Synthesis Of Transition Metal Based Electrocatalysts For Hydrogen Evolution Reaction

The increasing demand for energy and diminishing natural energy resources have led to a revolutionary era of discovering earth-abundant energy alternatives and designing efficient energy-storage devices. Hydrogen(H2) plays an important role in the energy sector. It is not only one of the most important feedstocks for the production of hydrocarbon fuels and chemicals, but also considered to be an ideal energy carrier for the renewable energy storage due to its high energy density and environmental friendliness, and hydrogen has been considered to be a promising energy source and a alternative for fossil fuel. Today, hydrogen manufacturing still mainly depends on the fossil fuel industry and suffers from low purity and high cost. One of the most efficient ways of producing H2 at low cost and high purity is water splitting into hydrogen and oxygen by electricity or sunlight. Electrocatalytic hydrogen evolution reaction(HER),as an important half-cell reaction involved in water splitting, is known as an efficient method for large-scale hydrogen production, and in this electrochemical process,efficient and low-cost electrocatalysts are indispensable. Pt-based materials are the best acid-stable HER catalysts, their wide use is hindered by their high cost and limited resources. Recent advances have revealed that nanostructured transition metal would be promising alternatives to Pt for the electrochemical generation of hydrogen from water.Therefore, it is of great importance to develop earth abundant, inexpensive and efficient non-precious metal HER catalysts. In this thesis, we mainly focused on the preparation of transition metals and their applications as electrocatalysts toward the HER. The main points of the thesis are addressed as follows:1. We developed a facile way to the in-situ growth of tungsten oxide(WO3) nanorods array on carbon cloth(WO3 NA/CC), the tungsten nitride nanorods array on carbon cloth(WN NA/CC) was prepared through the nitridation of corresponding WO3 NA/CC precursor with NH3. The use of the conductive CC as the substrates can not only increase the electronic transmission performance but also increase the contact area of WN NA and electrolyte and it is thus that more active sites were exposed. On the other hand, the good mechanical properties and thermostability of the WN promote the stability during the HER process. Therefore, as an integrated 3D non-noble-metal HER cathode, the WN NA/CC shows high catalytic activity and strong stability at all p H values. It needs overpotential of 198 m V to achieve current density of 10 m A/cm~2 and it maintains its catalytic activity for at least 60 h. Our present study would open up new avenues to explore the design of nanostructured electrode materials of transition metal nitrides.2. We prepared the molybdenum sulfide nanosheet arrays on Ti plate(Mo S2 NAs/Ti)via one-step low-temperature hydrothermal reaction as an integrated 3D hydrogen-evolving cathode. Acidic treatment produces Ti plate shows pore walls with micrometer-scale roughness and the direct growth on the 3D substrate promotes the electronic transmission and exposes more active sites. Besides, the metallic Ti can also ensures good mechanical adhesion. As novel HER electrocatalysts, the Mo S2 NAs/Ti shows superior activity as compared to the microparticles consisting of Mo S2nanosheets(Mo S2 MPs) in overall p H electrolytes. This electrode exhibits high catalytic activity in acidic media, displaying 10 and 100 m A/cm~2 at overpotentials of 108 and205 m V, respectively, and it operates stably within 55 h of operation. This facile synthesis process allows cost-effective preparation of other nanomaterials.