Controlled Synthesis Of Three-Dimensional Mo-based Sulfide And Performance Of Electrocatalytic Hydrogen Evolution

In the 21st century,the rapid development of the world economy has led to the excessive dependence and consumption of fossil energy,which leads to the continuous existence of energy shortage and environmental pollution.As a high energy density and sustainable clean energy,hydrogen energy is a potential solution to replace fossil energy in the future.Hydrogen evolution reaction(HER)from water electrolysis is an effective way of hydrogen energy generation and conversion.Two-dimensional(2D)MoS2 have been studied extensively due to their unique structure and extremely high surface area in HER.However,due to the fact that the unsaturated coordination S atoms mainly exist at the edge and rarely on the surface,the content of active sites is low.Furthermore,the catalytic activity of 2D MoS2 nanosheets was seriously affected.Hence,for MoS2,engineering structure design exposing more active sites is expected to significantly improve its HER performance.However,reasonable,and controllable modulation active sites are still very limited.Here,we started from the fact that molybdenum nanostructure catalysts have a variety of phase structures and polyvalence states,based on their unique physical and chemical properties,such as large specific surface area,easy surface modification and good near-infrared photothermal conversion efficiency.A three-dimensional(3D)monolithic Mo-based bimetallic electrocatalyst was designed and prepared to regulate the valence electron structure and improve the exposed active site,which provided an effective method for obtaining low-cost,stable,efficient and durable Mo-based HER electrocatalyst.The main contents are as follows:(1)The 3D Mo-Ni-S/NF spherical nanowires heterostructure electrocatalyst for overall water splitting.The Mo-Ni-S/NF spherical nanowire heterostructures were obtained by rapid cooling routs at low temperature to make more sulfur overflow from the surface of MoNiS nanosheet with partial nickel foam sulfide.Subsequently,the synthesized 3D Mo-Ni-S/NF catalyst in 1.0 M KOH solution has an overpotential of only 37 mV at 10 mA·cm-2,with a lower Tafel slope(52.5 mV·dec-1),and its catalytic performance is better than that of 10 wt%Pt/C catalyst.The over-potential of OER at 10 mA cm-2 is 170 mV,and the Tafel slope is also low(82.1 mV·dec-1),which is comparable to that of commercial RuO2(86.3 mV·dec-1).According to the calculation of density functional theory(DFT),replacing part of Ni atom with Mo atom can reduce the Gibbs free energy of free hydrogen adsorption in the reaction process,thus improving its HER performance.Mo-Ni-S/NF with different morphologies and structures can be prepared by adjusting cooling temperature and time.It can provide many active sites to improve the catalytic hydrogen generation,and then be used as a mechanical support carrier to adapt to the volume change.By controlling the cooling temperature and cooling time and the new method induced by molybdenum doping,the introduction of the second metal doping simultaneously promotes the overflow of more sulfur in the cooling process and produces a large number of sulfur edge defects,which further improves the performance of the catalyst,and can be widely used in catalyst modification.(2)Ni-MoS2/NF nanosheet catalyst for high-efficiency HER.Ni-MoS2/NF high activity non-noble metal HER catalyst was obtained by hydrothermal synthesis of spherical MoSv nanosheets as precursors after low temperature ultrasonic treatment.Ni and Mo interact with each other to form a stable nanosheet structure,and the thickness of precursor nanosheets can be controlled by changing the temperature of hydrothermal synthesis to obtain materials with stable structure and easy to peel.The intermetallic interaction between Ni and Mo and the generation of sulfur defects induced by the reduction of hydrazine hydrate can also adjust the electronic structure of the catalyst and improve the catalytic activity,which is better than the performance of 10%commercial Pt/C under high current.The methods of hydrazine hydrate reduction and transition metal adjustment of the structure and properties of catalysts can be widely used in the modification of other catalysts.In conclusion,this article is supported by nickel foam as the carrier and source of nickel,with seven ammonium molybdate tetrahydrate and thiourea molecular precursor,using hot water temperature rapid cooling,the structure of the synthesis of a series of different morphology integral transition of double metal molybdenum nickel sulfide catalysts,the spherical nanowires structure and the activity of nanometer structure can provide large line surface edge sites,the vacancy and fast rate of mass transfer for effective HER and OER.The method proposed in this paper can be extended to the synthesis of other metal-based Mo-S materials,which provides an effective way and technical support for obtaining various kinds and structures of Mo-S for sustainable clean energy storage and conversion.