Preparation And Performance Research Of Cobalt Boride Nanosheets For Electrocatalytic Oxygen Evolution

The increasingly serious environmental crisis and energy shortage have threatened the sustainable development of mankind,and it is urgent to explore new clean and renewable energy.Hydrogen energy has been extensively researched due to its high energy density,easy storage and transportation,and no pollution of the combustion products to the environment.As a new technology,electrocatalytic water splitting to produce hydrogen is not only a simple preparation process,but also inexhaustible raw materials.It is one of the most promising hydrogen production methods.The water splitting reaction involves two vital half-cell reactions,that is,anodic oxygen evolution reaction(OER)and cathodic hydrogen evolution reaction(HER).To date,practical application of water splitting is seriously limited by the sluggish anodic OER.The anode half reaction involves the transfer of four electrons and a high overpotential(?)that requires big energy consumption to produce H₂ at a practical rate.It has been proven that adding a catalyst can significantly reduce the overpotential and thus accelerate the reaction.At present,precious metal oxides(Ru O₂/Ir O₂)are still regarded as the benchmarked OER electrocatalysts.Their commercial applications are severely limited by high cost and scarcity.Therefore,development of non-precious metal catalysts for the OER is a key to open the door to large-scale application of hydrogen fuel.Cobalt boride(Co-B)emerge as typical representatives of highly active and inexpensive OER catalysts recently,not only has a wide range of raw materials,simple preparation methods,but also excellent catalytic performance.However,the research on Co-B catalyst still has the following problems:1.Factors affecting structure and morphology are not yet clear.2.Co-B catalyst has poor conductivity and stability,and is easy to agglomerate.This thesis has made in-depth research on Co-B catalyst from the following aspects:(1)A series of Co-B catalysts were prepared by chemical reduction method under the premise of equal amount of sodium borohydride(NaBH₄)and cobalt sulfate(CoSO₄),using the same concentration of NaBH₄ to reduce CoSO₄solutions of different concentrations.The structure analysis by X-Ray Diffraction(XRD)revealed that the catalysts prepared in different concentration of Co²⁺(0.1 M,0.01 M and 0.001 M)were all of amorphous structure.In order to determine their crystal structure,the three groups of samples were annealed at500?under an inert atmosphere,and it was found that the prepared Co-B was Co₂B structure.In addition to containing Co₂B,there is a small amount of Co⁰ in the three groups of samples,but the content of Co⁰ in the products prepared at different Co²⁺concentrations is different.The content of Co⁰ in Co₂B prepared at high Co²⁺concentration is lower than that at low Co²⁺concentration.SEM and TEM tests showed that the Co₂B prepared at high Co²⁺concentration was lamellar;Co₂B prepared at low Co²⁺concentration becomes a flocculent structure.The test results of OER catalytic performance show that the 0.01Co₂B prepared at high Co²⁺concentration has the best catalytic performance(2)A new carrier carbon material(Fe₂O₃/C)was prepared by arc discharge in ferrous sulfate(FeSO₄)solution.NaBH₄ reduces the mixed solution of CoSO₄and Fe₂O₃/C carrier by chemical reduction method.Co₂B is loaded with Fe₂O₃/C carrier to form Fe₂O₃/C@Co₂B catalyst with core-shell structure.Electrochemical performance tests show that Fe₂O₃/C@Co₂B has an over-potential reduction of 58 m V compared to pure Co₂B at a current density of10 m A/cm².The improvement in performance is attributed to the improved conductivity and stability of Fe₂O₃/C@Co₂B.The method in this paper is expected to provide a new idea for the preparation of carbon-supported metal boride(M-B).