Investigations On The Doping Modification Of Fe-based Catalysts And Their Electrocatalysis Performances

Electrocatalytic technology is a powerful tool to come ture some harsh chemical reactions at mild reaction conditions,and it can also realize the storage of waste electrical energy to chemical energy and the conversion of high value-added chemicals to solve the problem of uneven space-time distribution of clean energy,which show great application potential in the future.Based on the advantages of high reserves and low price of iron,this paper reported a variety of high-performance iron-based catalysts by doping measure,and explored their applications in electrocatalytic ammonia production as well as electrocatalytic seawater decomposition.Meanwhile,the reaction mechanisms of the catalysts are studied in detail,in order to provide useful ideas for the directional synthesis of high-performance iron-based catalysts.The main research contents are as follows:（1）More recently,the electrochemical N₂reduction reaction（NRR）has drawn dramatically attentions because it can not only operate in ambient conditions and cost-effective aqueous electrolytes,but also directly employ proton from water splitting as an H source,which has been recognized as an attractive and sustainable nitrogen fixation path to replace the century-old Haber-Bosch process in the future.Following the guidance of nitrogenase,the natural iron-based catalysts with remarkably high activity in nitrogen reduction reaction（NRR）may be a talent option to develop artifcial molecular mimics.However,the electrochemical NRR process of iron-based catalysts still suffers from the high overpotential,poor lifespan,and slow reaction kinetics of the hydrogenation process.Using a Pt-dopping MIL-88A as precursor,a Pt-doped Fe P/C hollow nanorod catalysts was fabricated through a controllable etching and in-situ carbonating process.Driven by the doped Pt atom,the catalyst solves the key kinetic problem about insuffcient proton feeding in the process of nitrogen reduction,and actively transfers protons to intermediates of the hydrogenation steps in NRR.Moreover,the as-prepared catalyst presents the highest NH₃yield value of 10.22μg h^-1cm^-2among multitudinous Fe based catalysts at lower potential of-0.05 V（vs.RHE）with an excellent Faraday effciency（FE）of 15.3%,which is higher than Fe P/C without the Pt-driven proton-feeding effect,and the cathodic current density presents no signifcant change within 50 h.In addition,the density functional theory（DFT）and attenuated total reflection surface-enhanced infrared absorption spectrum（ATR-SEIRAS）results verify the reaction path and protons-feeding kinetic process.（2）Seawater splitting is a hot technology that can convert resources into renewable new energy and solve the important problem of energy shortage in coastal areas.It is of great significance to prepare low cost Fe-based catalysts with and high performance to resist the widespread chlorine oxidation reaction in seawater splitting.In this study,under relatively mild conditions,we prepared the bifunctional catalyst with carbon quantum dots embedded in a multi active site of amorphous phosphate iron supported by foam nickel（a-CQDs-Fe P/NF）.Amorphous iron phosphide originally had a large number of active sites,the embedding of quantum dots enhance the conductivity of the catalyst.More importantly,the addition of quantum dots plays a key role in promoting the phase transition,thus speeding up the oxygen evolution reaction（OER）process.Similarly,the alkaline electrolytic cell combined with a-CQDs-Fe P/NF as bifunctional catalyst can still achieve the industrial level with a voltage of 1.97 V in alkaline seawater electrolyte at 1000 m A cm^-2.Ultimately,the embedded carbon quantum dots make the catalyst more stable under high current of1000 m A cm^-2within 200 h.Based on the synergistic effect of carbon quantum dots and amorphous iron phosphide can guarantee the activity of the catalyst,this study is expected to provide an economic and feasible catalyst design idea for industrial seawater electrolysis.（3）High specific surface active catalyst electrode have become the focus of research in recent years because of their ultra-high catalytic activity,excellent stability and good atomic level economy.In this study,graphene is coated on a nickel foam substrate to form a 3D stable base,and then Fe monodispersed NGPF catalyst and a small amount of Pt doped NGPF-Pt catalyst are prepared by the coordination of metal cations with N atoms in dopamine molecule at room temperature.The OER test in alkaline shows that the anodic overpotential of high density active substance catalytic electrode NGPF（anode）is 223 m V at 500 m A cm^-2and 254 m V at 1000 m A cm^-2.In addition,NGPF-Pt shows excellent HER performance with an overpotential of only 63 m V at 1000 m A cm^-2and a tafel slope as low as 28 m V dec^-1,which is better than most reported Pt-based catalytic materials.The outstanding performance may attribute to the strong coupling between graphene and dopamine,which supplies an extremely high specific surface area for adhesion of Fe and Pt ions,further reduces the charge transfer resistance to achieve the rapid transfer of electrons.Moreover,the durability test under the impact of high current density within 500 h shows that the electrolytic reaction still maintains 94%of initial value.