Synthesis Of Ni Fe-based Amorphous Organic-inorganic Hybrid Materials And Their Electrocatalysis For Overall Water Splitting

The harmful impact of human activities on the global environment and the increasingly serious energy crisis leads to the urgent need to develop green and efficient renewable energy.Hydrogen has attracted wide attention because of its advantages of environmental friendliness and sustainable development,and can be obtained by electrolysis of water in an environmentally friendly way.It is a key step for the development of hydrogen production industry to develop full solution hydroelectric catalysts with high catalytic performance,high stability and low price.Amorphous catalysts have the characteristics of short-range order and long-range disorder,and have more active sites than pure crystal materials,which is conducive to improving the catalytic performance of electrolysis water.Ni-Fe based materials are widely concerned in the field of electrolysis of water for hydrogen production due to their low price,abundant reserves and high intrinsic catalytic activity.However,organic compounds with abundant functional groups can effectively regulate the composition,morphology and micro-environment of inorganic metal materials.In this paper,three kinds of amorphous nickel-ferric organic compound hybrid materials were designed,and on the basis of the optimization of synthesis conditions and physical properties characterization,their full hydrolytic catalytic activities were investigated,which provided new possibilities for the development of new electrolysis water catalysts.The main research contents are as follows:（1）Using 50%（W%）phytic acid（PA）solution,ferric chloride hexahydrate（Fe Cl₃·6H₂O）and nickel chloride hexahydrate（Ni Cl₂·6H₂O）as raw materials,NiFe-PA was successfully prepared on nickel foam（NF）by two-step room temperature impregnation method.The NiFe-PA/NF catalyst was characterized by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Fourier infrared spectroscopy（FT-IR）.The results show that the NiFe-PA/NF catalyst is amorphous in the shape of scales.The catalytic performance of NiFe-PA/NF in water electrolysis was studied by linear sweep voltammetry（LSV）,cyclic voltammetry（CV）and voltage-time curve（P-T）.The experimental results show that the overpotential of NiFe-PA/NF oxygen evolution reaction is only 207 m V at the current density of 20 m A cm^-2,and the stability is as long as 175 hours at the current density of 100 m A cm^-2.The overpotential of hydrogen evolution reaction at 10 m A cm^-2 is 117 m V,and the stability can reach 75 h at 100 m A cm^-2.The total hydrolyzing device composed of NiFe-PA/NF can reach a current density of 10 m A cm^-2 with only a 1.61 V battery voltage.（2）Using nickel nitrate hexahydrate Ni（NO₃）₂·6H₂O,Fe Cl₃·6H₂O and terephthalic acid as raw materials,amorphous Ni-Fe bimetal-organic framework（a NiFe-MOF/NF）nanosheets were synthesized by hydrothermal method on pretreated nickel foam.The high conductivity polyaniline（PANI）particles were grown on the surface of a NiFe-MOF/NF by chemical oxidation method,and the organic-inorganic hybrid material catalyst PANI@a NiFe-MOF/NF was obtained.The morphology,composition and chemical structure of PANI@a NiFe-MOF/NF were investigated by X-ray energy spectroscopy（EDS）,X-ray diffraction（XRD）and transmission electron microscopy（TEM）.The results show that PANI@a NiFe-MOF/NF is a nanosheet cluster structure,and PANI is coated on the outer surface of a NiFe-MOF/NF.Electrocatalytic test results showed that the overpotential of oxygen evolution and hydrogen evolution was 270 m V(at 50 m A cm^-2 current density)and122 m V(at 10 m A cm^-2 current density),respectively.The stability of oxygen evolution for120 hours and hydrogen evolution for 110 hours can be maintained at the current density of50 m A cm^-2,respectively.With PANI@a NiFe-MOF/NF catalyst,the current density of 10 m A cm^-2 can be achieved with only 1.59 V battery voltage,and the stability can be maintained for more than 100 hours.（3）Using Ni Cl₂·6H₂O,Fe Cl₃·6H₂O and organic molecule thiourea（TU）as raw materials,the amorphous NiFe-TU hybrid material（NiFe-TU）was successfully grown on the pretreated nickel foam by a simple one-step drying method.The physical characterization results show that Tu is adsorbed on the surface of NiFe-TU modified electrode through coordination,and NiFe-TU is amorphous.NiFe-TU/NF was further used as an electrocatalyst for hydrogen evolution and oxygen evolution reactions.The results show that the overpotential of oxygen evolution reaction is only 243 m V when the current density is 50 m A cm^-2,and the potential remains stable within 120 hours.It was obtained that the overpotential of hydrogen evolution reaction was 125 m V when the current density was 10 m A cm^-2,and the potential remained stable within 125 hours.The total hydrolytic device composed of Nife-TU/NF can reach the current density of 10 m A cm^-2 with only 1.48 V battery voltage,and can maintain no significant potential change for 55 hours at this current density.