Design,Preparation And Electrocatalytic Performance Of Highly Efficent Ru-based Catalyst For Hydrogen Evolution Reaction

With environmental and energy issues deteriorating,the demand for renewable and clean energy is ever-increasing.As a new type of renewable energy,hydrogen energy satisfies the demands of green and environmental friendiness,thus is favored by people.Hydrogen production by electrolysis of water is a fast and efficient strategy,mainly through the cathode hydrogen evolution reaction（HER）,however,the reaction requires to overcome large energy barrier,resulting in high cost to be expend.The introduction of catalysts can greatly reduce the reaction energy barrier.At present,platinum-based catalysts are the most advanced HER catalysts,unfortunately,the high cost,instability and scaricity of Pt limite its commericial application.As a member of the platinum group metal,ruthenium exhibits excellent HER performance,but its price is much lower than platinum,thus an ideal alternative for platinum.Currently,the HER activity of Ru-based catalysts is still far inferior to Pt,especially in alkaline and neutral enviroment.Herein,Ru-based composite catalysts were desigined and prepared successfully by combining ruthenium with chromium oxide and functional three-dimensional graphene,and their electrocatalytic performance of HER in non-acidic media was investigated.Firstly,the ruthenium-chromium trioxide three-dimensional graphene（Ru-Cr₂O₃/NG）composite material was prepared by a thermal annealing route.Ru-Cr₂O₃/NG has been characterized by X-ray powder diffraction（XRD）,scanning electron microscope（SEM）,transmission electron microscope（TEM）,and X-ray photoelectron spectroscopy（XPS）.The results showed that the material had a three-dimensional layered porous structure.The atomic contents of Ru,Cr,and N were 8.62%,1.72%and7.71%,respectively.When the molar ratio of Ru and Cr₂O₃ was 5:1,the material displayed the best HER electrocatalytic activity.In alkaline medium,Ru-Cr₂O₃/NG presented the Tafel slope of 39 m V dec^-1,the overpotential(η₁₀)of 47 m V,and the C_dl of 25 m F cm^-2.The TOF at 100m V was as high as 6.4 s^-1,which was better than commercial Pt/C.In a neutral medium,the catalyst showed theη₁₀ of 53 m V,and the Tafel slope of 47 m V dec^-1,indicating the better HER performance as well.Density function theory（DFT）calculations showed that the introduction of NG and Cr₂O₃ enhanced the water-dissociation ability of Ru,thereby lowering the reaction energy barrier.Secondly,the transition metals Ni,Fe,Co were introduced to prepare the transition metal and nitrogen co-doped three-dimensional graphene supported ruthenium nanoparticle composites.The catalyst was characterized by SEM,XRD,TEM and STEM,and it was found that the ruthenium nanoparticles were 3 nm in diameter and was uniformly distributed on the graphene matrix.Electrocatalytic testing found that Fe and N co-doped three-dimensional graphene supported Ru nanomaterials（Ru/FNG）has the best HER performance,itsη₁₀ was 32 m V,and the Tafel slope was 39 m V dec^-1.When overpotential was 100 m V,the TOF value reached 10 s^-1,and C_dl value was as high as 28 m F cm^-2.In the neutral medium,itsη₁₀ was only 34 m V,and the Tafel slope was 50 m V dec^-1,which exceeded those of Ru/CNG,Ru/NNG and Ru/NG catalysts with the same Ru loading.Therefore,by adding transition metal Fe into N-doped graphene,the HER electrocatalytic performance of Ru could be effectively enhanced.Finally,the main group element aluminum was introduced into the nitrogen-doped graphene,and then ruthenium nanoparticles were loaded to prepare the aluminum-nitrogen co-doped three-dimensional graphene loaded ruthenium nanoparticles（Ru/ANG）composite material.The catalyst materials were characterized by TEM,SEM,XRD and XPS,and it was found that the contents of Al,Ru,and N were 0.56%,2.01%,and5.91%,respectively.The electrochemical performance test showed that in alkaline media theη₁₀ of Ru/ANG was 48 m V,and the Tafel slope was42 m V dec^-1.The TOF value when the overpotential was 100 m V was 9s^-1,and the C_dl value was 27 m F cm^-2.In neutral media,itsη₁₀ was 31 m V,and the Tafel slope was 56 m V dec^-1.After 20,000 CV cycles,the overpotential at 100 m V dropped by 18 m V and 32 m V,respectively,and the current density don’t show significant loss.Therefore,the catalyst has considerable application prospects in the field of alkaline and neutral electrolysis of water.Through introducing transition metals and N-doped graphene,a series of ruthenium-based electrocatalyst were designed and prepared successfully,and showed highly efficient electrocatalytic performance for HER,which paved the way for the development of HER electrocatalysts with low price and excellent performance.