Integrated X-ray L Absorption Spectra. Counting Holes in Ni Complexes

Wang, Hongxin; Ge, Pinghua; Riordan, Charles G.; Brooker, Sally; Woomer, C. G.; Collins, Terrence J.; Melendres, C. A.; Graudejus, O.; Bartlett, Nate C.-M.; Cramer, Stephen P.

doi:10.1021/jp9821026

Cited by 77 publications

(117 citation statements)

References 48 publications

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“…91 Regarding the chemistry of Co, from the XPS data reported in Figure 4c it is possible to observe the presence of Co (II) (OH)2, but not of Co (III) O(OH), in the post mortem sample. 75 The Co L3 edge spectrum of the pristine catalyst, shown in Figure 4g, is similar to that of the mixed oxide Co (II, III) 3O4, but the increased intensity of the feature near 777.8 eV, as well as the appearance of a new feature near 776.3 eV, indicates a higher concentration of Co (II) .…”

Section: Resultsmentioning

confidence: 90%

An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

et al. 2017

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Abstract. The oxygen evolution reaction (OER) is a critical component of industrial processes such as electrowinning of metals and the chlor-alkali process. It also plays a central role in the developing renewable energy field of solar-fuels generation by providing both the protons and electrons needed to generate fuels such as H 2 or reduced hydrocarbons from CO 2 . To improve these processes, it is necessary to expand the fundamental understanding of catalytically active species at low overpotential, which will further the development of electrocatalysts with high activity and durability. In this context, performing experimental investigations of the electrocatalysts under realistic working regimes, i.e. under operando conditions, is of crucial importance. Here, we study a highly active quinary transition metal oxide-based OER electrocatalyst by means of operando ambient pressure X-ray photoelectron spectroscopy and X-ray absorption spectroscopy performed at the solid/liquid interface. We observe that the catalyst undergoes a clear chemical-structural evolution as a function of the applied potential with Ni, Fe and Co oxyhydroxides comprising the active catalytic species. While CeO 2 is redox inactive under catalytic conditions, its influence on the redox processes of the transition metals boosts the catalytic activity at low overpotentials, introducing an important design principle for the optimization of electrocatalysts and tailoring of high performance materials.

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Section: Resultsmentioning

confidence: 90%

An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

et al. 2017

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“…Both the Ni L3-and the L2-edge sXAS clearly show that the spectral weight shifts towards higher energy during charge and goes back during discharge, which are indicative of increased (decreased) Ni oxidation states during delithiation (lithiation) processes 26 . Moreover, the spectral profile especially on the L3-edge changes dramatically.…”

Section: Results Andmentioning

confidence: 99%

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes

et al. 2015

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KEYWORDS: high voltage spinel, LiNi0.5Mn1.5O4, Ni(III), soft x-ray spectroscopy.2 ABSTRACT LiNi0.5Mn1.5O4 spinel is an appealing cathode material for next generation rechargeable Li-ion batteries due to its high operating voltage of ~4.7 V (vs. Li/Li + ). Although it is widely believed that the full range electrochemical cycling involves the redox of Ni(II)/(IV), it has not been experimentally clarified whether Ni(III) exists as the intermediate state, or a double-electron transfer takes place. Here, combined with theoretical calculations, we show unambiguous spectroscopic evidence of the Ni(III) state when the LiNi0.5Mn1.5O4 electrode is half charged.This provides a direct verification of single-electron-transfer reactions in LiNi0.5Mn1.5O4 upon cycling, namely, from Ni(II) to Ni(III), then to Ni(IV). Additionally, by virtue of its surface sensitivity, soft x-ray absorption spectroscopy also reveals the electrochemically inactive Ni 2+and Mn 2+ phases on the electrode surface. Our work provides the long-awaited clarification of the single-electron transfer mechanism in LiNi0.5Mn1.5O4 electrodes. Furthermore, the experimental results serve as a benchmark for further spectroscopic characterizations of Nibased battery electrodes.3

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“…l(c)) and that of K4[Fe(CN)6] ( Fig. l(d)) are indicative of a reduction in oxidation state as the 2p binding energy is reduced with lower oxidation states, and the intensity of the transitions is directly related to the number of electron holes in the 3d manifold (Wang et al (1998)). Significantly, there were no observable changes during multiple scans at the Fe L-edge for K.~[Fe(CN)6].…”

Section: Methodsmentioning

confidence: 97%

Soft X-ray photochemistry at the L _2,3-edges in K₃[Fe(CN)₆], [Co(acac)₃] and [Cp₂Fe][BF₄]

Collison¹,

Garner²,

McGrath³

et al. 1999

J Synchrotron Radiat

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Integrated X-ray L Absorption Spectra. Counting Holes in Ni Complexes

Cited by 77 publications

References 48 publications

An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes

Soft X-ray photochemistry at the L _2,3-edges in K₃[Fe(CN)₆], [Co(acac)₃] and [Cp₂Fe][BF₄]

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Integrated X-ray L Absorption Spectra. Counting Holes in Ni Complexes

Cited by 77 publications

References 48 publications

An Operando Investigation of (Ni–Fe–Co–Ce)Ox System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

An Operando Investigation of (Ni–Fe–Co–Ce)Ox System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi0.5Mn1.5O4 Electrodes

Soft X-ray photochemistry at the L 2,3-edges in K3[Fe(CN)6], [Co(acac)3] and [Cp2Fe][BF4]

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An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

An Operando Investigation of (Ni–Fe–Co–Ce)O_x System as Highly Efficient Electrocatalyst for Oxygen Evolution Reaction

Direct Experimental Probe of the Ni(II)/Ni(III)/Ni(IV) Redox Evolution in LiNi_0.5Mn_1.5O₄ Electrodes

Soft X-ray photochemistry at the L _2,3-edges in K₃[Fe(CN)₆], [Co(acac)₃] and [Cp₂Fe][BF₄]