Controllable Synthesis Of Platinum Nickel Alloyed Nanomaterials For Hydrogen Evolution And Oxygen Reduction Reactions

The destruction of environment and the shortage of energy are the important problems in the harmonious development of human,nature and society.The development of fuel cells and hydrogen energy provide a green,clean and sustainable strategy to solve these problems.Platinum?Pt?catalyst is the most efficient single metal catalyst in fuel cells and hydrogen evolution reaction?HER?.However,the high price,poor stability and high susceptibility to CO poisoning of Pt catalyst limit the further extensive promotion.Pt alloyed with transition metal nickel?Ni?,which is abundant in the earth,to form the three-dimensional?3D?bimetals alloyed nanoflowers,nanodendrities or nanopolyhedrons structure can not only reduce the cost,but also increase the catalytic activity area and active sites,and alleviate the poisoning of catalyst,thus improve the catalytic activity and stability.Herein,the flower/dendritic/polyhedron-structure of PtNi nanoparticles were prepared with different costructure-directing agents?citric acid,melamine,cytosine,respectively?by a simple solvothermal method,utilizing cetyltrimethylammonium chloride?CTAC?as the structural guiding agent.Transmission electron microscopy?TEM?,high-angle annular dark-field scanning-transmission electron microscopy-energy dispersive spectroscopy?HAADF-STEM-EDS?,X-ray diffraction?XRD?,and X-ray photoelectron spectroscopy?XPS?are applied to characterize the physical and chemical properties of the prepared PtNi nanoparticles.The formation mechanisms were also explored according to the characterization and experimental phenomena.The results showed that the prepared nanomaterials exhibited better catalytic performance?including HER and oxygen reduction reaction?ORR??compared with commercial Pt/C and/or Pt black catalysts.The specific contents are as follows:?1?The synthesis of Pt₆₆Ni₃₄ nanoflowers for hydrogen evolution reactionA simple solvothermal co-reduction method was developed for the fabrication of3D uniform Pt₆₆Ni₃₄ nanoflowers(Pt₆₆Ni₃₄ NFs)with highly rough surface and abundant active sites,where CTAC and citric acid were used as the costructure-directing agents.The prepared Pt₆₆Ni₃₄ NFs exhibited enhanced catalytic properties towards HER in both acidic and alkaline media.Specifically,the overpotential at 10mA cm^–2 and Tafel slope of Pt₆₆Ni₃₄ NFs(43 mV,33 mV dec^–1)were similar to commercial Pt/C(20 wt%,40 mV,31 mV dec^–1)in 0.5 mol L^–1 H₂SO₄.Moreover,Pt₆₆Ni₃₄ NFs displayed the smaller overpotential at 10 mA cm^–2?50 mV?and Tafel slope(57 mV dec^–1)as compared with Pt/C(63 mV,69 mV dec^–1)in 0.5 mol L^–1 KOH.And the catalyst exhibited superior durability for HER relative to Pt/C in both acidic and alkaline electrolytes.All these demonstrate the potential applications of Pt₆₆Ni₃₄ NFs in energy storage and conversion.?2?The synthesis of PtNi nanodentrites for hydrogen evolution reactionPtNi nanodentrites?PtNi NDs?were facilely synthesized in oleylamine?OAm?by a one-pot solvothermal method,using melamine and CTAC as co-structure-directing agents.The as-obtained catalyst showed superior catalytic activity and enhanced durability for HER relative to commercial Pt/C,home-made PtNi₃ nanocrystals?NCs?and Pt₃Ni NCs both in alkaline and acidic media.The enhanced HER activities are attributed to the bimetallic synergies and interface structures in PtNi NDs.This work provides an effective strategy to prepare highly efficient and durable electrocatalysts for HER.?3?The synthesis of Pt₄₇Ni₅₃ nanopolyhedrons for hydrogen evolution and oxygen reduction reactions3D Pt₄₇Ni₅₃ nanopolyhedrons?NPHs?were constructed by a facile one-pot solvothermal strategy,in which cytosine and CTAC worked as the co-structure directing agents.The Pt₄₇Ni₅₃ NPHs showed high catalytic activity and stability towards ORR and HER in comparison to Pt₁₃Ni₈₇ NCs,Pt₆₃Ni₃₇ NCs,commercial Pt black and/or Pt/C catalysts.Impressively,the mass activity of Pt₄₇Ni₅₃ NPHs was about 215.80 mA mg_Pt^–1 for ORR,which was approximately 4 times increase relative to Pt black(49.60mA mg_Pt^–1).These results demonstrate the broad application prospects of the synthesized nanocatalysts in energy storage and transformation.