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i i St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.1 Научно-технические ведомости СПбГПУ. Физико-математические науки. 15 (3.1) 2022
Conference materials UDC 544.6
DOI: https://doi.org/10.18721/JPM.153.139
Effect of thermal annealing on the composition of Ge-Co nanostructure obtained by electrochemical deposition
I. K. Martynova 1 I. M. Gavrilin 1
1 National Research University of Electronic Technology, Moscow, Russia H [email protected]
Abstract: Cobalt-based catalysts are one of the possible candidates for catalysts that accelerate the decomposition of water to produce energy. In this work, the one-dimension Ge-Co nanostructures have been prepared by electrochemical deposition in a three-electrode cell. The samples have been annealed in atmosphere at various temperature (300 °C, 450 °C, 600 °C). Effect of thermal annealing on the composition of Ge-Co nanostructure has been studied. The morphology of the obtained Ge-Co nanostructures has been investigated using scanning electron microscopy The method of X-ray diffraction analysis has been used to investigate composition changes of Ge-Co. Diffractograms show the presence of Co2GeO4 catalyst at an annealing temperature of 600 °C. The sample with this annealing temperature shows the best properties as oxygen evolution catalyst.
Keywords: Ge-Co nanostructures, oxygen evolution catalyst, Ge nanowires, electrochemical deposition
Funding: The work was supported by the Grant of the President of the Russian Federation no. МК 5839.2021.1.3 and by the State assignment 2020-2022 no. FSMR-2020-0018.
Citation: Martynova I. K., Gavrilin I. M., Effect of thermal annealing on the composition of Ge-Co nanostructure obtained by electrochemical deposition. St. Petersburg State Polytechnical University Journal. Physics and Mathematics. 15 (3.1) (2022) 232—236. DOI: https://doi. org/10.18721/JPM.153.139
This is an open access article under the CC BY-NC 4.0 license (https://creativecommons. org/licenses/by-nc/4.0/)
Материалы конференции УДК 544.6
DOI: https://doi.org/10.18721/JPM.153.139
Влияние термического отжига на фазовый состав наноструктуры Ge-Co, полученной методом электрохимического осаждения
И. К. Мартынова 1 н, И. М. Гаврилин 1
1 Национальный исследовательский университет «МИЭТ», г. Москва, Россия н [email protected]
Аннотация. В работе получены наноструктуры Ое-Со с помощью электрохимического осаждения. Исследовано влияние температурного отжига (300 °С, 450 °С, 600 °С) на фазовый состав этой структуры методом рентгеновского дифракционного анализа. Выявлено присутствие катализатора Со20е04 при температуре отжига в 600 °С. Образец при таком отжиге также показал наилучшие каталитические свойства.
Ключевые слова: наноструктуры Ое-Со, катализатор, нанонити Ое, электрохимическое осаждение
Финансирование: Исследование выполнено при поддержке гранта Президента Российской Федерации № МК 5839.2021.1.3 и Госзадания 2020-2022 № ФСМР-2020-0018.
© Martynova I. K., Gavrilin I. M., 2022. Published by Peter the Great St. Petersburg Polytechnic University.
Ссылка при цитировании: Мартынова И. К., Гаврилин И. М. Влияние термического отжига на фазовый состав наноструктуры Ое-Со, полученной методом электрохимического осаждения // Научно-технические ведомости СПбГПУ. Физико-математические науки. 2022. Т. 15. № 3.1. С. 232-236. БО1: https://doi.org/10.18721/ JPM.153.139
Статья открытого доступа, распространяемая по лицензии СС БУ-МС 4.0 (ИМ^:// creativecommons.Org/licenses/by-nc/4.0/)
Introduction
At present, due to the development of the global energy industry, there is a need to use clean and cheap fuel, including to reduce carbon dioxide emissions.
One of the ways to obtain ecological fuel is the electrolysis of water to produce hydrogen [1]. However, this process has a disadvantage, which is the slow reaction rate on conventional electrodes. To eliminate it, it is necessary to investigate various substances that accelerate electrochemical reactions, which are called catalysts. In this case, catalysts are needed for two processes on two electrodes: the hydrogen evolution reaction and the oxygen evolution reaction (OER). Oxygen evolution reaction (OER) is a limiting reaction in the process of generating molecular oxygen through chemical reaction, such as electrolysis of water into oxygen and hydrogen, and electrocatalytic oxygen evolution from oxides and oxoacids [2].
