Construction And Electrocatalytic Water Splitting Performance Of Nickel-based Self-supporting Nanocomposite Electrodes

Hydrogen energy is generally regarded as a potential energy carrier for future sustainable energy system due to its advantages of high energy density,high calorific value,abundant resources,zero carbon emissions and easy storage.Overall water splitting has the advantages of high conversion efficiency,low greenhouse gas release and high hydrogen purity,and has become a research hotspot in the field of hydrogen production.However,the high cost,complicated reaction steps,and diverse intermediates of electrocatalytic water splitting reaction for hydrogen production make the actual overpotential of HER and OER much higher than the theoretical value,resulting in a lot of energy waste and low efficiency.Therefore,electrocatalysts are urgently needed to improve the efficiency of water electrolysis.The practical application of precious metal catalysts is limited due to the low reserves and high cost.Therefore,it is imperative to explore inexpensive and environmentally friendly non-noble metal-based electrocatalysts,especially transition metal-based electrocatalysts,to replace noble metal-based electrocatalysts.In recent years,nickel-based materials have been widely used in electrocatalysis due to their various switchable valence states,stable chemical properties,and good hydrogenation activity.Based on this,this thesis takes nickel-based materials as the research goal,and starts from the structure and component design to construct nickel-based supporting nanocomposites with different morphologies to explore their electrocatalytic water splitting performance.The effects of morphology,interface engineering and polymetallic engineering on the catalytic activity of electrode materials were explored by X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The details are as follows:1.The Ni Mo O₄/Ni₃S₂/NF 2D/2D heterojunction electrode was synthesized by a simple two-step hydrothermal method,as a bifunctional water electrolysis catalyst.The effects of different reaction conditions on their morphology,structural composition and electrocatalytic performance were discussed.The results showed that the as-synthesized Ni Mo O₄/Ni₃S₂/NF electrode exhibited excellent catalytic performance for HER(η^-2_{10 m A cm}=80 m V)and OER(η^-2_{50 m A cm}=288 m V)in alkaline solution.Meanwhile,an alkaline water splitting electrolyzer was constructed using Ni Mo O₄/Ni₃S₂/NF as positive and negative electrodes,and the cell voltage was 1.52 V when the current density was 10 m A cm^-2.2.Compared with single-component nickel sulfides in the previous section,multimetallic nickel sulfides can exhibit significantly enhanced catalytic performance.In this section,unique sugar gourd-like hollow core-shell Ni Mo O₄·x H₂O@Ni-Co-S NCAs arrays were synthesized by using a simple metal-organic framework（MOF）engagement strategy and selective sulfurization,in which the Ni Mo O₄·x H₂O/NF nanorod arrays acted as skeleton.The effects of the hollow structure and multimetallic components on the electrocatalytic performance were discussed.The resulted show that the as-synthesized hollow core-shell Ni Mo O₄·x H₂O@Ni-Co-S NCAs/NF electrode simultaneously exhibited excellent HER(η^-2_{10 m Acm}=113 m V)and OER(η^-2_{50 m Acm}=261 m V)performance in 1.0 M KOH due to its unique structural and compositional advantages.Meanwhile,by integrating its bifunctional catalytic properties,the cell voltage was 1.503 V when the current density was 20 m A cm^-2.3.On the basis of the above-mentioned interfacial electronic coupling effect and the synergistic effect between multi-metal ions to promote the water electrolysis reaction,a three-dimensional core-shell Ni-Mo-S@Ni Fe LDH/NF electrocatalyst was constructed.Using Ni Mo O₄·x H₂O nanorods as precursors,Ni-Mo-S/NF nanorod arrays were obtained by vulcanization treatment.The study found that it has good HER performance,but unsatisfactory OER performance.To improve its OER performance,the Ni Fe LDH was wrapped on its surface to obtain a three-dimensional core-shell Ni-Mo-S@Ni Fe LDH/NF electrocatalyst.The catalyst exhibits excellent OER performance(η^-2_{100 m A cm}=274 m V)and water splitting activity(E^-2_{10 m Acm}=1.507 V).In addition,the catalyst was found to also have good urea oxidation performance.