Elucidation of Structure–Activity Correlations in a Nickel Manganese Oxide Oxygen Evolution Reaction Catalyst by Operando Ni L-Edge X-ray Absorption Spectroscopy and 2p3d Resonant Inelastic X-ray Scattering

Abstract

Herein, we report the synthesis and electrochemical oxygen evolution experiments for a graphene-supported Ni3MnO4 catalyst. The changes that occur at the Ni active sites during the electrocatalyic oxygen evolution reaction (OER) were elucidated by a combination of operando Ni L-edge X-ray absorption spectroscopy (XAS) and Ni 2p3d resonant inelastic X-ray scattering (RIXS). These data are compared to reference measurements on NiO, β-Ni­(OH)2, β-NiOOH, and γ-NiOOH. Through this comparative analysis, we are able to show that under alkaline conditions (0.1 M KOH), the oxides of the Ni3MnO4 catalyst are converted to hydroxides. At the onset of catalysis (1.47 V), the β-Ni­(OH)2-like phase is oxidized and converted to a dominantly γ-NiOOH phase. The present study thus challenges the notion that the β-NiOOH phase is the active phase in OER and provides further evidence that the γ-NiOOH phase is catalytically active. The ability to use Ni L-edge XAS and 2p3d RIXS to provide a rational basis for structure–activity correlations is highlighted.

Surface site density and utilization of platinum group metal (PGM)-free Fe–NC and FeNi–NC electrocatalysts for the oxygen reduction reaction

“…Instead, the main absorption peak is shifted to higher photon energies and was assigned to a Ni 3+ state with a minor Ni 2+ state contribution (Figure 1d). 34 This was further supported by XPS ( Figure S1d, e). The narrow-scan Ni 2p spectrum of FeNi-NC featured a broad peak in the 2p 3/2 region at ~854.2 eV, and a relatively weak satellite located at ~861 eV indicating the Ni 2+ oxidation state ( Figure S1d).…”

“…1c and d ) revealed further details about the chemical states of Fe and Ni. 39 Fig. 1c evidences Fe 2+ and Fe 3+ to be present in both Fe–NC and FeNi–NC, while the nitrogen-coordinated motif appeared to give rise to a characteristic “double resonance” feature in the 708 to 710 eV range.…”

“…Comparing the Fe and Ni L 3,2 -edge spectra of the Fe-NC and FeNi-NC catalysts (Figure 1c, d) revealed further details about the chemical states of Fe and Ni. 34 Figure 1c evidenced Fe 2+ and Fe 3+ to be present in both Fe-NC and FeNi-NC, while the nitrogen-coordinated motif appeared to give rise to a characteristic "double resonance" feature in the 708 to 710 eV range. The presence of this feature indicated a very similar chemical state of the Fe-N x sites in both catalysts.…”

In situ X-ray emission and high-resolution X-ray absorption spectroscopy applied to Ni-based bimetallic dry methane reforming catalysts

“…The NiCoO/γ-Al 2 O 3 catalyst was synthesized according to a previously reported protocol. 24,34 The NiO/γ-Al 2 O 3 catalyst was prepared by an adaptation of the reverse micellar method. 35 In this approach, two different aqueous mixtures were prepared by dissolving 2.3 g ammonium oxalate monohydrate and 3 g nickel acetate tetrahydrate in 15 mL demineralized water and stirring for 15 minutes.…”

Cryomilled Ni-Co-Se Enables Water Oxidation Electrocatalysts Durable at High Current Densities

“…The XANES of Ni L 3 -edge of the dry sample revealed that Ni had an oxidation state of 2+ before activation and increased to 3+ after activation suggesting the transformation of Ni to NiOOH. 31 Co had a mixed oxidation state of 2+/3+ on the surface implying that…”