Optimization Design Of Pt Based ORR Catalysts Through Dft Calculation

Pt based materials are widely used as catalysts in fuel cells and many heterogeneous catalytic reactions.Due to the high cost and limited resource of Pt,recent researches focused on decreasing Pt loading by tailoring the composition and structure of Pt based catalysts.Although it is experimental challenge to disclose the relationships between the molecular-scale structure and the catalytic activity,molecular simulation and computational chemistry can bridge this gap.Hence I made an optimization design of Pt based oxygen reduction reaction(ORR)catalysts,such as Pt,Pt3M and Pt/Pt3M,by density functional theory to reveal the cause of catalytic activity enhancement.At first,some calculations about pure Pt through the adsorption energy,the density of states(Density of states,DOS),the ORR mechanism on Pt were performed and the RDS(Rate determining step)of ORR is O*+ H+ + e-?OH*.Then transition metal Fe,Co and Ni were chosen as alloying elements with Pt because they could easily tailor the electronic and crystal structures ofPt based catalysts through the geometrical effect and ligand effect.After the alloying with transition atom,the d band center shifted toward low energy.The d band center of Pt,Pt3Fe,Pt3Co,Pt3Ni is-3.20 eV,-3.21 eV,-3.24 eV,-3.39 eV,respectively.The adsorption energy of small atom is also decreased.The adsorption energy of atom O on Pt,Pt3Fe,Pt3Co,Pt3Ni is 4.96 eV,-5.67eV,-5.44 eV and-4.96 eV respectively.Due to the decrease of the adsorption energy,the small atoms are easily to desorb and the follow-up steps can process successfully.Therefore,the RDS of ORR is 1.10 eV,1.09eV,0.85 eV,0.82 eV on Pt,Pt3Fe,Pt3Co and Pt3Ni respectively.The atom Ni is the smallest atom of the three and can tailor the structure and electronic stucture most and exhibit the best ORR catalytic activity.The Pt-skin is formed easily in the preparation process,so the effect of Pt-skin is studied.The calculation results exhibit that the Pt-skin can change the electronic structure and the arrangement of atoms.So that it can lower the lattice constant more obviously,cause the surface compressive stress.Pt-skin can also change the electronic structure through the ligand effect to shift d-band center toward low nenrgy(the d-band center of Pt,Pt-skin-Pt3Fe,Pt-skin-Pt3Co,Pt-skin-Pt3Ni is-3.20eV,-3.38eV,-3.42 eV,-3.519 eV).The energy barrier of RDS on Pt,Pt-skin-Pt3Fe,Pt-skin-Pt3Co,Pt-skin-Pt3Ni is 1.10eV,1.02eV,0.83 eV,0.789eV respectively.So the Pt-skin-Pt3Ni exhibit the best performance.Pt-skin-Pt3M/Vulcan catalyste were prepared.From the XRD patterns it can be seen the alloy catalysts maintain the fcc structure of Pt with a slightly compressed lattice constant,and the Pt-skin-Pt3Ni caused largest change.The XPS spectrum demonstrated the bonding energy of Pt-skin-Pt3M shifts toward lower energy,which implied the decrease of d band center.And the change of Pt-skin-Pt3Ni is the most.Finally,the ORR catalytic properties tests suggested the Pt-skin-Pt3Ni owns the most positive on-set potential and half-wave potential,which means Pt-skin-Pt3Ni has the best performance,even better than commercial Pt/C.All in all,the calculation results and the experiment results are fitted very well.Therefore,the method can be used to other system or other complex catalytic reaction.