Impact of CeOx Additives on Cathode Catalyst Layer Poisoning

Journal of The Electrochemical Society, 2014

CeOx is an excellent free radical scavenger to improve polymer electrolyte membrane durability. However, this metal oxide will dissolve during accelerated stress testing (AST), with the resulting cations transporting to the cathode catalyst layer (CCL) leading to performance reduction/degradation of the PEMFC. Controlling the rate of CeOx dissolution is therefore of great importance, as it may be possible to maintain sufficient Ce cations for free radical scavenging while minimizing the impact of these cations on the CCL. Here the effect of CeOx crystallite size on CeOx dissolution was investigated. Three CeOx additives were prepared having crystallite sizes of 6, 13, or 25 nm. An ex-situ method was used to evaluate the chemical stability of these three CeOx samples, as well as one commercially available CeOx. It was determined that surface area, rather than crystallite size, is the best predictor of chemical stability. In-situ membrane electrode assembly AST cycling was then performed, demonstrating that when low loadings of CeOx (0.006 mg/cm 2) are used, the ex-situ method correctly predicts trends in end of life (EOL) performance. Finally, it is shown that increasing the anode RH during AST cycling leads to significantly higher EOL performance losses.

Electrochimica Acta, 2014

Please cite this article as: A. Meléndez-Ceballos, V. Albin, S.M. Fernández-Valverde, A. Ringuedé, M. Cassir, Electrochemical properties of Atomic layer deposition processed CeO 2 as a protective layer for the molten carbonate fuel cell cathode, Electrochimica Acta (2014), http://dx.

Applied Surface Science, 2000

A CeO thin film has been subjected to Ar q bombardment at 298 K to induce the reduction of its outmost layers by 2 preferential removal of oxygen. An XPS study of the altered layer at normal and grazing angle has been carried out. The Ž. q Factor Analysis FA of the XPS spectra of this Ar reduced film shows that it has a stoichiometry close to Ce O , being 2 3 Ce 3q the dominant species at both collection angles. Simultaneously, the O1s spectra depict a lateral peak whose relative intensity is higher for those spectra recorded at grazing angle. Exposure to successive doses of O at 298 K of the reduced 2 layers produces the increase of the OrCe ratio and a progressive reoxidation of Ce 3q into Ce 4q as determined by FA of the Ce3d spectra. Simultaneously, the lateral component at the O1s peak also decreases, thus discarding that it is due to surface contamination by-OH or similar species, as previously suggested in the literature. After exposure to a high pressure of Ž. oxygen ca. 1 Torr , the XPS spectrum obtained at a normal collection angle shows an almost complete oxidation of the film to CeO. However, in the spectrum at grazing angle, Ce 3q species and the lateral component of oxygen are still detected. 2 Ž. The lateral O1s component is tentatively attributed to oxygen ions with unusual coordinations in a defective CeO x-2 x structure, while the remaining Ce 3q ions might be due to fully coordinated species. Enrichment of the surface of the defective cerium oxide with these oxygen species seems to be a result of the same structural rearrangements that favour the observed stabilization of Ce 3q species at the surface.

ECS Electrochemistry Letters, 2015

A CeO 2 supported membrane electrode assembly (MEA) was fabricated by hot-pressing CeO 2-coated electrodes and a PFSA ionomer membrane. Upon application of a combined chemical and mechanical accelerated stress test (AST), the CeO 2 supported MEA showed six times longer lifetime and 40 times lower fluoride emission rate than a baseline MEA without cerium. The membrane in the CeO 2 supported MEA effectively retained its original thickness and ductility despite the highly aggressive AST conditions. Most of the cerium applied on the anode migrated into the membrane and provided excellent mitigation of joint chemical and mechanical membrane degradation.

