Ni_xMo_y alloy/Graphitic Carbon Nitride(g-C₃N₄) Composites for Hydrogen Evolution Reaction in Alkaline Electrolyte

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 H₂ and O₂ 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_xMo_y alloy/g-C₃N₄ 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-C₃N₄ composites. Firstly, melamine was polymerized at 550°C, and the yellow product of g-C₃N₄ was fabricated. Secondly, nickel and molybdenum precursors are dispersed into diethylene glycol, DI water, and ammonium hydroxide to synthesize Ni_xMo_yO_z and then reduced at 400°C in Ar-H₂ gas atmosphere to obtain Ni_xMo_y alloy/g-C₃N₄ composites. The result showed that the 5-10 nm Ni₄Mo alloy particles were distributed randomly in the surface of sheet-like g-C₃N₄ forming which the (121), (310), and (312) planes of Ni₄Mo were investigated by high-resolution TEM. In NBED and XRD, we found the preferred orientation was (121) of Ni₄Mo. The electrochemical results showed that the overpotential at -10 mA/cm² of Ni₄Mo alloy/g-C₃N₄ is 462 mV and the Tafel slope is 95 mV/dec. According to the above result, the Ni₄Mo has active sites for HER. In (121) of Ni₄Mo, there are Ni atoms and Mo atoms and therefore we presumed that the Ni atoms are the dissociation sites for H₂O 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-C₃N₄ 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.