Atomic-level Design And Electrocatalytic Properties Of Metal-based Nanomaterials

With the increasing global energy demands and rising environmental pollution,major concerns have been raised for the development of sustainable energy pathways.As a clean,non-polluting energy with high utilization efficiency,hydrogen could be an attractive energy carrier besides fossil fuels.Water splitting and fuel cells represent two important devices for hydrogen generation and conversion.However,their efficiency is limited due to the sluggish kinetics of electrocatalytic oxygen evolution reaction(OER)in water splitting and oxygen reduction reaction(ORR)in fuel cells.Crucial to enabling the efficiency is the development of improved electrocatalysts.Although noble metals such as Pt,Ir,and Ru have been used as the commercial electrocatalysts,their low storage and high cost limit the widespread applications.Accordingly,developing highly efficient Pt-based catalysts for ORR and economic Co-based catalysts for OER is significantly important.In this dissertation,we present the development of efficient ORR and OER electrocatalysts at the atomic level.Moreover,mechanistic studies of the relationship between engineered properties and catalytic activity was also investigated in order to provide guidance for developing efficient electrocatalysts.Related research works are listed as follows:1.We have fabricated the octahedral Pd@PtNi core-shell nanocrystals with ultrathin PtNi alloy shell for ORR.The Pd@PtNi nanocrystals can be synthesized through controlling the reduction rate of precursors and deposition of metal atoms.The ultrathin PtNi alloy shells enclosed by {111} facets with tuned Pt/Ni atomic ratios enabled the decrease use of Pt,increased utilization efficiency of Pt atoms,and enhanced catalytic activity towards ORR.Experimental studies showed that the mass activity of as-obtained Pd@PtNi/C catalysts was 5 times higher than that of the commercial Pt/C catalysts.2.We have fabricated the lamellar Ag-doped cobalt selenide nanobelts with controllable conductivity via a versatile partial cation exchange method.For the metallic CoSe2 nanobelts,their electrical conductivity can be significantly enhanced by the addition of slight amount of Ag+ cations.Moreover,the relationship among the conductivity,active sites,and catalytic activities for Co-based catalysts was also investigated.Benefiting from the enhanced conductivity and the retained active sites,the as-prepared Ag-CoSe2 nanobelts exhibited enhanced activity towards OER relative to the CoSe2 nanobelts.3.We have fabricated the Au1-CoSe2 nanobelts with precisely engineered active sites for OER through controlling the deposition of slight amount of isolated Au atoms on CoSe2 nanobelts.Theoretical investigations showed that the decoration of Au atoms could shift up the d-band center of Co sites and thus facilitate the H2O adsorption.Moreover,the slight amount of Au atoms also ensures the effective exposure of Co sites.As results,the Aui-CoSe2 catalysts exhibited enhanced OER performance relative to pure CoSe2 catalysts,Au nanoparticle-deposited CoSe2 catalysts,and commercial Ir/C.4.We have fabricated the(CoMn)Se2 nanosheets with systematically engineered structural and electrical properties for OER via introducing Mn2+ cations in CoSe2 structures.With the introduction of Mn,the lattice structures,electronic structures,and electrical conductivity could be tailored and optimized.Moreover,the relationship among the structures,conductivity,active sites and catalytic activity was also investigated to understand the origin of high catalytic activity.Benefiting from the systematically engineered structures and conductivity,the(CoMn)Se2 catalysts exhibited remarkable OER activities relative to the pure CoSe2 catalysts and commercial IrO2.