Deviations from Vegard's law and evolution of the electrocatalytic activity and stability of Pt-based nanoalloys inside fuel cells by<i>in operando</i>X-ray spectroscopy and total scattering

Petkov, Valeri; Maswadeh, Yazan; Vargas, Jorge; Shan, Shiyao; Kareem, Haval; Wu, Zhi Peng; Luo, Jin; Zhong, Chuan Jian; Shastri, S. D.; Kenesei, Péter

doi:10.1039/c9nr01069f

Cited by 43 publications

(51 citation statements)

References 78 publications

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“…The higher Pt concentration in these alloys is most likely the reason for that, but it should be noticed that this law is seldom perfectly obeyed, as discussed in Refs. [47,48]. The evaluation of the L1 0 order parameter for the FePt reference layer revealed a high degree of ordering with a value of 0.93, which is close to the theoretical maximum S max of 1 [Fig.…”

Section: Structural Properties and Microstructuresupporting

confidence: 70%

L10 -ordered (Fe100−xCrx)Pt thin films: Pha

et al. 2020

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Chemically ordered L1 0 (Fe 100−x Cr x )Pt thin films were expitaxially grown on MgO(001) substrates by magnetron sputter-deposition at 770 • C. In this sample series, Fe was continuously substituted by Cr over the full composition range. The lattice parameter in the [001] growth direction steadily increases from L1 0 -FePt toward L1 0 -CrPt, confirming the incorporation of Cr in the lattice occupying Fe sites. With the observed high degree of chemical ordering and (001) orientation, strong perpendicular magnetic anisotropy is associated, which persists up to a Cr content of x = 20 at. %. Similarly, the coercive field in the easy-axis direction is strongly reduced, which is, however, further attributed to a strong alteration of the film morphology with Cr substitution. The latter changes from a well-separated island microstructure to a more continuous film morphology. In the dilute alloy with low Cr content, isolated Cr magnetic moments couple antiferromagnetically to the ferromagnetic Fe matrix. In this case, all Cr moments are aligned parallel, thus forming a ferrimagnetic FeCrPt system. With increasing Cr concentration, nearest-neighbor Cr-Cr pairs start to appear, thereby increasing magnetic frustration and disorder, which lead to canting of neighboring magnetic moments, as revealed by atomistic spin-model simulations with model parameters based on first principles. At higher Cr concentrations, a frustrated ferrimagnetic order is established. With Cr substitution of up to 20 at. %, no pronounced change in Curie temperature, which is in the range of 700 K, was noticed. But with further addition the Curie temperature drops down substantially even down to room temperature at 47 at. % Cr. Furthermore, x-ray magnetic circular dichroism studies on dilute alloys containing up to 20 at. % of Cr revealed similar spin moments for Fe and Cr in the range between 2.1-2.5 μ B but rather large orbital moments of up to 0.50 ±0.10 μ B for Cr. These results were also compared to ab initio calculations.

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Section: Structural Properties and Microstructuresupporting

confidence: 70%

L10 -ordered (Fe100−xCrx)Pt thin films: Pha

et al. 2020

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“…In this study, 0.25 wt%, 0.5 wt%, 1.0 wt%, and 5.0 wt% supported PtNiCo–PtNiOCoO catalysts were prepared and tested. Characterizations of the PtNiCo–PtNiOCoO nanoparticles with different compositions by HE-XRD indicated that these nanoparticles are the fcc-type structure characteristic of a solid solution 34 , 35 .…”

Section: Methodsmentioning

confidence: 99%

Surface oxygenation of multicomponent nanoparticles toward active and stable oxidation catalysts

Shan

Maswadeh

et al. 2020

Nat Commun

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The need for active and stable oxidation catalysts is driven by the demands in production of valuable chemicals, remediation of hydrocarbon pollutants and energy sustainability. Traditional approaches focus on oxygen-activating oxides as support which provides the oxygen activation at the catalyst-support peripheral interface. Here we report a new approach to oxidation catalysts for total oxidation of hydrocarbons (e.g., propane) by surface oxygenation of platinum (Pt)-alloyed multicomponent nanoparticles (e.g., platinum-nickel cobalt (Pt–NiCo)). The in-situ/operando time-resolved studies, including high-energy synchrotron X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy, demonstrate the formation of oxygenated Pt–NiOCoO surface layer and disordered ternary alloy core. The results reveal largely-irregular oscillatory kinetics associated with the dynamic lattice expansion/shrinking, ordering/disordering, and formation of surface-oxygenated sites and intermediates. The catalytic synergy is responsible for reduction of the oxidation temperature by ~100 °C and the high stability under 800 °C hydrothermal aging in comparison with Pt, and may represent a paradigm shift in the design of self-supported catalysts.

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“…We recognise that the peak B energy shift with electrodeposition time were not strictly linear (Fig. 6) and deviations from Vegard's law are often observed [58]. Nonetheless, we found that it still provides useful approximations as an alternative method for quantifying the amounts of the varying Cu species in the films.…”

Section: X-ray Absorption Spectroscopymentioning

confidence: 83%

Probing the electronic and geometric structures of photoactive electrodeposited Cu2O films by X-ray absorption spectroscopy

Yilmaz

Handoko

Parkin

et al. 2020

Journal of Catalysis

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Cu 2 O is an attractive photocathode for important renewable energy reactions such as water splitting and CO 2 reduction. Electrodeposition is commonly used to deposit Cu 2 O films on conductive substrates due to its simplicity and consistency. However, structural descriptors, linking electrodeposition parameters, film structure and the catalytic properties are elusive. A variety of Cu 2 O films reported by many research groups would often display vastly different electronic properties and catalytic activity, while appear indistinguishable under common characterisation tools. In this work, we take a systematic look into electrochemically deposited Cu 2 O and investigate the impact of deposition parameters towards the bulk and surface chemistry of the deposited film. Specifically, we employ high resolution XANES for thorough quantitative analysis of the Cu 2 O films, alongside more common characterisation methods like XRD, SEM and Raman spectroscopy. Photoelectrochemical (PEC) studies reveal an unexpected trend, where the highest PEC activity appears to correlate with the amount of Cu 2+ content. Other factors which also affect the PEC activity and stability are film thickness and crystallite grain size. Our study shows that the use of high resolution XANES, though not perfect due to possible self-absorption issue, is apt for extracting compositional descriptor in concentrated thin film samples from the pre-edge energy position analysis. This descriptor can serve as a guide for future development of more active Cu 2 O based films for wide range of PEC processes as well as for solar cell applications.

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Deviations from Vegard's law and evolution of the electrocatalytic activity and stability of Pt-based nanoalloys inside fuel cells byin operandoX-ray spectroscopy and total scattering

Abstract: Deviations from Vegard's law inherent for nanoalloy catalysts can explain their behavior under operating conditions.

Cited by 43 publications

References 78 publications

L10 -ordered (Fe100−xCrx)Pt thin films: Pha

L10 -ordered (Fe100−xCrx)Pt thin films: Pha

Surface oxygenation of multicomponent nanoparticles toward active and stable oxidation catalysts

Probing the electronic and geometric structures of photoactive electrodeposited Cu2O films by X-ray absorption spectroscopy

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