The Preparation Of Nickel-cobalt Composite Material And Its Application In The Fields Of Electromagnetic Wave Absorption And Electrocatalytic Hydrogen Evolution

Electromagnetic?EM?interference and radiation have been becoming the resources of severe environmental pollution,and bringing great harms to EM compatibility,human health and information assurance.Dielectric-magnetic hierarchical composite might be an available strategy to attenuated EM wave.Among all the heterostructures,core-shell and yolk-shell structures are desired for the attenuation of EM waves due to the synergistic effect of multi-component.The interfacial polarization caused by the existence of multi-interface,the multiple reflections,and scattering occurred in void space are all beneficial for the consumption of the EM energy.Second,efficient impedance matching between magnetic loss and dielectric loss is also necessary to achieve excellent MA performance.The prepared absorbing materials in this paper combined the characteristics of core-shell structure and the characteristics of magnetic loss and dielectric loss.The innovation points of this paper are to combine carbon spheres,NiCo₂O₄ and Fe₃O₄,which prepared core-shell structure that likes sea urchins.Its characteristics are as follows:?1?Carbon spheres were both good dielectric loss material and template for the growth of Ni Co₂O₄.?2?The spinous NiCo₂O₄ not only provided dielectric loss but also improved the surface area,which was good for the penetration and consumption of the microwaves.?3?The void space was beneficial for the multi-reflection of EM waves.?4?Fe₃O₄ provided magnetic loss.Therefore,the prepared core-shell structure effectively improved MA performance.The minimum reflection loss?RL?value of C@NiCo₂O₄@Fe₃O₄ reached-43.0 dB at 13.4 GHz with a thickness of 3.4 mm.Urea is an electro-oxidative species with the advantages of cheap,non-toxic and renewable.Replacing water with urea is a promising way for more energy-efficient electrolytic hydrogen production.Pt/C,RuO₂ or IrO₂ are the best catalysts for urea electrolysis,but their scarcity and high cost severely impede the applications.Therefore,it is very necessary to prepare non-noble metal catalysts which can be highly catalyzed.Transition metal sulfide is a good choice for electrolytic urea.CoS₂ outperforms the most transition metal dichalcogenides due to its excellent metallic nature and high catalytic activity.In addition,long-term stability of CoS₂ was observed in both acidic and alkaline operating environments.However,the development of efficient CoS₂ based bifunctional catalysts towards both urea oxidation reaction?UOR?and hydrogen evolution reaction?HER?has not been reported yet.We immobilized 1D CoS₂ nanoneedle array on Ti mesh?denoted as CoS₂ NA/Ti?,CoS₂ could expose abundant surface active sites to accelerate the electrolyte transportation,and facilitate the release of N₂ and CO₂ at anode and H₂ at cathode.The stable interaction between the Ti mesh and CoS₂ nanoneedle array could facilitate the electron transport,and prevent CoS₂ agglomeration during the urea electrolysis process.As a result,the electrocatalytic performance of CoS₂ NA/Ti can be achieved at a cell voltage of only 1.59 V to generate a current density of 10 m A cm^-2 for full urea splitting in1.0 M KOH with 0.3 M urea.