Structural Design Of Bimetallic Carbides And The Study Of Its Electrocatalytic Performance And Merchanuism

With the over-exploitation and widespread use of fossil fuels,human society are gradually facing serious environmental pollution and energy shortage problems.The development of new clean energy is imminent in order to promote the important strategy of"carbon peaking and carbon neutrality".Hydrogen energy is considered to be an ideal energy form due to its high specific energy and zero emissions of greenhouse gases.And fuel cells and electrochemical water splitting for hydrogen production are regarded as key technologies for realizing the hydrogen economy.However,the cathode oxygen reduction reaction（ORR）of the most widely used proton exchange membrane fuel cells（PEMFCs）is still difficult to get rid of the shackles of noble metal catalysts,resulting in the high cost of PEMFCs.Fortunately,a large number of non-noble metal catalysts with ORR property comparable to platinum group noble metal catalysts in alkaline media have been reported.Therefore,with the development of alkaline membrane technology,it is possible to replace PEMFCs with Alkaline exchange membrain fuel cells（AEMFCs）.However,the kinetic rate of the anodic oxidation reaction（HOR）in alkaline medium is 2-3 orders of magnitude slower than that in acidic medium,which becomes the bottleneck for the development of AEMFCs.On the other hand,the low efficiency of Alkaline water electrolyzers（AWEs）and the low purity of hydrogen products have also become constraints for the development of hydrogen energy economy.And proton exchange membrane water electrolyzers（PEMWEs）have the advantages of high efficiency,high hydrogen purity,fast response speed,and low ohmic loss,and are regarded as the next generation hydrogen production technology that is expected to replace AWEs.However,the anodic oxygen evolution reaction（OER）process is accompanied by four-electron transfer and the formation and transformation of complex intermediates.The kinetics are slow and require a high overpotential to cross the energy barrier.At present,a large number of reported non-precious metal OER catalysts can only be used in alkaline media,and OER in acidic media is still highly dependent on noble metal catalysts.Therefore,the design and development of basic HOR and acidic OER non-precious metal catalysts with high performance and good stability is the key to promoting the large-scale application of AEMFCs and PEMWEs,and is also an important part of promoting the development of hydrogen energy economy.Transition metal carbides（TMCs）have high electrical conductivity,good thermodynamic stability,and are stable over the full p H range.In particular,TMCs possess platinum-like electronic structures and catalytic properties,leading to a wide range of applications in a range of catalytic and electrocatalytic reactions.Therefore,TMCs are also considered as possible non-noble metal catalysts for basic HOR and acidic OER.However,the application of TMCs to alkaline HOR and acidic OER is only rarely reported,and its performance does not have significant advantages.In recent years,researchers have proposed to form binary transition metal carbides by introducing a second transition metal element into TMCs.Using the introduced transition metal,the d-band electronic structure of TMCs can be further tuned,and its electrical conductivity can be further improved.A series of catalytic reaction properties.In addition,heteroatom doping is also an effective strategy to improve the catalytic performance of TMCs,especially the doping of fluorine（F）element,because of its strong electronegativity and small atomic radius,can strongly tune the d-band electronic structure of TMCs to greatly improve the its electrocatalytic properties.Therefore,the research content of this paper is closely centered on the electronic structure design of TMCs.By constructing binary TMCs,basic HOR non-precious metal catalysts with performance comparable to Pt are designed and synthesized.On this basis,the F doping strategy is further utilized.,designed and prepared an acidic OER non-precious metal catalyst with performance far exceeding that of noble metal Ir/C.The research content of this paper is summarized as follows:（1）Synthetic Co_xMo_yC nanoparticles loaded on cobalt foam（Co_xMo_yC NR/CF）were treated by hydrothermal method and subsequent annealing.XPS results confirm that the electronic structure of binary TMCs can be tuned by controlling the configuration of Co_xMo_yC.Electrochemical test results show that the electrocatalyst with Co₃Mo₃C configuration（Co₃Mo₃C NR/CF）has the most excellent HOR performance.It can achieve a current density of 5.6 m A cm^-2 at 0.10 V vs.RHE and an exchange current density（j₀）of 1.84 m A cm^-2.At the same time,the Co₃Mo₃C NR/CF exhibited good stability(maintaining a current density of2.2 m A cm^-2 for more than 12 h).Its catalytic activity and stability are even due to noble metal Pt/C catalysts.Density functional theory（DFT）calculations reveal the catalytic mechanism:Based on suitable interplanar spacing,the d-band electronic structures of Co and Mo sites in the Co₃Mo₃C lattice are tuned,and their binding forces with adsorbed intermediates hydrogen（H*）and hydroxyl（OH*）are optimized,reducing the catalytic reaction barrier,the performance is improved.This study has scientific significance for the design and development of anode HOR non-precious metal catalysts for AEMFCs.（2）To further enhance the electrocatalytic performance of binary TMCs,the F atom doping strategy was applied to construct highly efficient acidic OER non-noble metal catalysts.According to the EPR and VSM characterization results,the electron spin states of the as-prepared titanium-tantalum binary TMCs（Ti Ta C₂ NP/rGO）are tuned compared to the corresponding reduced graphene oxide supported unit TMCs（Ti C NP/rGO and Ta C NP/rGO）,due to the appearance of Ti³⁺,eg electrons are generated in the 3d orbital,which is favorable for the adsorption of OER reactants.X-ray absorption spectra showed that the doping of F further adjusted the valence state,coordination environment and bond length of Ti Ta F_xC₂.The as-prepared Ti Ta F_xC₂ NP/rGO exhibited high catalytic activity(up to 100 m A cm^-2 at 490 m V),fast kinetic process(Tafel slope of only 36 m V dec^-1),and high stability for OER in acidic media.(27.4 m A cm^-2 can be maintained for 40 h),and its performance is even better than that of noble metal Ir/C catalysts.Furthermore,the as-prepared materials proved to have significant application potential.DFT calculations show that spin state tuning and F doping tune the electronic structure of Ti Ta C₂ NP/rGO,improve the adsorption of reaction intermediates,and enhance the OER catalytic performance of non-noble metal electrocatalysts in acidic media.This study has important scientific significance and application value for the design and development of efficient and stable non-precious metal catalysts for PEMWE anodes.（3）Further,we synthesized rGO supported F-doped Ti Mo C₂ NPs（Ti Mo F_xC₂ NPs/rGO）.Based on the spin state tuning of binary TMCs and the tuning of electronic structure by F doping,the as-prepared Ti Mo F_xC₂ NP/rGO exhibits excellent catalytic performance for acidic OER,which can reach a current density of 100 m A cm^-2 at 450 m V,Tafel The slope is only 61m V dec^-1,and the current density of 27.4 m A cm^-2 can be maintained for more than 35 h.This work further expands the application of TMCs in PEMWE anodes.