Operation of calcium-birnessite water-oxidation anodes: interactions of the catalyst with phosphate buffer anions

Ronge, Emanuel; Ohms, Jonas; Roddatis, Vladimir; Jones, Travis E.; Sulzmann, Frederic; Knop‐Gericke, Axel; Schlögl, Robert; Kurz, Philipp; Jooß, Christian; Skorupska, Katarzyna

doi:10.1039/d1se01076j

Cited by 4 publications

(7 citation statements)

References 66 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Consequently, the different surface chemistry in the initial state can only explain why the current density of the (010)-oriented film is more than 100% higher than that of the (001)-oriented film if Ca(OH) 2 plays an important role. Indeed, the role of Ca hydroxide species in the stabilization of active Mn 3+ states was discussed for another layered manganese oxide compound, namely, Ca birnessite . However, the valence states of Mn in both epitaxial orientations are 3.2 (010) and 3.3 (001), respectively, which are very similar and do not connect to the higher hydroxide surface concentration at the (010) films.…”

Section: Resultsmentioning

confidence: 99%

“…Indeed, the role of Ca hydroxide species in the stabilization of active Mn 3+ states was discussed for another layered manganese oxide compound, namely, Ca birnessite. 30 However, the valence states of Mn in both epitaxial orientations are 3.2 (010) and 3.3 (001), respectively, which are very similar and do not connect to the higher hydroxide surface concentration at the (010) films.…”

Section: Ruddlesden−popper Pcmo Epitaxialmentioning

confidence: 96%

See 1 more Smart Citation

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films

Ebrahimi,

Ottinger,

Belenchuk

et al. 2023

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

Studying the oxygen evolution reaction (OER) on anisotropic perovskite oxides with different surface orientations improves our understanding of how surface structure, chemistry, catalytic stability, and activity are related. Here, we present a comparative electrochemical study of (001)-and (010)-oriented epitaxial thin films of Ruddlesden−Popper (n = 1) Pr 0.5 Ca 1.5 MnO 4 (RP-PCMO) grown on Nb:SrTiO 3 (STNO) substrates of different orientations with using buffer layers. The results on epitaxial films are compared with those of the RP-PCMO powder. The OER activity and stability are studied using cyclic voltammetry and rotating ring disk electrodes under alkaline conditions. In addition, an analysis of their surface structure and chemistry by AFM and XPS before and after electrochemical measurements was carried out. The RP-PCMO powder shows high stability during electrochemical cycling. In contrast, the two differently oriented thin films are both corroding, while the (010)-oriented films reveal a higher activity and stability than the (001)-oriented ones. The variation in electrochemical activity and stability of the polycrystalline and single-crystalline RP-PCMO electrodes of different orientations is related to their different surface chemistry. In particular, it depends on the different Mn/Pr/Ca ratios and their different rates of Ca leaching, which is governed by the orientation-dependent Ca hydroxide surface concentration.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Ruddlesden−popper Pcmo Epitaxialmentioning

confidence: 96%

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films

Ebrahimi,

Ottinger,

Belenchuk

et al. 2023

J. Phys. Chem. C

Self Cite

View full text Add to dashboard Cite

show abstract

“…The involvement of lattice oxygen is strongly linked to the electronic structure of the catalyst ,, and in particular to the appearance of electron holes on lattice oxygen atoms, occurring in the presence of high M-O covalency resulting either from orbital overlap or from a negative charge transfer regime. It is not clear, however, whether the involvement of lattice oxygen is linked to the catalyst instability, , or whether the high covalency of the M-O bond could result in reduced dissolution and increases stability. , …”

Section: Discussionmentioning

confidence: 99%

Toward Realistic Models of the Electrocatalytic Oxygen Evolution Reaction

Jones,

Teschner,

Piccinin

2024

Chem. Rev.

Self Cite

View full text Add to dashboard Cite

The electrocatalytic oxygen evolution reaction (OER) supplies the protons and electrons needed to transform renewable electricity into chemicals and fuels. However, the OER is kinetically sluggish; it operates at significant rates only when the applied potential far exceeds the reversible voltage. The origin of this overpotential is hidden in a complex mechanism involving multiple electron transfers and chemical bond making/breaking steps. Our desire to improve catalytic performance has then made mechanistic studies of the OER an area of major scientific inquiry, though the complexity of the reaction has made understanding difficult. While historically, mechanistic studies have relied solely on experiment and phenomenological models, over the past twenty years ab initio simulation has been playing an increasingly important role in developing our understanding of the electrocatalytic OER and its reaction mechanisms. In this Review we cover advances in our mechanistic understanding of the OER, organized by increasing complexity in the way through which the OER is modeled. We begin with phenomenological models built using experimental data before reviewing early efforts to incorporate ab initio methods into mechanistic studies. We go on to cover how the assumptions in these early ab initio simulationsno electric field, electrolyte, or explicit kineticshave been relaxed. Through comparison with experimental literature, we explore the veracity of these different assumptions. We summarize by discussing the most critical open challenges in developing models to understand the mechanisms of the OER.

