Electrocatalysis of Ethanol Oxidation on Doped Octahedral Molecular Sieves of Manganese G. Sokolsky, S. Ivanov, T. Lobunets † , M. Demchenko, N. Ivanova 1 , T.Tomila † , O. Kobylinskaya National Aviation University, Cosmonaut Komarov Avenue 1, 04058 Kiev 58, Ukraine 1 Institute of General and Inorganic Chemistry of Ukrainian National Academy of Science, Palladin Avenue 32-34, 252680 Kiev 142, Ukraine † Institute for Materials Sciences Problems of Ukrainian National Academy of Science, 9 Krzyzanovsky Str. 3, 252142 Kiev 180, Ukraine Introduction The development of the direct methanol fuel cell (DMFC) has been a significant progress over the past decade. Manganese dioxide polymorphs including octahedral molecular sieves (OMS) of manganese with n×m edge-shared MnO6 octahedral chains that form one-dimensional tunnels is shown to be relatively cheap and promising alternatives to noble metals electrode materials in DMFC [1] as well as an active catalysts of oxidation of organic compounds [2]. Electrodeposition from fluoride containing electrolytes is a prospective method of nanomaterials preparation at high rate [3]. Dopant-ions can be the templates of the OMS’s tunnel size stabilisation during electrosynthesis. The aim of this study was to investigate electrocatalytic properties of OMS electrodeposited at the presence of dopants. Experimental The series of doped OMS samples was electrodeposited on a Pt anode in 0.2 M HF and 0.7 M MnSO4 containing 0.001–0.17 mole∙L -1 MOH (Li, Na, K, NH4 + ) or MSO4 (Fe 2+ , Co 2+ ) at a current density i = 0.1–10 A∙dm -2 . Powdered samples precipitated at the bottom of an electrolytic bath or film electrodes can be prepared depending on the current density value. Chemical analysis, XRD, TGA, FTIR, SEM data were the methods of samples characterisation. Surface area and the pore sizes were measured by a Quantachrome ASAP 2000M Micrometric Sorptometer. Manganese oxide film electrodes were used to study electrocatalytic properties in 2.5 mole∙L -1 H2SO4, 1.0 mole∙L -1 C2H5OH electrolyte. In this case, manganese dioxide films were electrodeposited galvanostatically onto the stainless steel of 1Cr18Ni10Тi grade from electrolytes indicated above. Results and Discussion Pore structure and surface area analysis of powdered samples obtained at 10 A∙dm -2 was made. Materials under study have developed surface within the range 100-200 m 2 /g. Figure 1 shows the micropores distribution in some electrodeposited samples. It can be seen that alkali-metal ions (curves 2-3) are the templates of OMS-2 (α-MnO2) channels stabilisation with tunnel size 0.46 nm unlike transition metal ions (for instance, Co 2+ , curve 4). On the other hand, manganese dioxide obtained without additives contains also significant number of OMS-2 2×2 one-dimensional tunnels that exceeds that one of doped sample with lithium. However, XRD- patterns of undoped sample are close to ramsdellite structure of γ - MnO2. Electrochemical behavior of manganese oxide film electrodes has been studied by voltammetry. Figure 2 shows Tafel plot η-logi of anode process on stainless steel 1Cr18Ni10Тi grade (1), Pt (2), undoped and doped by Na + MnO2.(3-4, respectively). The current densities of oxidation process of OMS anodes are by several orders of magnitude larger comparing with stainless steel and Pt anodes. In turn, doped OMS anodes reveal larger current density than undoped one. Figure 1. Differential distribution of micropores of undoped manganese dioxide sample (curve 1), doped by Li + (2); NH4 + (3); Co 2+ (4) on their size in accordance with Horvath-Kawazoe theory -2 0 2 4 6 0 25 50 η , mV vs Ag + /Ag log i , mA/cm 2 2 3 4 1 Figure 2. Overvoltage η dependence on log i of anode oxidation of ethanol: 1 – 1Cr18Ni10Тi; 2 – Pt; 3 – MnO2; 4 – MnO2 doped by Na + Acknowledgement. Authors would like to thank the Ministry of Education and Science and National Aviation University in Ukraine for the financial support within grant No. 0108U004063. References (1) Rebello, P.; Samant, V.; Figueredo, J. L.; Fernandes, J. B. J. Power Sources, 2006, 153, 36. (2) Suib, S.L. Chem. Innovation, 2000, 30, 27. (3) Ivanova, N.D.; Ivanov, S.V. Russian Chem. Rev. 1993, 62, 907. Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2010, 55 (1), xxxx View publication stats View publication stats