Synthesis Of Transition Metal Chalcogenides And Studies On Electrochemical Properties

With the energy crisis becoming more and more serious,the demand for clean and non-polluting renewable energy is becoming more and more urgent.Hydrogen energy is regarded as the most promising sustainable new energy in this century because of its high efficiency and zero emission.Electrolysis of water is one of the most effective methods to prepare high purity hydrogen.Electrolytic water catalyst materials are the core material of electrolytic water,and the activity,efficiency and cost of electrolytic water material are the important factors that restrict the commercialization process of electrolytic water.In this paper,with the aim of synthesizing high efficiency and low cost transition metal chalcogenides electrolytic water materials with excellent performance oxygen evolution and hydrogen evolution under strong alkaline conditions were synthesized by a simple one step hydrothermal method and cheap raw materials.The relationship between the structure of the electrocatalyst and its electrochemical performance as well as the formation mechanism of the catalyst material are further explained by using different raw materials,temperature and density functional theory?DFT?.This provides a new idea for the synthesis of new non-precious metal sulfur compounds.A phase-pure pentlandite Ni_4.3Co_4.7S₈ bifunctional electrocatalyst with efficient performance was synthesized via a hydrothermal process using commercial nickel foam as nickel source.The active metallic nickel sources,ionic cobalt source and chelating agent ethylenediamine play important roles in the formation of intermediate of phase-pure pentlandite Ni_4.3Co_4.7S₈ binary sulfide.The Ni_4.3Co_4.7S₈ electrocatalyst shows the lowest over-potential of 133.8 mV at 20 mA cm^–22 for OER and the over-potential of HER is 148.0mV at the current density of 10 mA cm^–2,furthermore the water splitting achieved 50 mA cm^-22 that the cell voltage was only 1.67 V.DFT calculations demonstrate that the high electrocatalytic activity of the phase-pure pentlandite Ni_4.3Co_4.7S₈ electrocatalyst for both OER and HER should be ascribed to the large molecular cluster structure and exposed?0-22?,?111?surfaces,possessing next-neighbor metal-metal bonds suitable for adsorption/desorption of reactants,intermediates and products.High surface area and rich terrace/edge defects offer high density of active sites for electrocatalytic reactions,endowing the high catalytic activity for both OER and HER.High DOS overlap on Fermi level,elevation of d-band center and high occupation of anti-bonding e_g d-orbitals,all of which are derived from the large molecular cluster structure and the synergistic effect between Ni ions and Co ions,should be the intrinsic reasons for the high electrocatalytic activity of the phase-pure pentlandite Ni_4.3Co_4.7S₈ electrocatalyst.Then,ultrathin?¹ nm?NiSe₂ and CoSe₂ nanosheets were synthesized in a facile hydrothermal process via the reduction of nickel,cobalt and selenium precursors.In order to further understand the formation mechanism of the monolayer NiSe₂ and CoSe₂,temperature-dependent morphology evolution experiment was carried out,the structure of nanosheets of them not only provide specific surface area and facilitate electron transport,so NiSe₂ and CoSe₂ exhibit excellent performance of oxygen evolution and hydrogen evolution.In addition,physical characterization?XPS et al?demonstrate that the formation of metal oxides has an important effect on the activity of the catalyst and metal atoms play an active role in the metal selenides.