One of the promising areas of research on effective and stable oxygen evolution catalysts (OECs) are cobalt-based catalysts because of its OER activity and thermal stability [3]. There are many known methods for the synthesis of a cobalt-based catalysts, such as a method of selective reduction-oxidation from metal nitrates for getting cobalt catalyst doping Ag [4] or synthesis by chemical reduction followed by a process of thermal oxidation, which allows to obtain a compound of cobalt with rare-earth materials: ruthenium and iridium in powder form [5]. There are also such methods for obtaining cobalt-based catalysts as the sol-gel method [6] and vacuum-diffusion method [7] and electrochemical deposition [8]. The electrochemical deposition method is characterized by the absence of a high vacuum system, its speed and the ability to vary the parameters of the process to obtain various materials.
In this work, we report about formation OEC based on the one-dimension nanostructure Ge-Co by electrochemical deposition and investigate effect of thermal annealing on the composition of this structure.
Materials and Methods
In the syntesis of Ge-Co nanostucture the 50 ^m-thickness titanium foil (batch VT 1—00) has been used as a substrate. These titanium samples have been previously cleaned in a mixture of H2O2:NH4OH:H2O (1:1:4) at 80 °C for 15 min, and then they have been washed in hot and cold deionized water for 5 min and dried. Then the samples surface has been activated in a mixture of HF:HNO3:H2O (1:2:6), washed in deionized water and dried again.
After that an array of spherical indium nanoparticles has been deposited by vacuum-thermal evaporation at the residual pressure of 1 * 10-5 Torr of material weighed portion of 35 mg from a Mo evaporator, placed at 40 cm from the substrate. After depositing the metals, the samples have been annealed in vacuum at 150 °C for 10 min.
Ge-Co structures have been formed on the substrates by electrochemical deposition in a three-electrode cell. A platinum plate has been used as an counter electrode, and a standard silver chloride electrode has been used as a reference one.
The solution contained 0.05 M of germanium (IV) oxide GeO2, 0.5 M of potassium sulfate Na2SO4 and 0.1 M of tartaric acid with the addition of 0.05 g CoCl2. The solution pH has been brought to 6.5 by adding NH4OH. The solution temperature has been controlled using a LAUDA Alpha thermostat (LAUDA, Germany).
© Мартынова И. К., Гаврилин И. М., 2022. Издатель: Санкт-Петербургский политехнический университет Петра Великого.
^St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.1
a) b)
Fig. 1. SEM images of Ge-Co nanowires: sample without annealing (a), annealing 300 °C (b), annealing 450 °C (c), annealing 600 °C (d)
Deposition has been performed at constant voltage of —1.3 V for 1 min at the solution temperature of 85 °C. The voltage has been set using Autolab PGSTAT302N potentiostat/galvanostat (Metrohm, Netherlands).
After deposition, the samples have been annealed in atmosphere at various temperature (300 °C, 450 °C, 600 °C).
The method of X-ray diffraction analysis (XRD) has been used to deteminate the crystalline phases (germanium, cobalt, their oxides, etc.) after the formation of the Ge-Co compound and to investigate the effect of annealing at different temperatures on the composition of Ge-Co.
X-ray diffraction patterns (diffractograms) of synthesized samples have been obtained using the RADIAN DR-02 device with a copper X-ray tube and a nickel filter.
CV measurements have been performed by sweeping the potential from a value of 0.1 to 1.2 V (vs Ag/AgCl) using Autolab PGSTAT302N and a three-electrode system.
Results and Discussion
The images of the morphology of the Ge-Co structures both with annealing and without it obtained by scanning electron microscopy are shown in Fig.1.
According to the SEM images, a structural transformation of nanowires is observed in the annealing process. In the image of the sample without annealing (Fig. 1,a), some nanowires formations with a thickness of 250 nm can be seen, but the nanowires structures are not predominant. At 300 °C more nanowires appear, the thickness of which varies from 150 to 200 nm (Fig. 1,b). Annealing at 450 °C and 600 °C has a similar effect on the morphology of Ge-Co nanowires (Fig. 1, c, d). Nanowires become less visible, the thickness of nanowires decreases to about 100 nm. However after annealing at 600 °C it can be noticed more nanowires than that after annealing at 400 °C.
The results of X-ray diffraction after annealing germanium nanostructures with cobalt Ge-Co at various temperature are shown in Fig. 2. The sample without annealing has peaks of two phases: crystalline germanium and titanium substrate.
At annealing temperatures of 300 °C and 450 °C, there is an increase in the intensity of germanium peaks, especially the first peak (27.3°) [9]. With an increase in the annealing temperature, a slight shift of the germanium peaks to the right to the reference values is also noticeable.
However, at an annealing temperature of 600 °C, the diffractogram shows a presence of germanium-cobalt compounds in the nanostructure, particularly cobalt germanate Co2GeO4 at 20 = 30—40° [4], which has not been observed at lower annealing temperatures. A well-marked phase of titanium oxide and a certain amount of the compound Ti5Ge3 are also visible.
