Atomic-scale Regulation Of Nanomaterials For Enhanced Catalytic Performance

The aggravating energy crisis and environmental pollution,arisen from the overuse of fossil energy,have made it an urgent issue to develop high-efficiency and renewable clean energy systems.Among these new energy technologies,catalysts are the most important component for rapid and stable energy conversion and storage.However,the anode and cathode electrochemical reactions usually include multistep proton and electron transfer.These processes not only decelerated the reaction kinetics,but also increased the reaction energy barrier and overpotential.While the highly-active electrocatalysts can dramatically promote the energy efficiency,as well as the development of energy technologies.As we know,the surface atoms of nanomaterials are the intrinsic active center for heterogeneous catalysis.Therefore,gaining insight into the catalytic mechanism of the atomic active sites on nanomaterials will provide a new perspective for bottom-up synthesis of excellent catalysts.This dissertation mainly took the active transition metal nanomaterials as research project based on the significant electrocatalytic reaction in energy conversion,and combined multiple atomic level control strategies to design electrocatalysts with well-defined nanostructure and superior activity.We aim to achieve the controllable synthesis of atomic facet,composition and coordination structure of nanocatalysts via fine thermodynamic and kinetic regulation,and uncover the localized electron structure and intrinsic active sites of the catalysts through high-resolution spectra and theoretical calculation.Detailed content includes the following aspects:1.Atomic synergistic effect and facet effect for efficient MOR.(a)We developed a general synthesis of well-defined PtRu nanocrystals with tunable morphology and facet,and demonstrated that the {11}-terminated PtRu nanowires possessed more than two times higher of intrinsic MOR activity than that of{100}-terminated PtRu nanocubes.(b)To further improve the MOR activity of Pt,we prepared uniform {520} facets enclosed PtPb intermetallic concave nanocubes.The high-index facet effect and the synergistic effect between Pt and Pb atoms endow the catalysts with much enhanced MOR activity than PtRu catalysts.2.Steric configuration effect for ORR.(a)We utilized the dual surfactants assistant soft-template method for preparation of highly-branched mesoporous AuPdPt nanoparticles.The porous and alloyed structure of the nanoparticles provided more available and active Pt atoms,thus the catalysts exhibited efficient improvement of ORR activity than solid catalysts.(b)We first prepared ultrathin ZIF-67 nanosheets with the salt-template assistance,and in situ carbonized into uniform graphene confined Co-N-C catalysts.Attributed to the confinement effect and active Co-Nx species,the non-noble nanomaterials exhibited better ORR performance than Pt catalysts.3.Coordination effect of single-atom sites for OER and enzyme-like catalysis.(a)We put forward a concept of single-atom nanozyme,and synthesized FeNs SA/CNF single-atom catalysts through mimicking the coordination structure of enzymic active center.Both kinetics experiments and DFT calculations revealed that the enzyme-like activity and catalytic mechanism of FeNs atomic sites are much closer to natural enzymes.The catalytic rate constant of FeN5 SA/CNF is 70 times greater than that of the commercial Pt/C.(b)We synthesized ultrathin CoNi-MOF nanosheet arrays via a novel self-dissociation-assembly strategy.This catalyst exhibited well-defined atomic structure as well as excellent OER activity and stability.We employed the XAS spectra to definitely uncover the intrinsic OER active sites of coordinatively unsaturated metal nodes.Therefore,in this dissertation,we demonstrated the feasibility and great efficiency for rational design of both nanocatalyts and atomically dispersed catalysts from the above perspective of atomic structure.