Evolution of the nanostructure of Pt and Pt–Co polymer electrolyte membrane fuel cell electrocatalysts at successive degradation stages probed by X-ray photoemission

Ali, Mubarak; Witkowska, Agnieszka; Abbas, Mamatimin; Gunnella, R.; Cicco, Andrea Di

doi:10.1016/j.jpowsour.2014.08.028

Cited by 11 publications

(5 citation statements)

References 25 publications

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“…The ZFO-C electrodes under consideration were prepared using carbon coated ZnFe 2 O 4 particles, with the structural properties described in the Supporting Information, following the procedures described in previous works ,− and briefly described in the Supporting Information. Electrodes at selected lithiation levels were prepared, stored under controlled conditions, and inserted into the sample chambers for X-ray measurements (see for example refs and for XAS and XPS, respectively). The electrochemical performance of the electrodes was measured by galvanostatic intermittent titration technique (GITT), as shown in Figure a, and the results are in line with previous findings. ,− GITT measurements were performed, as a series of galvanostatic steps (10 min each) at a current rate C/20, corresponding to 50 mAg –1 , followed by open-circuit relaxation periods of 60 min.…”

Section: Resultsmentioning

confidence: 99%

“…The surface and chemical sensitivity of X-ray photoemission spectroscopy (XPS) was used to get a deeper insight on the evolution of the uppermost SEI layers, i.e., in direct contact with the electrolytic salt. The C 1s XPS spectra reported in Figure have been collected using a laboratory source (Al Kα, photon energy h ν = 1486.6 eV) and an hemispherical analyzer (see for example ref and references therein). The kinetic energy of the collected photoelectrons ( E kin ∼ 1200 eV) corresponds to a typical electron mean free path of ∼2 nm and to maximum EPDs of about 5 nm.…”

Section: Resultsmentioning

confidence: 99%

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Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Rezvani

Gunnella

Witkowska

et al. 2017

ACS Appl. Mater. Interfaces

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Advanced metal oxide electrodes in Li-ion batteries usually show reversible capacities exceeding the theoretically expected ones. Despite many studies and tentative interpretations, the origin of this extra-capacity is not assessed yet. Lithium storage can be increased through different chemical processes developing in the electrodes during charging cycles. The solid electrolyte interface (SEI), formed already during the first lithium uptake, is usually considered to be a passivation layer preventing the oxidation of the electrodes while not participating in the lithium storage process. In this work, we combine high resolution soft X-ray absorption spectroscopy with tunable probing depth and photoemission spectroscopy to obtain profiles of the surface evolution of a well-known prototype conversion-alloying type mixed metal oxide (carbon coated ZnFeO) electrode. We show that a partially reversible layer of alkyl lithium carbonates is formed (∼5-7 nm) at the SEI surface when reaching higher Li storage levels. This layer acts as a Li reservoir and seems to give a significant contribution to the extra-capacity of the electrodes. This result further extends the role of the SEI layer in the functionality of Li-ion batteries.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Rezvani

Gunnella

Witkowska

et al. 2017

ACS Appl. Mater. Interfaces

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“…On the other hand, Pt 3 Co/C showed decreases in the rate constants of the redox reactions for the voltage cycling as the number of ADT cycles increased. Although the Pt-skin structure with Pt–Co alloy core is reported to enhance electrochemical activity and stability, the addition of Co cannot perfectly suppress the deactivation of the cathode electrocatalyst. − The time-resolved XAFS study suggested that ADT brought about not only decreases in the number of the active sites on Pt 3 Co/C but also changes in the reactivity on each active site on the electrocatalyst. The study showed a different mechanism of the degradation processes of the Pt/C and Pt 3 Co/C cathode electrocatalysts for ADT, suggesting the intrinsic deactivation of Pt 3 Co/C cathode electrocatalyst under identical conditions.…”

