Preparation Of Self-supported Ni-based Nanoporous Materials And Their Performances For Electrochemical Water Splitting

With the increase of environmental pollution and energy crisis,it is urgent to develop clean and efficient new energy to promote the sustainable development of human social.Hydrogen is considered to be the most clean and renewable energy for large-scale applications due to its large combustion value,the combustion product only water,as well zero carbon emission.Electrocatalytic water splitting of hydrogen production is considered as the most promising hydrogen production technology owing to the advantages of simple process,non-pollution,and high-purity hydrogen.At present,noble metal-based electrocatalysts,such as Pt-based materials for hydrogen evolution reaction（HER）and Ru/Ir-based materials for oxygen evolution reaction（OER）,possess excellent electrocatalytic performances.However,expensive prices and rare reserves have seriously impeded their widespread practical applications in water electrolysis.A large amount of effort has been devoted to the development of transition metal-based catalysts,especially for self-supporting transition metal-based catalysts to replace noble metal catalysts.The design of nanoporous structures is also widely used to further enhance the electrocatalytic activity of transition metal-based nanomaterials.Besides,the self-supporting transition metal catalyst prepared by in-situ construction on the conductive substrate,not only reduce the cost of the catalyst,but also accelerate the electron transport rate and expose the number of more active sites,thus improving the electrocatalytic performance and structural stability of the material.Therefore,it is crucial to the development of low-cost and highly efficient transition metal catalysts to promote the development of hydrogen technology toward water splitting.This paper focuses on the construction of self-supporting transition metal electrocatalyst with specific composition and nanoporous structure by in situ,which can achieve a significant the acceleration of the reaction kinetics for water splitting,thus greatly enhancing the electrocatalytic performance.The main research contents are as follows:1.Using nickel foam as the substrate and metal source,Ni Zn intermetallic and Ni heterostructure is in situ constructed on the nickel foam surface（TMP Ni Zn-Ni/NF）by electrodeposition-annealing-corrosion strategy,and it is used as the HER electrocatalyst for water splitting.Benefitting from high density reactive sites and fluent mass transfer as a result of trimodal porous architecture and strong electronic modulation from Ni Zn intermetallic,TMP Ni Zn-Ni/NF primely overcomes the sluggish hydrogen evolving kinetics with superior catalytic performances comparable to Pt/C and many other reported similar electrocatalysts.TMP Ni Zn-Ni/NF only required the low overpotential of 233 m V at high rate of 600 m A cm^-2with the small Tafel slope at 47.3 m V dec^-1 in 1.0 M KOH solution.TMP Ni Zn-Ni/NF also exhibits exceptional catalytic durability toward HER with almost no current loss under the overpotential of 100 m V for 50 h.Theoretical calculations reveal thatβ₁-Ni Zn intermetallic itself has low Gibbs free energy for H adsorption(ΔG_H*),while it can also greatly decrease theΔG_H*of heterojuncted Ni,thus increasing the catalytic activity of the catalyst.2.Using the porous Ni Zn/Ni heterostructure in situ constructed on the NF surface as the substrate,a firm Ni Fe Zn-OH nanosheet network array is distributed on the hierarchical porous Ni Zn-Ni/NF surface by a one-step redox reaction with Fe Cl₃ solution（Ni Fe Zn-OH/Ni Zn-Ni/NF）.Ni Fe Zn-OH/Ni Zn-Ni/NF shows low overpotentials of（?）_50/600around 235/284 m V for OER and（?）_50/600 around 73/212 m V for HER,small Tafel slopes of46.1 and 41.1 m V dec^-1,and prolonged catalytic durability in an alkaline medium because of the strong synergistic effects of Zn doping,multiple interface engineering,and integral three dimensional free-standing scaffold.As bifunctional catalysts,Ni Fe Zn-OH/Ni Zn-Ni/NF required a low electrolytic voltage of 1.49 V at 20 m A cm^-2(1.61 V at 100 m A cm^-2)with a sustained and stable output for 40 h during water splitting.3.With nickel foam as the substrate,the nanoporous Co Fe Zn alloy supported on the hierarchical porous Ni Zn intermetallic/Ni heterojunction surface（Co Fe Zn/Ni Zn-Ni/NF）is prepared via electrodeposition alloy-annealing-corrosion strategy used as the OER electrocatalyst for water splitting.The as-made Co_1.5Fe₁Zn/Ni Zn-Ni/NF exhibited excellent OER activity with an overpotential of 391 and 440 m V to achieve 600 and 1004 m A cm^-2 in1.0 M KOH solution,respectively.Meanwhile,Co_1.5Fe₁Zn/Ni Zn-Ni/NF showed outstanding catalytic stability during OER with almost no current loss under the overpotential of 350 m V for 100 h.The high catalytic activity and stability of Co_1.5Fe₁Zn/Ni Zn-Ni/NF are attributed to the high density of catalytic active sites,interface effects,and the integrated construction of a three dimensional conductive skeleton.4.Using Ni Fe foam as the substrate and metal source,bimodal porous Fe Ni Zn alloy and Fe Ni₃ intermetallic heterojunction in situ constructed on the surface of Ni Fe foam（Fe Ni Zn/Fe Ni₃）is prepared through the electrodeposition-annealing-corrosion strategy as highly efficient electrocatalyst for overall water splitting.Benefiting from moderated electronic structure,maximum exposure of active surface sites,and unique three dimensional conductive structure,Fe Ni Zn/Fe Ni₃ exhibits superior electrocatalytic activity with extremely low overpotentials of 244/322 and 84/190 m V to achieve a current density of 50/600 m A cm^-2for OER and HER in 1.0 M KOH solution,respectively.The two-electrode electrolyzer constructed based on this material only needs a cell voltage of 1.578 V at a current density of100 m A cm^-2,which is significantly lower than Pt/C/Ni Fe（-）||Ru O₂/Ni Fe（+）（1.691 V）.In addition,the as-prepared sample showed high corrosion resistance with steady run for 100 h in alkaline medium for overall water splitting,showing great application potential as a bifunctional catalyst for electrolysis water.