Preparation Of Low Iridium Load Catalysts And FeP-CoP Nano-Heterostructures Catalysts And Their Water Electrolytic Properties

At present,the energy resources in the world still mainly come from the burning of fossil fuels such as coal,oil and gas.However,these energy sources are not renewable and bring many pollution problems,leading to global energy crisis and serious environmental pollution.To solve these problems,it is urgent to develop clean and renewable energy sources that can replace fossil fuels.Nowadays,solar energy,wind energy,tidal energy,and biomass energy that nature can provide have been successfully developed.However,due to regional constraints or seasonal factors,the supply of these energy sources is intermittent.Hydrogen energy is considered to a promising clean energy in the future due to its high energy density and abundant source.Electrocatalytic water splitting plays an important role in the field of hydrogen production due to its advantages of producing high-purity hydrogen that matches with industrial requirements,simple process flow and operation.The design and synthesis of highly efficient electrocatalysts is crucial to promote the rapid development of hydrogen production from water splitting.Recently,researchers have developed a variety of catalysts for application of water electrolysis.The noble metal based catalysts possess satisfactory electrocatalytic performance,but the high cost greatly limits the application in industrial production.Therefore,we aim to design and synthesize low-cost and efficient electrocatalysts for water electrolysis in this paper from two aspects:（1）Reducing the cost of noble metal based electrocatalysts through the design and synthesis of an Ir-N/P/C/WO₂-900 material with low iridium loading.First,Ir was encapsulated in vacant polyoxometalates（POMs）by chemical synthesis.The special structure of POMs benefits the uniform dispersion of the active Ir sites.Then,to increase the conductivity of the sample,a layer of highly conductive carbon layer was coated on the surface by annealing the sample coated with dopamine.The synthesized samples exhibit excellent oxygen evolution（OER）and hydrogen evolution（HER）performance under acidic（0.5 M H₂SO₄）and alkaline（1 M KOH）conditions.The overpotentials at the current density of 10 m A cm^-2 for OER and HER are 300,76 m V（0.5 M H₂SO₄）and 250,22 m V（1 M KOH）,respectively.In addition,the electrocatalytic performance obtained by using the Ir-N/P/C/WO₂-900 as both cathode and anode for water splitting is also considerable.Under acidic and alkaline conditions,the cell voltages required to achieve the current density of 10 m A cm^-2 are 1.63 V and1.58 V.The characterization and performance analysis of the materials indicate that the catalytic performance may come from:（1）the unique anionic structure of POMs can evenly disperse the Ir and avoid the aggregation of the active sites,which effectively increases the utilization of precious Ir;（2）Coated amorphous carbon layer can improve the conductivity of the material and enhance the electron transfer.（2）Reducing the cost of electrocatalysts by using non-noble transition metals instead of precious metals.Interface engineering is one of the effective methods to improve the electrocatalytic activity of materials.Firstly,based on Density Functional Theory（DFT）,it is predicted that the OER reaction barrier of Fe site at the interface of Fe P-Cop heterogeneous structure is lower than that of Fe site in Fe P nanoparticles,Co site in Co P nanoparticles and Co site in heterogeneous structure.Therefore,based on the results of DFT calculation,we design and synthesiz the Fe P-Co P heterogeneous structure by metal-organic framework（MOFs）limited phosphating method.The performance test results are consistent with expectations.Fe P-Co P has the lowest OER overpotential（230 m V）at 10 m A·cm^-2 current density,compared with Fe P（470 m V）and Co P（340 m V）,and is better than most transition metal-based catalysts.The Tafel analysis of Fe P-Co P heterostructures shows the lowest slope of 90.3 m V dec^-1,compared with Fe P nanoparticles（NPs）(137 m V dec^–1)and Co P NPs(114 m V dec^–1).At the same time,the impedance test results also show that the Fe P-Co P heterostructure has rapid electron transfer kinetics.In addition,Fe P-Co P shows excellent long-term stability within 24 hours,and after long term stability test,the morphology and structure characterization results proved that the sample is very good to maintain the original appearance and composition.The excellent electrocatalytic activity and long-term stability of Fe P-Co P are due to the synergistic effect of Fe P and Co P.