Research On Ni/Fe-based Non-precious Metal Composite Catalysts Used As Oxygen Evolution Electrodes At High Current Densit

With the growth of population and the progress of industrial modernization,the human need for energy is increasing.However,the depletion of traditional fossil fuels and environmental pollution are becoming increasingly serious.Therefore,the development of clean,efficient and sustainable new energy sources as alternatives to fossil energy has become one of the hot spots of contemporary scientific.Hydrogen is ideal as an alternative to traditional fossil fuels,with the advantages of high conversion efficiency,clean and non-polluting.Among the current methods of hydrogen production,hydrogen production through electrocatalytic water splitting has proved to be a very promising technology for the production of high purity hydrogen,which has attracted high attention from scientific researchers.The electrocatalytic water splitting includes anodic oxygen evolution reaction（OER）and cathodic hydrogen evolution reaction（HER）.The OER process is mechanically complex,the kinetic process is sluggish,and often requires a high overpotential to drive the reaction,which becomes a key factor restricting the efficiency of hydrogen production from electrocatalytic water splitting.Therefore,it becomes particularly important to develop efficient OER catalysts to reduce the overpotential in catalytic reactions.At present,noble metal catalysts（Ru O₂ and Ir O₂）show excellent catalytic performance in OER process,but the high cost and scarcity of resources are long-term insurmountable problems in the actual production and application process.Therefore,designing OER catalysts with high activity,high stability,low cost and easy synthesis is the key to promoting the application of electrocatalytic water splitting.Based on the synergistic effects of multi-active component catalysts in the catalytic process,as well as the inherent disorder,abundance of defect sites in the amorphous structure,and the high electrical conductivity of the crystalline structure.In this work,several kinds of nickel foam（NF）self-supported Ni/Fe-based non noble metal composite catalysts were designed and prepared,including metal sulfides,oxides,layered doule hydroxide（LDH）,such as Fe MOF-Ni₃S₂,Fe Ni₂S₄-Ni Fe LDH and Ni Fe（OH）_x-Co₃O₄,and the morphology,structure and catalytic performance of OER at high current densities were also investigated.The main works of this thesis is as follows:1.The Fe MOF-Ni₃S₂/NF catalyst were successfully prepared by growing Ni₃S₂and Fe MOF on conductive nickel foam（NF）substrates using the conventional hydrothermal/solvothermal method.The catalytic performance of Fe MOF-Ni₃S₂/NF catalyst for OER was investigated in alkaline media.The results showed that the OER overpotential was only 243 m V when the current density was 100 m A·cm^-2.Even at high current densities of 500 and 1000 m A·cm^-2,the overpotential was only 283 and309 m V.The excellent OER activity is attributed to the large electrochemically active surface area,the high conductivity and the synergistic effect between Fe MOF and Ni₃S₂.In addition,the chronopotentiometry curves（CP）show that the voltage of Fe MOF-Ni₃S₂/NF catalysts can remain stable at different current densities for a longer period of time.At 100 and 500 m A·cm^-2,the catalytic activity remained relatively stable before and after long-term CP testing,and the crystal structure and microscopic morphology of the catalysts were not significantly changed.This work provides new ideas for the development of low-cost,highly active,and stable MOF-metal sulfide OER catalysts at high current densities,which would have great application prospects in industrial water electrolysis.2.The Ni Fe LDH/NF catalyst was firstly prepared on NF substrate by hydrothermal reaction,and then local sulfidation of Ni Fe LDH/NF was performed using a solvothermal reaction（using Na₂S as an S source）.The obtained Fe Ni₂S₄-Ni Fe LDH/NF catalyst with morphology of nano-flower spheres,and the catalytic performance for OER was examined in 1.0 M KOH medium.The results showed that the Fe Ni₂S₄-Ni Fe LDH/NF catalyst had excellent catalytic performance for OER with an overpotential of only 213 m V at a current density of 10 m A·cm^-2.Even at the high current densities of 500 and 1000 m A·cm^-2,the overpotentials are only 283 and 295 m V.At the same time,the catalyst also maintained extremely high catalytic stability.The overpotential decay generated at 1000 m A·cm^-2 in LSV curve is only 8 m V after 40 h of testing at 500 m A·cm^-2.After the local sulfidation process,the synergistic effects between the generated Fe Ni₂S₄ component and Ni Fe LDH,as well as the the open,exposed micron-sized bloom-like structure make the OER catalytic performance of Fe Ni₂S₄-Ni Fe LDH/NF superior to that of the single active component Ni Fe LDH/NF catalyst and Ru O₂/NF catalyst,which has high research prospects and industrial application value.3.The two-component Ni Fe（OH）_x-Co₃O₄/NF catalyst was successfully prepared by hydrothermal reaction,tube furnace roasting and electrodeposition techniques,and their catalytic OER reaction performance was investigated.The combination of amorphous Ni Fe（OH）_x and sea urchin-like Co₃O₄ with a porous structure results in Ni Fe（OH）_x-Co₃O₄/NF catalyst with low OER overpotential（243 m V）at a current density of 100 m A·cm^-2 and achieves industrially required high current density values of 500 and 1000 m A·cm^-2 at overpotentials of 268 and 281 m V.In addition,the potential can maintain high stability both at different constant current densities and at continuously varying current densities.The strong synergistic effect among the phase interfaces between the crystalline Co₃O₄ prepared by high-temperature calcination and the amorphous surface layer Ni Fe（OH）_x constructed by electrodeposition technique has significantly improved the OER performance of the catalyst,which is not only superior to that of the single-component Ni Fe（OH）_x/NF and Co₃O₄/NF catalysts,but also surpasses that of the commercial Ru O₂/NF catalysts.This work shows the importance of synergistic integration of different morphological nanocomponents for obtaining excellent catalytic activity.