Study On Controllable Synthesis Of Nickel-based Alloy Carbon Nanocomposite And Its Electrocatalytic Performance By Sinle Precursor Method

Hydrogen energy is seen as a clean and renewable alternative to fossil fuels,helping to alleviate growing energy demand and deteriorating environmental problems.In view of the advantages of stable yield and high purity of the products obtained,hydrogen production by electrolysis of water is an important way.In order to achieve a high-efficiency reaction pathway,a highly active catalyst is required to overcome the large overpotential and Kinetic lag effect.However,most of the current high-performance catalysts are noble metal-based catalysts(such as Pt,Ru,and Ir)with high cost and low reservation.Therefore,it is essential to develop electrocatalytic water splitting catalytic materials with high earth-abundance and low prices.According to reports,the VIII 3d transition metal-based(Ni,Co,Cu,etc.)catalyst exhibits competitive electrolytic water catalytic activity with abundant reserves and low cost,and has been studied by scholars extensively.Moreover,compared with single-metal catalysts,the transition metal alloy catalysts can provide a better strategy due to their ideal bimetallic synergistic promotion.This thesis takes Ni-based alloy as the research object,and salicylate intercalated layered double hydroxides as single precursors.One-dimensional nickel-cobalt alloy carbon nanocomposites and three-dimensional nickel-copper alloy carbon nanocomposites with high-dispersion and high-purity were controllably synthesized through one-step solid-state pyrolysis.We studied the application of this material in the field of electrocatalysis.The following is the detailed research content:1.We used cheap and easily available nickel nitrate,cobalt nitrate and sodium salicylate as raw materials to constract a salicylate intercalated layered nickel and cobalt hydroxides in the water phase by co-precipitation method.Using it as a single precursor,one-dimensional NixCoy@C(x:y is the molar ratio of the metal)alloy nanocomposites were synthesized controllably through one-step solid-state pyrolysis,after we adjusted the conditions of the calcined temperature,time and atmosphere.The precursors and NixCoy@C alloy carbon nanocomposites were characterized by SEM,XRD,HRTEM,Raman,FT-IR,TG,BET,XPS and other tools.The results show:In a neutral environment,the metal cations and the salicylate anions undergo bidentate bridging and self-assemble in the solution to form well-dispersed one-dimensional rod-shaped nickel cobalt hydroxides precursors with a length of about 600 nm and a diameter about 40 nm.After calcined in the nitrogen atmosphere,the nanocomposites still maintain the morphology of one-dimensional nanorods.Salicylate anions were thermally decomposed to form graphitized carbon while emitting reducing gases such as H2,reducing Ni2+ and Co2+ to metals,and forming uniformly dispersed CoNi alloy nanoparticles with a particle diameter of about 10 nm.The calcined nanorods do not contain metal oxides,carbides or any other impurity phases which show high crystallinity and purity with large specific surface area(600?:154.69 m2·g-1;900?:103.96 m2·g-1)and abundant oxygen-containing functional groups(C-O,O-H,C-OH,C-O-M(M stands for Ni/Co),etc.).Due to the uniform one-dimensional porous carbon morphology,unique graphite carbon coating structure and abundant oxygen-containing functional groups,the adsorption of the electrolyte and the transmission of electrons were accelerated,thereby promoting the nanocomposites to exhibit excellent catalytic performance in electrocatalysis.In the electrocatalytic hydrogen evolution reaction(HER)test,Ni3Co1@C-9 catalyst possesses the best performance,only needs 124 mV to reach a current density of 10 mA cm-2 in the base solution with 20-hours stable work.In the electrocatalytic oxygen evolution reaction(OER)test,Ni3Co1@C-6 catalyst possesses the best performance,only requires 388 mV to reach a current density of 10 mA cm-2 in alkaline conditions.After 16 hours of continuous work under this overpotential,the Ni3Co1@C-6 catalyst still has a current density retention rate of 92%.2.Based on the preparation of the nickel-cobalt hydroxides precursors,three-dimensional salicylate intercalation nickel and copper hydroxides precursors were prepared by changing the composition and ratio of the metal,replacing the metal Co with Cu and adding urea to the raw materials.Using it as a single precursor,we synthesized three-dimensional alloy nanocomposites NixCuy@C(x:y is the molar ratio of the metal)controllably by adjusting the calcined temperature,time and atmosphere through one-step solid-state pyrolysis.The products were characterized by SEM,XRD,HRTEM,Raman,TG,BET,XPS and other tools.The results show that the precursor has a good three-dimensional flower-like structure,and the added urea concentration has a certain effect on the morphology;After calcination,the product still maintains a three-dimensional structure,and a large number of carbon nanotubes embedded with NiCu alloys nanoparticles with the diameter of 6-12 nm appear on the stacked nanosheets.The three-dimensional structure and the generation of carbon nanotubes provide a large specific surface area and a richer pore structure,exposing more active sites.Crucially,electronegative oxygen functional groups can be formed on the surface of CNTs to capture metal cations,and strong electrostatic interactions among these functional groups can efficiently improve the dispersity of catalysts,further preventing the catalyst materials from aggregation.In addition,the abundant oxygen-containing functional groups also promote the adsorption and removal of the electrolyte,accelerate the transmission of electrons,and improve the performance of electrolyzed water.In the HER test,Ni4Cu1@C-400 exhibits the best performance,only requires 92 mV to reach a current density of 10 mA cm-2 with the good stability in alkaline solution.In the OER test,Ni4Cu1@C-500 shows the best performance.It only needs 345 mV to reach a current density of 10 mA cm-2 along with the good stability in alkaline solution,which is better than the commercial RuO2 catalyst(365 mV).Then we used Ni4Cu1@C-500 both as the cathode and anode respectively to conduct the overall water splitting test in 1.0 M KOH solution.It only needs a voltage of 1.584 V to reach a current density of 10 mA cm-2 with the favorable stability,better than the performance of different types of non-noble metal catalysts reported in most of the literature.In summary,without additional carbon sources and reducing agents,we used organic-inorganic layered hydroxides as single precursors to synthesize multi-alloy carbon nanocomposites controllably—Ni3Co1@C&Ni4Cu1@C.The raw materials are cheap and easily available,and the synthesis method is simple and controllable.The prepared catalysts possess excellent catalytic activity and stability in HER,OER and OWS test which is equivalent to that of noble metal-based catalysts,which shows potential application value in industry,energy,environment and other fields.