Yu-Chin Shen1,Jow-Lay Huang1,Sheng-Chang Wang2,Yu-Min Shen1
National Cheng Kung University1,Southern Taiwan University of Science and Technology2
Yu-Chin Shen1,Jow-Lay Huang1,Sheng-Chang Wang2,Yu-Min Shen1
National Cheng Kung University1,Southern Taiwan University of Science and Technology2
Hydrogen energy is regarded as the most promising renewable and clean energy to replace the fossil energy. The noble metals (i.e. Pt, Ru, Ir) were widely utilized to split the water into H<sub>2</sub> and O<sub>2</sub> due to the low Gibbs free energy, however, the high cost and limited availability hinder the commercialization. Recently, transition-metal-based catalysts were developed and achieved good performance and attracted a lot of attention from many research groups. Although these materials have high abundance, they have poor anti-acid corrosion. The cost and instability of catalysts limited the widespread applications in future. Hence, we study HER (hydrogen evolution reaction) in alkaline electrolytes to develop highly efficient and durable electrocatalysts in alkaline electrolytes. Graphitic carbon nitride has been studied intensively, but, it has poor conductivity and few active sites for HER. Therefore, we synthesized Ni<sub>x</sub>Mo<sub>y</sub> alloy/g-C<sub>3</sub>N<sub>4</sub> composites to replace the platinum electrode in 1.0 M KOH electrolyte in this study. A wet chemistry method and calcination were utilized to synthesize NixMoy alloy/g-C<sub>3</sub>N<sub>4</sub> composites. Firstly, melamine was polymerized at 550°C, and the yellow product of g-C<sub>3</sub>N<sub>4</sub> was fabricated. Secondly, nickel and molybdenum precursors are dispersed into diethylene glycol, DI water, and ammonium hydroxide to synthesize Ni<sub>x</sub>Mo<sub>y</sub>O<sub>z</sub> and then reduced at 400°C in Ar-H<sub>2</sub> gas atmosphere to obtain Ni<sub>x</sub>Mo<sub>y</sub> alloy/g-C<sub>3</sub>N<sub>4</sub> composites. The result showed that the 5-10 nm Ni<sub>4</sub>Mo alloy particles were distributed randomly in the surface of sheet-like g-C<sub>3</sub>N<sub>4</sub> forming which the (121), (310), and (312) planes of Ni<sub>4</sub>Mo were investigated by high-resolution TEM. In NBED and XRD, we found the preferred orientation was (121) of Ni<sub>4</sub>Mo. The electrochemical results showed that the overpotential at -10 mA/cm<sup>2</sup> of Ni<sub>4</sub>Mo alloy/g-C<sub>3</sub>N<sub>4</sub> is 462 mV and the Tafel slope is 95 mV/dec. According to the above result, the Ni<sub>4</sub>Mo has active sites for HER. In (121) of Ni<sub>4</sub>Mo, there are Ni atoms and Mo atoms and therefore we presumed that the Ni atoms are the dissociation sites for H<sub>2</sub>O and Mo atoms are the adsorption sites of hydrogen. In future, we will study the electrochemistry performance of different Ni/Mo ratios and alloy/g-C<sub>3</sub>N<sub>4</sub> ratio composites. Further, we will prove that Ni was the active site and Mo was the absorption site toward hydrogen by in-situ Raman spectroscopy. We will also investigate in-situ TEM for studying the transformation of electrocatalysts during HER.