Section: Discussionmentioning

confidence: 99%

Kinetics and Mechanism of Redox Processes of Pt/C and Pt₃Co/C Cathode Electrocatalysts in a Polymer Electrolyte Fuel Cell during an Accelerated Durability Test

et al. 2016

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The degradation of Pt electrocatalysts in membrane electrode assemblies (MEAs) of polymer electrolyte fuel cells under working conditions is a serious problem for their practical use. Here we report the kinetics and mechanism of redox reactions at the surfaces of Pt/C and Pt3Co/C cathode electrocatalysts during catalyst degradation processes by an accelerated durability test (ADT) studied by operando time-resolved X-ray absorption fine structure (XAFS) spectroscopy. Systematic analysis of a series of Pt LIII-edge time-resolved XAFS spectra measured every 100 ms at different degradation stages revealed changes in the kinetics of Pt redox reactions on Pt/C and Pt3Co/C cathode electrocatalysts. In the case of Pt/C, as the number of ADT cycles increased, structural changes for Pt redox reactions (charging, surface, and subsurface oxidation) became less sensitive because of the agglomeration of catalyst particles. It was found that their rate constants were almost constant independent of the agglomeration of the Pt electrocatalyst. On the other hand, in the case of Pt3Co/C, the rate constants of the redox reactions of the cathode electrocatalyst gradually reduced as the number of ADT cycles increased. The differences in the kinetics for the redox processes would be differences in the degradation mechanism of these cathode electrocatalysts.

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“…These observations confirm the Co nanofilms-induced modification of electronic properties or geometric structure of Pd nanoparticles. The Co 2p 3/2 XPS peaks in Figures 3D,E show that Co states of the exposed Co atoms consist of Co metal (Co 0 ) and Co oxides (Co 2+ ) (Ali et al, 2014 ; Yun et al, 2015 ). After the two shakeup satellite peaks associated with the Co (2p) line of Co 2+ are taken into account (Xiao et al, 2015 ), the major Co 2p 3/2 XPS peaks with the typical binding energy around 782 eV correspond to Co 2+ oxides.…”

Section: Resultsmentioning

confidence: 99%

Oxygen Reduction Activity and Stability of Composite Pdx/Co-Nanofilms/C Electrocatalysts in Acid and Alkaline Media

Chen

Shi

et al. 2018

Front. Chem.

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The morphology tuning of Pd and Pd-M nanoparticles is one of the significant strategies to control the catalytic activity toward oxygen reduction reaction (ORR). In this study, composite Pdx/Co-nanofilms/C electrocatalysts of Pd nanoparticles implanted onto Co nanofilms were synthesized on an immiscible ionic liquid (IL)/water interface for ORR. The Pd nanoparticles implanted onto Co nanofilms show a marked distortion of crystal lattice and surface roughness. These Pdx/Co-nanofilms/C electrocatalysts exhibit enhanced activity for ORR compared with Pd/C and PdxCo/C catalysts in both acid and alkaline solutions, in which the Pd3/Co-nanofilms/C catalyst displays the highest ORR mass activity. The superior ORR mass activities of the fabricated Pdx/Co-nanofilms/C catalysts may be mainly attributed to their larger catalytic areas, which are conferred by the rough surface of Pd nanoparticles with a distorted crystal lattice, and the synergistic effect between the surface Pd atoms and the 2D Co nanofilm substrate. The relationship between ORR mass activity and Pd/Co atom ratio varies in different electrolytes. Furthermore, by using proper heat-treatment methods, the Pdx/Co-nanofilms/C catalysts exhibit improved cycling stability compared with pure Pd/C catalyst after extended potential cycling.

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Evolution of the nanostructure of Pt and Pt–Co polymer electrolyte membrane fuel cell electrocatalysts at successive degradation stages probed by X-ray photoemission

Cited by 11 publications

References 25 publications

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Kinetics and Mechanism of Redox Processes of Pt/C and Pt₃Co/C Cathode Electrocatalysts in a Polymer Electrolyte Fuel Cell during an Accelerated Durability Test

Oxygen Reduction Activity and Stability of Composite Pdx/Co-Nanofilms/C Electrocatalysts in Acid and Alkaline Media

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Evolution of the nanostructure of Pt and Pt–Co polymer electrolyte membrane fuel cell electrocatalysts at successive degradation stages probed by X-ray photoemission

Cited by 11 publications

References 25 publications

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Is the Solid Electrolyte Interphase an Extra-Charge Reservoir in Li-Ion Batteries?

Kinetics and Mechanism of Redox Processes of Pt/C and Pt3Co/C Cathode Electrocatalysts in a Polymer Electrolyte Fuel Cell during an Accelerated Durability Test

Oxygen Reduction Activity and Stability of Composite Pdx/Co-Nanofilms/C Electrocatalysts in Acid and Alkaline Media

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Product

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Kinetics and Mechanism of Redox Processes of Pt/C and Pt₃Co/C Cathode Electrocatalysts in a Polymer Electrolyte Fuel Cell during an Accelerated Durability Test