In Situ Synthesis Of Amorphous Nickel-Iron/Nitrogen-Containing Polymer Composite For Electrocatalysis Of Overall Water Splitting

The development of multi-functional electrocatalysts with high catalytic activity,high stability and low cost is essential for energy conversion and storage.Generally,the higher the crystallinity of a catalyst,the better its catalytic activity.In recent years,amorphous catalysts have received more and more attention because of their flexible composition,mild preparation conditions and favorable charge transfer.However,amorphous alloy catalysts have some problems,such as small specific surface area and poor stability,which makes them unsuitable for industrial applications.In addition,the introduction of nitrogen-containing polymers with strong coordination is expected to improve the stability of amorphous catalysts because they are rich in lone-pair electrons and have stronger binding force with metals.At the same time,nitrogen-containing polymers with reducibility may provide defect sites with high catalytic activity for metal atoms.Based on this,three kinds of amorphous nickel-iron/nitrogen-containing polymers were designed and their applications as electrochemical catalysts in oxygen evolution reaction?OER?,hydrogen evolution reaction?HER?,and nitrogen reduction reaction?NRR?.The main work is as follows:?1?NiFeO_xH_y-pMel catalysts were grown in situ on three-dimensional nickel foam?NF?by combining electropolymerization,impregnation and calcination methods.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,Raman spectroscopy and other characterization methods have proved that amorphous plate-like NiFeO_xH_y-pMel/NF electrodes have been successfully prepared.Linear scanning voltammetry?LSV?,voltage-time curve?P-T?,and cyclic voltammetry?CV?and other electrochemical characterization methods were used to investigate the catalyst's electrolytic water catalytic performance,electrolytic water stability,and electrochemical surface area.The experimental results show that the oxygen holes induced by melamine in NiFeO_xH_y-pMel/NF electrodes have high OER and HER catalytic activity,and they only require low overpotentials of 185 mV and 187 mV at a current density of 20 mA cm^-2.Using NiFeO_xH_y-pMel as bifunctional catalyst can be used for effective and stable overall splitting,in which the battery voltage is only 1.518 V at 10 mA cm^-2.?2?The NiFeO_x-Mel catalysts with flower cluster structure was successfully prepared by simple evaporation drying method using ferric nitrate hexahydrate?Fe?NO₃?₃·9H₂O?,nickel nitrate hexahydrate?Ni?NO₃?₂·6H₂O?and melamine?Mel?as raw materials.The morphology and structure of the materials were characterized by scanning electron microscope?SEM?,X-ray diffraction?XRD?,X-ray energy dispersive spectrometer?EDX?,Raman spectroscopy and X-ray photoelectron spectroscopy?XPS?.The effects of evaporation drying time,drying temperature and raw material ratio on the catalytic activity of the catalysts were investigated by electrochemical techniques such as LSV,P-T,CV and EIS.The results showed that the NiFeO_x-Mel catalyst showed excellent OER and HER activity in alkaline medium.For the OER,the overpotential and Tafel slope of NiFeO_x-Mel catalyst at 30 mA cm^-22 current density were 243mV and 134 mV·dec^-1,respectively.For the HER,the overpotential and Tafel slope required for the catalyst to achieve a current density of 30 mA cm^-22 are 207mV and181mV·dec^-1,respectively.In addition,as HER and OER catalysts,NiFeO_x-Mel catalyst can maintain stability for at least 200h,which has potential industrial application value.?3?The NiFeCr-PEI catalysts with three functions of OER,HER and NRR was successfully prepared by simple evaporation drying method using ferric nitrate hexahydrate?Fe?NO₃?₃·9H₂O?,chromium chloride hexahydrate?CrCl₃·6H₂O?,nickel nitrate hexahydrate?Ni?NO₃?₂·6H₂O?and polyethyleneimine?PEI?as raw materials.Electrochemical characterization methods were used to test the catalytic performance of NiFeCr-PEI catalyst for hydrogen evolution and oxygen evolution,and the electrocatalytic nitrogen fixation performance of the catalyst was also studied.The results show that the NiFeCr-PEI catalyst shows excellent OER and HER activities in alkaline media.For the HER,at a current density of 30 mA cm^-2,the required overpotential and Tafel slope of the NiFeCr-PEI/NF electrodes were 206 mV and 118 mV·dec^-1,respectively.For the OER,the overpotential and Tafel slope at 50 mA cm^-2current density are 240 mV and 34 mV·dec^-1,respectively.In addition,NiFeCr-PEI/CP electrodes can achieve high efficiency of NRR electrocatalysis.This catalyst attains a high Faradic efficiency of 3.32%and a high NH₃ yield of 1.26×10^-10mol·s^-1·cm^-2at-0.70 V versus reversible hydrogen electrode.