The Study On Nickel-iron Boride Composites And Their Activities For Electrocatalytic Oxygen Evolution

Hydrogen energy is a promising choice because of its unique advantages of high energy density,environmental friendliness,strong sustainability,easy production and strong applicability.Electrocatalytic decomposition of water to produce hydrogen is a good way to use sufficient water on earth or even seawater as raw materials.At the same time,the utilization of hydrogen energy does not produce any pollution,and the product water can be easily recycled.Under standard conditions,the theoretical voltage of electrocatalytic cracking water is 1.23 V.However,a higher voltage of 1.6-2.0 V is often required due to overpotential generated by polarization and solution resistance.In addition,the electricity cost of cracking water accounts for about 80 percent of the total cost of industrial production.Therefore,it is urgent to develop a durable,efficient and low overpotential electrolysis water catalyst.Noble metal based electrocatalysts（such as Pt,Ru O₂,Ir O₂,etc.）have the most advanced catalytic activity,but their large-scale application is limited due to their insufficient reserves and high cost.Therefore,it is necessary to develop a kind of low cost and high efficiency electrocatalyst.The design of non-noble metal boride electrocatalyst with high efficiency and high stability is the key to the development of electrochemical water oxidation technology,but it is challenging.Morphology and electronic structure will largely determine the activity and stability of amorphous boride catalyst.Here,we developed a series of amorphous nickel-iron boride oxygen evolution reaction（OER）catalysts through simple sodium borohydride reduction and hydrothermal reduction,and tested and characterized the electrochemical properties of the prepared materials.The detailed research contents are as follows:（1）Amorphous boride WFeNiB was synthesized on nickel foam substrate by chemical reduction method,and the effects of different metal elements on the activity and stability of electrochemical OER were studied.The metal substrate of WFeNiB catalyst not only plays a physical role in loading the catalyst,but also actively participates in the activation process of catalyst phase by controlling the charge transfer in the OER process.It was found that the doping of W,Fe andNimetal elements had a certain synergistic effect on the OER performance of the electrocatalyst,thus improving the OER performance.It was found that the surface of WFeNiB@NF had a nanoparticle structure,which was beneficial to expose more active sites.The experimental results show that WFeNiB@NF catalyst exhibits good OER activity and long-term stability in1.0 mol L^-1 KOH solution.When the current density reaches 10 m A cm^-2,the overpotential of WFeNiB@NF catalyst is only 223 m V,and the slope of Tafel is only38.83 m V dec^-1.Through cyclic voltammetry test,WFeNiB@NF has an electrochemical active surface area of 101.3 cm~2.After 12 h stability test,the overpotential increases by only 4%,indicating that it has good chemical stability.（2）In order to overcome the shortcomings of transition metal borides with poor electrical conductivity and limited active centers,a three-dimensional（3D）FeNiB/rGO@NF composite was successfully prepared by hydrothermal reduction of graphene oxide（rGO）flakes on nickel foam（NF）and in-situ growth ofNiFe B nanoparticles on this basis.The results show that FeNiB/rGO@NF composite has excellent electrocatalytic performance.By analyzing the microstructure and electrochemical properties of FeNiB/rGO@NF,it was found that the composite structure composed of rGO and FeNiB had a synergistic effect.On the one hand,the composite structure can effectively increase the specific surface area of the material,inhibit the agglomeration of nanoparticles and expose a large number of rich active sites.On the other hand,both rGO and NF can improve the conductivity of FeNiB,improving the transport capacity of electrons and ions.In addition,FeNiB/rGO@NF showed very good OER catalytic performance,with an overpotential of 197 m V at 10 m A cm^-2 and a Tafel slope of 64.77 m V dec^-1.And the material has good durable stability.（3）To further improve the performance of the catalyst,nickel foam is used as the substrate,which forms the thinnest oxide layer on its surface to facilitate charge transfer,minimize metal dissolution during OER and provide excellent long-term stability.Therefore,the OER performance of FeNiB was enhanced by reducing graphene oxide on nickel foam,followed by hydrothermal growth of manganese dioxide.It was found that FeNiB/Mn O₂/rGO@NF catalyst had better performance and stability.In 1.0 mol L^-1 KOH solution,the current density of 50 m A cm^-2 can be achieved at 266 m V with ultra-low overpotential,which is further adjusted by manganese dioxide,and the material also has excellent stability.In order to achieve high conductivity,low overpotential and long-lasting activity,the design of electrochemical water decomposition catalyst with good performance and simple preparation is the key in the field of energy conversion.In this paper,three different composite materials were prepared by chemical deposition of boride particles,hydrothermal reduction of graphene oxide and hydrothermal growth of manganese dioxide nanomaterials on nickel foam as conductive substrate.Through various characterization and electrochemical tests,the OER properties of the three materials were found to be very good.In this paper,a simple synthesis strategy is described to synthesize three new transition metal catalysts as cheap alternatives to precious metals to achieve efficient water decomposition.