Study On Preparation And Performance Of MoS₂ Decorated Ni-based Self-Supporting Catalytic Electrode

Hydrogen energy is one of the most promising clean energy sources.Electrolysis of water is the development direction of hydrogen production in the future,and the main bottleneck of industrial hydrogen production from water splitting is shortage of catalytic electrode with high activity,robust stability,easypreparation and low cost.It has been proven that the active sites of the MoS2 edge is similar to that of Pt,which can be a fascinating catalyst for hydrogen evolution.However,MoS2 itself has problems such as low catalytic activity and poor conductivity.The catalytic activity and electrical conductivity of MoS2 is expected to improve by loading MoS2 onto metal substrate.Commercial Ni foam(NF)is a common porous substrate,and its large porosity can provide sufficient space for MoS2 growth.However,the mechanical properties of NF are poor,and the bonding strength of NF with MoS2 is not strong enough to meet the stability requirements of electro-catalytic hydrogen evolution under the high current.Therefore,in view of the above problems,a highly active IT phase MoS2 through a hydrothermal synthesis was first prepared and 1T-MoS2 on the NF substrate was loaded to fabricate MoS2@NF self-supporting electrode.The morphology of well-distributed nano-rods arrays formed on the electrode surface after hydrothermal sulfurization can not only facilitate the fully contact with the electrolyte but also promote the fast escape of generated bubbles from the electrode.By finely regulating the addition of ammonia to regulate the crystal structure of MoS2,the NH4+/NH3 in ammonia can be used as a layering agent to convert part 2H phase MoS2 into 1T phase MoS2.Due to the excellent catalytic hydrogenation activity of 1T phase MoS2,the MoS2@NF electrode has a high catalytic water decomposition efficiency and shows a low overpotential of 73 mV at a current density of 10 mA·cm-2.The hydrothermal sulfurization process also lays the basic preparation method for MoS2 decorating the nickel metal.In order to improve the catalytic stability and mechanical performance of the MoS2 decorated nickel-based self-supporting electrode,the porous nickel substrate was innovatively prepared using powder metallurgy technology,including normal pressure atmosphere sintering and spark plasma sintering(SPS).The as-obtained nickel substrates have appropriate porosity,which can not only provide sufficient space for the growth of catalysts,but also disperse the stress in catalysts growth process,promoting the combination of MoS2 and substrate,further increasing the stability and durability of hydrogen evolution reaction(HER).By regulating the sintering temperature,the shape and structure of the porous nickel substrate were precisely controlled.The MoS2@porous nickel electrode obtained by loading MoS2 on the porous nickel substrate prepared by SPS presintering and atmosphere sintering at 800? shows better HER activity than that of MoS2@NF electrode,with a low overpotential of only 56 mV at a current density of 10 mA·cm-2,and the stable HER can be conducted even at higher potentials of 200 and 300 mV for 100 h.In addition,this sintered porous nickel substrate has good mechanical property with a tensile strength of 158.8 MPa.The SPS process was used further to shorten the preparation time of the substrate from 2 h to 2 min,significantly enhancing the production efficiency reducing the costs.In addition,the pore structure of the products can be controlled by the sintering temperature and the mold,which makes the selectivity of porous nickel substrate more flexible.A new porous nickel substrate with a large porosity in the upper layer and a small porosity in the bottom layer was prepared by using this method.Although the HER performance of this electrode is slightly reduced,the excellent stability can be retained.At the same time,the electrode also shows a good activity for oxygen evolution reaction(OER)with an overpotential of 223 mV at a high current density(100 mA·cm-2),showing the possibility of being used as a dual-function catalytic electrode in industrial electrolytic water splitting.Finally,the preparation process of electrode was further optimized,and a new integrated forming method to prepare MoS2 decorated porous nickel selfsupporting electrode was developed.MoS2 is loaded on the porous nickel matrix in the form of bulk doping for the first time,which determines that the electrode can carry out machining without worry about the wear or loss of catalytic active phase,showing a high universality.Although the HER and OER activity of the as-obtained electrodes are reduced compared with other electrodes studied in this work,lower production costs and simpler preparation processes may give them a broader perspective.In addition,the electrode can steady conduct HER at a higher overpotential(350 mV)for more than 130 h,which can be expected to meet the requirements of industrial hydrogen production for durability at the high power of catalytic electricity.To sum up,a new technology for preparing MoS2 decorated porous nickel selfsupported electrode by powder metallurgy and wet chemistry was proposed.A three-dimensional porous nickel substrate with controllable morphology and structure was obtained,and a nickel-based self-supporting catalytic electrode with high catalytic activity,strong stability,easy preparation and low cost was constructed,which provided a new idea for the development of industrial electrocatalytic materials for hydrogen evolution.