Oxygen vacancy formation and migration in Sr- and Mg-doped LaGaO_3:a density functional theory study

Oxygen vacancy formation and migration in La0.9Sr0.1Ga0.8Mg0.2O3-5 （LSGM） with various crystal symmetries （cubic, rhombohedral, orthorhombic, and monoclinic） are studied by employing first-principles calculations based on density functional theory （DFT）. It is shown that the cubic LSGM has the smallest band gap, oxygen vacancy formation energy, and migration barrier, while the other three structures give rise to much larger values for these quantities, implying the best oxygen ion conductivity of the cubic LSGM among the four crystal structures. In out calculations, one oxygen vacancy migration pathway is considered in the cubic and rhombohedral structures due to all the oxygen sites being equivalent in them, while two vacancy migration pathways with different migration barriers are found in the orthorhombic and monoclinic symmetries owing to the existence of nonequivalent O1 and 02 oxygen sites. The migration energies along the migration pathway linking the two 02 sites are obviously lower than those along the pathway linking the O1 and 02 sites. Considering the phase transitions at high temperatures, the results obtained in this paper can not only explain the experimentally observed different behaviours of the oxygen ionic conductivity of LSGM with different symmetries, but also predict the rational crystal structures of LSGM for solid oxide fuel cell applications.

Curvature and Size Effects on Reactivities of Mono-to Octa-vacancies in a(5,5) Single-walled Carbon Nanotube

Defect curvature was developed based on our previously proposed direction curvature theory. Defect curvature, as a universal criterion, was used to identify vacancy formation energies E_f of mono-vacancies to octa-vacancies in a（5,5） tube. An ab initio calculation results showed that E_f decreased with increasing the defect curvature K_（V_s）（s = 1~8）. The structures with removed carbon atoms along zigzag chain or the tubular axis were the most stable in each kind of Vs, because their corresponding K_（V_s） was the largest. In addition, local product structures disturbed the variation rule of E_f as K_（V_s）. There was an odd-even oscillation rule in the smallest E_f among each kind of Vs as the s value and vacancies V2, V4 and V6 were more stable. The stabilities of the related vacancy structures were confirmed by two dissociation processes.

Revealing the role of mo doping in promoting oxygen reduction reaction performance of Pt_(3)Co nanowires

Highly active and durable electrocatalysts towards oxygen reduction reaction(ORR)are imperative for the commercialization application of proton exchange membrane fuel cells.By manipulating ligand effect,structural control,and strain effect,we report here the precise preparation of Mo-doped Pt_(3)Co alloy nanowires(Pt_(3)Co-Mo NWs)as the efficient catalyst towards ORR with high specific activity(0.596 mA cm^(−2))and mass activity(MA,0.84 A mg^(−1)_(Pt)),much higher than those of undoped counterparts.Besides activity,Pt_(3)Co-Mo NWs also demonstrate excellent structural stability and cyclic durability even after 50,000 cycles,again surpassing control samples without Mo dopants.According to the strain maps and DFT calculations,Mo dopants could modify the electronic structure of both Pt and Co to achieve not only optimized oxygen-intermediate binding energy on the interface but also increased the vacancy formation energy of Co,together leading to enhanced activity and durability.This work provides not only a facile methodology but also an in-depth investigation of the relationship between structure and properties to provide general guidance for future design and optimization.

Density functional theory study of formaldehyde adsorption and decomposition on Co-doped defective CeO_(2) (110) surface

Formaldehyde as an air pollutant to adverse health effects for humanity has been getting attention.The adsorption and dissociation of formaldehyde(HCHO)on the CoxCe1−xO_(2)−δ(110)surface were investigated by the density functional theory(DFT)calculations.We calculated the oxygen vacancy formation energy as the function of its site around dopant Co in detail.The results showed that Co doping was accompanied by compensating oxygen hole spontaneous formation.The adsorption configurations and bindings of HCHO at different locations on the CoxCe1−xO_(2)(110)were presented.Four possible pathways of oxidation of formaldehyde on the catalytic surface were explored.The results suggested that formaldehyde dissociation at different adsorption sites on the doped CeO_(2)(110)—first forming dioxymethylene(CH2O_(2))intermediate,and then decomposing into H2O,H2,CO_(2),and CO molecules.It was found that the presence of cobalt and oxygen vacancy significantly prompted the surface activity of CeO_(2).