show abstract

“…The characterization of phosphorus species has been carried out in natural and synthetic materials using a variety of methods [6][7][8][9][10]28,[35][36][37][38], featuring, e.g., infrared and Raman spectroscopy [39,40], neutron scattering [41], 31 P nuclear magnetic resonance spectroscopy [10,[42][43][44], and X-ray spectroscopy techniques [9,36,[45][46][47][48][49][50]. For the CoCat, the properties of the P species were studied by various approaches [6][7][8][9][10]18,35].…”

Section: Introductionmentioning

confidence: 99%

“…In electrodeposited amorphous CoCat films, phosphorus was found to be present as orthophosphate (PO 4 3− ) [7]. In related Ca-birnessite MnO X structures, P-rich surface layers were observed, and two possible P binding modes were suggested, with phosphate either directly bound to O-vacancies in the [ MnO 6 ] layers or phosphate associated with Ca 2+ in the interlayer space forming Ca/PO 4 /H 2 O complexes [38]. Replacing phosphorus with arsenic in the CoCat facilitated (technically easier) XAS studies at the As K-edge [28] and revealed two possible binding motifs, with arsenate either bridging two Co centers at the margins of the CoCat layers or substituting cobalt ions within the oxide layers.…”

Section: Introductionmentioning

confidence: 99%

Phosphate Coordination in a Water-Oxidizing Cobalt Oxide Electrocatalyst Revealed by X-ray Absorption Spectroscopy at the Phosphorus K-Edge

et al. 2023

View full text Add to dashboard Cite

In the research on water splitting at neutral pH, phosphorus-containing transition metal oxyhydroxides are often employed for catalyzing the oxygen evolution reaction (OER). We investigated a cobalt–phosphate catalyst (CoCat) representing this material class. We found that CoCat films prepared with potassium phosphate release phosphorus in phosphate-free electrolytes within hours, contrasting orders of magnitude’s faster K+ release. For P speciation and binding mode characterization, we performed technically challenging X-ray absorption spectroscopy experiments at the P K-edge and analyzed the resulting XANES and EXAFS spectra. The CoCat-internal phosphorus is present in the form of phosphate ions. Most phosphate species are likely linked to cobalt ions in Co–O–PO3 motifs, where the connecting oxygen could be a terminal or bridging ligand in Co-oxide fragments (P–Co distance, ~3.1 Å), with additional ionic bonds to K+ ions (P–K distance, ~3.3 Å). The phosphate coordination bond is stronger than the ionic K+-binding, explaining the strongly diverging ion release rates of phosphate and K+. Our results support a structural role of phosphate in the CoCat, with these ions binding at the margins of Co-oxide fragments, thereby limiting the long-range material ordering. The relations of catalyst-internal phosphate ions to cobalt’s redox-state changes, proton transfer, and catalytic activity are discussed.

show abstract

Operation of calcium-birnessite water-oxidation anodes: interactions of the catalyst with phosphate buffer anions

Abstract: Investigating the interfaces between electrolytes and electrocatalysts during electrochemical water oxidation is of great importance for an understanding of the factors influencing catalytic activity and stability. Here, the interaction of...

Cited by 4 publications

References 66 publications

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films

Toward Realistic Models of the Electrocatalytic Oxygen Evolution Reaction

Phosphate Coordination in a Water-Oxidizing Cobalt Oxide Electrocatalyst Revealed by X-ray Absorption Spectroscopy at the Phosphorus K-Edge

Contact Info

Product

Resources

About

Operation of calcium-birnessite water-oxidation anodes: interactions of the catalyst with phosphate buffer anions

Abstract: Investigating the interfaces between electrolytes and electrocatalysts during electrochemical water oxidation is of great importance for an understanding of the factors influencing catalytic activity and stability. Here, the interaction of...

Cited by 4 publications

References 66 publications

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Thin Films

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr0.5Ca1.5MnO4 Thin Films

Toward Realistic Models of the Electrocatalytic Oxygen Evolution Reaction

Phosphate Coordination in a Water-Oxidizing Cobalt Oxide Electrocatalyst Revealed by X-ray Absorption Spectroscopy at the Phosphorus K-Edge

Contact Info

Product

Resources

About

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films

Orientation-Dependent Oxygen Evolution Activity of Epitaxial Ruddlesden–Popper Pr_0.5Ca_1.5MnO₄ Thin Films