Study On Controllable Synthesis And Electrocatalytic Performance Of Atomic Scale Bimetallic Catalysts

With the intensification of energy consumption and climate warming,many clean energy conversion technologies(such as fuel cells,metal-air batteries,and CO₂ and N₂reduction)have been developed at home and abroad to alleviate the energy crisis and climate problems.For the clean energy conversion technologies,the development of high-performance electrocatalysts is essential to help reduce energy barriers and promote the kinetics of electrochemical processes.Among them,although noble metal catalysts(such as Pt/C,Ir O₂ and Ru O₂)have played many advantages,the practical applications are greatly limited by their scarcity and high cost.In order to reduce the cost of catalysts,various strategies have been developed,such as alloying,hybridization,and reducing the size of nanoparticles to the atomic scale of bimetallic catalysts and single-atom catalysts.Among them,atomic-scale bimetallic catalysts have high atom utilization,a controllable coordination environment,and strong synergy between different metal atoms,making them useful in many catalytic reactions(such as N₂fixation,CO₂ reduction,and H₂ oxidation)shows excellent activity and selectivity.In view of this,this thesis designed and controlled synthesis of multiple sets of atomic-scale bimetallic catalysts,and studied their electrocatalytic performance.The specific research content is as follows:(1)Inspired by the biological nitrogenase,a simple dissolution-carbonization method was used to design and synthesize an iron-molybdenum sub-nanocluster and a single atom coexisting on porous N-doped carbon catalyst(FeMo/NC),and apply it in the electrocatalytic N₂ reduction(NRR)to synthesize ammonia.N₂ was close to,adsorbed on and interacted with Fe and Mo in FeMo/NC catalyst.The Fe and Mo through electron transfer play a key role in activating the N₂ molecules.Therefore,in the NRR test,FeMo/NC catalyst can reach a maximum Faraday efficiency of 11.8±0.8%for NH₃ production in a neutral electrolyte,and the yield rate of NH₃ is 26.5±0.8?g h^-1 mg^-1_cat..In addition,within 100000 s,the Faraday efficiency change of the catalyst is negligible,and the current density decreases slightly.The advantage and innovation of this work lies in the development of a synergistic,atomic-scale bimetallic electrocatalyst,which can efficiently produce NH₃,and provides a demonstration for the design of efficient and durable catalysts in which sub-nano clusters and single atoms coexist.(2)We designed and synthesized CuSn diatomic non-noble metal(CuSn/NC)fixed on N-doped carbon,which can effectively reduce CO₂.Through spherical aberration correction electron microscopy and synchrotron radiation characterization analysis,it is found that the atomic structure of Cu-Sn is Cu N₂Sn N₂.The in-situ near-ambient pressure X-ray photoelectron spectroscopy test shows that the structure is the active center and activates CO₂ through electron transfer.Compared with copper supported on N-doped carbon(Cu/NC)and Sn supported on N-doped carbon(Sn/NC),the CuSn/NC catalyst exhibits high CO selectivity at-0.75 V with a Faraday efficiency of 99.1%.Moreover,it showed good electrolysis stability for 24 h.The CuSn/NC catalyst can weaken the C-O bond and distort the CO₂ configuration to help chemisorption and activate CO₂.(3)We designed and synthesized a RuNi bimetallic atom catalyst(RuNi/NC)supported on nitrogen-doped carbon,and applied it to the electrocatalytic H₂ oxidation reaction(HOR).Through the spherical aberration correction electron microscope,the RuNi atom pair can be clearly observed.Electrochemical tests show,RuNi/NC catalyst HOR exhibits excellent activity in an alkaline medium,the apparent current density of the overpotential?=50 m V was 1.36 m A cm^-2,with the commercial Pt/C catalyst(1.42m A cm^-2).In addition,the exchange current density of RuNi/NC(1.36 m A cm^-2_disk)is significantly greater than that of Pt/C(1.24 m A cm _Pt^-2).Moreover,the RuNi/NC catalyst also exhibits excellent HOR electrochemical stability.The synergistic effect of RuNi bimetallic atoms enhances the adsorption of Had intermediates,thereby enhancing its HOR performance.The above work successfully prepared bimetallic atoms uniformly dispersed on N-doped carbon substrates.These bimetal catalysts exhibit excellent electrocatalytic performance benefitig from their maximized atoms utilization and the synergistic effect of bimetal.These works provide new pathway for the design and synthesis of high-efficiency and robust bimetal electrocatalysts.