Design Of Pt-modified Manganese Oxide Catalysts For Hydrogen Evolution Performance

As a clean,efficient,and sustainable energy source,hydrogen energy is regarded as the most promising clean energy source for development.Compared with traditional industrial hydrogen production methods,water electrolysis is considered to be one of the simplest and most efficient technologies for hydrogen production.At present,Pt catalysts are the most efficient catalysts for HER,due to the limitation of precious metal reserves and cost,it has become a hot research topic in this field to enhance Pt atom utilization and prepare low loading precious metal catalysts with high catalytic activity.Research has shown that only the superficial platinum atoms are involved in the electrocatalytic hydrogen evolution reaction,which leads to the low efficiency of the atomic utilization of platinum.Reducing the size of Pt nanoparticles to clusters or isolated single-atom states can significantly reduce the number of precious metals used and enhance their atomic utilization.However,practical applications of these low-size materials are severely hampered by intrinsic complexities,such as atom clustering and migration due to high surface energy during synthetic post-processing or catalytic reactions.Therefore,the nature of the support plays a crucial role in the catalytic activity and stability of the low-size supported catalyst.To address the above problems,this thesis proposes an electrochemical in situ synthesis strategy to synthesize a series of Pt-supported manganese oxide catalysts with different Pt sizes on manganese oxide support using the disproportionation effect of manganese.The preparation,electronic structure,HER performance,and catalytic mechanism of catalysts are systematically investigated by combining various testing and characterization techniques.The details of the study are as follows:（1）Controlled synthesis and alkaline hydrogen evolution reaction study of Mn O₂-supported Pt clusters.Mn O₂ nanosheets were synthesized on nickel foam substrates using the electroplating method.The Mn was dissolved into the solution during the cycling process by the potential cycling method among electrochemical deposition while anchoring Pt atoms in vacancies.Characterization by XPS,XRD,EPR,and Raman demonstrated that Pt atoms were anchored in Mn ion vacancies,and the[Mn O₆]octahedral confining effect effectively inhibits Pt atom migration and aggregation.The results of spectral data analysis and theoretical calculations confirm that charge transfer occurs locally after Pt doping,indicating a strong interaction between Pt and the support,further stabilizing the active Pt atom.Electrochemical test results show that the catalyst has an excellent electrocatalytic activity for hydrogen evolution in an alkaline electrolyte（1.0 M KOH）.The HER performance of this catalyst requires only 47 m V overpotential to reach a current density of 100 m A cm^-2 with a low Tafel slope of 44 m V dec^-1,as well as a good mass activity and turnover frequency at a potential of-0.05 V.The ability to electrolyze continuously for 80 h at a current density of 10 m A cm^-2indicates that the catalyst also has excellent stability.（2）Precise synthesis and hydrogen evolution performance study of Mn₃O₄-supported Pt single atoms.Use the same electrochemical deposition method as Pt _AC-Mn O₂.Unlike Pt _AC-Mn O₂,the Mn₃O₄ support has a spinel structure（tetrahedral and octahedral coexistence）,allowing selective anchoring of Pt to octahedral sites using electrochemical potential cycling.Characterization by STEM,XPS,EPR,and XAFS demonstrates that isolated Pt atoms are preferentially embedded in octahedra with Mn³⁺ionic vacancies.In addition,the Pt modification can effectively adjust the valence band of the catalyst to move toward the Fermi energy level,lowering the work function and facilitating the escape of electrons.Our results reveal that the electron transfer between Pt and Mn₃O₄ induced a moderate rise in the d-band center of the catalyst,enhancing the H₂O adsorption affinity and effectively promoting hydrolysis and optimizing intermediate adsorption and desorption.The potential advantages of electrochemical deposition strategies and the possibility of enhancing the overall catalytic activity through electronic structure properties are demonstrated in this thesis.The electrochemical cyclic voltammetry achieves the dissolution and anchoring of metal species in one step,and the vacancy anchoring and local coordination of the support effectively inhibit Pt atom migration.Meanwhile,the interaction between the active metal and the support changes the electron transfer,which affects the adsorption and desorption of reaction intermediates and accelerates the reaction kinetics.