Preparation Of Cobalt-based Bimetallic Composite Electrocatalysts And Study On The Water Splitting Activities

The huge consumption of traditional fossil energy makes today's society face serious environmental pollution and energy crisis.Because of its high energy density and calorific value of combustion,hydrogen has gradually become the first choice to replace traditional fossil energy.Electrocatalytic water splitting as a green,clean and pollution-free method of hydrogen production has attracted much attention.In the process of electrocatalytic water splitting,the efficient,stable and cheap electrocatalyst is the key to achieve large-scale hydrogen production.It is well known that precious metals and their oxides have high electrocatalytic properties,but their applications are greatly limited by their serious scarcity and high price.Therefore,it is the first choice to search for non-noble metal catalysts with abundant reserves and low price.Transition metals are statistically high in the earth's crust and easy to mine.In addition,the transition metal atom has a unique electronic structure and strong redox capacity,which makes it widely used in the electrocatalytic water splitting.Therefore,a series of cobalt-based bimetallic sulfides,nitride compounds and phosphates were prepared in this paper.The element composition,structure morphology and electrochemical performance of the catalyst were analyzed by different characterization and analysis methods,and the electrocatalytic reaction mechanism was further explored.The specific research content is as follows:1.ZnCo₂S₄@NiFe-LDH/NF?ZCS@NFL/NF?composite electrocatalysts with core-shell structure were successfully prepared by hydrothermal-sulfuric-hydrother-mal method with nickel foam as the substrate.SEM,TEM,XRD,XPS and other characterization methods were used to analyze the morphology,structure and element composition of the samples,and electrochemical testing was conducted on the electrochemical workstation.The results showed that the catalyst exhibited excellent hydrogen evolution performance?HER?in 1 M KOH solution.At current density of10 mA cm^-2,the overpotential is only 110 mV,which is better than many reported cobalt or nickel-based catalysts.The stability test results by chronopotentiometric show that after 48 h,the current density has no obvious downward trend and shows good stability.This improved HER catalytic performance can be attributed to the not only unique core-shell architecture contributing to abundant active sites and rapid mass/charge transport,but also the synergistic effect between ZnCo₂S₄ and NiFe-LDH components benefiting for easy H₂O dissociation and fast HER kinetics.2.The porous structure of Co₃FeN_x catalyst was successfully prepared by ligand exchange reaction and nitridation treatment with metal-organic frameworks as template.The optimal reaction conditions were founded by regulating the different concentrations of ligand K₄[Fe?CN?₆].The postsynthetic ligand exchange reaction plays an important role in the formation of mesoporous nanostructure and the insertion of iron atoms.The electrochemical test results showed that when the concentration of K₄[Fe?CN?₆]was 10 mg mL^-1,Co₃FeN_x exhibited the best electrocatalytic oxygen evolution performance?OER?.In alkaline media,when the current density is 10 mA cm^-2,the oxygen evolution overpotential is only 270 mV.Moreover,Co₃FeN_x maintained high catalytic activity after continuous operation for40 h.Due to the unique porous structure and the insertion of iron atoms,more reactive sites are provided,the electron transport rate is accelerated,and the electrocatalytic activity is enhanced.3.Taking Co₃O₄ derived from metal-organic frameworks as the main body,the prussian blue analogues?CoFe PBA?was loaded on the surface of the nanosheet,and then the CoP@CoP-Fe electrocatalyst was prepared by low-temperature phosphating.By adjusting the reaction time,the successful preparation of CoP@CoP-Fe electrocatalysts with different loads was realized.The test results showed that when the reaction time was 24 h,the CoP@CoP-Fe catalyst exhibited excellent OER performance.When the current density was 10 mA cm^-2,the oxygen evolution overpotential was only 240 mV,and the Tafel slope was only 54.8 mV dec^-1.The results of 100 h stability test show that the catalyst can still maintain excellent catalytic activity.This well-aligned three-dimensional?3D?structure and the synergistic effect of Co and Fe make it have excellent electrocatalytic performance and stability to OER in alkaline electrolyte.