Electronic Modulation Of Ni-based Nanocomposites And The Electrocatalytic Performance Of Oxygen Evolution Reaction

At present,the over-exploitation and super-utilization of traditional fossil energy(coal,oil,natural gas,etc.)make mankind face severe energy and environmental problems.Therefore,the development of renewable energy is of great significance to achieve sustainable development.Common energy sources are wind,hydro,and solar.As a clean,non-polluting renewable energy carrier,hydrogen is expected to solve energy and environmental problems.The electrolysis of water for hydrogen production is considered to be the reverse reaction of hydrogen combustion,resulting in an energy cycle with zero carbon emissions.Electrocatalytic water splitting processes include anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER),where OER is a four-electron transfer process that requires high energy to overcome the energy barrier of the reaction.Among many catalysts,noble metal oxides are recognized as excellent OER catalysts,such as IrO2 and RuO2.However,high cost and low abundance hinder their large-scale practical application.Therefore,it is necessary to find cost-effective metal-free precious metal catalysts.Most electrolyzers use alkaline electrolytes due to the low equilibrium half-cell potential,and many non-precious metal catalysts show high activity in alkaline media.Therefore,from the perspective of catalyst performance and cost,the development of efficient OER electrocatalysts in alkaline media can facilitate the industrial application of electrocatalytic water splitting.Among them,transition metal-based electrocatalysts have attracted much attention due to the type of crystal type and electronic structure regulating chemical reactivity,theoretically high efficiency,and thermodynamic stability and corrosion resistance.However,the control of the electronic structure of transition metal-based electrocatalysts,the construction of structures with more active sites,and the exploration and design of low-cost,high-abundance,high-performance,and stable electrocatalysts are still research priorities.Based on this,we designed and synthesized a series of nickel-based nanocomposite electrocatalysts from the perspective of regulating the electronic structure of transition metal-based nanomaterials,and used them for efficient and stable electrochemical oxygen evolution reaction.The content of this thesis specifically involves the following three aspects:1.Ni3Se2/Ni3S2/NF heterostructures were synthesized by solvothermal and hydrothermal methods on nickel foams.The catalyst exhibits excellent OER performance with a low overpotential of 251 and 312 mV at 50 and 100 mAcm-2,respectively.Experimental results prove that theinterface of Ni3Se2/Ni3S2/NF heterostructure triggers the generation of abundant catalytically active sites,while regulates the electronic structure of Ni central active site resulting in fast charge-transfer capacity and superior electrochemical performance.2.A Fe2O3/Ni(OH)2 catalyst with rich crystalline-amorphous interface was introduced.Fe2O3 heterostructures embedded on Ni(OH)2 nanosheets were synthesized by one-step hydrothermal method.Abundant crystal-amorphous interfaces are formed between Fe2O3 particles with good crystallinity and Ni(OH)2 nanosheets with a large amount of amorphous structure,which enhance the interaction between Fe and Ni and accelerate the electron transfer in the OER process.Meanwhile,a large number of defects in the material provide a large number of active sites.The experimental results show that Fe2O3/Ni(OH)2 catalyst has good electrocatalytic performance and excellent stability.The material has an overpotential of 256 and 288 mV at a current density of 50 and 100 mA cm-2,respectively.What’s more,it has a low tafel slope of 45.72 mV Dec-1.It still maintains good stability after 36 h OER process.3.A Ni(OH)2/NiOOH-Vo catalyst with abundant oxygen vacancy was developed.The Ni(OH)2/NiOOH-Vo micron flower structure contains abundant oxygen vacancies that regulate the electronic structure of the active site.The two-component structure can regulate the mutual transformation of Ni2+ and Ni3+ to achieve an equilibrium state,which is more conducive to the activation of the active site in the OER process,thus enhancing the adsorption of the reaction intermediates.The electrocatalytic activity was enhanced by lowering the reaction free energy barrier.The experimental results show that The Ni(OH)2/NiOOH-Vo catalyst has good electrocatalytic performance and excellent stability.The material has an overpotential of 262 and 287 mV at a current density of 50 and 100 mA cm-2,respectively.And it exhibits a low Tafel slope of 77.85 mV Dec-1.Moreover,the overpotential hardly changes under continuous 12 h electrolysis test,indicating that it has good stability.