Phase transformations in CoZnO/CoZn nanostructures depending on the difference in applied potentials

https://doi.org/10.1016/j.surfcoat.2020.125495Get rights and content

Highlights

  • Zn – Hexagonal/ZnCo2O4 – spinel → Zn – Hexagonal/Co2.34Zn10.63 → Co– Hexagonal/Co2.34Zn10.63

  • CoZnO/CoZn -type structures

  • Results of the assessment of crystallographic characteristics

  • Diagram of phase transformations in CoZnO nanostructures

Abstract

The dynamics of phase transformations in CoZnO/CoZn nanostructures of the Zn – Hexagonal/ZnCo2O4 – spinel → Zn – Hexagonal/Co2.34Zn10.63 → Co– Hexagonal/Co2.34Zn10.63 type depending on the difference of the applied potentials is presented. As a production method, the method of electrochemical synthesis was used, in which polymer track membranes with pore diameters of 400 nm and a length of 12 μm were used as templates. The study found that at small potential differences (1.25–1.75 V), the presence of oxygen is observed in the structure of nanowires, which is introduced into the crystalline structure during the synthesis. In this case, an increase in the difference in the applied potentials above 1.75 V leads to an increase in the cobalt concentration in the structure of the nanowires accompanied by the displacement of oxygen and the formation of the Co/Zn structure with a stoichiometric ratio of 1:1. It was found that all the nanostructures under study during the life tests of the applicability of these nanostructures as cathode materials of lithium-ion batteries retained their operability after 400 cycles of life tests, which indicates their high resistance to degradation. Moreover, for samples containing a high concentration of cobalt in the structure, the lifetime reaches more than 800 cycles, which is explained by the high stability of these nanostructures to degradation processes.

Introduction

One of the promising materials among the entire variety of nano- and microstructures obtained today by various synthesis methods are tetrahedral binary compounds of the type AIIBVI – AIIIBV with both semiconductor and magnetic properties if one of the elements is magnetic [[1], [2], [3]]. Interest in these types of compounds is due to the wide range of their application in various microelectronic applications, catalysis, as sources of nutrition and storage, as well as many others. Of the greatest interest among these compounds are structures based on cobalt, zinc, their compounds or various oxide forms [[4], [5], [6], [7], [8], [9], [10]]. CoZnO/CoZn -type structures have good mechanical properties, such as strength, resistance to external influences, optical properties, which are due to the presence of a wide forbidden zone of zinc oxide, chemical stability and lack of toxicity, magnetic and conductive properties, which are due to the presence in the structure of cobalt having high magnetization and coercive force [[11], [12], [13], [14], [15]]. As a rule, such structures are obtained by the sol-gel method or by the chemical method, which make it possible to obtain various kinds of nano- and microparticles with unique properties. It should be noted that, as a rule, the obtained nanostructures are CoZnO oxide compounds with a low percentage of cobalt not exceeding 5–10 at.% [[16], [17], [18]]. Moreover, there are not so many works devoted to the preparation of cylindrical structures in the form of nanowires or nanotubes, which indicates the difficulty of obtaining structures of a similar geometry [19,20]. One of the methods for producing cylindrical nano- and microstructures is the electrochemical synthesis of nanostructures using various porous matrices as templates [[21], [22], [23], [24], [25]]. The application of these methods allows one to obtain nano- and microstructures of cylindrical or conical geometry with a large aspect ratio of 100 to 1000, as well as diameters of 50 nm to 1 μm. Moreover, the structures synthesized by these methods have a good degree of crystallinity, high strength properties, etc. [[22], [23], [24], [25], [26], [27], [28]]. Control of the formation process of nano- or microstructures are usually performed via chronoamperogramm, allowing precise control of the process of filling the pores in the template that gives the possibility of obtaining different heights structures [29,30]. In turn, changes in the synthesis conditions, such as the difference in the applied potentials during deposition, the temperature of the electrolyte solution, and the acidity of the solution, have a significant effect on the structural properties and phase composition of the synthesized nano- or microstructures [31,32]. By changing the synthesis conditions, one can obtain both oxide forms and structures with different content of elements in the structure, leading to a change in the phase composition of the synthesized objects. Moreover, among the variety of various nano- and micromaterials, oxide structures with both magnetic and electrical properties occupy a leading role among other materials [[33], [34], [35], [36]]. Interest in them is due to the huge prospects of their application both in microelectronics, where such values as conductivity, magnetization, coercivity, and as various catalysts or sensors play a particularly important role [[37], [38], [39], [40], [41], [42], [43], [44], [45]].

Based on the foregoing, it is of interest to study the possibility of controlling the phase composition of CoZnO/CoZn nanostructures by changing the difference in applied potentials during electrochemical synthesis of nanostructures. Polymeric track membranes based on polyethylene terephthalate, which have proven themselves as templates for the synthesis of nanostructured materials, were used as templates for the synthesis.

Section snippets

Experimental part

Scheme 1 presents the experimental conditions and research methods.

Results and discussions

Unlike other synthesis methods, the electrochemical synthesis method allows one to obtain nanostructured and microstructural materials not only of a well crystallized phase with high strength and conductive properties, but also by changing the difference in applied potentials to change the phase composition of the synthesized nanostructures, which plays a significant role in changing the properties of materials. A change in the phase composition due to an increase or decrease in the difference

Conclusion

The paper considers the processes of phase transformations in CoZnO/CoZn nanostructures depending on the difference in applied potentials during the electrochemical synthesis of nanostructures. The resulting nanostructures are polycrystalline nanowires whose phase composition varies according to the Zn – Hexagonal/ZnCo2O4 – spinel → Zn – Hexagonal/Co2.34Zn10.63 → Co– Hexagonal/Co2.34Zn10.63 scheme depending on the synthesis conditions. The study found that at small potential differences

Funding

This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (No. BR05235921).

CRediT authorship contribution statement

K.K. Kadyrzhanov: Conceptualization, Funding acquisition, Project administration, Resources, Supervision, Writing - original draft, Writing - review & editing. A. Zikirina: Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing - original draft, Writing - review & editing. K. Egizbek: Data curation, Formal analysis, Investigation, Methodology, Software, Validation, Visualization, Writing - original draft, Writing - review & editing. A.L.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. We have to note that this manuscript is original, and not being or having been submitted for publication to other journals.

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