Functional Optimization Of Iron Based Electrocatalysts

With the growing demand of energy,the rapid consumption of non-renewable fossil fuels and the growing concern of environmental issues,the development of green and sustainable energy sources is imminent.Hydrogen is considered as an ideal clean fuel because of its high combustion heat and high energy capacity.As an advanced energy conversion technology,electrocatalytic water splitting has attracted much attention due to its high energy conversion efficiency and energy utilization as well as the environmental friendliness.Electrocatalytic water splitting is considered to be one of the most effective methods for hydrogen generation.However,due to the sluggish four-electron transfer process of oxygen evolution reaction（OER）,it often requires an excessively high overpotential to achieve water splitting which greatly limits the development of water electrolysis for hydrogen production.Therefore,although the cathode reaction is hydrogen evolution reaction（HER）,it is very important to prepare OER or urea oxidation reaction（UOR）electrocatalysts to reduce the overpotential of water splitting and increase the hydrogen production amount.In this thesis,the electrocatalytic performance of iron-based electrocatalysts was optimized by heteroelement incorporation.The specific research contents are as follows:1.We synthesized Ni（OH）₂ nanosheets/F-doped Ni₃S₂ nanorods bifunctional electrocatalysts through one-step hydrothermal sulfuration method in situ growth on nickel foams,in which fluorine doping displays dual effects.On the one hand,fluorine doping can facilitate the formation of Ni（OH）₂ nanosheets/Ni₃S₂ heteronanorods through one-step in situ growth on nickel foams.The unique heterostructure enables the well exposure of abundant active sites and highly active heterointerfaces.On the other hand,the uniform incorporation of fluorine can effectively optimize the electronic structure of Ni₃S₂ and increase the electron density of its Fermi level,contributing to the improved electrical conductivity and charge transfer efficiency,further improving the electrocatalytic activity on OER and UOR.The optimal heterostructure presents a low overpotential of 360 mV to reach the OER current density of 100 mA·cm^-2.Finally,this heterostructure also displays a superior UOR anodic peak current of about 322.9 mA·cm^-2,Which exhibits excellent bifunctional catalytic activity for water and urea oxidation.2.Fe-incorporated Ni（OH）₂ multiphase electrocatalysts were prepared successfully by electrochemical deposition and followed hydrothermal method on carbon cloth for OER.On the one hand,iron incorporation induces partial transformation fromβ-Ni（OH）₂ toα-Ni（OH）₂,forming the Ni（OH）₂ multiphase.On the other hand,iron doping can adjust the electronic structure of Ni（OH）₂ and boost the generation of catalytically active Ni³⁺.Due to the addition of iron,both the conductivity and charge transfer efficiency are improved.Meanwhile,owing to the multilayered structure of Ni（OH）₂ multiphase,more active sites are exposed.The optimal Fe-incorporated Ni（OH）₂ multiphase electrocatalyst displays excellent catalytic activity,including low overpotential,large current density,and long-term durability.It is comparable to the reported OER catalysts,which provides the possibility forenergy conversion.3.The production of hydrogen via water electrolysis is considered as a feasible strategy to exploit renewable energy and relieve the crisis of energy and environment.Compared with water electrolysis,the introduction of urea not only improves the energy conversion efficiency of urea electrolysis but also is suitable for wastewater treatment.Herein,we highlight an electrocatalyst of nickel incorporated Co₉S₈ nanosheet arrays grown on carbon cloth for electrocatalytic overall urea splitting.The incorporation of nickel can enhance the electrical conductivity and charge transfer efficiency of Co₉S_8.Its unique nanosheet structure exposes more active sites to boosting the overall urea splitting.The optimal nickel incorporated Co₉S₈/carbon cloth catalysts reveal remarkable catalytic activity.For HER,only 0.296 V vs.RHE is required to reach the current density of 100 mA·cm^-2.It only takes 1.28 V vs.RHE to reach the current density of 10 mA·cm^-2for UOR,which is comparable to reported UOR or OER catalysts.Based on the above-mentioned excellent electrocatalytic performance,overall urea splitting based on Ni-Co₉S₈/carbon cloth as bifunctional catalyst is achieved with the potential of 1.52 V at 10 mA·cm^-2.