Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts

Enman, Lisa J.; Stevens, Michaela Burke; Dahan, Meir Haim; Nellist, Michael R.; Toroker, Maytal Caspary; Boettcher, Shannon W.

doi:10.1002/ange.201808818

Cited by 39 publications

(43 citation statements)

References 41 publications

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“…9 The nickel oxyhydroxide has been investigated as an active phase for OER 45,46 and the iron oxyhydroxide possibly plays a crucial role. 47 Nevertheless, while the iron peak is surely masked because of the OER, the nickel oxidation (considered vital for high OER performance) can be experimentally detected and thus, studied by means of CVs. [48][49][50] Keeping this in mind, Luan et al studied the proton diffusion coefficient during Ni(OH) 2 oxidation that can be estimated for diffusionlimited reactions using the Randles-Sevcik equation.…”

Section: Resultsmentioning

confidence: 99%

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

et al. 2019

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Layered double hydroxides (LDHs) are low dimensional materials that act as benchmark catalysts for the oxygen evolution reaction (OER). Many LDH properties affecting the OER have been studied to reach the optimal efficiency but no systematic studies concerning the influence of the interlayer space have been developed. In this context, these materials allow a large tunability in their chemical composition enabling the substitution of the interlayer anion and therefore modifying exclusively the basal space. Here, we synthesize by anion exchange reactions a surfactantintercalated family of NiFe-LDHs with increasing basal spacing ranging from 8.0 to 31.6 (one of the largest reported so far for a NiFe-LDH) while the electrochemical OER performance of this family of compounds was explored to analyse the interlayer distance effect keeping similar morphology, dimensions and metallic composition. Results show the increase of the LDH basal space undergo to lower Tafel slopes, higher electrochemical surface area and a reduction of the resistance related to the chemisorption of oxygen leading to better kinetic behaviour, showing an optimum enhancement of the electrocatalytic performance for the NiFe-dodecyl sulphate (basal space of 25 ). Interestingly, the NiFe-dodecyl sulphate exhibits optimum proton diffusion values, indeed a further increment in the basal space compromises the onset potential, a fact that could be related to an increase in the hydrophobicity between the layers. Moreover, by judicious tuning of the interlayer space, it is possible to reach a Tafel slope value for the most spaced LDH (NiFe-octadecyl sulphate, basal space of 31.6 ), similar to the one obtained for exfoliated NiFe nanosheets, showing a much better long-time stability due to the three-dimensional robustness of the catalysts. This work illustrates the importance of molecular engineering in the design of novel highly active catalysts and provides important insights into the understanding of basic principles of oxygen evolution reaction in NiFe-LDHs.

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Section: Resultsmentioning

confidence: 99%

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

et al. 2019

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“…These results indicate that the OER active phase of CFCO catalysts comprises aggregates of randomly stacked (Co, Fe)OOH nanosheets. Thus, the amorphous Fe-modyfied cobalt oxyhydroxides derived from Brownmillerite-type CFCO are promising OER catalysts with good electrocatalytic activity and long-term durability under strongly alkaline conditions.The in situ formation of an OER electrocatalytically active CoOOH phase has been also reported in other systems [32][33][34][35][36][37][38][39][40][41]. Zhou et al reported that catalysts based on the simple Prussian blue analog NaxCoFe(CN)6 form a CoOOH active phase with the replacement of oxygen vacancies by the hydroxyl groups driven by an applied electric field 32.…”

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confidence: 77%

“…34 In this case, the active phase has been assigned to γ-CoOOH clusters embedded in phosphate glass matrices by Yoshida et al 35 Enman et al found that Fe species in CoOOH avoid the oxidation of Co spices and proposed the different OER mechanism in CoOOH and Fe-doped CoOOH. 36 Most of the above-mentioned studies show that catalyst might undergo modification through clusters formation and/or surface modification under standard OER conditions. Herein, we extended the durability studies to one month leading to polarization of the catalyst with total electric charge of the order of ∽10 5 C cm -2 .…”

Section: Discussionmentioning

confidence: 99%

Highly Durable Oxygen Evolution Reaction Catalyst: Amorphous Oxyhydroxide Derived from Brownmillerite-Type Ca₂FeCoO₅

Sato

Aoki

Takase

et al. 2020

ACS Appl. Energy Mater.

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Brownmillerite-type Ca2FeCoO5 (CFCO) is a highly active electrocatalyst for the oxygen evolution reaction (OER). In this study, we identified the actual catalytically active phase of this oxide formed via the long-term OER and, moreover, demonstrated that the active phase can persist during the OER for four weeks without significant loss of electrocatalytic activity. The long-term durability tests were carried out on CFCO via continuous galvanostatic OER in 4 mol dm -3 KOH aqueous solution for periods ranging from a few hours to one month, and the specimens submitted to the tests were characterized by means of electrochemical measurements and structural analysis using scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Auger electron spectroscopy, and X-ray absorption fluorescence spectroscopy. CFCO was readily converted to amorphous cobalt oxyhydroxides with 10% of Fe substituents through the OER process, and these compounds had a similar local rearrangement to the layered γ-CoOOH-type structure. This transformation involved large morphological changes of the oxide particles because of the extensive dissolution of Ca and Fe, yielding skeletal grains made of oxyhydroxide nanosheet aggregates. The extended durability studies with total polarization charge density of the order of 10 5 C cm -2 revealed that (Co, Fe)OOH like compound is the actual electrocatalytic phase.

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“… 616 Moreover, the further oxidation of Fe 3+ species to a higher oxidation state was described, implying a high electrochemical activity of these sites. 617 , 618 …”

Section: Examplesmentioning

confidence: 99%

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

2020

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During the last decades, X-ray absorption spectroscopy (XAS) has become an indispensable method for probing the structure and composition of heterogeneous catalysts, revealing the nature of the active sites and establishing links between structural motifs in a catalyst, local electronic structure, and catalytic properties. Here we discuss the fundamental principles of the XAS method and describe the progress in the instrumentation and data analysis approaches undertaken for deciphering X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Recent usages of XAS in the field of heterogeneous catalysis, with emphasis on examples concerning electrocatalysis, will be presented. The latter is a rapidly developing field with immense industrial applications but also unique challenges in terms of the experimental characterization restrictions and advanced modeling approaches required. This review will highlight the new insight that can be gained with XAS on complex real-world electrocatalysts including their working mechanisms and the dynamic processes taking place in the course of a chemical reaction. More specifically, we will discuss applications of in situ and operando XAS to probe the catalyst’s interactions with the environment (support, electrolyte, ligands, adsorbates, reaction products, and intermediates) and its structural, chemical, and electronic transformations as it adapts to the reaction conditions.

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Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts

Cited by 39 publications

References 41 publications

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Highly Durable Oxygen Evolution Reaction Catalyst: Amorphous Oxyhydroxide Derived from Brownmillerite-Type Ca₂FeCoO₅

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

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Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts

Cited by 39 publications

References 41 publications

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Influence of the Interlayer Space on the Water Oxidation Performance in a Family of Surfactant-Intercalated NiFe-Layered Double Hydroxides

Highly Durable Oxygen Evolution Reaction Catalyst: Amorphous Oxyhydroxide Derived from Brownmillerite-Type Ca2FeCoO5

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

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Highly Durable Oxygen Evolution Reaction Catalyst: Amorphous Oxyhydroxide Derived from Brownmillerite-Type Ca₂FeCoO₅