A DFT+U investigation of hydrogen adsorption on the LaFeO₃(010) surface

Abstract

The ABO perovskite lanthanum ferrite (LaFeO) is a technologically important electrode material for nickel-metal hydride batteries, energy storage and catalysis. However, the electrochemical hydrogen adsorption mechanism on LaFeO surfaces remains under debate. In the present study, we have employed spin-polarized density functional theory calculations, with the Hubbard U correction (DFT+U), to unravel the adsorption mechanism of H on the LaFeO(010) surface. We show from our calculated adsorption energies that the preferred site for H adsorption is the Fe-O bridge site, with an adsorption energy of -1.18 eV (including the zero point energy), which resulted in the formation of FeOH and FeH surface species. H adsorption at the surface oxygen resulted in the formation of a water molecule, which leaves the surface to create an oxygen vacancy. The H molecule is found to interact weakly with the Fe and La sites, where it is only physisorbed. The electronic structures of the surface-adsorption systems are discussed via projected density of state and Löwdin population analyses. The implications of the calculated adsorption strengths and structures are discussed in terms of the improved design of nickel-metal hydride (Ni-MH) battery prototypes based on LaFeO.

Understanding electrochemical switchability of perovskite-type exsolution catalysts

“…On oxides, hydrogen often adsorbs by an oxidative dissociation process forming surface hydroxyls 36,37 . Also on perovskite-type oxides chemisorption of hydrogen usually proceeds together with an electron transfer as shown in DFT studies on SrTiO 3 38 and LaFeO 3 39,40 . Thus we suggest oxidative hydrogen dissociation as the first step of H 2 reduction also on LSF:…”

Driving Towards Highly Selective and Coking‐Resistant Natural Gas Reforming Through a Hybrid Oxygen Carrier Design

“…[63][64][65] LFO (010), despite its relatively low thermodynamic stability, still possesses a significant population in the equilibrium morphology. [48,63] In addition, the (010) surface has been reported to be the active surface for other perovskite families, [66] thus it is considered in this work. The catalytic activity of all LFO (121), (100), and (010) planes in cleaving the CÀ H bond of CH 4 were investigated, and the results are compared with that of FO, one of the most promising material for CLPO of CH 4 .…”

“…[41][42][43][44] The generalized gradient approximation (GGA) of Perdew, Burke, and Ernzehof (PBE) was used to account for electron exchange correlation effects. [45] Spin-polarized DFT + U formalism of Dudarev et al was employed to address the on-site Coulomb interactions between the localized Fe 3delectrons, [46,47] and the chosen effective U value for LFO and FO were 4.64 eV and 4.0 eV, [48,49] respectively. The LFO material considered in this work is in an orthorhombic perovskite structure (Pnma 62) with the G-type anti-ferromagnetism as shown in 2a, [50] and the FO has a hexagonal corundum structure (R � 3C) with its ground state adopting an antiferromagnetic ordering along the hexagonal (0001) axis as presented in Figure 2b.…”

DFT Analysis of NO Adsorption on the Undoped and Ce-Doped LaCoO3 (011) Surface

“…Its lattice parameters are a = b = c = 5.3778 Å, α = β = γ = 60.8° (see Figure 1b). Before studying NO adsorption, we needed to determine relative stabilities of the (011), (111), and (010) surfaces, which are the frequently discussed surface slabs in perovskites such as LaFeO 3 , LaMnO 3 , and SrTiO 3 [38,39,40,41,42]. The relative surface energy, E surf , can be determined using the following formula: E surf = (E slab − nE bulk )/2A.…”

“…The relative surface energy, E surf , can be determined using the following formula: E surf = (E slab − nE bulk )/2A. In this equation, E slab and nE bulk represent the energies of the relaxed LaCoO 3 slab and an equal number (n) of bulk LaCoO 3 atoms; A indicates the area of relaxed LaCoO 3 slab; and the constant (2) reflects the fact that every slab has two surfaces [38,43]. By means of the formula, we obtained that surface energies of the (011), (111), and (010) surfaces are 1.334, 1.883, and 1.887 J·m −2 , respectively.…”