The Shape-controlled Synthesis Of Pt-Ni-Cu Ternary Alloy Nanocrystals For Electrocatalytic Applications

In recent years,due to the depletion of fossil fuel such as coal,petroleum,natural gas,the environment has been polluted seriously.Also,the amount of fossil fuel is much limited.Thus,to explore a technology which is clean and has a higher energy conversion efficiency is of significant importance to deal with the pollution.Especially,Proton Exchange Membrane Fuel Cell(PEMFC)is a device which can convert chemical energy directly to electricity at room temperature.Owing to the raw materials abundant,the higher energy conversion efficiency and enviroment friendly,the PEMFC is an important aspect of the future research.Pt-based metals are the most used catalyst for the PEMFC.The morphology-controlled of monometallic or binary metallic alloy nanoparticles(NCs)have been extensive investigated.Great advances have been made in this area.While the synthesis of ternary alloy NCs is barely reported due to the formidable difficulties in controlling the nucleation/growth kinetics of NCs in the presence of multiple metal precursors with different reduction potentials.In the present work,we report a synthetic strategy that allows the one-pot fabrication of Pt-Ni-Cu ternary alloy NCs with controlled morphologies by using glycine to mediate the sequential reduction kinetics in an aqueous solution.By simply varying the concentration of glycine and hexachloroplatinic acid and using NiCl2,CuCl2 and H2PtCl6 as metal sources in the growth solution,four different shapes of Pt-Ni-Cu alloy NCs,that is,crossed,dendritic,concave nanocubic(CNC)and rough octahedral(ROH)NCs were prepared.Specifically the crossed and CNC Pt-Ni-Cu ternary alloy NCs are covered by high-index {hk0} facets.The role of glycine in tuning the rate of the nucleation and growth of Pt-Ni-Cu alloy NCs were extensively investigated.Vital role of glycine was demonstrated to alter the reduction kinetics of metal precursors and therefore determine the final morphology of Pt-Ni-Cu ternary alloy NCs.The time-sequential experiments demonstrat that the growth mechanism of crosses,dendrites and ROHs are crystal growth,self-assembly and growth-etching process,respectively.The electrocatalytic activities of these Pt-Ni-Cu alloy NCs toward methanol and formic acid oxidation were tested.To our great surprise,Pt-Ni-Cu ROH NCs without HIFs exhibit higher electrocatalytic activity than Pt-Ni-Cu crossed and CNC NCs with HIFs.And,all Pt-Ni-Cu alloy NCs exhibited higher electrocatalytic activity than commercial Pt/C and Pt black.Based on the X-ray diffusion and high-resolution transmission electron microscopy analysis,it can be concluded that the higher degree of alloy and higher density of atoms with lower coordination numbers play important roles on the catalytic activity.