Study Of Structure-Activity Relationship Of Composite Pd(Pd_xAu)/Co-nanofilms/C Electrocatalysts Adjusted On ILs/Water Interface

Low Temperature Fuel Cells?PEMFC,AFC,DAFC?have attracted much attention due to their simple structure,friendly environment,high energy density,easy to carry,etc.As limited Pt resource,the high cost,easily poisoned by CO and lack of stability,Pt-based catalysts can not achieve the commercialization of fuel cell.So the development of efficient and inexpensive catalyst has become the main problem at present.Furthermore,Pd has a lower price and abundant reserves,and similar valence shell structure and the lattice constant to those of Pt.But in alkaline media,Pd-based catalysts have high stability and activity for Ethanol Oxidation Reaction and Oxygen Reduction Reaction.This work Pd?Pd_xAu?/Co-nanofilms/C were synthesized on an immiscible ionic liquid/water interface by a sequential reduction approach and explored their activity and stability of palladium.The results are as follows:?1?Carbon-supported composite electrocatalysts of Pd nanoparticles implanted on Co nanofilms?Pd_x/Co-nanofilms/C?were synthesized on an immiscible ionic liquid/water interface by a sequential reduction approach.Controllable metal nanostructures?Pd nanoparticles,Co nanofilms?and highly dispersed Pd_x/Co-nanofilms on carbon are achieved through simple strategies.The Pd nanoparticles implanted on Co nanofilms evidently exhibit crystal lattice distortion and surface roughness.Thus prepared Pd₃/Co-nanofilms/C catalyst demonstrates the highest activity toward ethanol oxidation reaction?EOR?,with the lowest onset potential shifting negatively about 100 mV,the most negative peak potential?lower 20 mV of Pd/C?,and the highest peak current compared with those of Pd₃Co/C?1.46 times of Pd/C?and pure Pd/C catalysts in alkaline solution.Chronoamperometric results also demonstrate higher current values produced by the Pd₃/Co-nanofilms/C catalyst.We proposed that the EOR activity enhancement of Pd_x/Co-nanofilms/C catalysts may be attributed to a modulation of the structural properties of Pd nanoparticles through the 2D Co-nanofilm substrate,as well as a synergistic effect between Pd nanoparticles and the Co-nanofilm substrate.?2?The morphology tuning of Pd and Pd-M nanoparticles is one of the significant strategies to control the catalytic activity towards oxygen reduction reaction?ORR?.In this study,composite Pd_x/Co-nanofilms/C electrocatalysts of Pd nanoparticles implanted onto Co nanofilms were synthesized on an immiscible ionic liquid?ILs?/water interface for ORR.These Pd_x/Co-nanofilms/C electrocatalysts exhibit enhanced activity for ORR compared with Pd/C and Pd_xCo/C catalysts in both acid and alkaline solutions,in which the Pd₃/Co-nanofilms/C catalyst displays the highest ORR mass activity.In acid and alkaline media,the active area of Pd₃/Co-nanofilms/C catalysts is 1.12 times and 1.46 times of Pd/C,while the quality activity of Pd₃/Co-nanofilms/C catalysts is 1.6 times and 1.76 times of Pd/C,respectively.The superior ORR mass activities of the fabricated Pd_x/Co-nanofilms/C catalysts may be attributed to their larger catalytic areas,which are conferred by the rough surface of Pd nanoparticles with an unclear crystal lattice,and the synergistic effect between the surface Pd atoms and the 2D Co nanofilm substrates.The relationship between ORR mass activity and Pd/Co atom ratio varies in different electrolytes.Furthermore,by using proper heat-treatment methods,the Pd_x/Co-nanofilms/C catalysts exhibit improved cycling stability compared with pure Pd/C catalyst after extended potential cycling.?3?With the same surface synthesis technology,we prepared Pd_xAu/Co-nanofilms/C catalysts to improve the electrocatalytic activity of ethanol oxidation and oxygen reduction.Pd_xAu/Co-nanofilms/C catalysts have a PdAu alloy structure and smaller particles.Electrocatalytic properties of the prepared Au@Pd/C catalysts are characterized cyclic voltammetry?CV?,ethanol oxidation?EOR?,oxygen reduction?ORR?in alkaline solution.In the catalyst,the effects of Au are different in the ethanol oxidation and oxygen reduction reaction.For example: Pd₃Au/Co-nanofilms/C catalyst showed excellent electrocatalytic activity for ethanol oxidation,attracted to Au leads to Pd lattice expansion,d band center shift,thus accelerating the adsorption of the intermediate product in the surface of the catalyst?CH₃COads?desorption.While PdAu/Co-nanofilms/C catalyst showed excellent quality activity of oxygen reduction?1.89 times of Pd/C?,attracted to Au facilitate the transfer of H₂O₂ to the metal active site.