211 Effect of treatment temperature on electrocatalytic activity of manganese/ ruthenium mixed oxide composites for oxygen evolution reaction

Recently, development of efficient catalysts toward OER has been a challenging task. Oxygen evolution occurs on noble metal catalysts but noble metal oxides such as RuO2 are generally more active electrocatalysts [1]. The synergic effect of two elements in the mixed oxide has been studied to obtain the more stable and low-cost efficient catalysts [2, 3]. The most stable anode electrodes are prepared by thermal decomposition of metal precursors deposited on titanium substrates [4]. In this work, we prepared manganese-Ruthenium composites by the method of thermal decomposition and were surveyed the Effect of treatment temperature on electrocatalytic activity of OER over three annealing temperatures. Titanium sheets which were used as coating bases, first were polished and were degreased with caustic soda, hydrochloric acid, and finally, with acetone. In order to investigate the effect of manganese ratio on the catalytic properties of ruthenium coating, six different manganese-ruthenium weights were prepared from MnCl2.6H2O and RuCl3.xH2O, according to table 1. Also, isobutyl alcohol was used to investigate the effect of alcohol in sol-gel method. After the heating process, the thickened solution was applied to coating titanium electrode samples by repeated immersion-drying method. Finally, the surface oxidation by heat treatment was performed in a temperature-controlled furnace at a temperature of 350, 450 and 600 °C for nine hours. The voltammetry techniques were used to survey the efficiency and compare the results of the prepared prototypes. A conventional three electrode setup consisting of the prepared working electrode, Ag/AgCl reference electrode and Pt rod as the counter electrode in the 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 212 presence of 1 M KOH electrolyte. The material specification of coating specimens is shown in Table 1. As an example, the cyclic voltammograms of specimens with different ratio of Mn/Ru were compared in Figure 1. It is clear that the catalysts containing %100 Mn have high overpotential than the rest of the catalysts. Adding Ru reduces this gradually. It can be concluded that the addition of ruthenium ratio increases catalyst activity. However, the low price of manganese against ruthenium suggests that the optimum Mn:Ru ratio is 50:50, which does not show significant difference compared with 25:75 ratio. Furthermore, the addition of alcohol to a sol-gel solution increases the performance of the catalyst. The results of temperature test in thermal treatment also shows that ascending the temperature of oxidation increases the overpotential and the TOEFL gradient and consequently the catalytic activity decreases. This is related to different compositions of manganese oxides (MnxOy). SEM images confirm the effect of temperature and the ratio of Mn/Ru in surface layout on catalytic efficiency. It can be seen outstanding changes in surface morphology consist of abundant cracking and roughness at oxidation temperatures of 450 and especially 600 °C. Table 1- material specification of coating specimens in a certain annealing temperature. Figure 1. Cyclic voltamograms of specimens at 350 °C.