Study On Activity And Stability For Water Electrolysis Of Carbon Encapsulated Nimo-based Hierarchical Materials

Energy and environment are two major issues in today's world,and the development of clean energy has always been the pursuit of scientific researchers.Hydrogen is regarded as a clean,flexible and renewable energy source,and is expected to be the ultimate energy source in the future society.Among various H2 production techniques,the water electrolysis by renewable energy is one of the most effective and eco-friendly methods,and has promising potency for large-scale application.However,the commonly used cathodic Pt-type catalysts and anodic Ru/Ir-type catalysts have high cost and poor stability,which greatly restrict the development of water electrolysis process.Therefore,the development of a non-noble metal catalyst for water splitting with high activity,stability and low price is a research hotspot in the field of new energy.Given the NiMo alloy is regarded as one of the most active non-precious transition metals for HER,and doping non-metallic element can promote the stability and corrosion resistance of catalyst,we report a simple hydrothermal-pyrolytic method to develop a 3D self-supported hierarchical NiMo-based material named Ni@NCNT/NiMoN/NF.The prepared electrode possesses three advantages:1)This hierarchical structure not only enlarges the surface area and spatial utilization,but also enhances electron-transfer rate.2)N-doped carbon layers can not only effectively protect active sites,but also modulate the surface electron distribution.3)NiMoN and Ni act as dual active sites for HER.Then,the transition metal layered double hydroxide(LDH)nanosheets were loaded by electrodeposition on the surface of Ni@NCNT/NiMoN/NF,and the performance of this composite as catalyst for overall water splitting is studied.The main works are as follows:First,the preparation conditions of the hierarchical NiMo-based material were explored and optimized,and the obtained Ni@NCNT/NiMoN/NF-8 exhibits the best catalytic performance for HER.The advantages of morphology and structure were verified by SEM,HRTEM,Raman,XRD and XPS results.It demands extremely low overpotentials of 18 mV and 236 mV in 1.0 M KOH,31 and 96 mV in 0.5 M H2SO4 to achieve current densities of 10 and 200 mA cm-2,respectively.Furthermore,it shows excellent durability and anti-oxidation.Second,we prepared transition metal LDH nanosheets on the surface of Ni@NCNT/NiMoN/NF by electrodeposition to enhance the OER activity.Through the optimization of metal species,deposition time and deposition current,the NiFe LDH-Ni@NCNT/NiMoN/NF with the best OER performance was prepared.Last,NiFe LDH-Ni@NCNT/NiMoN/NF was adopted as both cathode and anode and its stability and oxidation resistance were tested,which delivers 10 and 100 mA cm-2 at very low cell voltage of 1.51 and 1.69 V respectively,and it shows robust stability under powered-off and polarity exchange state.Compared with most of the reported electrocatalysts for water splitting,this material has better activity,superior durability and anti-oxidation ability.