Surface termination and subsurface restructuring of perovskite-based solid oxide electrode materials

Abstract

The surface and near-surface composition in perovskite-based electroceramics is analysed at the atomic scale using highly surface sensitive low-energy ion scattering (LEIS).

Understanding and Controlling the Work Function of Perovskite Oxides Using Density Functional Theory

“…From Table 2, one can see that the pristine (001) surfaces have a lower surface energy and thus more stable than (011) and (111) surfaces, consistent with previous DFT studies. [47,51,59] Recent experimental [60][61][62][63][64] and computational studies [57,64,65] show that numerous perovskite materials exhibit segregation of alkaline earth elements such as Sr and Ba. From our current calculations, the overall order of stability is: γ(001) < γ(111) < γ(011).…”

“…As discussed previously, cation segregation has been observed in many perovskite materials. [50][51][52][53][54][55][56][57][60][61][62][63][64][65][66] To ascertain if Ba segregation may occur in SrVO 3 , we calculated the formation energy of substituting Ba in place of Sr for the two cases illustrated in Figure 7, and also calculated the segregation energy of dilute Ba (25% Ba substitution in the middle of the surface slab) to the surface of SrVO 3 . The energy to substitute Sr for Ba, ΔE sub , was calculated using the equation…”

Evolution of the electrochemical interface in high-temperature fuel cells and electrolysers

“…Since the difference in cation size seems to largely drive surface segregation and reorganisation processes 31 , it seems that perovskite structures are fundamentally prone to such effects. Usually it is the larger A-site cations that segregate to the surface, forming AO islands 15,31,32 or an An+1BnO3n+1 RP-type layer 16,32,33 which can be several nanometres thick 16 (see Figure 4a). This in turn means that the B-sites are less exposed to the free surface, or otherwise obstructed from contact with the reactants 16,32 .…”

“…Usually it is the larger A-site cations that segregate to the surface, forming AO islands 15,31,32 or an An+1BnO3n+1 RP-type layer 16,32,33 which can be several nanometres thick 16 (see Figure 4a). This in turn means that the B-sites are less exposed to the free surface, or otherwise obstructed from contact with the reactants 16,32 . Since the transition metal cations on the B-site are generally responsible for the catalytic, oxygen and electron transfer functions, this has obvious negative effects on material and implicitly SOC performance.…”

“…Various techniques are used to probe the surface at various depths, including secondary ion mass spectrometry (tens to hundreds of nm) 14,15 , X-ray electron spectroscopy (XPS, 1-10 nm) and low-energy ion scattering (the outer atomic monolayer, i.e. the very surface involved in reactions with the gas phase) 15,16 . Raman spectroscopy can be used to map surface species (e.g., oxygen, sulphur, carbon, hydrocarbons and water) involved in the electrode reactions.…”