Design And Electrocatalytic Properties Of Transition Metal-based Nanostructures

With the exhaustion of fossil fuels and the emergence ofenvironmental problems like greenhouse effect,there is an urgent need to develop sustainable energy systems.Renewable energy technologies including fuel cells,water electrolysis,and carbon dioxide electro-reduction have been an attractive way to solve both global energy and environmental crisis because of their low pollution and high efficiency,thus receiving an ocean of research interest.Electrocatalyst is at the heart of next-generation renewable energy systems.However,the costly price and sluggish kinetics of commercial noble metal catalysts have greatly hindered the development of renewable energy technologies.Exploring cost-effective and highly-efficient electrocatalysts has become a research hotspot.Aiming at solving the above problems,this thesis focuses on the design and performance optimization of noble metal alloy and inexpensive metal nanostructures,the structure-activity relationship is investigated at the same time.The detailed research includes:1.Ultrathin branched PtRuFe ternary nanodendrites and their electrocatalytic performance towards methanol oxidation.PtFe bimetallic nanodendrites were prepared through one-pot synthesis,the Pt/Fe galvanic reaction and oxidative etching induced by I-/O2 jointly led to the formation of ultrathin nanodendrites.Ternary PtRuFe ultrathin nanodendrites were further prepared,which exhibited enhanced electrocatalytic methanol oxidation activity when compared with PtFe bimetallic catalyst and commercial Pt/C catalyst.2.Surface Au-decorated PtFe nanostructure was designed,the superior anti-CO poisoning capability of PtFeAu nanocatalyst enhanced both electrocatalytic activity and stability towards methanol oxidation.Density functional theory was firstly employed to demonstrate the weak CO adsorption on the surface of PtFeAu nanostructure,then we prepared Au-decorated PtFe nanocatalysts and experimentally confirmed their superior anti-CO poisoning capability and the excellent activity/stability for electrocatalytic methanol oxidation.3.Oxygen vacancies were introduced into single-crystalline ultrathin Co304 nanosheets,the electrocatalytic oxygen evolution activity of such defect-rich Co3O4 nanosheets is even better than noble-metal Ir02 catalyst.The oxygen defects were introduced into single-crystalline ultrathin Co3O4 nanosheets by mild solvothermal reduction using ethylene glycol under alkaline condition.Electrochemical analysis and density functional theory reveal the defect effect:oxygen vacancies on the(111)facets of Co3O4 structure leads to the exposure of second-layered Co metal sites,which leads to the lowered oxygen evolution reaction activation energy and improved electrical conductivity resulting in enhanced electrocatalytic oxygen evolution activity,even better than commercial Ir02/C catalyst.4.Tuning the local atomic structure and introducing Fe-O-Fe couples into NiFe layered double hydroxide to enhance the electrocatalytic oxygen evolution activity.In contrast to traditional fabrication method using Ni2+ and Fe3+ as feeding salts,we introduced Fee+together with Ni2+ and Fe3+ for co-precipitation to construct Fe-O-Fe moieties.Raman and electrochemical analysis,together with in-situ X-ray absorption spectra,reveal that the Fe-O-Fe motifs could stabilize high-valent metal sites at low overpotentials,thereby enhancing the oxygen evolution activity.5.Engneering the three-phase contact interface on superwetting Cu electrode to control CO2 electroreduction selectivity.By surface polytetrafluoroethylene modification,the aerophobic/hydrophilic Cu nanowire array electrode surface turned to be aerophilic/hydrophobic.The modified Cu electrode showed different contact behavior towards CO2,electrolyte and gas/liquid products,which tuned CO2 reduction kinetics,thus controlling the reaction selectivity.In addition,the interface engineering strategy could also be applied in metal-oxide systems.