.Electrochemical tests show that the catalyst exhibits excellent electrocatalytic performance and stability in both OER(?10=278 m V)and HER(?10=75 m V),outperforming most currently reported bifunctional electrocatalysts.In addition,the two-electrode electrolyzer composed of this bifunctional electrocatalyst only requires a cell voltage of 1.59 V at a current density of 10m A cm-2.This excellent electrocatalytic activity is mainly attributed to the synergistic effect between Co4S3 and 1T-WS2,in addition,the ultrathin nanosheet array structure provides a large electrochemical active surface area,which improves the charge transport rate and facilitates the diffusion of electrolytes.3.Nb-Co Se2/CC catalyst:In the preparation process of this catalyst,we first grew the precursor on the carbon cloth by a continuous two-step hydrothermal method,and then obtained the target catalyst(Nb-Co Se2/CC)through argon calcination in a tube furnace.The catalysts were characterized by SEM,XRD,TEM,BET,ICP,XPS and contact angle tests,and the morphology,material structure,specific surface area,actual metal content,chemical valence and hydrophilicity of the catalyst were further obtained.etc.Electrochemical studies show that the catalyst exhibits excellent OER performance,requiring only an overpotential of 220 m V at a current density of 10 m A cm-2,which is comparable to the performance of Ru O2,and when the two-electrode electrolyzer composed of Pt/C is tested for overall water splitting,a cell voltage of 1.93 V was required to achieve a current density of 500 m A cm-2with excellent durability. |
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