State of the Active Site in La_1–xSr_xCoO_3−δ Under Oxygen Evolution Reaction Investigated by Total-Reflection Fluorescence X-Ray Absorption Spectroscopy

Abstract

Recent developments in hydrogen energy devices have furthered the research on sustainable hydrogen production methods. Among these, the water splitting process has been considered a promising hydrogen production method, particularly, in alkaline media. The lack of information on the reaction active sites under the conditions of the oxygen evolution reaction (OER) hinders establishing guidelines for catalyst development. In the case of powder catalysts, many operando techniques also measure bulk information, and therefore, extracting information on the reaction active sites is challenging. Accordingly, film electrodes were used in this study, and the electrochemical performance and reaction kinetics of perovskite-type La1–x Sr x CoO3−δ films as OER catalysts synthesized by pulsed laser deposition were investigated. By combining ex situ X-ray absorption spectroscopy (XAS) and operando total-reflection fluorescence X-ray absorption spectroscopy (TRF-XAS), we succeeded in observing a significant oxidation state change on the surface of La0.6Sr0.4CoO3−δ, which indicated that the active surface sites were formed upon applying the OER potential. This surface reconstruction resulted in numerous active sites at the reaction interface, thereby enhancing the OER activity. This study provides definitive evidence for the surface reconstruction of OER catalysts, which enhances the fundamental understanding of OER catalyst behaviors, and can inspire the design of active OER catalysts by suitable surface modulation.

Atomistic Insights into Activation and Degradation of La0.6Sr0.4CoO3−δ Electrocatalysts under Oxygen Evolution Conditions

“…Here, the lower strontium content, which is typically associated with a lower catalytic activity within the La 1– x Sr x CoO 3−δ group may result in a higher stability and slower transformation of the perovskite surface. Interestingly, significant changes in the cobalt oxidation state were observed by operando XAS studies of La 0.6 Sr 0.4 CoO 3−δ in the near-surface region, while for an LaCoO 3−δ reference sample, little to no changes in the cobalt valence were detected . Here, the authors report the reduction in the Co oxidation state at open-circuit potential, while an oxidation of cobalt is observed under an applied potential of 1.4 V vs RHE, where the authors assume an intact perovskite surface of the LSCO catalyst at these rather mild conditions.…”

“…Interestingly, significant changes in the cobalt oxidation state were observed by operando XAS studies of La 0.6 Sr 0.4 CoO 3−δ in the nearsurface region, while for an LaCoO 3−δ reference sample, little to no changes in the cobalt valence were detected. 53 Here, the authors report the reduction in the Co oxidation state at opencircuit potential, while an oxidation of cobalt is observed under an applied potential of 1.4 V vs RHE, where the authors assume an intact perovskite surface of the LSCO catalyst at these rather mild conditions. Both studies hence emphasize the important role of Sr doping for the evolution in the surface chemistry of LSCO electrocatalysts under OER conditions, which is furthermore related to the transient degradation behavior described in the present study.…”

Structural evolution of a water oxidation catalyst by incorporation of high-valent vanadium from the electrolyte solution

“…S21†). 67–69 Notably, both O K-edge spectra of VNi-AC-1 collected in TEY and FY modes exhibited V 3d states (V L 2 -edge) and the hybridized O 2p–V 3d(t 2g ) states (O K-edge) (Fig. S21†).…”

Preface for the 66th Special Feature “Novel Aspects and Approaches to Experimental Methods for Electrochemistry”

“…Over a long period of time, He has devoted himself to the research and development of electro-catalyst materials and their synchrotron analysis under in-situ/operando conditions. [201][202][203][204][205] Naoya NISHI is currently an associate professor in Graduate School of Engineering, Kyoto University. He earned Ph.…”