Designing The Ptco-based Heterostructure Catalysts For Oxygen Reduction/Hydrogen Evolution Reactions

Hydrogen energy,with low carbon emissions,is considered as an important carrier for achieving transformation to green economy.Fuel cells and water electrolysis are two key technologies for realizing hydrogen economy.Oxygen reduction reaction（ORR）and hydrogen evolution reaction（HER）are important cathodic processes of fuel cells and water electrolysis technologies,respectively,but their high overpotentials and slow kinetics limit the development of hydrogen economy.So far,Pt-based catalysts are still the widely used ORR and HER catalysts due to their high activity.However,the high cost and poor durability hindered their further applications.Therefore,it is significant to develop efficient,stable,and low-cost platinum-based catalysts.As known,the activity of the catalyst is highly correlated with the adsorption strength of reaction intermediates,and researchers have tried various strategies to optimize theORR/HER performance by regulating the electronic structure of the catalyst and changing the adsorption strength of H*and oxygen-containing intermediates（O*,OH*,OOH*）.Among them,constructing heteostructure catalysts can integrate the components with different advantages,regulate the electronic structure of catalysts and the adsorption energy of key intermediates by the synergistic effects between the different components,thus reduce the use of precious metals,and enhance the catalytic activity has great application prospects.This thesis aims to improve the catalytic performance and reduce the cost of Pt-based catalysts.The PtCo-Pt Sn/C,PtCoW-CeO₂/C,Pd Mo-PtCo/C and Pt_xCo_yW/C catalysts were synthesized by composite design through strategies of constructing heterostructures,heteroatom doping,morphology modulation and carrier optimization,and the conformational relationships between their electronic structures and catalyst performance were systematically investigated.The main research contents are as follows:（1）Combining the advantages of Pt-based bimetallic alloy and heteostructure,a PtCo-Pt Sn/C heterojunction catalyst is prepared by applying the principle that the difference in metal reaction enthalpies upon adsorption results in segregation during the high-temperature reduction process due to differences in migration rates.The electrochemical results demonstrate that the catalyst has good intrinsic activity for ORR with mass activity of 1158 m A mg^-1 Pt.Moreover,its of only decreases by 27.4%after 30,000 cycles,exhibiting high stability.In addition,its shows small HER potential in 1.0 M KOH(η-₁₀=-25 m V),1.0 M PBS(η-₁₀=-18 m V),and 0.5 M H₂SO₄(η-₁₀=-21 m V)solutions,and can stably perform 100,000 cycles in all three solutions.Theoretical calculation results indicate that the enhanced activity is attributed to the electronic interaction between PtCo and Pt Sn,which modulates the d-band center of Pt,reducing the binding energy between the catalyst and reaction intermediates,and enhanceing the intrinsic activity of the catalyst.Meanwhile,the charge redistribution at interface between PtCo and Pt Sn accelerates water dissociation and adsorption-desorption of hydrogen to achieve faster hydrogen recombination.Furthermore,the strong electronic interaction between PtCo and Pt Sn effectively prevents phase separation,reduceing the leaching of non-noble metal,Ostwald ripening and migration of Pt,hence improving the durability of the catalyst.（2）The PtCoW-CeO₂/C catalyst is prepared by pyrolysis and solvent method.Research shows that the strong interaction between PtCoW and CeO₂/C,as well as the alloying effect brought by W-doped PtCo can synergistically optimize the adsorption and desorption of H*/O*on the surface of Pt,thereby enhancing the intrinsic activity of the catalyst.The composite support constructed by CeO₂ and carbon effectively alleviates the shedding of nanoparticle caused by the corrosion of support.In addition,the escape effect between Pt and CeO₂ effectively promotes the spillover of surface oxygen-containing protons on Pt atoms,reducing the coverage of OH*,to slow down the dissolution rate of Pt nanoparticles by preventing the formation of Pt-oxide phase,thus improving the reaction efficiency.The above research results indicate that strong metal-support is an effective way to enhance theORR performance of PtCo alloy.（3）Pd Mo-PtCo/C,a two-dimensional alloy nanosheet that PtCo alloy shell encapsulated Pd Mo,is synthesized by a two-step solvent thermal method.It exhibits excellent ORR activity,which is 11 times that of the commercial Pt/C,And it also shows good HER activity in full p H range,with potentials of only-22.0 m V（1.0 M KOH）,-20.0 m V（1.0 M PBS）,and-18.0 m V（0.5 M H₂SO₄）at-10 m A cm^-2.In addition,it can stably operate-20 m A cm^-2 for 40h.The excellent catalytic activity is mainly attributed to the synergistic effect between PtCo and Pd Mo,which adjusts the electronic structure of Pt and effectively improves the intrinsic activity of the catalyst.And the ultra-thin two-dimensional nanosheet structure with a larger specific surface area of Pd Mo-PtCo/C is conducive to enhancing electron transfer ability and increasing specific surface area to expose more active sites,thus effectively promoting the diffusion of electrolytes and the rapid release of H₂ bubbles.This work shows that the regulation of micro-morpholpgy and the construction of heterojunctions can effectively enhance the catalytic performance of catalysts,and provides new ideas for the preparation of efficient Pt-based catalysts.（4）Pt_xCo_yW/C one-dimensional nanowires catalyst is constructed applying heteroatom doping strategy through thermal injection method.The electronic interaction between components can promote the enhancement of electrochemical activity,while reducing the content of Pt.Furthermore,the element distribution and lattice strain of the catalyst are controlled by regulating the elemental composition,which balances the activity and stability.The relationship between ORR activity and internal strain of the synthesized Pt_xCo_yW/C catalysts showes a volcano trend with Pt₃Co₃W/C demonstrating the best activity.For ORR,it exhibites a good half-wave potential of 0.933V_RHE,excellent mass activity(1534.78 m A mg^-1 Pt),and cyclic stability（30,000 cycles）.For HER,it exhibites low onset potentials[-20.0 m V（1.0 M KOH）,-19.0 m V（1.0 M PBS）,and-16.0 m V（0.5 M H₂SO₄）],small Tafel slopes,and long-term cyclic stability（50,000 cycles）.Therefore,appropriate compressive strain can maximize catalytic activity.Additionally,strong bonds of W-Pt and W-Co can be formed with Pt and Co atoms through the doping of W,which contribute to stabilize Pt and Co in the Pt-Co-W system to effectively alleviate the corrosion of Co/Pt,thus improving the stability of the catalyst.