Controllable Construction And Investigation On The Catalytic Activity Of Hierarchical Structure Molybdenum-based Electrocatalysts

Hydrogen has the advantages of cleanliness,sustainability,and high energy density,which is considered as an ideal carbon-free energy source to replace traditional fossil fuel systems.One of the ideal ways to prepare high-purity hydrogen is water splitting reaction,which includes two half reactions,namely,the hydrogen evolution reaction(HER)at the cathode and the oxygen evolution reaction(OER)at the anode.The overall efficiency of water splitting depends on the catalyst used in electrode reaction.Although the currently used noble metal based electrocatalysts have high electrocatalytic performance(such as Pt/C for HER and Ru O₂/Ir O₂ for OER),their high cost and scarcity have seriously limited their large-scale applications.Therefore,the development of low-cost and efficient transition metal catalysts with hydrogen/oxygen evolution performance has aroused great interest.However,the activity and stability of most transition metal-based electrocatalysts are still far from satisfactory.In view of this,we designed and synthesized a series of molybdenum-based electrocatalysts for efficient,stable and economical water electrolysis from the perspectives of optimizing element composition,regulating microscopic morphology,and improving combination mode.The main research contents include the following aspects:(1)In order to reduce the overpotential of hydrogen evolution reaction and the cost of hydrogen production in electrolysis.Here,Mo O₃ nanobelts were used as precursors to thermally react with Niions to form the hierarchical NiMo O₄ multilevel microsphere,and then the hierarchical microsphere(Mo NiHM)was obtained by further in-situ reduction reaction.The catalyst had suitable crystal structure,porous nanosheets and large BET surface area,which could enhance the intrinsic catalytic activity and showed excellent electrocatalytic activity for hydrogen evolution.Its initial potential was only-7 m V@1 m A cm^-2 and good stability of hydrogen production.Using Mo NiHM as cocatalyst and Cd S NWs as photocatalyst,the photocatalytic activity of the nanocomposite catalyst was 21.4 times higher than that of pure Cd S NWs under visible light irradiation.In this study,we explored the use of low-cost and efficient non noble metal Mo NiHM as cocatalyst to replace expensive noble metal cocatalyst for photocatalytic hydrogen production.(2)In the interests of solving the problem of corrosion and instability of transition metal oxide OER electrocatalysts in acidic electrolyte,we used carbon nanotubes composite Mo O₃nanobelts to suction and filter into Mo O₃ NB/CNT-M flexible membrane as the precursor,heat treatment in Ar/H₂ atmosphere and further in-situ selenization to obtain multi-level structure Mo Se₂ nanosheets dispersed on Mo O₂nanobelts composite electrode(Mo Se₂NS/Mo O₂NB/CNT-M).Characterization of its structure and electrochemical properties showed that the porous structure of Mo Se₂NS/Mo O₂NB/CNT-M film exposed the active sites to the maximum extent,promoted ion/electron diffusion and the strong coupling effect of CNT and Mo Se₂ NS/Mo O₂ NB,which made Mo Se₂NS/Mo O₂NB/CNT-M had excellent HER and OER activity and stability.The electrolytic cell constructed by Mo Se₂NS/Mo O₂NB/CNT-M(-)//Mo Se₂NS/Mo O₂NB/CNT-M(+)had excellent performance.The voltage required to drive10 m A cm^-2current density was only 1.63 V.(3)For the sake of further reducing energy consumption,on the basis of adjusting the catalytic process of hydrogen evolution at the interface by alloy particles,the heterojunction structure of oxides with high conductivity and alloy was constructed by changing the thermal reduction atmosphere,so as to improve the intrinsic catalytic activity and conductivity of the electrocatalytic materials,reduce the overpotential of hydrogen evolution reaction and oxygen evolution reaction,and reveal regulating mechanism of transition metal alloy/oxide interface on hydrogen evolution reaction and oxygen evolution reaction,and further reveal the"structure-activity relationship"between the interface and catalytic activity.Mo O₂ was a semiconductor oxide with good conductivity and chemical stability.Therefore,we chose our self-made hexagonal Mo O₂ nanosheets as the substrate and molybdenum source.Through epitaxial growth and changing the reaction atmosphere,NiMo and Co Mo O₄ nanosheet arrays were in situ vertically grown on the Mo O₂ nanosheet substrate as the cathode HER and anode OER,respectively.A large amount of dispersed NiMo had a high catalytic activity,while the 3D porous nanosheet array supported by Mo O₂ nanosheets exposed more active sites and act as a cocatalyst in the process of synergistic catalysis,and improved the conductivity of the catalyst array.At the interface of NiMo/Mo O₂,electrons transfered from metal like Mo O₂ to NiMo,which improved the activity of hydrogen evolution of NiMo and also improved the catalytic activity of Co Mo O₄ as the active center of oxygen evolution reaction,promoted the whole water decomposition process and improved the energy efficiency of water electrolysis.The preparation method is simple and easy to obtain,which provides a practical and direct idea for the development of low-cost,high activity and stable structure catalysts for hydrogen production from water decomposition.