Preparation Of La-Ni And Ti-Fe-Ni Alloys By Electroreduction Of Solid Mixture In Molten Salts

Hydrogen energy economy is one of the strategic directions for the development of various countries,and its development needs the preparation and storage of hydrogen.At present,hydrogen production from electrolytic water is an important research topic.Noble metal catalysts are often needed to reduce overpotential in the process of electrolytic water.Therefore,it is of great significance to develop non-noble metal catalysts which are stable and active in alkaline environment.In the traditional process,the preparation of metals and alloys are complex,energy-consuming and time-consuming.FFC-Cambridge process is a method of direct electroreduction of solid oxide to metal or alloy in molten salt,which reduces the energy consumption and simplifies the preparation process.Some transition metals,such as lanthanum,titanium and iron,which form alloys with nickel and become excellent hydrogen storage materials.The specific structure and properties also make some hydrogen storage materials have excellent hydrogen evolution properties.The purpose of this paper is to study two different hydrogen storage materials.One is to prepare pure La Ni₅ alloy from two different raw materials in a short time at high potential,and to study the hydrogen evolution reaction of one products.The other is ternary Ti-Fe-Ni alloy.Its preparation and electrochemical hydrogen evolution properties are to be studied.The main research contents and conclusions are as follows:1.Molybdenum cavity electrode(MCE)was used to determine the electrolytic potential of La(OH)₃+Ni O mixture in CaCl₂ salt at 850?by cyclic voltammetry.The alloy materials were electrolyzed at different electrolytic potential for 2 hours to determine the potential of forming the alloy at-1.58V.The reaction mechanism of alloy formation was studied in different time electrolysis(within 2 hours)at low potential-1.6V,which showed Ni O was deoxidized into elemental Ni,and the transition state of La underpotential deposited on Ni to form alloys.The hydrogen evolution properties of the products of-1.6V electrolysis at different time were investigated.It was found that the products with 40min had the highest hydrogen evolution activity.The alloy was prepared by increasing the electrolytic potential (-2.0V and-2.1V).It was found that the alloy with-2.1V electrolysis for 40 minutes had the best hydrogen evolution performance,which was<200 m V different from the overpotential of 20%Pt/C at 10 m A/cm².Changing the atomic ratio of La and Ni was to explore the hydrogen evolution activity.It was found that the plate La₂Ni₇ alloy was formed when La:Ni=1:3,and the other proportions were La Ni₅ alloy.The hydrogen evolution performance of La Ni₅ alloy was better and improved with the increase of Ni content.2.The electrolytic potential of the reduction was determined by cyclic voltammetry of La OCl+Ni O mixture in CaCl₂ salt at 850?with a molybdenum cavity electrode. The potential of forming alloy was-1.75V,then electrolysis for 40 min at different reduction peaks(-0.8V and-1.8V).Compared with the electrolytic products of sintered Lanthanum-Nickel composite oxides,La OCl was a kind of rare earth material which was stable and fast to reduce to alloys.After 40 minutes and 30 minutes electrolysis of high potential-1.9V and-2.0V,the actual energy consumption of-2.0V electrolysis for 30 minutes was 3.9374 k Wh/kg-La Ni₅,and the current efficiency was 33.94%.According to the above conclusions,the mechanism of forming alloys was analyzed,Ni O was deoxidized into elemental Ni,and the La OCl underpotential deposited on Ni to form alloys.The products were prepared by choosing different cell voltage electrolysis for 40 minutes.La OCl and Ni were obtained by electrolysis at low cell voltage,and alloys were formed at high cell voltage.The current efficiency of electrolysis at 3.2V cell voltage for 40 minutes was only 35.77%.The electrolytic products for 40 min at 3.2V cell voltage at different temperatures were studied.It was found that the alloy prepared by electrolysis at 850?was more complete than that at 800?and 820?.It also indicated that the complete alloy still needed certain temperature in a short time.3.Two-electrode system was used to electrolyze the mixtures of Ti O₂+Fe₂O₃+Ni O at different cell voltages of 1.1V,1.8V,2.5V and 3.0V for 1h in CaCl₂ at 850?.The low cell voltages were mainly Ni-Fe alloys and impurity Ca Ti O₃.At high cell voltages,Ni-Ti alloys were dominant and contained a little Ni-Fe alloys.The reaction mechanism was obtained by electrolysis at 2.9V,3.0V and 3.1V high cell voltage for different time(15min-3h),Ni O and Fe₂O₃ deoxidized to form Ni-Fe alloy,and then Ti formed to form more stable Ni-Ti alloy.It was found that the materials electrolyzed at 2.9V,3.0V,3.1V high cell voltages for 2 hours had the best hydrogen evolution performance.Ti Fe Ni₃ materials electrolyzed at 2.9V for 2 hours were the best materials.The overpotential was 240m V different from 20% Pt/C under current density of 10 m A/cm².Improving the electrolytic conditions,it was found that the hydrogen evolution properties of products with Ni atom content of 3,3.5 and 4 were balanced and better for different proportions of materials.The optimum hydrogen evolution activity was Ti Fe Ni₃ at 820?for 2 h electrolysis,the overpotential of the material with current density of 10 m A/cm² was close to 200 mV.