Molybdenum Carbides Supported By Nitrogen-Doped Carbon As Electrocatalysts For Hydrogen Evolution Reaction

Hydrogen is an important new energy. Hydrogen has high combustion efficiency, and its product is water. Moreover, hydrogen is an ideal renewable energy carrier, which can store the other forms of energy into chemical bond. Electrolysis of water is an important method of hydrogen production with advantages of high efficiency and highly pure hydrogen. However, the hydrogen evolution reaction(HER) often requires large overpotentials and suffers, high energy consumption, departing from the development of new energy. Although, the noble metals, in particular, platinum, can efficiently catalyze HER, the high price and limited resource of noble metals severely prohibit their utilization. Developing effective electrocatalysts with low cost and high abundance still remains urgent. In this thesis, we synthesize the metals and metal carbides supported by nitrogen-doped carbon as electrocatalysts for hydrogen evolution reaction. In this material, nitrogen doping will improve the dispersion of active material, enhance the electronic conductivity, and thereby optimize the HER activity. The main content of the article is as follows:1. Molybdenum carbide supported by nitrogen-doped carbon was achieveed via the hydrothermal preparation of MoOx/polysaccharide from glucose, melamine and ammonium molybdate, which further evolved to MoCx/CN evenly integrating nanoparticles with conducting carbon nitride after carbonization. This work demonstrated that the simple synthetic method can control catalytic performance by alter the amount of the melamine. Meanwhile, the MoCx/CN exhibited an excellent activity for HER with a high current density of 72 mA cm-2 at η = 300 mV, which was significantly higher than the unsupported molybdenum carbide catalyst, as well as the related catalysts reported in literatures.2. Molybdenum carbide supported by nitrogen-doped carbon were fabricated through the pyrolysis of melamine and ammonium molybdate ground mixture. By low temperature(400 oC) heat treatment, followed by high temperature roasting, the active electrocatalyst was acquired. When the overpotential is 300 mV, it obtained a current density of 55 mA cm-2. Additionally, we induced carbon nanotube(CNT) into ground mixture to further improve the dispersity and electronic conductivity which favored the HER.3. Metal cobalt nanoparticles embedded in nitrogen doped carbon catalyst were synthesized through the pyrolysis of cobalt and cyanamide hybrids. By the characterization of SEM, TEM and XRD, the structure of the materials and synthetic regulations were investigated. Electrochemical tests found that the catalyst activity was low, owing to CN_x can’t encapsulate the metal cobalt that was washed by acid.4. We preliminarily explored the synthesis of CN_x from glucose and melamine, and studied the morphology variation and electrocatalytic performance. It was found that a few of platinum dissolved in the electrolyte when it served as counter electrode LSV test. Subsequently, platinum depositing on CN_x presented the high activity for HER. This finding on one hand, provides a new method for the preparation of highly active, low load of platinum-based catalyst; on the other hand, indicate that precious metals should aviod as the counter electrode in the electrochemical test of non-noble metal catalyst, and graphite rod is an alternative.