Rgulation And Research Of Heteroatom/Defect Doping Of Fe-Based Compound For Electro Catalytic Property

In order to respond positively to the national call for energy conversion and the concept of sustainable development,the development of new energy and the exploration of new chemical industry technique become the most important topic to the human beings and the whole society.Among the most solutions,the electrocatalytic water splitting and the electrocatalytic reduction of nitrogen to ammonia have become two new energy conversion technologies with high application prospects.Among them,the electrocatalytic hydrogen evolution reaction?HER?can convert electrical energy into clean hydrogen energy efficiently.In addition,the process of ammonia production by electrocatalytic nitrogen reduction?NRR?at room temperature is promising to be a new ammonia production process replacing Haber-Bosch method due to the advantages of safe,controllable and no carbon dioxide emission.However,as for either the HER or the NRR process,there are still great chanllenges to improve the reaction rate owing to the lack of cheap,non-toxic and efficient catalysts.Thus,the design of electrocatalyst with high-performance and high-activity becomes the focus of the electrochemical energy conversion and ammonia production process.In view of this,this paper proposes the following five research schemes:1.The electrocatalytic oxygen evolution reaction?OER?as the half reaction of electrocatalytic water splitting,its complex four-electron process brings about the sluggish kinetic,thus seriously hindering the hydrogen production.Therefore,the exploration of efficient OER catalyst becomes another way to realize the practical application of hydrogen energy.Unfortunately,recent researches found that Mo-based oxides has inferior OER performance due to the low activity and the slow charge transfer process.Therefore,it is of great significance for the practical application of hydrogen energy in the near future to explore appropriate technology and strategy to improve the OER activity of Mo-based oxides.Considering the excellent activity of Co-based materials for OER and the abundant active sites of amorphous materials,we successfully synthesized the amorphous Co-doped MoO_x?Co-MoO_x?nanosphere with unique core-shell structure as the highly efficient OER catalyst.Benefited from the amorphous structure as well as the introduction of Co atoms,the active sites and the charge transfer process of Mo-based oxides are well-optimized,which can greatly improve the OER activity.In alkaline electrolyte,the Co-MoO_x only needs a low overpotential?340 mV?to attach the current density of 10 mA cm^-2,a small Tafel slope(49 mV dec^-1)and a little charge transfer resistance?27??,which can even compare to those reported catalysts.Moreover,the catalyst also exhibits excellent stability in alkaline electrolyte,indicatimg that the material has great potential to be an ideal electrocatalyst for the industrial production of hydrogen energy.In this work,the strategy of hetero-atom doping and the design of amorphous framework can promote the OER activity significantly,which opens a new path for the study of hydrogen energy in the future2.Considering the important role of crystal defects for the modulation of electronic structure,here in our work,the oxygen vacancy was created on the surface of CoFe₂O₄ nanosheet via the room temperature reduction treatment.The electronic structure and active site were successfully regulated along with the introduction of oxygen vacancy,so both the OER and HER activity could be improved,which is expected to be beneficial for the promotion of electrocatalytic water splitting.At the same time,the density functional theory was employed to explore the origin of catalytic activity.It found that the band gap of CoFe₂O₄ is decreased after the introduction of oxygen defects,which could accelerate the charge transfer process,thus leading to the enhanced activity.In addition,the adsorption energy of H₂O molecules before and after the introduction of oxygen vacancy shown that the adsorption energy is greatly reduced after the creation of oxygen vacancy.Considering that the adsorption of H₂O molecules is the rate-determining step for water splitting,the reduction of adsorption energy greatly promotes the improvement of catalytic activity.As confirmed by both the theory analysis and the experimental results,the CoFe₂O₄ with oxygen vacancy exhibits excellent activity for overall water splitting,which is expected to be an ideal electrocatalyst for practical application of hydrogen energy.3.The Co-doped FeS₂ nanospheres with porous strcture is synthesized by hydrothermal reaction and is adopted as the excellent electrocatalyst for overall water splitting successfully.Firstly,the electronic structure and active site are well-optimized by the doping of Co,thus endows Co-FeS₂ with excellent bifunctional electrocatalytic activity.Secondly,through the introduction of heteroatoms with high activity,the activity of Fe-site is activated and the new active site of Co-site is created.In addition,considering the close position of Co and Fe in the periodic table,the introduction of Co can effectively optimize the electronic structure of FeS₂,achieving rapid charge transfer,and enhanced kinetic process of electrocatalytic reaction4.We synthesized the CoFeO_x?OH?_y/CoO_x?OH?_y core-shell nanospheres with amorphous interface via the one-step reaction.Benefited from the existence of amorphous interface,the separation and transportation of active intermediates?such as,H*or OH*?are greatly improved.Meanwhile,the shell constituted by the roughly three-dimensional?3D?interlaced nanosheets is beneficial for the increment of the specific surface area and the active sites,which brings about the improvement of atomic utilization of catalyst.Furthermore,the abundant grain boundaries and the lattice distortion of amorphous structure create numerous active sites,which further enhanced the catalytic activity.Due to the regulation and modification of the amorphous interface,the catalytic activity is not only greatly enhanced,but also endowed with excellent bifunctional electrocatalytic activity to realize the fastly overall water splitting.As for three electrode system,the overpotential for OER is as low as 324 mV to attach the current density of 10 mA cm^-2,and the overpotential for HER is as low as 263 mV to attach the same value.When the catalyst was used as the both anode and cathode for overall water splitting,the cell voltage is as low as 1.59 V to achive the current density of 10 mA cm^-2.5.The Fe-doped Ni₂P catalyst with ultrathin nano-sheets structure for highly-efficient NRR process was successfully prepared via hydrothermal and phosphating reaction.The electronic properties of Ni₂P is well optimized brought by the introductiuon of Fe atoms.At the same time,the adsorption of N₂ and activation of N?N triple bond are optimized as well along with the doping of Fe atoms,which is the premise to improve the activity and selectivity of NRR catalyst.Furthermore,after the introduction of Fe,the activity of Ni-site is improved and the new active site of Fe-site is created simultaneously,which was also favor to the improvement of electrocatalytic performance.As expected,the Fe-doped Ni₂P catalyst shown the excellent NRR performance,with that the NH₃ yield and the Faraday efficiency being88.51 g h^-1 mg^-1_cat.and 7.92%,respectively.In this work,the crystal structure and electronic property are optimized successfully via the introduction of Fe atoms,which provide a new material platform for NRR process.