Sol-gel preparation and electrocatalytic properties of RuO2 for oxygen evolution reaction in alkaline water electrolysis

Electrochemically splitting water into oxygen, electrons and protons occurs at the anode. The protons transfer to the cathode, to be reduced to molecular hydrogen which is noteworthy today as a carbon-free renewable energy carrier [1]. Alkaline water electrolysis is proposed as a harmless and reliable technology. Currently, it is well-known the overpotential of anodic oxygen evolution reaction (OER) depends on the catalyst components [2]. RuO2 as efficient and stable OER catalyst displays an exchange current density comparable to Pt, but much lower cost [3, 4]. In this work, we report a sol-gel synthesis method of ruthenium oxides in alcoholic medium followed by thermal decomposition of polymeric precursors that allows to minimize final price. We used nickel sheets as the coating bases. The nickel sheets were first polished completely and were degreased with caustic soda, hydrochloric acid, and finally, acetone. The sol-gel method was used for coating the bases. For this purpose, a suspension of RuCl2.xH2O and isopropyl or isobutyl alcohols precursors was made as the sol solution. Also, to study the effect of nickel ion, NiCl2.6H2O was added simultaneously. For covering the nickel sheets by sol suspension, the method of immersion-drying was used. Coated specimens were transferred to the furnace at 350 °C for thermal treatment. The immersion-drying steps followed by thermal curing were repeated 8 times. Finally, the sample was heated to 400 °C for 30 minutes. The voltammetric techniques were used to survey the efficiency and compare the results of the prepared prototypes. The cyclic and linear sweep voltmetery was performed using an Autolab potentiostat-galvanostat with a scanning rate of 10 mV/s in a three electrodes setup consisting of the prepared working electrode, platinum rod as the auxiliary electrode and Ag/AgCl reference electrode in the presence of 1 M KOH electrolyte. Working electrode 13th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 22- 23 Nov, 2017 243 were possessed the surface area of 0.5 cm2 coating. The material specification of coating specimens is shown in Table 1. Figure 1 compares the obtained results. It can be seen that the sol-gel coatings of ruthenium oxide improve significantly the catalytic properties of oxygen production in OER than bare nickel. Ruthenium metal is expected to be much more active in terms of chemical activity, having the overpotential to be less. Therefore, the presence of ruthenium and nickel depletion in coatings leads to lower onset potentials and larger TOEFL slopes. On the other hand, the catalytic activity of the anode is limited by the excessive increase in ruthenium ratio in the coating content. This proves that metal/metal oxide nature and composition of composite coating is very important in the catalytic activity of the anode. Also, the addition of nickel ions to sol suspension is accompanied by a decrease in the TOEFL slopes, which confirms the weaker catalytic ability of nickel oxides for the OER. However, optimizing the amount of nickel salt in the coating layer can significantly reduce the cost of production. Table 1- material specification of coating specimens. Figure 1. Cyclic voltamograms of specimens.