Reversibility of Ferri-/Ferrocyanide Redox during Operando Soft X-ray Spectroscopy

Risch, Marcel; Stoerzinger, Kelsey A.; Regier, Tom; Peak, Derek; Sayed, Sayed Youssef; Shao‐Horn, Yang

doi:10.1021/acs.jpcc.5b04609

Cited by 25 publications

(29 citation statements)

References 66 publications

(133 reference statements)

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“…The introduction of ferri/ferrocyanide redox couple can disturb such stability. Furthermore, ferricyanide and ferrocyanide complexes become unstable over time and precipitate as coordination polymers related to Prussian Blue (ferric hexacyanoferrate) (see, for example, [ 68 ] and references therein). Any change in the nanofluid composition due to undesired chemical reactions between its ionic species results in the change of thermoelectric voltage and power-output behavior.…”

Section: Resultsmentioning

confidence: 99%

Multifunctional Magnetic Nanocolloids for Hybrid Solar-Thermoelectric Energy Harvesting

et al. 2021

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Present environmental issues force the research to explore radically new concepts in sustainable and renewable energy production. In the present work, a functional fluid consisting of a stable colloidal suspension of maghemite magnetic nanoparticles in water was characterized from the points of view of thermoelectrical and optical properties, to evaluate its potential for direct electricity generation from thermoelectric effect enabled by the absorption of sunlight. These nanoparticles were found to be an excellent solar radiation absorber and simultaneously a thermoelectric power-output enhancer with only a very small volume fraction when the fluid was heated from the top. These findings demonstrate the investigated nanofluid’s high promise as a heat transfer fluid for co-generating heat and power in brand new hybrid flat-plate solar thermal collectors where top-heating geometry is imposed.

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Section: Resultsmentioning

confidence: 99%

Multifunctional Magnetic Nanocolloids for Hybrid Solar-Thermoelectric Energy Harvesting

et al. 2021

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“… 18 A similar effect was reported for Fe L-edge XAS with the dose-dependent reduction of Fe III to Fe II compounds. 21 , 40 …”

Section: Resultsmentioning

confidence: 99%

X-ray-induced sample damage at the Mn L-edge: a case study for soft X-ray spectroscopy of transition metal complexes in solution

Kubin

Kern

Guo

et al. 2018

Phys. Chem. Chem. Phys.

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X-ray induced sample damage can impede electronic and structural investigations of radiation-sensitive samples studied with X-rays. Here we quantify dose-dependent sample damage to the prototypical MnIII(acac)3 complex in solution and at room temperature for the soft X-ray range, using X-ray absorption spectroscopy at the Mn L-edge. We observe the appearance of a reduced MnII species as the X-ray dose is increased. We find a half-damage dose of 1.6 MGy and quantify a spectroscopically tolerable dose on the order of 0.3 MGy (1 Gy = 1 J kg−1), where 90% of MnIII(acac)3 are intact. Our dose-limit is around one order of magnitude lower than the Henderson limit (half-damage dose of 20 MGy) which is commonly employed for protein crystallography with hard X-rays. It is comparable, however, to the dose-limits obtained for collecting un-damaged Mn K-edge spectra of the photosystem II protein, using hard X-rays. The dose-dependent reduction of MnIII observed here for solution samples occurs at a dose limit that is two to four orders of magnitude smaller than the dose limits previously reported for soft X-ray spectroscopy of iron samples in the solid phase. We compare our measured to calculated spectra from ab initio restricted active space (RAS) theory and discuss possible mechanisms for the observed dose-dependent damage of MnIII(acac)3 in solution. On the basis of our results, we assess the influence of sample damage in other experimental studies with soft X-rays from storage-ring synchrotron radiation sources and X-ray free-electron lasers.

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“…S3). This reference was calibrated against molecular oxygen as described elsewhere [38,50]. All spectra were normalized by the subtraction of a straight line obtained by fitting the data before the L 3 edge and division by a polynomial function obtained by fitting the data after the L 2 edge (Fig.…”

Section: X-ray Absorption Spectroscopy (Xas)mentioning

confidence: 99%

Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

Villalobos

Golnak

et al. 2020

J. Phys. Energy

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Manganese oxides have received much attention over the years among the wide range of electrocatalysts for the oxygen evolution reaction (OER) due to their low toxicity, high abundance and rich redox chemistry. While many previous studies focused on the activity of these materials, a better understanding of the material transformations relating to activation or degradation is highly desirable, both from a scientific perspective and for applications. We electrodeposited Na-containing MnO x without long-range order from an alkaline solution to investigate these aspects by cyclic voltammetry (CV), scanning electron microscopy (SEM) and X-ray absorption spectroscopy (XAS) at the Mn-K and Mn-L edges. The pristine film was assigned to a layered edge-sharing Mn 3+/4+ oxide with Mn-O bond lengths of mainly 1.87 Å and some at 2.30 Å as well as Mn-Mn bond lengths of 2.87 Å based on fits to the extended X-ray fine structure (EXAFS). The decrease of the currents at voltages before the onset of the OER followed power laws with three different exponents depending on the number of cycles and the Tafel slope decreases from 186±48 to 114±18 mV dec-1 after 100 cycles, which we interpret in the context of surface coverage with unreacted intermediates. Post-mortem microscopy and bulk spectroscopy at the Mn-K edge showed no change of the microstructure, bulk local structure or bulk Mn valence. Yet, the surface region of MnO x oxidized toward Mn 4+ , which explains the reduction of the currents in agreement with literature. Surprisingly, we find that MnO x reactivates after 30 minutes at open-circuit (OC), where the currents and also the Tafel slope increase. Reactivation processes during OC are crucial because OC is unavoidable when coupling the electrocatalysts to intermittent power sources such as solar energy for sustainable energy production.

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Reversibility of Ferri-/Ferrocyanide Redox during Operando Soft X-ray Spectroscopy

Cited by 25 publications

References 66 publications

Multifunctional Magnetic Nanocolloids for Hybrid Solar-Thermoelectric Energy Harvesting

Multifunctional Magnetic Nanocolloids for Hybrid Solar-Thermoelectric Energy Harvesting

X-ray-induced sample damage at the Mn L-edge: a case study for soft X-ray spectroscopy of transition metal complexes in solution

Reversible and irreversible processes during cyclic voltammetry of an electrodeposited manganese oxide as catalyst for the oxygen evolution reaction

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