Synthesis Of Platinum Group Metal-based Alloy Nanocrystals And Their Electrocatalytic Properties

It has been paid wide attention for the platinum group metal-based bimetallic alloy nanomaterials due to their excellent catalytic performance.In addition,microwave method is widely used in chemical synthesis because of its fast heating,simple and high energy efficiency.In recent years,our research group has applied microwave method to the shape-controlled synthesis of platinum group metals and their alloy nanoparticles,and achieved a series of achievements.It is shown that not only can uniform and well-defined platinum group metal nanoparticles with different morphologies been fast synthesized by microwave irradiation,but also does obvious advantage to the synthesis of alloy nanocrystalline exhibit.In this paper,microwave was employed in syntheses of platinum group metal-based bimetallic alloy nanoparticles,and their electrochemical performances were also investigated.By means of microwave heating method,trioctahedron Ir-Pd nanocrystals were successfully synthesized by using Ir?acac?₃ and H₂PdCl₄ as precursors,tetraethylene glycol?TEG?as a solvent,ascorbic acid?AA?as a reducing agent,polyvinylpyrrolidone?PVP?as a stabilizer,and KI as a morphology controller.The products were characterized by TEM,STEM,SEM,XPS,XRD and other instruments.The formation mechanism of trioctahedron Ir-Pd nanocrystals was discussed by regulating relevant parameter.The selective growth of Pd-Ir nanocrystal was suppressed by the selective adsorption of KI on some special planes of nanocrystals.The formation of trioctahedron Ir-Pd nanocrystals should be ascribed to the existence of KI which was advantageous to the co-reduction of the metallic precursors by regulating oxidation-reduction potential,as well as microwave irradiation which also promoted co-reduction.The performance of electrocatalytic oxidation of formic acid showed that the catalytic activity of Ir-Pd concave octahedral nanocrystals was 2.5,1.7 and 2.5 times that of Pd black,Pd small nanoparticles and Ir small nanoparticles,respectively.By means of microwave heating method,Ir-Pt porous cubic nanocrystals were successfully synthesized by using Ir?acac?₃ and H₂PtCl₆ as precursors,TEG as a solvent,AA as a reducing agent,PVP as a stabilizer,and KI as a morphology controller.The products were characterized by TEM,SEM,XPS and XRD.The formation mechanism of Ir-Pt porous cubic nanocrystals was investigated by adjusting relevant parameters.The synergistic reduction of AA and TEG promoted the selective accumulation and growth of Pt atoms and Ir atoms on the nucleus.The reduction potential was reduced due to the oordination of I?ions with the precursor H₂PtCl₆,resulting in the co-reduction of the two metal precursors to form porous cubic nanocrystals.In addition,the electrochemical catalytic performance of Ir-Pt porous cubic nanocrystals was tested by electro-oxidation of formic acid and methanol.The results show that the catalytic activity of Ir-Pt porous cubic nanocrystals was 1.7 and2.2 times that of commercial Pt black for the electro-oxidation of formic acid and methanol,respectively.By means of microwave synthesis method,the uniform and well-defined concave cubic Pt-Cu nanocrystals with an average size of 40 nm were also successfully prepared by using H₂PtCl₆ and CuCl₂ as the precursors,TEG as both a solvent and a reducing agent,PVP as a stabilizer in the presence of an appropriate amount of KI.The products were characterized by TEM,STEM,SEM,XPS,XRD and other instruments.The effects of microwave irradiating time,the amounts of KI and PVP upon the formation of Pt-Cu concave cubic nanocrystals.The results showed that the Pt-Cu concave cubic nanocrystals were generated by the co-reduction of the mixed metallic precursors.In the reaction system,the optimum molar ratio of H₂PtCl₆/CuCl₂/KI/PVP was 2/1/70/100.An appropriate microwave irradiation time as well as an appropriate amount of KI was advantageous to the co-reduction of the mixed metallic precursors.The use of KI was critical to the formation of Pt-Cu concave cubes.On the one hand,the coordination of I?ions with the precursor[PtCl₆]^2-was favorable for the co-reduction of the two metal precursors by lowering the reduction potential.On the other hand,the selective adsoption of I?ions on some special lattice planes promoted the oriented growth of Pt-Cu alloy nanocrystals.In addition,the quick thermal effect caused by microwave irradiation also facilitated the co-reduction of the mixed metallic precursors.Electrochemical tests show that the catalytic activity was improved compared with commercial Pt black.The catalytic activity of Pt-Cu concave cubes was 2.6 and 1.8 times that of Pt small particles and commercial Pt blacks for the electro-oxidation of formic acid,respectively,while 2.3and 2.0 times that of Pt small particles and Pt black for the electro-oxidation of methanol.