Catalysis Today, 2018

CeO 2 is widely used as a catalyst support component due to its redox property of oxygen storage and release. This unique feature, which is usually referred to as "oxygen storage capacity" (OSC), can be quantitatively evaluated by different methods and techniques. Since the oxygen release benefits oxidation reactions, catalytic activity can be correlated with OSC. The measured amount of OSC can be influenced by a number of factors, such as the nature of the reducing agent, the conditions of reducing gas flow and operation temperature, the aging, the composition, and physical and geometric properties of CeO 2-based materials, and the type of analytical technique used. Therefore, these influencing factors include, but are not limited to, the use of H 2 or CO as reducing agent, continuous or pulsed feed of reducing agent, the presence of other elements in the CeO 2 structure, particle size and surface area, supported catalyst components and aging, etc. This review paper focuses on the measurement of OSC, the effect of influencing factors, and the role of OSC in the typical reactions that occur in automotive emission control like oxidation, NO reduction, water gas shift, and reforming reactions. Furthermore, this review addresses the reactions in which the catalytic activity can be correlated with OSC.

Journal of the European Ceramic Society, 2021

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Solid State Ionics, 1992

Electrochemical impedance spectroscopy was used to examine doped CeO2 as a mixed-conducting electrode material for solid oxide fuel cells. Sintered oxide disks with a composition of Ceo.gM0.~ O: (M = Co, Ni, and Mn) were used at 1000 ° C in two types of cell: Pt/Ceo.oM0.~OJPt and Ce0.gM0.jO2/9% Y203-ZrO2/Pt. The impedance spectra for the cell containing two platinum electrodes exhibited three depressed semicircles, with the highest-frequency semicircle corresponding to the bulk oxide. Oxygen reduction on Ni-and Co-CeO2 electrodes in air was studied as a function of voltage using the Y203-ZrO2 cell. The spectra in this case exhibited two distinct semicircles, with the high-frequency relaxation being ascribed to O2 reduction at the cathode and the other to mass transport of O2 or O 2- .

Applied Surface Science, 2014

Investigation of cerium oxide thin film deposition on silicon and silicon oxide is important due to many possible applications of cerium oxide based micro-systems in electronics and catalysis. rf-Magnetron sputtering is technologically the most suitable method of preparation of such systems. Mechanism of film growth is strongly influenced by interaction of Ce atoms with the substrate and their oxidation by oxygen containing rf plasma. We show using hard X-ray photoelectron spectroscopy with high information depth that cerium is reducing silicon oxide by forming complex silicate phase at the interface with Ce in the 3+ state. For this reason composition of very thin films of cerium oxide is strongly influenced by thin film-substrate interaction. A coating of the silicon oxide substrate by an intermediate thin carbon film provides conductive substrate for electrocatalytic applications and decreases the silicon oxide substrates-cerium oxide interaction essentially. .cz (V. Matolín). FC, the catalyst is the key to performance and, therefore, the most critical component. However, standard wet-process techniques for powder catalyst are incompatible with on-chip -FC technology. Planar on-chip -FCs, therefore, require novel catalysts prepared by thin-film technologies such as thin-film (TF) sputtering.

Applied Catalysis A-general, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Journal of Solid State Electrochemistry, 2018

Dy-and Tb-doped CeO 2-Ni cermets for highly active solid-oxide fuel-cell (SOFC) anodes were fabricated by a one-pot electrodeposition process. Undoped, singly-doped, and co-doped powders were synthesized in an X-ray amorphous state, heat treated in air, and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) at different crystallization stages. In particular, in situ TEM analyses were carried out during heating in an oxygen atmosphere, in order to follow the evolution of structure and morphology and to understand the role of the dopants. The key structural effect of dopants was the inhibition of grain coarsening during heat treatment. Functional tests were carried out with micro-single chamber SOFCs, fed with a CH 4 /O 2 mixture, the anodes of which were prepared with the CeO 2-Ni powders synthesized in this study. A correlation was established between the electrocatalytic performance and the morphology of the anodic material, pinpointing that the finer and more homogeneous nanocrystalline structure of the doped powders results in better-defined and more active catalytic sites, thus improving the performance of the cell. Keywords Solid-oxide fuel-cell. CeO 2-Ni cermet. Dy and Tb doping. Electrodeposition. In situ TEM