Uncovering The Role of Oxygen in Ni-Fe(OxHy) Electrocatalysts using In situ Soft X-ray Absorption Spectroscopy during the Oxygen Evolution Reaction

Abstract

In-situ X-ray absorption spectroscopy (XAS) at the oxygen K-edge was used to investigate the role of oxygen during the oxygen evolution reaction (OER) in an electrodeposited Ni-Fe(OxHy) electrocatalyst in alkaline pH. We show the rise of a pre-peak feature at 529 eV in the O K-edge spectra, correlated to the appearance of a shoulder at the Ni L3-edge and formation of oxidized Ni3+/4+-O. Then, for the first time, we track the spectral changes in a dynamic fashion in both the soft and hard X-ray regimes during cyclic voltammetry (in situ CV-XAS) to obtain a fine-tuned resolution of the potential-related changes. The pre-peak feature at the O K-edge likely signifies formation of an electron deficient oxygen site. The electrophilic oxygen species appears and disappears reversibly in correlation with the Ni2+ ↔ Ni3+/4+ process, and persists during OER catalysis as long the metal is oxidized. Our study provides new insight into OER electrocatalysis: Before onset of the O-O bond formation step, the catalytic oxyhydroxide has accumulated electron deficiencies by both, oxidation of transition metal ions and formation of partially oxidized oxygen sites.

Boosting Neutral Water Oxidation through Surface Oxygen Modulation

“…In the O K‐edge sXAS spectra of RuIrCaO x and RuIrO x samples (Figure 2a), the shoulder peak of ≈529 eV in the spectrum of RuIrCaO x confirms the generation of electrophilic lattice oxygen sites (formally O I− species) at catalyst surface. [ 26 ] According to the lattice‐oxygen‐participated mechanism (LOM) for OER, [ 27,28 ] the surface electrophilic O I− sites of RuIrCaO x catalyst undergo a nucleophilic attack of water molecules or hydroxyl groups and further form OO bond and release O 2 . The surface electrophilic lattice oxygen sites participate in the OER process, with lattice oxygen as an active OER intermediate.…”

Oxygen-evolution reaction by nickel/nickel oxide interface in the presence of ferrate(VI)

“…Using XANES, Dau's group detected Ni(IV) 19 . Jin, Alp, and Stah detected Fe(IV) by the operando Mössbauer spectroscopic studies of a 3:1 Ni:Fe layered hydroxide 20 .…”

Advances in Understanding Mechanisms of Perovskites and Pyrochlores as Electrocatalysts using In‐Situ X‐ray Absorption Spectroscopy

“…[44] As a result of in-situ SXAS analysis, Lange et al clearly confirmed a variation in a hybridized bond between oxygen 2p and nickel 3d orbitals of a NiÀFe(O x H y ) catalyst during the OER. [45] In this context, electrocatalysts based on metal oxides including perovskite and pyrochlore oxides are required to be intensively investigated by using in-situ XAS for probing oxidation states and local structure during the ORR and OER.…”