Surface Charge State Modulation Of Metallic Nanomaterials And Investigation On Electrocatalysis

The conversion and shortage of electrochemical energy is one of the most efficient solutions to solve the energy crisis.As the surface propertie of metallic nanomaterials are easily modulated by morphology control and surface electronic state regulation.The design of metallic nanomaterials have been widely used in the field of catalysis,energy and biosensor due to their unique properties.Scientists focus on recent research concerning surface chemical modification strategies to effectively engineer the intrinsic physical and chemical properties of metallic nanomaterials.According to the research background above,surface and interface of metallic nanomaterials can be modulated by morphology control and surface electronic state regulation.The main contents and results of this thesis are summarized as following:1.We have demonstrated a simple,facile,and size controllable seed mediated growth approach for the fabrication of palladium porous single-crystalline nanoflowers containing enriched high catalytic activity {100} facets and atomic steps with high-index-facets as active sites that present significantly enhanced electrocatalytic activity,high anti-poisoning and stability toward ethanol oxidation in alkaline media.The forming mechanism of the Pd PSNFs was investigated based on the study of time-dependent morphology evolution by TEM imaging during the growth process.The present study provides a facile method for the synthesis of porous Pd-based catalysts dominated by the desired high catalytic activity facets and demonstrates their potential applications in catalysis.2.In summary,we have demonstrated a facile and diversified seed-mediated supersaturation-controlled epigrowth approach for the fabrication of Pd@Pt core-shell nanostructures by adjusting the pH value in the reaction system.The formation mechanism of the Pd@Pt core-shell NCs was investigated based on the study of time-dependent morphology evolution by taking TEM snapshots during the growth process.The asprepared well aligned Pd@Pt core-island shell NCs present both significantly enhanced electrocatalytic activity and favorable long-term stability toward ORR in alkaline media.For the first time,the present work provides a facile strategy for controllable deposition of Pt on the Pd substrate at a sub 10 nm scale by adjusting pH and demonstrates a potential possibility via supersaturation theory for designing excellent fuel cell catalysts.3.In conclusion,a newly designed HER catalyst-Pd modified on the basal plane of a defect-rich Mo S2 nanosheet(DR-Mo S2)was determined by DFT calculations to be highly active toward the HER.The heterostructure was implemented by synthesizing and assembling a disk-like Pd nanostructure(Pd NDs)onto the basal plane of DR-Mo S2 while retaining its active sites.The synergistic regulation of both the structure and electronic states caused the Pd NDs/DR-Mo S2 heterostructure to exhibit exceptional HER properties with a low onset-overpotential,small Tafel slope,extremely high exchange current density and robust HER durability.These results represent,for the first time,a non-Pt-metal-modulated Mo S2 catalyst that approaches the performance of the benchmark Pt/C catalyst with superior catalytic activity and favorable reaction kinetics compared with catalysts previously reported in the literature.The study demonstrates the potential for HER catalytic performance improvement of layered TMDs by midification of the lamellar metal nanostructure,which will open a new pathway for improving the HER activity of catalysts through synergistic structural and electronic modulations.4.In this study,we demonstrated a universal and up-scalable synthetic strategy for the fabrication of substrate phase variable single atom catalyst.A variety of analytical techniques illustrated that the phase of Mo S2 transformed from the semi-conductive to the metallic phase under the effect of the strain induced by the lattice mismatch between Mo S2 and Co.After the acid leaching process,redundant Co was removed while the single atom Co-anchoring remained.The single atom Co-metallic Mo S2(SA Co-M Mo S2)catalyst exhibits a startlingly Pt-like HER activity with the low overpotential(40 m V at 10 m A cm-2),low Tafel slop(32 m V dec-1),high turnover frequency(12.616 s-1),excellent long-term and cycling stability.These HER properties are better than those of the best-characterized edge sites,the metallic basal plane and,to the best of our knowledge,any single atom or TMD based HER catalyst reported to date.Our results demonstrate a new strategy for the study of the relationship between the single atom loading content and the phase variable substrate,also help accelerating the large scale application of proton exchange membrane(PEM)electrolyzers and solar photo-electrochemical(PEC)water electrolyzers.