Controllable Synthesis Of Platinum-coblt Composite Catalyst With Enhanced Electrocatalytic Properties

Up to now,the long-term use and excessive combustion of fossil fuels have led to a series of problems such as energy crisis and environmental pollution.Therefore,the development and research of clean and renewable alternative energy has become an urgent need to solve these problems.Proton exchange membrane fuel cells?PEMFCs?have been considered as an effective alternative to fossil fuels in recent years,owing to their advantages of cleanness,stability and high energy conversion efficiency.Pt metal catalysts in PEMFCs are limited in commercial applications due to their high scarcity and high susceptibility to CO poisoning.To overcome this disadvantage,cheap 3d transition cobalt?Co?was introduced into metal Pt in this study,and two-dimensional carbon nano-materials with large specific surface area,high conductivity and other excellent properties were used as the supports,whereby PtCo nanoparticle composite catalysts were synthesized by one-pot solvothermal method.In this paper,hexadecyl trimethylammonium chloride?CTAC?or L-proline was used as regulation molecule,pyrrole,ethylene glycol and 1-nitroso-2-naphthol were used as reducing agents,respectively,with regulating the feeding ratio of two metal precursors,PtCo composite catalysts were regulated in the controllable synthesis.All the obtained PtCo nanoparticle composite catalysts were characterized by Fourier transform infrared spectroscopy?FTIR?,thermogravimetric analysis?TGA?,X-ray photoelectron spectroscopy?XPS?,transmission electron microscopy?TEM?.On this basis,the synthesis mechanism and catalytic applications?including oxidation reaction of methanol and ethylene glycol,the oxygen reduction and hydrogen evolution reaction?of the above catalysts were studied.The results indicated that the PtCo nanoparticle composite catalysts prepared in this research work showed better catalytic performance with potential applications in fuel cells due to the synergistic effect between Pt and Co and the enhancement of dispersion and stability of the Pt particles,when compared with commercial Pt black or Pt/C catalysts.The main contents of this thesis are as following:?1?Synthesis and electrocatalytic properties of monodisperse Pt₇₁Co₂₉9 lamellar nanoflowersBimetallic alloyed Pt₇₁Co₂₉9 lamellar nanoflowers?LNFs?with abundant active sites were obtained by a one-pot solvothermal method,where CTAC and1-nitroso-2-naphthol served as co-structure-directors,while oleylamine?OAm?as the solvent and reducing agent.The fabricated Pt₇₁Co₂₉9 LNFs exhibited the higher mass activity(MA,128.29 mA mg^–1)for oxygen reduction reaction?ORR?than those of home-made Pt₄₈Co₅₂2 nanodendrites?NDs?,Pt₇₉Co₂₁1 NDs and commercial Pt black with the values of 39.46,49.42 and 22.91 mA mg^–1,respectively.Meanwhile,when the voltage is 0.75 v,the values of MA(666.23 mA mg^–1)and specific activity(SA,2.51 mA cm^–2)of the constructed Pt₇₁Co₂₉9 LNFs for methanol oxidation reaction?MOR?are superior than those of Pt₄₈Co₅₂2 NDs(213.91 mA mg^–1,1.99 mA cm^–2),Pt₇₉Co₂₁1 NDs(210.09 mA mg^–1,1.12 mA cm^–2)and Pt black(57.03 mA mg^–1,0.25mA cm^–2)catalysts.The Pt₇₁Co₂₉9 LNFs also exhibited the best durable ability relative to the referenced catalysts.These results all show that Pt₇₁Co₂₉9 LNFs catalyst has a good application prospect in fuel cell.?2?Synthesis and electrocatalytic properties of polypyrrole sheets supported dendritic coblt-platinum nanoclustersDendritic CoPt nanoclusters supported on sheet-like polypyrrole were prepared by facile one-pot solvothermal method,in which CTAC was used as the morphological regulation molecule,pyrrole as the reducing agent,and oleylamine as the co-reducing agent,respectively.In other words,two kinds of metal precursor salts were mixed into oleylamine,and pyrrole was in-situ polymerized to form PPy sheets under the high temperature and high pressure condition,finally frabricating PtCo NCs/PPy.Physical characterization such as TEM,XRD and FTIR proved that CoPt formed the stable alloy structure,and this alloy structure was successfully loaded on the polypyrrole sheet.This architecture had larger electrochemically active surface area?EASA?of 30.95 m² g^–11 than the home-made Pt₁Co₃ nanoparticles?NPs?/PPy,Pt₃Co₁ NPs/PPy and commercial Pt/C catalysts,and exhibited superior catalytic performances for ethylene glycol reduction reaction?EGOR?and oxygen reduction reaction?ORR?.Specifically,in 0.1 mol L^-11 HClO₄ solution,the mass activity?MA?of PtCo NCs/PPy(178.91 mA mg^–1)for ORR was higher than Pt/C(100.7 mA mg^–1).The MA of PtCo NCs/PPy for EGOR in 0.5 mol L^–11 KOH was 1097.72 mA mg^–1,which was 2.49-,2.65-,1.14-higher than the referenced Pt₁Co₃ NPs/PPy,Pt₃Co₁NPs/PPy and Pt/C catalysts.In addition,PtCo NCs/PPy also exhibited greater stability and durability in ORR and EGOR when compared with commercial Pt/C.?3?Synthesis and electrocatalytic properties of PtCo nanocrystals supported on reduced graphene oxideUsing L-proline as the morphological regulation molecule,ethylene glycol as the reducing agent,the sheet-like PtCo nanocrystals were efficiently loaded into reduced graphene oxide?rGO?by a simple solvothermal method.By exploring the influence of Pt:Co feeding ratio and introducing rGO as a support,Pt₂₉Co₇₁1 NPs/rGO,Pt₈₃Co₁₇NPs/rGO,Pt₅₂Co₄₈8 NPs,commercial Pt/C and Pt black were synthesized as the referenced catalysts under the same experimental conditions,and a series of characterization techniques were used to analyze the aboved structures.Results have shown that PtCo composite catalyst can effectively load into the rGO sheet structure.When the metal precursor Pt/Co ratio is 1:1,Pt₇₈Co₂₂2 NCs/rGO catalyst with the highest catalytic activity and the best stability in ORR and hydrogen evolution reaction?HER?obtained.The content of the two metals in Pt₇₈Co₂₂2 NCs/rGO alloy was analyzed by EDS technique.