Correlating Orbital Composition and Activity of LaMn_xNi_1–xO₃ Nanostructures toward Oxygen Electrocatalysis

Abstract

The atomistic rationalization of the activity of transition metal oxides toward oxygen electrocatalysis is one of the most complex challenges in the field of electrochemical energy conversion. Transition metal oxides exhibit a wide range of structural and electronic properties, which are acutely dependent on composition and crystal structure. So far, identifying one or several properties of transition metal oxides as descriptors for oxygen electrocatalysis remains elusive. In this work, we performed a detailed experimental and computational study of LaMn x Ni 1– x O 3 perovskite nanostructures, establishing an unprecedented correlation between electrocatalytic activity and orbital composition. The composition and structure of the single-phase rhombohedral oxide nanostructures are characterized by a variety of techniques, including X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and electron microscopy. Systematic electrochemical analysis of pseudocapacitive responses in the potential region relevant to oxygen electrocatalysis shows the evolution of Mn and Ni d-orbitals as a function of the perovskite composition. We rationalize these observations on the basis of electronic structure calculations employing DFT with HSE06 hybrid functional. Our analysis clearly shows a linear correlation between the OER kinetics and the integrated density of states (DOS) associated with Ni and Mn 3d states in the energy range relevant to operational conditions. In contrast, the ORR kinetics exhibits a second-order reaction with respect to the electron density in Mn and Ni 3d states. For the first time, our study identifies the relevant DOS dominating both reactions and the importance of understanding orbital occupancy under operational conditions.

Decoupling the impact of bulk and surface point defects on the photoelectrochemical properties of LaFeO3 thin films

“…4), this trend suggests that increasing covalency of the Fe-O bond has a positive effect on the electron transfer dynamics to O 2 , removing surface V Fe which can act as a hole trapping site. 30,31 Finally, Fig. 9a and b display the effect of the La : Fe bulk ratio on the photoresponses associated with the hydrogen evolution reaction (HER) in Ar-purged 0.1 M Na 2 SO 4 electrolyte at pH 12 under the chopped illumination of 405 nm with a photon ux of 5.42 Â 10 19 m À2 s À1 .…”

“…4), this trend suggests that increasing covalency of the Fe–O bond has a positive effect on the electron transfer dynamics to O 2 , removing surface V Fe which can act as a hole trapping site. 30,31…”

Recent Advances on Perovskite Electrocatalysts for Water Oxidation in Alkaline Medium

“…126,127 For example, Fermin et al conducted detailed experimental and theoretical computational studies on LaMn x Ni 1-x O 3 perovskite, establishing a correlation between the orbital composition and the corresponding OER activity. 128 Systematic electrochemical results showed that the OER activity of LaMn x Ni 1-x O 3 decreased with the increase of Mn content, which proved that the surface composition has a crucial function on the OER activity of LaMn x Ni 1-x O 3 . Zongping Shao et al reported a comparative study of the undoped SrCoO 3-δ (SCO) and the SrCO 1-y Si y O 3-δ with doping 5% Si (Si-SCO).…”

What X-ray absorption spectroscopy can tell us about the active state of earth-abundant electrocatalysts for the oxygen evolution reaction

“…[122][123][124] Identification of the relevant redox couples is thus a natural choice for mechanistic discussions and has led to the recent insight that the OER is a first order reaction with respect to the Mn density of states, while the ORR is of second order. 125 Moreover, the Mn 3+/4+ redox couple is essential for the evolution of oxygen in natural photosynthesis as well as for electrodeposited Mn oxides 126 because Mn 4+ togetherwith Mn 3+ has been proposed as a necessity for the OER and because its midpoint potential is similar to that of the OER. The M 3+/4+ redox couple is likewise important for the OER on other transition metal oxides, 126 where the detection of M 4+ has been correlated with oxygen evolution for a Co oxide.…”