The Simple And Efficient Synthesis Methods For CoNi-based Composites And Their Electrocatalysis For Overall Water Splitting

The 2021 State Council government report clearly states that"we will take solid steps to achieve emission peak and carbon neutrality,formulate an action plan for achieving carbon emission peak by 2030,and optimize the industrial structure and energy structure."Accelerate the adjustment of energy structure,clarify the direction of energy development with green and low-carbon as the main goal,and develop new and efficient renewable energy is an important way to achieve the above"double carbon"goal.Hydrogen energy is a promising candidate for"carbon neutrality",and the production of hydrogen by electrocatalytic total hydrolysis without other incidental pollutant emissions is one of the most promising hydrogen production methods.However,the current electrolytic water technology still suffers from expensive catalysts,cumbersome synthesis steps,the low catalytic efficiency,catalytic activity and stability need to be further improved.Based on this,three kinds of simple and efficient cobalt-nickel-based composites were designed,and on the basics of physical characterization and electrochemical tests,the composition of the materials and their electrocatalytic activity for oxygen evolution reaction（OER）/hydrogen reaction reaction（HER）/overall water splitting were investigated.The main contents are as follows.（1）Amorphous phytate-nickel-carbon composites（Co Ni PO-C/NF）were synthesized by impregnation combined with flame combustion method using Nickel foam（NF）as the conductive substrate,Ni²⁺and Co²⁺as the metal sources,phytate as the carbon and phosphorus source,and ethanol as the catalyst synthesis heat source.The morphology and composition of the catalysts were characterized by Raman spectra（Raman）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）and Fourier infrared spectroscopy（FT-IR）.The catalytic performance of Fe Co Ni O_x-C/NF electrolytic water was investigated by electrochemical characterization using linear sweep voltammetry（LSV）,cyclic voltammetry（CV）and voltage-time curves（P-T）.The results showed that the catalyst is spherical,and has good HER/OER/overall water splitting performance and excellent stability.The OER overpotential at a current density of 10 m A cm^-2 is only 170 m V,and the HER overpotential at a current density of 10 m A cm^-2 is only 79 m V.The overall water splitting device composed of Co Ni PO-C/NF electrode can reach the current voltage of 10 m A cm^-2with only 1.47 V battery voltage,and can maintain excellent stability for 170 hours at current density of 100 m A cm^-2.（2）NF was placed in ethanol solution containing Fe³⁺,Co²⁺,and Ni²⁺ions,and the 3D tremella-like Fe Co Ni O_x-C/NF composite was rapidly synthesized by the"flame method"by igniting ethanol.In this experiment,ethanol provided the carbon source,promoted the dispersion of metal ions on NF,and provided the heat energy for the catalyst growth through combustion reaction.A series of physical characterization and electrochemical tests were carried out,the test results showed that the overpotential of the 3D tremella-shaped catalyst was only 176 m V for OER at a current density of 20 m A cm^-2 and 69 m V for HER at a current density of 10 m A cm^-2,which were lower than those of the corresponding noble metal catalysts.The application of Fe Co Ni O_x-C as a bifunctional catalyst for the electrocatalytic properties of overall water splitting showed that only 1.40 V was required to achieve a cell voltage of 10 m A cm^-2 current density.At the same time,Fe Co Ni O_x-C/NF exhibited high stability and corrosion resistance,and the OER/HER/overall water splitting catalytic stability could be maintained for at least 170 hours at current density of 100 m A cm^-2.This work provides a new idea for the design and facile synthesis of efficient and stable catalysts for electrolytic water.（3）Ars-Fe Co Ni composites were prepared in situ on NF substrates by a simple evaporative drying method using iron nitrate,cobalt nitrate and the dye molecule alizarin red（3,4-dihydroxy-9,10-dioxo-2-anthracenesulfonic acid,Ars）for bifunctional electrocatalysis of HER and OER.The morphological characterization and compositional analysis of the catalyst were performed by SEM,TEM,XRD and XPS,and the results showed that Ars-Fe Co Ni had a flower-like particle shape;the electrocatalytic performance of the catalyst was investigated by LSV,CV and P-T electrochemical techniques.The results showed that the overpotential of OER of Ars-Fe Co Ni/NF at 50 m A cm^-2 current density was only 260 m V,and the overpotential of HER at 10 m A cm^-2 current density was 123 m V.The results of the test on the overall water splitting device composed of Ars-Fe Co Ni/NF electrodes showed that a cell voltage of only 1.51 V was required to achieve a current density of 10 m A cm^-2,and could be maintained at a current density of 100 m A cm^-2 for nearly 170 hours of stability.