Preparation Of Nanoporous Ruthenium-based Alloy And Their Water Splitting Performance

Hydrogen energy is considered to be one of the most promising clean energy sources.Electrochemical water splitting is one of the main effective ways to produce high-purity hydrogen.The water splitting is composed of two half reactions:Hydrogen evolution reaction(HER)and Oxygen evolution reaction(OER).During the reaction,voltage is applied to produce hydrogen in the cathode and produce oxygen in the anode.The key to improving the efficiency of water splitting is to optimize the electrode structure and reduce the overpotential on the electrode.In order to reduce the energy consumption of electrolysis and improve the efficiency of hydrogen evolution,high-efficiency HER catalysts must be used.At present,the catalysts with the best performance for hydrogen evolution and oxygen evolution are platinum(Pt),iridium oxide(Ir O₂)and ruthenium oxide(RuO₂),respectively.It is difficult to meet the large-scale application needs of hydrogen produced by electrolyzed water in the energy field due to the limited reserves and high price of precious metal materials.Alloying is an important method that can effectively improve the activity of catalysts and realize the new functions of heterogeneous catalysts.However,the existing methods are difficult to obtain high-efficiency alloy catalysts.Therefore,it is the key and difficult point to optimize the design of metal alloy catalysts and prepare the electrocatalysts with high efficiency in the current international research on electrocatalytic water splitting.To solve the above problems,this work developes nanoporous ruthenium-based alloys for electrochemical water splitting by alloy design ideas and dealloying method.(1)A three-dimensional nanoporous np-Cu_100-xRu_x(x=12,47,65)alloy is prepared as a high-performance platinum-free catalyst for HER by a dealloying process.Significantly,the optimized nanoporous alloy Cu₅₃Ru₄₇ exhibits remarkable catalytic activity for HER with nearly zero onset overpotential and ultralow Tafel slopes(?30and?35 mV/dec)in both alkaline and neutral electrolytes,achieving a catalytic current density of 10 m A/cm² at low overpotentials of?15 and?41 mV,respectively.Operando X-ray absorption spectroscopy experiments,in conjunction with DFT simulations,reveal that the incorporation of Ru atoms into the Cu matrix not only accelerates the reaction step rates of water adsorption and activation but also optimizes the hydrogen bonding energy on Cu and Ru active sites,improving the intrinsic activity for HER.(2)Nanoporous Co-Ru alloys with different atomic ratios are successfully prepared by melt spinning and electrochemical dealloying.Singnificantly,np-Co₄₈Ru₅₂exhibits excellent electrocatalytic performance with ultralow Tafel slopes(?22.5mV/dec)in alkaline electrolytes,achieving a catalytic current density of 10 m A/cm² at low overpotentials of?18 mV,which is better than commercial Pt/C catalyst.X-ray photoelectron spectroscopy results show that there is a strong electronic coupling effect between Co and Ru,together with the nanoporous structure for promoting the hydrogen evolution reaction.(3)The nanoporous Co-Ru alloy is prepared by traditional metallurgical methods combined with chemical dealloying,then Co-RuO₂ 150?,Co-RuO₂ 250?,and Co-RuO₂ 350?are finally obtained.Among them,Co-RuO₂ at 250?exhibits the best OER performance in acid electrolyte(0.5 M H₂SO₄),achieving a catalytic current density of 10 m A/cm² at low overpotentials of?169 mV.Furthermore,Operando X-ray absorption spectroscopy experiments reveal that Ru is gradually oxidized,and covalent bond becomes shorter during the OER process,which could reduce the energy barrier of intermediate desorption and promote the OER process.In summary,we have successfully developed the nanoporous Cu-Ru and Co-Ru alloy catalysts for electrocatalytic water splitting by a dealloying method.In terms of hydrogen evolution,electrochemical dealloying was used to precisely control the atomic ratio of Co and Ru.The as-prepared HER catalysts exhibit an excellent performance under alkaline conditions.In terms of oxygen evolution,benefiting from the unique three-dimensional interconnected porous structure and the in situ constructed oxygen vacancy defects,the nanoporous Co doped RuO₂ catalyst achieves a highly efficient acidic oxygen evolution.These works provide an important theoretical basis and practical approach to the design and research of high-performance electrocatalysts.