Synthesis And Electrochemical Properties Of Nickel-based Heterointerface Electrocatalysts

Energy storage and conversion based on H₂O,H₂,and O₂ is currently the focus of research.It mainly includes production of hydrogen from electrolyzed water,metal-air batteries,and fuel cells.In these energy storage and conversion systems,several important electrochemical reactions are involved,such as oxygen reduction reaction(ORR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER),and small molecules electro-oxidation reaction.Due to the sluggish reaction kinetics,a catalyst is needed to accelerate the above reactions.Therefore,the development of highly efficient electrocatalysts with practical application prospects is key to achieving these energy conversions.In this thesis,four types of heterogeneous interface catalysts,including C/Cu S/Ni S₂,N-C/Ni₃Fe,Cu₄N/Ni₃N,and C/Ni₃N/Ni,are designed and constructed through performance optimization strategies,such as interfacial engineering,morphology control and element doping.Rechargeable zinc-air batteries with high power density and enhanced stability are developed.In addition,the low-energy-consumption electrolyzed water is used for efficient and stable hydrogen production,and the simultaneous production of high-value organic products and hydrogen.The main research results are as follows:(1)Based on hydrothermal method and subsequent high-temperature calcination,copper-nickel sulfide nanoparticles supported on graphene were prepared.It was confirmed that Cu₁Ni₂-S/G has a larger specific surface area,higher concentration of sulfur vacancies,and electronic interaction at the interface.Graphene matrix can anchor nanoparticles and stabilize the catalyst structure.At the same time,it can provide high-speed two-dimensional electronic conductive channels to ensure rapid charge transfer.The constructed graphene/metal-sulfide heterointerface and Cu S/Ni S₂ heterointerface can induce the charge transfer generated at the interface and possibly optimize the electronic structure and promote the adsorption/desorption of intermediates.Cu₁Ni₂-S/G showed excellent ORR activity.E_onset,E_1/2,and limiting diffusion current densities were 0.91 V,0.77 V,and 5.57 m A cm^-2,respectively.In addition,after 20 h stability test,the current retention exceeds 90%,showing outstanding durability.The zinc-air battery assembled based on Cu₁Ni₂-S/G catalyst has a stable open-circuit voltage of1.34 V and its calculated power density is close to commercial Pt/C&Ir O₂.(2)Ni₃Fe-GA₁aerogel was prepared by a hydrothermal self-assembly and subsequent high-temperature calcination.Pyrrole and NH₃ are simultaneously used as nitrogen sources to increase the nitrogen content and increase the percentage of pyridine-N.Furthermore,the addition of pyrrole monomer in the self-assembly process can inhibit the agglomeration of graphene sheets,improve the porosity,and facilitate the preparation of macroporous ordered structures.The 3D hierarchical structure with high porosity possesses more exposed active surfaces,enhances the accessibility of the electrolyte and provides a multi-dimensional electron transport pathway.It was confirmed by XPS and theoretical calculations that there is a strong electronic interaction between Ni₃Fe and N-doped graphene,which can cause the redistribution of charges at the interface and adjust the electronic structure.After compounding with graphene,the center of the d-band moves downwards relative to the Fermi level,which can optimize the adsorption energy of the reaction intermediate,thereby speeding up the catalytic kinetics.This catalyst shows excellent OER and ORR activities.For the OER,the overpotentials were 239 and 289 m V at current densities of 10 and 100 m A cm^-2,respectively.The Tafel slope was 44.8 m V dec^-1,and excellent durability with no delay after 10 h was obtained.For the ORR,the initial and half-wave potentials were0.93 and 0.80 V,respectively,and the current retention was 78%after a stability test for 20000 s.An assembled zinc-air battery exhibited a stable open circuit voltage(1.44V).Compared with the commercial Pt/C&Ir O₂ mixture catalyst,it has higher power density and specific discharge capacity as well as better charge-discharge cycling performance.