Manipulating The Surface Composition And Electronic Structure Of Pt-based Alloy To Boost Their Electrocatalytic Performances

Proton Exchange Membrane Fuel Cells(PEMFC)fuel cell have been typically considered as the most promising energy conversion substitute because their exceptional energy conversion efficiency and environmental friendliness.The essential material of electrocatalyst are straightly influence the overall cost,performance and durability of the fuel cell.Pt-based electrocatalysts is regarded as the most widely study catalyst for fuel cells.Nevertheless,the traditional Pt-based electrocatalysts have a series of problems such as high price,poor stability,low catalytic activity and low utilization efficiency of Ptatoms.Aiming at the above-mentioned key scientific problems in the existing platinum-based catalyst research system,this paper taking the surface composition and electronic structure of Pt-based electrocatalysts into account,taking Pt-based high-efficiency catalysts as the main research line,the following three aspects of work have been carried out:(1)Herein,we have successfully transformed solid PtNPs into a hollow PtFe alloy with a Pt-skin surface that was covered with a thin layer of a porous NC shell via the nanoscale kirkendall effect and space-confined pyrolysis.Our approach allows direct transformation of solid PtNPs into hollow PtFe alloy featuring a Pt-skin surface without NP sintering.Meanwhile,a thin-layer NC shell formed in situ can protect the NPs from detachment and agglomeration throughout the harsh fuel-cell operating conditions.The mass activity and specific activity of H-PtFe/C@NC at 0.9 V reach 1.35mA/cm² and 0.993 A/mg _Pt,respectively,which are much higher than the commercial Pt/C catalyst(0.268 mA/cm² and 0.193 A/mg _Pt).DFT calculations reveal that such hollow PtFe alloys with a Pt-skin surface can effectively decrease the d-band center and weaken the adsorption of nonreactive oxygenated species on the Ptsurface,leading to an enhancement of the ORR activity.In the stability test,as compared with the commercial Pt/C catalyst,the as-prepared hollow H-PtFe/C@NC catalyst exhibited more excellent point chemical stability.After 20,000 CV cycles,the mass activity H-PtFe/C@NC catalyst is still as high as 0.722 A/mg _Pt,which is only 27.3%lower than the initial mass activity.After 20,000 CV cycles,the mass activity of commercial Pt/C catalyst is 0.071 A/mg _Pt,which is 63.2%lower than the initial mass activity.The approach presented here for the structural evolution from solid PtNPs to a Pt-skin hollow PtFe alloy with controlled size,structure,and composition can be readily applied to other multimetallic electrocatalysts.Herein,a method for directly converting solid single-phase PtNPs into a hollow PtFe alloy with controlled size,structure,and composition under high temperature conditions has been developed,which enriching the synthesis of nanomaterials and providing the theoretical guidance to prepare low-Pt,high-performance,long-life Pt-based catalysts.(2)On the basis of the above research methodologies,we have successfully prepared three model sample(Pt₁Ru_0.5@NC/C,Pt₁Ru₁@NC/C,Pt₁Ru₂@NC/C)through precisely manipulating the adding of precursor Ru³⁺.surface composition of Pt-Ru bimetallic NPs.We tune the location and content of Ru on PtRu alloy surface through a thermally driven interfacial diffusion route that allows for selectively transforming the solid PtNPs supported on carbon(Pt/C)into Pt-rich PtRu alloy,Ru-rich PtRu alloy and PtRu alloy with moderate surface atom ratio of Ptto Ru.By correlating the surface Ptand Ru contents with MOR activity,we can conclude that a relatively low or high surface Ru content is not beneficial to the MOR.This phenomenon can be explained by the famous Watanabe-Motoo bifunctional mechanism,in which the insufficient Ru in Pt₁Ru_0.5@NC/C catalyst cannot effectively remove the CO species,while the redundant of Ru in Pt₁Ru₂@NC/C catalyst would result in a relative low number of active Ptsites for the methanol dehydrogenation.The Pt₁Ru₁@NC/C catalyst with the optimum Ru and Ptcontent on the surface can balance these composition-dependent ensemble effects,which synchronously promote the MOR activity and anti-CO poisoning ability.We also correlated their MOR pathway and activity with the location and content of Ru in PtRu alloy by applying in-situ Fourier transform infrared-diffuse reflection spectrum(FTIRs).Our insights establish that the Pt-skin-rich PtRu alloy catalyst featured a MOR pathway through HCOO^-intermediate,while the Ru-skin-rich PtRu alloy catalyst exhibit a CO intermediate pathway.Different from the solely MOR pathway in Pt-skin-rich and Ru-skin-rich samples,the PtRu alloy with medium surface atom ratio of Ptto Ru,which possess the best MOR activity and anti-CO poisoning ability,demonstrate a mixed pathway through HCOO^-and CO intermediate.Significantly,our work reported that the pathway of MOR on Pt-Ru alloy can be controlled by precisely manipulating the surface composition of Pt-Ru bimetallic NPs.(3)By using the differences in the atomic radius and diffusion migration rates of Fe and Ru atoms during high temperature processes,we designed a PtFe@PtRuFe core-shell nanostructure,composed of an ordered PtFe intermetallic core covered with a3-5 atomic-layer-thick PtRuFe shell.The well-defined PtFe@PtRuFe core-shell nanostructure exhibits excellent anti-CO poisoning ability and resistance to Fe leaching,achieving a higher MOR activity,anti-CO poisoning ability and stability as compared to the state-of-the-art PtRu/C catalysts.The as-prepared PtFe@PtRuFe exhibits the highest specific activity of 1.30 mA.cm^-2,which is 1.57 and 8.6 times higher than those of the PtRu/C(0.83 mA.cm^-2)and Pt/C(0.15 mA.cm^-2),respectively.On the other hand,the current peak ratio of I_f(the forward peak current)/I_b(the backward peak current)for PtFe@PtRuFe is calculated to be 12.7,which is great higher than the PtRu/C(6)and Pt/C(0.72)catalyst,indicating the enhanced MOR activity of the PtFe@PtRuFe.The CO anodic oxidation on the PtFe@PtRuFe catalyst surface(0.39 V)starts much earlier than on the commercial PtRu/C(0.43 V)and Pt/C(0.83 V)catalysts,indicating improved anti-CO poisoning ability.The enhanced performance of MOR activity and anti-CO poisoning ability of the PtFe@PtRuFe catalyst is ascribed to their well-defined core-shell structured and their favorable composition.This novel core-shell structured nanocatalyst provide a new direction to reduce the usage of noble metal,precisely adjusting the surface composition and atomic arrangement,enhance the activity and stability of multi-metallic alloy nanocatalyst.