The first peak of germanium becomes indistinguishable due to the presence of titanium oxide, which leads to the overlap of two peaks and its sharp increase.
Fig. 2. X-ray diffractograms of Ge-Co samples after annealing at different temperatures
Fig. 3. CV curve of initial/annealing Ge-Co samples and titanium substrate
Additionally obtained Ge-Co samples after annealing and without it have been also tested for the OER activity in a solution of 1 M NaOH. Graphics of current density-voltage curve (CV curve) based on the results of the sample study are shown in Fig. 3. This figure also shows the CV curve of a pure titanium substrate obtained for comparison.
According to the graph of the titanium substrate, it can be seen that the current density almost does not change in the voltage range, which means that there are practically no electrochemical processes.
The current density for Ge-Co samples (except for the sample after annealing at 600°C) at a potential of 0.2 V to 0.5 V indicates reactions caused with the oxidation of germanium and cobalt. At a potential of 0.5 V, the current density increases due to the beginning of oxygen release. For a sample without annealing, the current density increases more slowly compared to annealing samples, which indicates its lower OER activity.
At the same time, with an annealing at 600 °C, reactions caused only with the release of oxygen are observed on the sample (the current density begins to increase only at a potential of 0.5 V) due to the presence of a cobalt germanate. It can be concluded that the annealing temperature at 600 °C is the most optimal temperature for the formation of an oxygen evolution catalyst based on Ge-Co nanostructure.
Conclusion
In the present work nanostructures Ge-Co have been prepared by electrodeposition from the aqueous solution. The effect of thermal annealing on the composition of Ge-Co has been investigated. According to the results of X-ray diffraction, with an increase in the annealing temperature, the crystal phase of germanium decreases and germanium compounds with cobalt are formed. On an annealing temperature at 600 °C, a compound cobalt germanate Co2GeO4 is found that could be a good oxygen evolution catalyst.
Acknowledgments
The "Educational and Methodical Center of Lithography and Microscopy", M.V. Lomonosov Moscow State University Research Facilities Sharing Centre was used.
St. Petersburg Polytechnic University Journal. Physics and Mathematics. 2022 Vol. 15, No. 3.1
REFERENCES
1. Chen X. L., Li C. N., Gratzel M. T., Kostecki R. M., Nanomaterials for renewable energy production and storage, Chemical Society Reviews. 41 (23) (2012) 7909—7937.
2. She Z.W., Kibsgaard J. K., Dickens C. F., Chorkendorff I. K., J.K., Combining theory and experiment in electrocatalysis: Insights into materials design, Science. 355 (6321) (2017) 1 12.
3. Zhe X. Y., Wenchao L. S., Xiaohui W. Z., Bing W. X., Novel Cobalt Germanium Hydroxide for Electrochemical Water Oxidation, ACS Applied Materials & Interfaces. 10 (36) (2018) 30357-30366.
4. Dong R. T., Du H. X., Sun Y. T, Huang K. W., Selective reduction-oxidation strategy to the conductivity-enhancing Ag-decorated Co-based 2D hydroxides as efficient electrocatalyst in oxygen evolution reaction, ACS Sustainable Chemistry & Engineering. 6 (10) (2018) 13420-13426.
5. Xue Z. H, Su H., Yu Q. Y., Wang H. H., Janus Co/CoP nanoparticles as efficient Mott-Schottky electrocatalysts for overall water splitting in wide PH range, Advanced Energy Materials. 7 (12) (2017) 16023-16034.
6. Su C., Wang W., Chen Y., Yang G., SrCo(0.9)Ti(0.100(3-5) as a new electrocatalyst for the oxygen evolution reaction in alkaline electrolyte with stable performance, ACS applied materials & interfaces. 7 (32) (2015) 17663-17670.
7. Corona-Guinto J.L., Carde^-Garcia L., Martнnez-Casillas D.C., Sandoval-Pineda J.M., Performance of a PEM electrolyzer using RulrCoOx electrocatalysts for the oxygen evolution electrode, International Journal of Hydrogen Energy. 38 (2013) 12667-12673.
8. Huang B., Wang Y., Zhan S., Ye J., One-step electrochemical deposition of Schifff base cobalt complex as effective water oxidation catalyst, Applied Surface Science. 396 (2017) 121-128.
9. Crystallography Open Database URL: http://www.crystallography.net/cod/. Accessed May 13, 2022.
THE AUTHORS
MARTYNOVA Irina K.
[email protected] ORCID: 0000-0002-6128-5244
GAVRILIN Ilya M.
[email protected] ORCID: 0000-0002-0278-1598
Received 22.05.2022. Approved after reviewing 04.07.2022. Accepted 04.07.2022.
© Peter the Great St. Petersburg Polytechnic University, 2022