(3)Cu₁Ni₂-N nanosheets supported on a carbon cloth substrate were prepared based on a solvothermal method and subsequent high-temperature calcination in ammonia gas.The Cu₁Ni₂-N nanosheets were composed of nanoparticles with an average size of 6 nm.The electrode processes rich Cu₄N/Ni₃N heterogeneous interfaces,higher electronic conductivity,larger specific surface area and super-hydrophilic electrode surface.It was confirmed by XPS analysis that there is a strong electronic interaction between Cu₄N and Ni₃N at the heterointerface,which can induce the redistribution of charge at the interface.The DFT calculation results show that the Cu₄N/Ni₃N heterointerface can optimize the center position of the d-band,improving the adsorption energy of the reaction intermediate,and reducing the reaction barrier.The catalyst showed excellent HER and hydrazine oxidation reaction(Hz OR)activities.For HER,the overpotentials were 71.4 and 252 m V at a current density of 10 and 200m A cm^-2,respectively,and excellent durability(60 h)was obtained.For Hz OR,it has an ultra-low potential(0.5 m V)and good durability at a current density of 10 m A cm^-2.Applying it to hydrazine-assisted hydrogen production,the working voltage of the electrolytic cell is only 0.24 V at a current density of 10 m A cm^-2,and it can run stably for more than 75 h,showing excellent low-energy electrolytic hydrogen production performance.Through ex-situ SEM,TEM,XRD,and XPS characterization analyses,it can be found that during the HER and Hz OR reaction process,Ni(OH)₂ will be generated on the surface of Cu₁Ni₂-N nanosheets,which may facilitate the hydroxyl species adsorption.In addition,disordered structures and a large number of defects can be generated during the electrolysis process,which can provide more catalytic sites for the reaction.(4)The C@Ni-N/Ni electrode was prepared by a simple solvothermal method,impregnation,and high-temperature calcination through ammonia gas.It exhibits a porous nanosheet morphology with high porosity,and the nanosheets are bent and overlapped to form a 3D network structure.This bestows the electrode with a large specific surface area and good electrolyte permeability,which is favorable for the catalytic reactions.The strong electronic interaction of the C,Ni₃N,and Ni interfaces in C@Ni-N/Ni was determined by XPS analysis,which could induce the redistribution of charges at the interface,and possibly optimize the electronic structure.The electron transfer at the Ni₃N/Ni interface was calculated by DFT,and the electrons in the Ni flowed to Ni₃N.The electrons transfer phenomenon may be achieved through the hybridization of Ni 3d-N 2p-Ni 3d orbits.After the electrons are transferred to the Ni atom in Ni₃N,the extra electrons can stabilize the H intermediate and promote the HER reaction kinetics.In addition,the electrons in Ni may also flow to C,so that the Ni atoms at the interface are electron-deficient,which is conducive to the adsorption of H intermediates.This interfacial recombination can simultaneously improve the adsorption activities of the Ni metal atoms and Ni atoms in Ni₃N,thereby reducing the reaction barrier and promoting reaction kinetics.The C@Ni-N/Ni electrode showed Pt-superior HER activity,with overpotentials of 13.5 and 115.7 m V at current densities of 10 and 100 m A cm^-2,respectively,and showed excellent HER durability(48 h without delay).In addition,the electrode can catalyze the electro-oxidation of a variety of small organic molecules,including hydrazine,urea,ethanol,methanol,isopropanol,and glycerol.Due to the multifunctional catalytic activity,the C@Ni-N/Ni electrode achieved 0.097,1.44,1.44,1.47,1.54,and 1.36 V respectively in an alkaline electrolytic cell containing the above-mentioned small molecules.Through ex-situ SEM,XRD,and XPS characterization analysis,it was found that in the electrolytic system such as hydrazine,ethanol,and urea,Ni(OH)₂ will be generated in situ on the surface of C@Ni-N/Ni,which may be favorable for hydroxyl adsorption.Favorable active sites are provided,which accelerates catalytic kinetics.C@Ni-N/Ni electrode is used as the cathode and anode of the electrolytic cell.It is driven by solar cells to achieve low energy consumption to produce hydrogen and produce high-value organic small molecules.The polysilicon solar cell is used to drive the hydrazine-assisted hydrogen production electrolytic cell.Under outdoor conditions,an electrolytic voltage of 0.859 V and an electrolytic current of 81.3 m A can be achieved.A commercial monocrystalline silicon solar panel is used to drive an ethanol reforming electrolytic cell.Under outdoor conditions,its operating voltage is 2.77 V and the electrolytic current can reach 1.02 A.Efficient simultaneous preparation of H₂ and acetate products is achieved.