Preparation Of Nickel Foam Supported Transition Metal Based Catalysts For Electrocatalytic Water Splitting

Hydrogen is a kind of efficient and pollution-free clean energy,and electrolysis of water is one of the most effective and convenient methods to produce hydrogen.In order to reduce the energy consumption and cost of hydrogen production by electrolysis of water,it is urgent to develop high-efficient,stable and low-cost non-noble metal-based catalysts（such as Fe,Co,Ni and other transition metal-based catalysts）to replace the precious Pt,Ru,Ir noble metal-based catalysts.In recent years,transition metal sulfides and hydroxides have been considered as promising catalyst materials for electrolysis of water due to their excellent properties.On the other hand,nickel foam（NF）with large specific surface area,good electrical conductivity,favorable gas diffusion and high mechanical strength is often used as a catalyst support.In this thesis,the research progress of electrolytic water catalysts was briefly reviewed firstly,and then we focused on the in-situ preparation of binderless transition metal based electrolysis water catalysts by using foam nickel as carrier and nickel source.Four new kinds of nickel foam supported transition metal based catalysts were successfully prepared,including the Ni₃S₂/Mo S₂/Fe OOH hierarchical microspheres assembled from nanoribbons,Ni₃S₂/Co₃S₄/Fe OOH flower-like microspheres constructed by Ni₃S₂/Co₃S₄ nanosheets and Fe OOH nanoparticles,Ni（OH）₂/Fe OOH/NF with in-situ grown Ni（OH）₂ nanosheets decorated by Fe OOH nanoparticles,and Ni Fe（CN）₅NO/Ni₃S₂/NF with rod-like hierarchical structure assembled by nanosheets.Various techniques such as X-ray diffraction（XRD）,field emission scanning electron microscopy（FESEM）,transmission electron microscopy（TEM）,high resolution transmission transmission（HRTEM）,X-ray photoelectron spectroscopy（XPS）and energy analysis spectroscopy（EDS）were used to characterize and analyze the composition,structure,and morphology of the as-prepared catalysts.The electrocatalytic performances of these materials were systematically investigated.The main points are as follows:1.Ni₃S₂/Mo S₂/Fe OOH hierarchical microspheres assembled by nanoribbons were grown on the surface of NF by a simple one-step hydrothermal method.Ni₃S₂/Mo S₂/Fe OOH exhibits excellent bifunctional catalytic performance in 1.0 M KOH solution,with low overpotentials of 219 m V for OER at 100 m A cm^-2 and 76m V for HER at 10 m A cm^-2,due to the synergistic effect between the different components and the unique microsphere structure.When Ni₃S₂/Mo S₂/Fe OOH was used as electrodes of electrolyzer for overall water splitting,it only needs a very low battery voltage（1.52 V）to reach the current density of 10 m A cm^-2,which is comparable to the state-of-the-art Pt-C||Ir O₂ electrolyzer（1.50 V）.The cost-efficient and high-performance Ni₃S₂/Mo S₂/Fe OOH bifunctional catalyst exhibits a potential application prospect in industrial hydrogen production.2.Ni₃S₂/Co₃S₄/Fe OOH flower-like microspheres assembled by Ni₃S₂/Co₃S₄nanosheets and Fe OOH nanoparticles were in-situ grown on NF by a one-pot hydrothermal method.Due to the abundant active sites on the interface of the heterostructure,the Ni₃S₂/Co₃S₄/Fe OOH exhibits excellent bifunctional electrocatalytic performance in 1.0 M KOH solution,with overpotential of 158 m V for HER and 181 m V for OER at the current density of 10 m A cm^-2.Even at a large current density of 100 m A cm^-2,the overpotential for OER was only 229 m V.More importantly,the symmetric electrolyzer based on Ni₃S₂/Co₃S₄/Fe OOH electrodes only needs a low voltage of 1.58 V to reach a current density of 10 m A cm^-2 in 1.0 M KOH,and exhibits good durability during a long-term（50 h）chronoamperometry test.3.Ni（OH）₂/Fe OOH/NF electrocatalyst assembled by Ni（OH）₂ nanosheets and Fe OOH nanoparticles was in-situ grown on NF by a one-step hydrothermal method.In the hydrothermal process,Ni（OH）₂ nanosheets were directly in situ grown on NF,and Fe³⁺cations could be slowly generated from the corrosion of stainless steel powder（SNPs）to form Fe OOH nanoparticles in alkaline environment,resulting in the Ni（OH）₂/Fe OOH composite with Ni（OH）₂ nanosheets modified by Fe OOH nanoparticles.Due to the synergistic effect of iron and nickel at the interface,the Ni（OH）₂/Fe OOH/NF catalyst exhibits excellent OER performance in alkaline medium.It has an ultra-low overpotential of 156 m V at the current density of 10 m A cm^-2,and a small Tafel slope of 40 m V dec^-1.In addition,it shows good electrocatalytic stability for OER in a long-term chronoamperometry test of 30 h.The Ni（OH）₂/Fe OOH/NF electrocatalyst with low cost and excellent OER performance possesses great promise for practical water splitting application.4.Novel Ni Fe（CN）₅NO/Ni₃S₂/NF rod-like hierarchical structure assembled by nanosheets was synthesized by a simple two-step strategy.NF was firstly vulcanized by thiourea under hydrothermal condition to obtain Ni₃S₂/NF,and then the Ni₃S₂/NF was reacted with Na₂Fe（CN）₅NO·2H₂O in ethylene glycol to form Ni Fe（CN）₅NO/Ni₃S₂/NF.Thanks to the synergistic effect between Ni₃S₂ and Ni Fe（CN）₅NO as well as the unique morphology and microstructure,the catalyst exhibits excellent OER electrocatalytic activity and stability in 1.0 M KOH solution.At the current density of 10 m A cm^-2,the overpotential is only 162 m V,and the Tafel slope is as low as 26 m V dec^-1.A long-term chronopotentiometry test of 17 h verified its good durability for OER.These results demonstrate that Ni Fe（CN）₅NO/Ni₃S₂/NF is a promising OER electrocatalyst for practical water splitting.This study provides a new idea and strategy for the design and synthesis of novel and efficient OER electrocatalysts.