MIL-derived Iron Nickle-Based Catalysts For Electrocatalysis Of Oxygen Evolution

Under the background of energy crisis and environmental pollution,electrocatalytic water splitting was in the spotlight as a sustainable and clean hydrogen production strategy.The complex steps of oxygen evolution reaction(OER)occurring on the anode involve multiple steps of adsorption and reaction of intermediates,which lead to severe kinetic barriers.Although ruthenium-based and iridium-based precious metals catalysts have shown excellent OER performance,scarce natural reserves and high catalyst costs have prevented them from meeting demand.Therefore,it is of great application value to develop and design efficient,cheap and stable new OER catalysts.In this study,a bimetallic nanorod Fe0.75Ni0.25S2 electrocatalyst was synthesized by a solvothermal conversion of precursor FeNi-MOF using TAA as sulfur source.The rod-like Fe0.75Ni0.25S2 catalyst was used in the OER,then,the effects of sulfuration temperature and sulfuration time on the capability of the electrocatalyst were explored.The evaluation results demonstrated that the overpotential of Fe0.75Ni0.25S2 was reduced by 68 mV compared with the original FeNi-MOF,and Fe0.75Ni0.25S2 could be stable for 40 h under the reaction conditions.After the optimization of the synthesis conditions,it was found that the catalyst had a good activity after solvothermal 12 h at 120℃,and the overpotential of 247 mV was required to obtain the baseline current density of 10 mA cm-2 under alkaline condition,and the Tafel slope was as low as 47.6 mV dec-1.XRD,FT-IR,Raman,ICP,EDS,SEM,TEM,HS-LEIS,N2-physical adsorption desorption,XPS and other characterization methods were intended for judging the physical and chemical features of precursor FeNi-MOF and Fe0.75Ni0.25S2.The results show that the Fe0.75Ni0.25S2 catalyst derived by sulfurization has the structural characteristics of high mesoporous content,which is conducive to the transfer of charge and substance,and the sulfurization can expose more active area.Through XPS and Raman characterization,it was found that amorphous hydroxide species were formed during the activation process of the catalyst,which is the actual active component of the reaction.It was found that the sulfide species did not disappear completely in the reaction process,but still played a role in improving the conductivity of the reaction,and synergistic effect with hydroxide species resulted in the low overpotential in the OER.The Fe0.75Ni0.25S2 catalysts synthesized under different conditions were tested and it was found that the introduction of sulfur to a greater extent in the reaction process lead to the increase of electrochemical active area as well as the reduction of charge transfer resistance.But the subsequent structural collapse would educe the lessening of the electrochemical active area and the increment of the charge transfer resistance.In addition,the FeNix-MIL-53 catalyst was prepared by one-pot method,then the impact of different amount of Ni introduction on the physical and chemical features of the electrocatalyst as well as the performance variation of electrocatalytic OER was examined.On this basis,a third high-valence metal W was further doped.The results show that the FeNi2.4W0.05-MIL-53 catalyst synthesized with the introduction of Ni(x=2.4)and W(y=0.05)exhibits good reaction performance.The overpotential of 235 mV was required to obtain the baseline current density of 10 mA cm-2 under alkaline condition,and the Tafel slope was as low as 43.3 mV dec-1.It also has good stability.Through characterization,it can be found that with the increase of the amount of Ni introduced,the crystal structure and morphology do not change significantly.The synergistic effect between the bimetallic species could improve the activity of the catalyst,but excessive introduction of Ni metal will lead to morphology change and composition amorphous,resulting in the decline of activity.Doped W metal has a similar phenomenon,a small amount of doping lead to the strong interaction between the high-valence metal and transition metal.The interaction improves the oxidation state of active center metal,further affect the adsorption O2 molecules and affinity of polar water molecules.But excessive doping will also lead to the formation of new phase and reduced crystallinity,resulting in the decline of activity.