Oxygen evolution reaction on electrolytic nickel-based composite coatings in an alkaline solution
Magdalena Popczyk, Antoni Budniok University of Silesia, Institute of Materials Science, Bankowa 12, 40-007 Katowice, Poland
Quarterly No. 4, 2008 pages 397-402
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abstract Ni+W+Si and Ni+W+Mo+Si composite coatings were obtained by electrodeposition of crystalline nickel from an electrolyte containing suspension of suitable metallic and non-metallic components (W, Mo and Si). These coatings were obtained under galvanostatic conditions, at the current density of jdep. = 0.100 A cm–2 and at the temperature of 338 K. For comparison the Ni coating was also obtained and investigated in the same manner. Obtained coatings were modified in the air atmosphere by thermal treatment at the temperature of 973 K during 1 hour. Thermal treatment of obtained coatings changes their phase composition. X-ray diffraction pattern showed that the Ni+W+Si coating is composed of three phase structures, i.e., nickel, tungsten and silicon. The phase composition for the Ni+W+Si coating after thermal treatment in the air is markedly different. The main peaks corresponding to the W coexist with the new ones corresponding to new phases: NiWO4 and two forms of SiO2. X-ray diffraction pattern showed that the Ni+W+Mo+Si coating is composed of four phase structures, i.e., nickel, tungsten, molybdenum and silicon. The phase composition for the Ni+W+Mo+Si coating after thermal treatment in the air is also markedly different. This may be concluded from the presence new peaks corresponding to new phases: NiWO4, NiMoO4 and SiO2. The phase composition for the Ni coating after thermal treatment in the air is different in comparison with Ni as-deposited coating. The main peaks corresponding to the Ni coexist with the new ones corresponding to new phase: NiO, what suggests that the nickel coating was also oxidized. The electrochemical activity of thermally treated coatings was studied in the process of oxygen evolution reaction (OER) from 5 M KOH solution using electrochemical impedance spectroscopy (EIS) method. It was found that Ni+W+Mo+Si composite coating after thermal treatment in the air is characterized by enhanced electrochemical activity towards oxygen evolution as compared with Ni+W+Si and Ni coatings after thermal treatment in the air. This coating to characterize least values of the logarithm impedance module log |Z|, phase angle , charge-transfer resistance Rct, and greatest values of double-layer capacitance Cdl. Thus obtained coating may be useful in application as electrode material for the oxygen evolution reaction. Keywords: composite coatings, oxygen evolution reaction (OER), electrochemical impedance spectroscopy (EIS)