Synthesis Of Iron-based Phosphides And Their Electrochemical Hydrogen Evolution Properties

We have been suffering from our excessive reliance on fossil fuels.Environmental pollution,economic crisis and regional security issues are severe.As the demand of energy increasing sharply,the fossil fuels are increasingly depleted.Searching for a clean and renewable alternative of fossil fuels is imminent.Hydrogen energy is a kind of clean energy,which is abundant and non-polluting.But the traditional preparation methods are complicated and costly.Water splitting is a simple and efficient method for obtaining high-quality hydrogenic energy.However,the presence of cathode overpotential increases energy consumption and cost.Therefore,developing a kind of electrocatalyst with high catalytic activity,low cost and low cathode overpotential is the key to hydrogen producting.The transition metal phosphide is a high-quality cathode material for electrolyzing water,and the iron phosphide get widespread attention because of its high raw material reserves of raw materials,low cost,non-toxicity,good chemical stability and catalytic activity in both alkaline and acidic solutions.Based on the researches of electrochemical hydrogen evolution and nanomaterials technology,this article was focused on researching some simple and convenient methods to obtain high-performance iron phosphide catalysts with different morphological features for electrochemical hydrogen evolution.The main research contents of this article are as follows:?1?Synthesized a kind of layered iron glycolate hollow microsphere precursors with nanosheet subunits,FeCl₃·6H₂O,ethylene glycol and ethylenediamine as raw materials,under 150°C solvothermal environment.Regulated the amount of ethylenediamine,catalysts with different morphologies were obtained.When the amount of ethylenediamine was 3 m L,a hollow iron phosphide sheet microsphere?FeP-3?was obtained.When the amount of ethylenediamine was increased to 8 mL,it was changed into a microsphere with thick pieces.The precursor was converted into FeP hollow microspheres by the low-temperature phosphating treatment of sodium hypophosphite.SEM analysis showed that the morphology was not damaged,and the sheets on the surface were remained intactly.The polarization curves of electrochemical tests indicated that the overpotential of iron phosphate catalyst?FeP-3?which had hollow structure and a dense lamellar structure was 144 mV at a current density of 10 mA cm^-2.Its Tafel slope was 58 mV dec^-1 and FeP-3 showed good cycle stability and high catalytic activity for hydrogen evolution reaction.?2?Synthesized urchin-like iron oxyhydroxide precursors with multiple burrs,FeSO₄·7H₂O,glycerol,and deionized water as raw materials,under 150°C solvothermal environment.In order to get microspheres with multiple burrs and high specific surface area,we regulated the ratio of glycerol to deionized water.When the ratio of water and glycerol was 37:3,standard sea urchin microspheres were obtained.Iron oxyhydroxide was phosphatized by PH₃ which produced from the thermal decomposition of sodium hypophosphite,and then FeP sea urchin microspheres were obtained.The main electrochemistry test results were polarization curves and Tafel plots.At a current density of 10 mA cm^-2,the overpotential of sea urchin microspheres was 143 mV,and the Tafel slope was 60mV dec^-1.The hydrogen evolution performance was excellent.However,when the addition amount of glycerol was further increased,the morphology changed into irregular smooth particles.?3?Fe?NO₃?₃·9H₂O,glycerol and isopropanol were used as raw materials,iron glycerate precursors were synthesized under 90°C solvothermal environment.Through changing the addition amount of deionized water,different core-shell structures were obtained.When the amount of water was 1.3 m L,the precursor was a completely hollow lamella nanosphere,as the amount of water was further increased,the nanosphere has broken.Using the same phosphating method as the above experiments,the precursors were converted into FeP nanospheres with stable morphology.Electrochemical hydrogen evolution tests were performed.The electrochemical polarization curve showed when the current density reached 10 mA cm^-2,the overpotential of the electrode was about 134 mV,and the corresponding Tafel slope was 64 mV decade^-1.The electric double layer capacitance and the electrochemically active specific surface area obtained from CV curves also showed the good hydrogen evolution catalytic performance of the hollow lamella nanospheres.