Nickel and Nickel Hydroxide synergism in Alkaline HER as the Non Nobel Metal Nanoparticles Decorated on the Reduced Graphite Oxide

The development of clean electrochemical energy conversion technologies such as fuel cells and electrolyzers is considered for both of high performance and cost effective properties. Therefore, many attempts have noticed to replace Pt group metals by non-noble ones such as nickel, cobalt and etcetera. For this purpose, it is necessary to improve non noble metals catalytic activity by various methods such as development of supports, hybridization and alloying. In this work, a novel catalyst was synthesized by hybridization of nickel and nickel hydroxide on the reduced graphite oxide (Ni-3Ni(OH)2. 2H2O /rG) via a facile and cost effective glycerol mediated solvothermal procedure. The catalyst was evaluated toward the hydrogen evolution reaction (HER) and compared with Ni-rG and 3Ni(OH)2, 2H2O/rG which had been synthesized with the same method. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR) techniques. After that, the catalysts were investigated for HER activity by using a conventional three-electrode electrochemical cell in alkaline media. Fig. 1 shows the XRD patterns of the samples at three furnace temperatures. Interpretation of results clearly showed that by increasing the furnace temperature, nickel characteristic peaks appears at 2θ= 44.3, 51.7 and 76.2 ○ which were corresponded to (111), (200) and (220) planes of cubic Ni (JCPDS 04-0850) [1]. The HER activities of three catalysts were investigated in KOH (1 M) solution. As shown in Fig. 2, Ni-3Ni(OH)2. 2H2O /rG shows the highest electrocatalytic activity compared with others due to synergetic effect between nickel and nickel hydroxide. The edges of Ni(OH)2 participate in dissociative adsorption of water and the production of hydrogen and hydroxyl intermediates [2]. Then, hydrogen adsorption and recombination into H2 on the nearby Ni sites would be take place. For this reason, lowest tafel slope (b), onset overpotential (ηonset), η10 (overpotential at 10 mA cm-2) and η50 as well as highest exchange current density (j0) were obtained for Ni-3Ni(OH)2. 2H2O /rG. 39 Figure 1. XRD patterns of (a) 3Ni(OH)2. 2H2O/rG, (b) Ni-3Ni(OH)2. 2H2O /rG and (c) Ni/rG Figure 2. LSV of HER curves for the samples in 1 M KOH at 298 K with a scan rate of 5 mV s−1.