Tailoring The Structures, Properties And Catalytic Properties For O₂ Of Fe₁₃@Pt_42-nAu_n Nanoparticles By Au Subsritution

The structure and atomic ratio determine the electronic, magnetic, catalytic and other properties of trimetallic nanoparticles. Fe13@Pt42 and Fe13@Pt42-nAun (n=0-12) core-shell nanoparticles were investigated using first-principles calculation. The structural, electronic, magnetic and catalytic properties of the nanoparticles with and without Au doping were analyzed by density functional theory. We optimized the structures of Fe13@Pt42 and Fe13@Pt42-nAun (n=1-12) firstly and 2-6 isomers were considered for Fe13@Pt42-nAun in every atomic ratios. The structure with the lowest energy was chosen to investigate the structural, electronic and magnetic properties. In addition, the dissociation of O2 on the surface of Fe13@Pt42-nAun (n=0,1,2) were calculated. We searched the translated states with the CI-NEB method and analyzed the density of states and molecue orbitals for initial states. The main changes and findings were list as follows:1. For the most stable structures of Fe13@Pt42-nAun, top site is a preferential site for Au atom to substitute. In addition, Au atoms prefer to substitute the closer Pt atoms at top sites in Fe13@Pt4oAu2 NPs. Edged Pt atoms are substituted by Au atoms only being found in Fe13@Pt39Au3 and Fe13@Pt37Au5 NPs.2. With the substitutions, higher stabilities are achieved in Fe13@Pt41Au1 (T, E) and Fe13@Pt4oAu2 NPs comparing with Fe13@Pt42. Fe13@Pt41Au1 (T) is the most stable structure for all the structures. However, an increasing of the Au atoms is not causing an enhancement in stability. The NPs with higher Au atomic ratios have lower stability. The the bond lengthes are changed and structures are slightly deformed with Au substitution. Both of the atomic ratios and substituted sites effect the bond length.3. The substitution of Au induces the decrease of the charge transfer but the electrons are still transferring from shell atoms to core Fe atoms. Furthermore, substitutions result in the shift of the d-orbitals of Fe, Pt and Au atoms. The average bond length of Fe-Fe, Bader charge of center Fe, spin splitting of Fe d-band center and local magnetic moment of center Fe reveal a similar tendency with the increasing of Au atoms, demonstrating the electronic and magnetic properties strongly depend on the average bond lengths.4. Higher adsorption energy is obtained with the horizontal adsorption of O2. The adsorption site with the highest adsorption energy of O2 is not changed with the Au substitution. For the Fe13@Pt42, Fe13@Pt41Au1 and Fe13@Pt4oAu2 NPs, the most stable combined site for O2 is T-B-E site, namely, two O atoms connect with the TOP Pt and EDGE Pt respectively. The O2 is prefer to adsorb far away from the Au atoms in the substituted facet. The adsorption energy of O2 decreased with the increasing of Ro-pt.The substitution of Au decreases the adsorption energy of O atom, which is favor to the desorption of O atoms from the NPs and promotes the oxidation reduction reaction.5. The energy barrier for the dissociation of O2 is about 0.5?1.1 eV and the strong adsoption of O2 is necessary. In addtion, the reaction and dissociation energy effect the activity of dissociation. Finnally, there are some direct connections between the properties of O2 and the catalytic activity, for instance, the bond length and oscillation frequency of O2. Both of the adsorption energy and active barrier are decreased with the substitution of Au, the substitution improved the catalysis of O2 dissociation, but the exothermic reaction is changed into endothermic reaction.