Platinum-based Alloy Catalyst Structure Control And Its Research On Fuel Cell Anode Electrocatalytic Process

Fuel cells that use small organic molecules(e.g.methanol and ethanol)or hydrogen as anode fuel can power clean electric vehicles.Those possible fuel cells electrocatalytic reaction mechanisms are obtained through in-situ electrochemical spectroscopy techniques and density functional theory calculations,providing theoretical guidance for further development of novel nanocatalysts.As advanced nanocatalysts for fuel cells electrochemical reactions,alloy nanomaterials have greatly improved electrocatalytic activity and stability and have attracted widespread attention.So far,with the improvement of nanotechnology and characterization methods,researchers can purposely synthesize alloy nanocatalysts with specific physical properties and excellent chemical performance.What is noteworthy is that engineering the near-surface/surface nanostructure is a promising strategy to improve the electrocatalytic performance of alloys,which can maximize the exposure and utilization of active sites.In this paper,the researchs on the electrocatalytic reaction of fuel cell anodes(including methanol oxidation,formic acid oxidation,and hydrogen oxidation)is carried out,focusing on regulating thenear-surface/surface structure of three alloy nanocatalysts of PtRu,PtRu3,and PtAu to enhance their electrocatalytic activity,durability and anti-CO poisoning ability.The main results are as follows:1.PtRu nanoalloy supported on porous graphitic carbon(PC)has been successfully prepared via a facile and clean method involving co-reduction the precursors of Pt and Ru at 300℃ by H2(PtRu/PC-L)followed by thermal treatment at a higher temperature(700℃,PtRu/PC-H).This strategy has synthesized smaller Pt and PtRu nanoparticles(ca.<3 nm);what’s more,they are all homogeneous deposited en the surface of PC.PtRu/PC-H nanocatalyst displays higher alloying degree,Pt-increased structure,stronger electronic interaction between Pt and Ru atoms,as well as superior electrocatalytic performance and excellent CO-poisoning tolerance.The mass activity and specific activity on PtRu/PC-H nanoalloy is 4.08 and 8.80 times higher than that of the Pt/PC nanocatalyst,respectively.From in-situ FTIR spectra,we can discover PtRu/PC-H nanoalloy improves the ability of cleavage C-H bond and alleviates the COad poisoning on active sites.The PtRu/PC-H nanocatalyst exhibits maximum power density in single methanol fuel cell test than other nanocatalysts,which more than three-fold than that of commercial Pt/C as the anode catalyst.2.Near-surface designing of alloy nanocatalysts can reasonably tailor the surface chemical properties and further improve the sluggish H2 electrooxidarion performance in alkaline electrolyte.However,huge hurdles still need to be overcome to construct alloy nanomaterials with precise near-surface composition and smaller particle size.Herein,ultra-small PtRu3/PC binary nanoparticles(<2 nm)family,with two near-surface atomic compositions(Pt-increased and Ru-increased),evenly distribute on the surface of PC via adsorption-induced surface segregation methods.XPS results and electrochemical tests demonstrate the transformation of near-surface atomic composition after annealing PtRu3/PC nanocatalyst;when anneal in CO atmosphere,forming a Pt-increased nanostructure(500 ℃,PtRu3/PC-2),while the Ru-increased structure appeared in Ar heat treatment(700℃,PtRu3/PC-3).Remarkably,the Ru-increased nanocatalyst exhibits up to 38.8-fold and 9.2-fold HOR improvement in mass activity and exchange current density,compared with the Pt/PC counterpart,respectively.Three PtRu3/PC nanocatalysts all possess the appropriate hydrogen binding strength and oxophilic property,which is more favorable towards HOR in alkaline electrolyte than that of Pt/PC nanocatalyst.This study might open a new route to develop efficient HOR nanocatalysts from the perspective of near-surface atomic engineering.3.The reduction potential of chloroauric acid is higher than that of chloroplatinic acid,so the phase separation is more likely to occur by the co-reduction method.For the PtAu alloy system,the atomic composition on the surface can be quantified by a simple electrochemical method.We snccessfully prepared the PtAu/C alloy by changing the pH during the chemical reduction process.The surface atomic composition and sample morphology of the PtAu/C alloy were regulated by changing the amount of NaOH added in the synthesis process.With the enhancement of the alkaline environment,the atomic ratio of Pt/Au on alloy surface gradually decreased,and when 100 mg NaOH was added,the PtAu alloy with a nanonetwork structure appeared.Electrochemical tests showed that the PtAu/C-2 nanocatalyst synthesized by adding 50 mg NaOH had the highest mass activity for the electrocatalytic oxidation of methanol and formic acid molecules,which were 2.7 times and 74.4 times than that of commercial Pt/C,respectively.We also annealed the PtAu/C-2 sample with a Pt/Au atomic ratio of 1.4:1,and found that the Au components on the surface of the sample increased significantly after annealing,and even obtained a PtAu/C alloy with a surface Au content of 96.6%.The Au-rich structure on the surface of PtAu/C alloy can change the oxidation pathway of formic acid molecules,from partial direct oxidation pathway to almost complete direct oxidation pathway without producing CO poisoning species.