CoPt And NiPt Alloy Catalysts: Preparation, Self-Assembly, Electrocatalytic And Anomalous IR Properties

Synthesis,especially the controlled synthesis,characterization and properties of nanomaterials are the most important tasks in nanoscience because they have unusual properties that could not possessed by corresponding bulk materials.CoPt and NiPt nanomaterials have attracted multidisciplinary attentions because of their special magnetic, catalytic and optical properties.In this paper,CoPt and NiPt nanomaterials with different structure were prepared by chemical reduction and galvanic displacement reaction,and their magnetic,electrocatalytic and anomalous IR properties were studied.The main experiments and results are given as follow:(1) Synthesis and properties of one-dimension(1D) chain-like CoPt nanomaterials.Two kinds of 1D CoPt nanomaterials were prepared by galvanic displacement reaction.One is a solid structure(CoPt-a),the other is a hollow structure(CoPt-b).The results of magnetic measures showed that both CoPt-a and CoPt-b are superparamagnetic.The blocking temperatures of CoPt-a and CoPt-b are 10.0 K and 9.0 K.The coercivities are 520 Oe and 740 Oe obtained at 5 K,respectively.The results of CV demonstrated that the 1D chain-like CoPt-a and CoPt-b nanomaterials exhibit better electrocatalytic properties for CO oxidation than that of bulk Pt does in 0.1 M H₂SO₄.The current peak potentials of CO oxidation are shifted negatively by 140 mV and 160 mV comparison with bulk Pt electrode,respectively.It is clearly that the catalytic activity of the hollow CoPt-b nanoparticles is much higher than that of commercial Pt/C catalyst for electrooxidation of methanol.The oxidation density on CoPt-b nanoparticles is nearly 1.9 times than that on Pt/C catalyst.The remarkably high activity of CoPt-b nanomaterials may come from the effect of the cooperating function of Co element and the special hollow structure.The fact that both CoPt-a and CoPt-b nanomaterials loaded on GC or Au substrates produce abnormal infrared effects(AIREs) has confirmed that the anomalous IR features were generated mainly by the 1D chain-like CoPt nanomaterials, and that the influence of the substrate materials on the IR spectral features may be neglected in the present study.The current study demonstrated that 1D nanomaterials also show AIREs for the first time,and thrown a new insight into understanding the origin of anomalous IR properties observed on low-dimensional nanomaterials.(2) Synthesis and properties of monodispersed NiPt nanomaterials.Galvanic displacement reaction was introduced to synthesize monodispersed NiPt nanoparticles successfully for the first time.The size,composition and morphology can be well controlled by varying reaction temperature and ratio of the reactants.A probable mechanism for the formation of the NiPt nanoparticles was proposed based on a series of assistant experiments. The obtained NiPt nanopaeticles are superparamagnetic too.The blocking temperature is 7.8 K with a coercivity of 517 Oe at 5 K.In situ electrochemical FTIRS employing CO adsorption as probe reaction demonstrated that NiPt/GC or NiPt/Au electrodes exhibit characteristics of Fano-like infrared effects either in result spectra or single spectra.The substrate materials do not affect significantly the anomalous IR features,as illustrated by the similar anomalous IR features observed for CO adsorbed on both NiPt/GC and NiPt/Au electrodes.The results demonstrated that dispersed NiPt nanomaterials obtained by chemical method display characteristics of Fano-like infrared effects for the first time,and are of significant academic importance in understanding the origin of anomalous IR properties observed on low-dimensional nanomaterials.(3) Properties of methanol electrooxidation of CoPt and NiPt nanomaterials with a hollow structure.Two kinds of NiPt nanomaterials were prepared by galvanic displacement reaction.One is a hollow structure(NiPt-a),the other is a solid structure(NiPt-b).The results of CV demonstrated that the electrocatalytic activity of NiPt-a nanoparticles is much higher than that of commercial Pt/C catalyst for the electrooxidation of methanol.The oxidation density on NiPt-a nanoparticles is nearly 1.9 times than that on Pt/C catalyst.The remarkably high activity of the NiPt nanomaterials for oxidation of methanol may come from the bifunctional mechanism,electron effect,chemical effect and the special hollow structure of the nanomaterials.The electrooxidation of methanol on CoPt-b and NiPt-a nanoparticles was studied on the molecular level by in situ FTIR.The poisonous intermediates CO observed on CoPt-b/GC electrode displays AIREs while shows Fano-like infrared effects on NiPt-a/GC electrode.The results are of significant academic importance in developing catalysts of fuel cell. (4) Synthesis,self-assembly and IR optical properties of core-shell CoPt nanomaterials. We have synthesized spherical CoPt nanoparticles by modified galvanic displacement reaction,successfully.The results of HRTEM,XPS,XRD indicated that product has a core-shell structure,and can be signed as CoPt@Pt.An ordered monolayer film of CoPt nanoparticles was obtained on the Si wafer by a L/L interface technique.In situ FTIR transmission spectrum study indicated that the ordered self-assembled monolayer film of CoPt nanoparticles(CoPt_a) shown Fano-like infrared effects while the multilayer disordered CoPt nanoparticles(CoPt_d) give an enhanced IR adsorption.The results afford a new method to synthesize nanomaterials with a core-shell structure,and develop the Liquid/Liquid self-assembly technology.The results in the current paper have contributed to understand deeply the special properties of CoPt,NiPt nanomaterials,and are of significant academic importance in understanding the origin of the anomalous IR properties of low-dimensional nanomaterials,as well as developing of new type DMFC electrocatalysts.