Synthesis Of Co₂FeAl Alloy Catalysts And Modulation Of Their Electrocatalytic Hydrogen Evolution Reaction Performance

In recent years,with the continuous intensification of global climate change issues and concerns about traditional petrochemical energy consumption,hydrogen energy is considered one of the important directions for future energy development.Among them,the electrolysis of water for hydrogen evolution technology,as one of the most mature hydrogen production methods,has received much attention.The process of electrolyzing water to produce hydrogen requires the participation of catalysts,and precious metal-based catalysts have been widely used in this field due to their high activity and good selectivity.However,due to its expensive price and limited resources,its application is limited to some extent.In this context,transition metal-based catalysts have become a highly regarded alternative.Compared to precious metal-based catalysts,transition metal-based catalysts have advantages such as low cost and abundant resources.In recent years,many scholars have conducted relevant research and demonstrated that transition metal-based catalysts exhibit good activity and stability in hydrogen production by electrolysis of water.There are currently multiple methods for further optimizing the performance of catalysts.For example,by regulating the surface morphology of materials,doping with heteroatoms,and surface modification,the catalytic performance of catalysts can be improved.These regulatory measures provide broad space for the application of transition metal-based catalysts.This article has studied the performance regulation of transition metal-based catalysts from multiple aspects,and the main results are as follows:Firstly,Co₂FeAl alloy electrocatalysts with excellent performance and high stability were prepared by coprecipitation method.The surface morphology,crystal structure,and elemental composition of the material were characterized and analyzed using X-ray diffraction,scanning electron microscopy,transmission electron microscopy and X-ray photoelectron spectroscopy methods.The main research focuses on the impact of changes in annealing temperature on the catalytic performance of the catalyst.As the annealing temperature changes,the crystallinity,surface morphology and crystal orientation of the material will also change accordingly.When the annealing temperature is 670℃,the overpotential is 262 m V at a current density of 10 m A cm^-2.After adjusting the annealing temperature to 620℃,the catalytic performance of Co₂FeAl alloy electrocatalysts was significantly improved,and the overpotential of the material decreased to 149 m V.Furthermore,further stability test is conducted on the material.After 1000 cycles of cyclic voltammetry characteristic testing,the overpotential only increased by 3 m V and it can work stably for twelve hours at the overpotential,demonstrating excellent stability.Density functional theory calculations show that near the Fermi level,the synergistic effect between different metal atoms in the alloy changes the electronic structure of the system and improves the overall catalytic activity.Secondly,the catalytic performance of Co₂FeAl alloy electrocatalysts was optimized by surface treatment of the material using plasma in N₂ atmosphere.Select Co₂FeAl alloy prepared at an annealing temperature of 670℃as the optimization object,and optimize the treatment results by adjusting the power and bombardment time of N₂ plasma.Research has found that all samples treated with N₂ plasma have significantly improved their catalytic performance,especially when the plasma power is 200 W and the bombardment time is 300 s,the optimization effect on Co₂FeAl catalyst is most obvious.The N-Co₂FeAl catalyst obtained under this condition can achieve a current density of10 m A cm^-2 with only an overpotential of 152 m V,which improves its performance by 41.9%compared to the untreated Co₂FeAl catalyst（with an overpotential of 262 m V）.The electrochemical stability of the sample was tested.After 1000 cyclic voltammetry tests,the overpotential only increased by 5 m V,indicating that its catalytic activity remained at an excellent level.From the experimental results,it can be seen that the electronic and coordination structures of Co₂FeAl nanospheres can be adjusted by N₂ plasma treatment to promote charge transfer,accelerate the dissociation kinetics of water,optimize its crystal structure,and make Co₂FeAl alloys appear complex structures composed of amorphous,polycrystalline and mixed crystals,providing additional active site,which is an effective method to improve the catalytic performance of electrocatalysts.Finally,the catalytic performance of the material is further optimized through the synergistic effect of high valence metal doping and high-temperature annealing.Mo and W atoms were doped into Co₂FeAl alloy by coprecipitation method,and the catalytic performance of the catalyst was adjusted by changing the annealing temperature and doping concentration.Research has found that the Co₂FeAl Mo_1.5 alloy catalyst(Co₂FeAl Mo_1.5-750℃)prepared at an annealing temperature of750℃and a doping concentration of 27 at.%exhibits the best catalytic activity for hydrogen evolution reactions in alkaline solution.At a current density of 10 m A cm^-2,it exhibits a low overpotential of 71 m V and a Tafel slope of 110 m V dec^-1.After 1000 cyclic voltammetry tests,its overpotential only increased by 2 m V and can operate stably for 20 hours at the overpotential,demonstrating excellent stability.Compared with undoped materials,doped materials have significantly improved catalytic performance.This is attributed to the low charge transfer resistance,appropriate crystallinity,additional amorphous area,and polycrystalline structure of the material due to high valence metal doping.