Design And Synthesis Of Ru-Based Nanomaterials And Study On Their Performance Of Electrocatalytic Hydrogen Evolution Reaction

Hydrogen,as an environmental-benign,sustainable energy carrier with carbonfree content,has been considered a promising star for new energy development.Electrochemical water splitting is a commercial recognized approach for hydrogen generation.However,it is limited by the sluggish kinetics and the large overpotential for Hydrogen evolution reaction（HER）.Therefore,highly efficient electrocatalysts are required to reduce the overpotential and accelerate the electrocatalytic reaction.Platinum,a precious metal,has been considered as the best catalyst for hydrogen evolution reaction due to its low overpotential and fast reaction kinetics.Nonetheless,the scarcity and high expense greatly impede its application as catalytic materials.Ruthenium,a precious metal,is far less expensive than Pt,but has similar hydrogen bond strength as Pt and excellent durability,and can neglect the energy barrier of water dissociation,is considered an ideal alternative to Pt.In this thesis,Ruthenium-based electrocatalysts with different nanostructures and electronic properties were rationally engineered by green and facile synthesis methods to improve the HER performance of the catalysts.The relationship between the structure,electronic properties and catalytic activity of the composites was also analyzed by electrochemical tests and various characterization methods.The principal cotents of the thesis are discussed as follows:Ni₃S₂ nanorod arrays were decorated with Ru nanoparticles through an in-situ reduction method.The obtained Ru@Ni₃S₂ demonstrates an enhanced electrocatalytic performance toward HER in alkaline media suggested by an overpotential of-19.8 mV to attain a current density of 10 mA cm^-2 and a Tafel slope of 33.2 mV dec^-1.Both the in-situ formed Ru nanoparticles and the adsorbed Ru³⁺ions are responsible for the electrocatalytic hydrogen evolution reaction.During the long-term stability test,the adsorbed Ru³⁺on Ni₃S₂ nanorod would be converted to Ru（OH）3,leading to the attenuated electrocatalytic activity.This drawback can be overcome by further surface modification with polyaniline（PANI）.The obtained PANI-Ru@Ni₃S₂ exhibits a comparable catalytic HER activity with Ru@Ni₃S₂ but an extraordinary stability with a continuous electrolysis at a current density of 20 mA cm^-2 for 35 hours.Three-dimensional MoO₂ nanosheets stacking structures decorated with Ru nanoparticles（Ru@MoO₂ NSS）were synthesized by hydrothermal impregnation and subsequent annealing process and used as highly efficient pH-universal catalysts toward hydrogen evolution reaction.During the synthesis process of Ru@MoO₂ NSS,the MoO₂ nanosheets were derived from a multilayer stacking structure formed by the layer-by-layer assembly of Ru³⁺ions and MoO₃ nanosheets,of which the nanosheets were the products of cracked nanotubes owing to the etching effect of RuCl₃.As a consequence of the unique structure evolution during the synthesis,the obtained Ru@MoO₂ NSS demonstrates a superb electrocatalytic activity toward HER in basic,acidic as well as neutral medias.To achieve a current density of 10 mA cm^-2,the required overpotentials are 11 mV in 1 M KOH,59 mV in 0.5 M H₂SO₄ and 41.23 mV in 1 M K-Bi solutions,respectively.In particular,Ru@MoO₂ NSS also shows an extraordinary long-term electrochemical stability in pH-universal electrolytes.DFT calculations indicate that the excellent electrocatalytic performance of Ru@MoO₂ NSS is mainly due to the synergistic effect between Ru and MoO₂ resulting in more favorable adsorption and desorption behavior of water molecules.Selenium-enriched RuSe₂（Ru_xSe）nanocrystals as efficient electrocatalysts for HER have been synthesized via a facile hydrothermal method followed by a calcination process.The catalytic activity of the obtained Ru_xSe nanocrystals in alkaline media is greatly dependent on the calcination temperatures.The nanocrystals obtained at 400℃（Ru_xSe-400）demonstrated a highest HER activity,providing a current density of 10 mA cm^-2 at a low overpotential of 45 mV and a corresponding Tafel slope of 31.4 mV dec^-1.Density functional theory（DFT）calculations reveal that the enhanced catalytic HER performance of Ru_xSe-400 could be attributed to the excessive Se on RuSe₂ nanocrystal surface,which could reduce the energy barrier for water dissociation as well as facilitate charge transfer.