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Compositionally graduated thin films of a SrTi 1 − x Fe x O 3 − y (STFO) perovskite electrocatalysts were successfully prepared by High Throughput Physical Vapour Deposition (HT-PVD) using evaporative sources. X-ray diffraction confirmed a continuous solid solution of the cubic perovskite structure with an increase in the lattice parameter with increasing x from 0.392 ± 0.001 nm for SrTiO 3 to 0.386 ± 0.001 nm for SrFeO 3 . A Raman mode corresponding to an O-stretching vibration was observed which is disallowed by symmetry in the cubic structure suggests a localised lattice distortion. The perovskites exhibited poor conductivity for low values of x ( ρ < 7 × 10 − 8 S cm − 1 ) but conductivity increased with increasing Fe content before reaching a plateau at ρ = 0.041 S cm − 1 for x > 0.75. Increasing electrocatalytic activity towards the oxygen evolution reaction (OER) with increasing Fe content was observed, characterised by a 100 μA onset potential varying monotonically from 1.52V RHE (x = 0.2) to 1.40V RHE (x = 0.85). The high OER activity was however found to correlate with low electrode stability, consistent with the participation of lattice oxygen in the OER mechanism. The latter was evidenced by the redox electrochemistry associated with reversible oxygen intercalation. SrTi 0.5 Fe 0.5 O 3 − y exhibited the optimal composition with good OER activity and electrode stability. Low electrocatalytic activity towards the oxygen reduction reaction (ORR) was observed for all oxygen stoichiometric compositions. The ORR did not occur until after reduction of the films suggesting that surface reduction is required for the creation of the active surface sites. ORR activity on the oxygen sub-stoichiometric perovskites showed the opposite trend with compositional variation to OER activity on the oxygen stoichiometric perovskites. [ABSTRACT FROM AUTHOR]

Researchers increasingly recognize that, as with standard supportedheterogeneous catalysts, the activity and selectivity of supported metal electrocatalysts are influenced by particle size, particle structure, and catalyst support. Studies using model supported heterogeneous catalysts have provided information about these effects. Similarly, model electrochemical studies on supported metal electrocatalysts can provide insight into the factors determining catalytic activity. [ABSTRACT FROM AUTHOR]

Abstract: The surface redox behaviour, the stability, and the electro-oxidation of CO on model platinum–tin surface alloy catalysts has been studied by ex situ electrochemical measurements. The Pt(111)–Sn(2×2) and Pt(111)–Sn(√3×√3)R30° surfaces have been prepared and characterised in UHV by vapour deposition of Sn on Pt(111) and the surfaces subsequently transferred for electrochemical investigation. A surface redox couple, which is associated with the adsorption/desorption of hydroxide on the Sn sites, is observed at 0.28VRHE/0.15VRHE in H2SO4 electrolyte on both surfaces. Evidence that it is associated with the adsorption of OH comes from ex situ photoemission measurements, which indicate that the Sn atoms are in a metallic state at potentials below 0.15VRHE, and an oxidised state at potentials above 0.28RHE. Specific adsorption of sulphate anions is not associated with the surface process since there is no evidence from photoemission of sulphate adsorption, and the same surface couple is observed in HClO4 electrolyte. A second surface redox couple, associated with further oxidation of the Sn sites in the alloy surfaces, is observed at 0.8VRHE/0.58VRHE. CO is adsorbed from solution at 300K, with saturation coverages of 0.37±0.05ML and 0.2±0.05ML, respectively. The adsorbed CO is oxidatively stripped at the potential coincident with the adsorption of hydroxide on the tin sites at the lower potential of 0.28VRHE. This strong promotional effect is unambiguously associated with the bi-functional mechanism. The Sn induced activation of water, and promotion of CO electro-oxidation, is sustained as long as the alloy structure remains intact, in the potential range below 0.5VRHE. The instability of the alloy surface at higher potentials is associated with the second redox couple. The redox behaviour at higher potentials is modified by the presence of CO in stripping experiments, with couples now observed at 0.78VRHE/0.56VRHE, and 0.9VRHE/0.70VRHE. This behaviour may be associated with enhanced oxidation through the exclusion of sulphate anions at the surface by CO. [Copyright &y& Elsevier]

Highlights: [•] A high-throughput methodology is used to synthesise and screen PdCu alloys. [•] The expected equilibrium phases of the PdCu alloys were identified using XRD. [•] Pd in Cu results in reversible surface oxidation of Cu and oxide destabilisation. [•] This is a result of bi-functional and electronic effects of Pd in Cu, respectively. [•] The most active catalyst is in a narrow compositional region around 84%at. Cu. [ABSTRACT FROM AUTHOR]