| Physico-chemical justification of electrochemical synthesis of carbonaceous materials in molten salts. Inessa Novoselova1; 1INSTITUTE OF GENERAL AND INORGANIC CHEMISTRY, Kyiv, Ukraine; PAPER: 43/Molten/Regular (Oral) SCHEDULED: 12:35/Fri. 25 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: Carbon nanomaterials have been widely used in modern devices and high tech [1-2]. This is the reason why the obtaining of carbonaceous materials in molten salts has attracted great interest among researchers. Various carbon products such as carbon nanotubes, carbon nanofibers, carbon nanoparticles, and graphene have been successfully prepared in molten salts by electrochemical reduction processes [3-5]. This paper is devoted to the physicochemical substantiation of the choice of composition of the electrolytic bath and the electrode materials for the generation of carbon nanostructures of different morphologies from molten salts, based on the thermodynamic calculation of the decomposition voltages of various carbonates and analysis of the metal - carbon, and metal carbide - carbon state diagrams. An analysis of the decomposition voltages of lithium, sodium, potassium, calcium, barium, and magnesium carbonates with different versions of cathode products (elemental carbon, carbon monoxide, metal and carbide) in the range of 300-1900 K have showed that for K2CO3 deposition of alkali metals on the cathode is a most energetically profitable process at all temperatures. For Na2CO3, it is possible to obtain carbon at T < 1000 K. With temperature increase, the predominant process is the reduction of alkali metals. For Li2CO3, CaCO3, BaCO3, and MgCO3 at T < 950 K, carbon deposition will be more advantageous at higher temperatures including reduction up to CO. The decomposition of CO2 flows at more positive potentials compared with carbonate systems. However, low activity of CO2 in carbonate-containing melts will prevent the significant contribution of this reaction to the electrode process. Thermodynamic calculations of the dependence of the carbon deposition potentials from carbonate anion on the acidity of the melt (concentration of oxide ions) show the possibility of displacing this potential up to 0.8 V. This can be done by changing the acid-base properties of the melt. On the basis of the analysis of binary phase diagrams of Me-C and MeC-C, criteria for selecting the cathode material for generation of the tubular structure of graphite are established. The diagrams should contain: (1) solid solutions of C-Me at a temperature of 700-900°C and sufficient solubility of carbon (up to ~ 1 at.%) in the metal should be observed; (2) after saturation of the solid solution with carbon, the precipitation of graphite from the metal should occur without the formation of intermediate carbide phases; (3) in the case of the formation of carbides, the diffusion of carbon in the solid С-Ме solution, and in the MeС carbide phase should flow with high speed and quickly reach the concentration of carbon saturation for graphite deposition. References: [1] C. Liu, F. Li, L.P. Ma, H.M. Cheng, Adv.Mater. 22 (2010) E28-E62. [2] S.L. Candelaria, Y. Shao, W. Zhou, X. Li, J. Xiao, J.G. Zhang, Y. Wang, J. Liu, J. Li, G. Cao, Nano Energy 1 (2012) 195-220. [3] C. Schwandt, A.T. Dimitrov, D.J. Fray, Carbon 50 (2012) 1311-1315. [4] I.A. Novoselova, N.F. Oliinyk, S.V. Volkov, A.A. Konchits, I.B. Yanchuk, V.S. Yefanov, S.P. Kolesnik, M.V. Karpets, Phys. E Low-dimen. Syst. Nanostruct. 40 (2008) 2231-2237. [5] I.A. Novoselova, S.V. Kuleshov, S.V. Volkov, V.N. Bykov, Electrochimica Acta 211 (2016) 343-355. |
