Controllable Synthesis Of Ni-based Nanomaterials As Electrocatalysts For Hydrogen Evolution Reactions

Hydrogen production from electrocalytic water splitting has attracted much attention due to the unique advantages such as high efficiency,cleanliness and non-pollution.Moreover,the prepared hydrogen with high purity and no CO impurities which can be used as an ideal fuel for the hydrogen-oxygen fuel cell.The main problem of this technology is the high consumption of electric energy,which makes the production cost on the high side.During the process of electrolytic water reaction,a large part of the energy loss stems from the overpotential of hydrogen evolution and oxygen evolution;thus many researchers have widely and deeply explored the issue,expecting to reduce the energy loss in the energy conversion process.Precious metals such as Pt,Ir and Ru,with high activity and stable performance,are efficient electrolytic water catalysts,but the reserves are limited and the costs are high,so they are mainly used to study the mechanism of hydrogen evolution and oxygen evolution process.Nowadays,the main research focuses on the research of transition metal-based catalysts such as Ni,Co,Fe and other noble metals.In this Thesis,Ir-Ni/nanoparticles are synthesized by simple impregnation-reduction method,and by changing the ratio of Ir-Ni and synthesis temperature,the author has prepared nickel-based catalysts with different structures,thereby exploring the influence of alloying on hydrogen evolution performance.And the author has found that different Ir-Ni ratios can obtain different crystal forms.When the content of Ir is lower,the crystal form is Ir,and Ni enters the crystal lattice of Ir,resulting in crystal lattice shrinkage.When the content of Ni is higher,the crystal form is Ni,and Ir enters the crystal lattice of Ni,bringing about the crystal lattice expansion of Ni,which makes the Ni-based catalyst still enjoys high catalytic activity.And the catalyst activity of IrNi₅-400 with the sample of crystal lattice expansion of nickel is optimal when Ir enters the nickel crystal lattice.Therefore,the cheaper element B is introduced into the crystal lattice of Ni through chemical reduction and annealing treatment to form interstitial compounds,which causes the crystal lattice expansion of nickel,thereby obtaining the hydrogen evolution catalytic activity much better than that of elemental nickel.The introduction of B not only expands the crystal lattice of nickel,but also makes the materil with oxidation layers of B₂O₃,and the heterostructure of nickel metal monomer is formed,which effectively enhances the catalytic activity of alkaline hydrogen evolution.By regulating and controlling the crystal form and electronic structure of nickel,the catalytic activity is improved.The stability of the catalyst,however,is still required to be further improved.Therefore,dicyandiamide and citric acid ligand are introduced in the subsequent synthesis process to obtain metal complex precursor.Carbon layer is formed by carbonization during annealing treatment,which is coated on the surface of Ni-based metal particles,inhibits the aggregation and growth of metal particles in the synthesis process,reduces the dissolution loss of the catalyst in the catalytic process and improves the catalytic stability of the material.Moreover,CNT grows from metal particles,which improves the conductivity of the catalyst,has a larger specific surface area,and can fully contact with the electrolyte,which is conducive to mass transfer process and catalytic activity.