Preparation Of Cobalt-based Nanotube And Its Application In Electrolysis Water

In the future society energy crisis is increasingly serious,looking for clean energy to replace traditional fossil energy is a hot research topic in today’s society.Because hydrogen has the advantages of high energy density and no pollution,research on hydrogen conversion technology has an important impact on the development of new energy.Water electrolysis technology can produce hydrogen stably and quickly,but its application is limited due to the high reaction energy barrier between the two half reactions（HER and OER）that constitute water electrolysis.Therefore,the preparation of catalysts that reduce the reaction energy barrier is the key to large-scale application of water electrolysis technology.Although noble metal based electrocatalysts exhibit excellent activity,the high cost and low abundance of precious metals limit development.To date,a large number of transition metal-based electrocatalysts have been developed as substitutes for precious metal catalysts.However,its performance is still difficult to meet the needs of practical applications.Morphology design and composition regulation are effective strategies to improve catalyst activity.However,at present,there is still a lack of simple and efficient synthesis schemes to achieve simultaneous control of catalyst structure and composition.Based on the above problems,a series of high efficiency and low cost co-based hollow nanotubes were prepared controllable in this paper,taking morphology design and composition regulation as the starting point,combined with the development of synthesis scheme.The prepared co-based hollow nanotube as catalyst showed excellent performance in water electrolysis reaction.The specific research contents are as follows:1.A simple and efficient method for the preparation of cobalt oxide nanotubes was developed based on morphology design.This method does not depend on the use of template agent,only through wet chemical reaction and high temperature calcination can be prepared cobalt oxide with good hollow tubular structure.Through the morphology and structure characterization analysis,it is confirmed that the developed method can not only effectively regulate the material structure,but also prepare the cobalt oxide nanohollow tube.At the same time,it also showed good ability in compositional regulation.In addition,Co₃O₄ nanohollow tubes with different components of Co O and Co₃O₄ can be prepared only by changing the calcination atmosphere during the synthesis process.In addition,the formation mechanism of hollow structure was studied by TEM.The experimental results show that with the increase of temperature,the removal of organic matter and the crystallization of cobalt oxide are carried out simultaneously,thus promoting the formation of hollow structure.The OER reaction was catalyzed by two kinds of cobalt oxide nanohollow tubes.The experimental results show that both the prepared Co O and Co₃O₄ nanohollow tubes exhibit excellent OER catalytic activity,and only 320 m V and 343 m V overpotential are required to reach the current density of 10 m A cm^-2.However,the comparison of Co O nanoparticles and Co₃O₄ nanoparticles requires larger overpotential to achieve the same current density,which well confirms the effectiveness of the hollow structure design.2.Metal ion doping is one of the effective strategies to improve catalyst activity.Based on the hollow structure synthesis scheme in the previous chapter,Fe doped Co O nanohollow tube was prepared by combining structural design and composition control.This method is simple and efficient.It does not need to rely on template agent to construct hollow structure,and it also does not need to take additional metal doping steps.Fe doping can be realized only by introducing Fe salt in situ in the wet chemical reaction process of synthesizing hollow structure.The successful introduction and uniform distribution of Fe in Co O nanohollow tubes were confirmed by elemental distribution and chemical composition analysis.The morphology and structure analysis show that the introduction of Fe does not destroy the tubular structure of Co O.The introduction of Fe effectively regulates the electronic structure of Co O.Due to the advantages of hollow structure and the synergistic effect of Fe and Co,the prepared Fe doped Co O nanotube can be used as efficient OER catalyst.Under alkaline test conditions,Fe doped Co O nanohollow tube only needs 282 m V overpotential to reach the current density of 10 m A cm^-2,and has excellent cycling stability.However,the same current density of Co O nanotube and Co O nanoparticles without doping treatment requires greater overpotential,which effectively confirms the enhancement effect of Fe doping and hollow structure design on catalyst activity.3.The design and preparation of bifunctional catalysts with excellent HER and OER catalytic activities is an important research content in water electrolysis technology.Cobalt-based phosphating compounds have been proved to be a promising bifunctional catalyst.In this chapter,Mn-doped Co P/Co₂P nanohollow tubes were prepared based on structural design and component regulation.The synthesis scheme involved is simple and efficient.Firstly,Mn/Co-based nanorods were prepared by wet chemical method and then phosphating at low temperature to obtain Mn-doped Co P/Co₂P with good hollow tubular structure.The morphology,structure,elemental distribution and chemical valence of the samples were analyzed by TEM,SEM,XRD and XPS,which fully verified the effective doping of Mn and the construction of hollow tubular structure.Mn doping effectively regulates the electronic structure of cobalt-based phosphide and improves the catalytic activity of the material.The Mn-doped Co P/Co₂P nanotube has excellent HER and OER activities,and the corresponding overpotential is 82 m V and 309 m V at the current density of 10 m A cm^-2,which is superior to Co P/Co₂P nanotube and Co P/Co₂P nanoparticles.Based on the bi-functional catalytic properties of the Mn-doped Co P/Co₂P hollow nanotube,its full hydrolysis performance was studied.The experimental results show that the prepared material has good hydrolysis performance,and the corresponding voltage is 1.67 V at the current density of 10 m A cm^-2,and it maintains excellent stability within 50 h.In this paper,a series of co-based hollow nanotubes were successfully prepared based on the template-free method combined with structural design and composition control.Due to the reasonable design of structure and composition,the prepared co-based hollow nanotube exhibits excellent catalytic activity and cyclic stability in water electrolysis reaction.This paper provides feasible ideas and schemes for the design and preparation of efficient,stable and low-cost non-noble metal electrolysis water catalyst.