Theoretical Study On Electrocatalytic Performance Of Oxygen Reduction Reaction Of Metal Nanoparticles Doped With Non-metallic Elements

As a new energy technology,proton exchange membrane fuel cells have many advantages such as higher energy density and conversion rate,green,clean and environmental protection.The development of this new energy technology is of great significance to the renewal and optimization of the world energy system.As we all know,the important reason that hinders the rapid development of this technology and the wide practical application is the sluggish kinetics of the oxygen reduction reaction involved in the PEMFCs cathode,which requires the development of high-performance catalytic.materials.At present,non-metallic carbon-based materials have attracted much attention,and many important progresses have been made.Although carbon-based materials have many advantages such as low cost,high activity,and diverse structures,there are still limitations that prevent them from being widely commercialized in terms of precise synthesis methods and material stability.The precious metal system is still the most widely used catalytic material with the best ORR catalytic performance.The research of precious metal catalysts has also continued,through the study of various modification methods to improve its catalytic performance,so that it has higher efficiency,and strive to convert the inevitable high cost as much as possible into application value.However,there is still a great room for improvement in terms of catalytic activity and stability,especially the stability and durability of precious metal-based catalysts.Therefore,exploring new,efficient,and potentially useful modification strategies is still an important means to enhance the performance and application value of precious metal catalysts.In this paper,based on the calculation of density functional theory and combined with the design concept of non-metallic doping modification,a systematic study on precious metal nanoparticles was carried out,including N,B or P doped Pt,Pd or Ag nanoparticles.1.Non-metallic atoms doped into Pt,Pd or Ag nanoparticles expanded the metal crystal structure,tensile stress would be generated inside the structure,and tensile stress may cause the adsorption of oxyhydrogen intermediates to become stronger,which is detrimental to the ORR catalytic activity of Pt and Pd,but has a positive effect on the ORR catalytic activity of Ag.2.Non-metallic elements doping enhanced the thermodynamic stability and electrochemical stability(durability)of Pt,Pd and Ag nanoparticles.By comparing the cohesive energy of each doped structure with that of pure metal nanoparticles,whether it is N,B or P doping significantly increased the cohesive energy of the structure,which indicates that the doping of non-metallic atoms will make the thermodynamic stability of the nanoparticles is improved.Meantimes,the calculation of atom removal energy shows that the non-metallic atom doping will also enhance the durability of the metal nanoparticles.3.The doping of non-metal atoms significantly improved the ORR catalytic activity of Pt,Pd and Ag nanoparticles.The B atom doping had the greatest improvement in the activity of Pt,Pd and Ag.The ORR overpotentials reached 0.317 V,0.442 V and 0.374 V,respectively.Doping with non-metal atoms would make the charge distribution on the surface of the metal nanoparticles more localized.4.Non-metallic elements doping shifted the d-band center of the Pt,Pd and Ag nanoparticles to promote the ORR catalytic activity.Calculating the progected density of states and the d-band center for each doped structure,the results show that the unconventional hybridization of the p-orbital of non-metallic atoms and the d-orbital of metal atoms makes the d-band center of Pt and Pd shift negatively and the d-band center of Ag shifts positively,which is in good agreement with the previously reported d-band center theory.The above calculation results and conclusion indicate that the doping of non-metal atoms will promote the thermodynamic stability,durability and ORR catalytic activity of Pt,Pd and Ag nanoparticles.This demonstrates that the non-metallic doping modification strategy may show extremely effective effect and universal applicability to the performance improvement of the metal system catalyst.At present,since most of the widely used catalytic materials are still precious metal-based catalysts,the above conclusions also indicate that the non-metallic doping modification method is also of great significance for enhancing the practical application value of the precious metal catalyst.Meanwhile,the above conclusions also have good guide for the experimental synthesis of catalysts with related structures.