Praseodymium Cerium Oxide Research Articles

Praseodymium-Cerium Oxide-Infiltrated Perovskite Cathode with Superior Electrochemical Performance for Solid Oxide Fuel Cells.

This study presents a high-performance solid oxide fuel cell employing a perovskite cathode, strontium iron molybdenum oxide [Sr2Fe1.5Mo0.5O6-δ (SFM)], infiltrated with praseodymium-cerium oxide [Pr0.2Ce0.8O2-δ (PCO)], a fluorite. This infiltration notably enhances the oxygen reduction reaction kinetics and long-term stability. Evidence of enhanced stability is seen through minimized impedance degradation over 50 h. Furthermore, PCO infiltration improves the cathode's resistance to chromium poisoning by suppressing strontium degradation. Compared to the bare SFM cathode, the PCO-infiltrated SFM composite cathode doubles the cell's power density at 800 °C.

Pr-doped CeO2-loaded Ru-based catalysts for ethylene methoxycarbonylation

The industrial production of methyl propionate synthesized via methoxycarbonyl esterification of ethylene achieved 100% atom economy. In this study, we synthesized ruthenium-loaded praseodymium-cerium oxide (Pr-CeO2) catalysts by precipitation impregnation and...

Electrical Conductivity and Electrochemical Performance of Pr Doped Ceria

PCO (Praseodymium Cerium Oxide) solid solution (0-50% PrOx) has been prepared by the conventional solid-state ceramic processing of mixed CeO2 and PrOx powders in the desired stoichiometry at 1500°C in air. Synthesized powder has been characterized for phase chemistry and lattice structure. Electrochemical characteristics of the synthesized powder has been examined using electrochemical impedance spectroscopy. The observed increase in the electrical conductivity of PCO are associated with increased concentration of oxygen vacancies created by replacement of Ce4+ ions with Pr+3 ions. The addition of PrOx also lowered the polarization and ohmic losses.

High-Temperature Piezoelectric Resonators: Electroacoustic Properties and Applications of Langasite-Type Crystals

Piezoelectric devices based on high-temperature stable single crystals are of increasing interest due to a wide range of potential applications, such as actuators and resonant gravimetric sensors. The latter require highly accurate resonant-frequency measurements at temperatures as high as 1000 °C, and this can only be achieved with narrow resonance peaks and correspondingly low acoustic loss at these temperatures. Relevant atomistic defects in langasite (La3Ga5SiO14, LGS) and catangasite (Ca3TaGa3Si2O14, CTGS) are reviewed with respect to their impact on electrical conductivity and acoustic loss. The focus on these crystals also enables a comparison of electroacoustic properties of partially disordered (LGS) and ordered (CTGS) crystals and the formulation of approaches for reducing acoustic loss and enhancing device performance.Starting with defect chemistry models for LGS and CTGS, electrical conductivities as a function of temperature and oxygen partial pressure are considered. One result of this analysis is that contributions of oxygen ions to the total conductivity are determined to be relatively small in the studied crystals. Temperature-dependent acoustic loss of LGS and CTGS crystals is also studied. Two independent techniques, contact resonant piezoelectric spectroscopy, and a contactless tone-burst excitation technique, are applied. Contributions to the measured acoustic loss are determined by fitting loss-related functions for point defects and conductivity-related relaxations. The extracted fit parameters, in particular the activation energies of the processes, are discussed and compared with that of the electrical conductivity. The losses are caused by a superposition of several mechanisms including conductivity-related relaxations, point-defect relaxations and intrinsic phonon-phonon loss.The long-term stability of the crystals is also evaluated at 1000 °C with respect to fundamental materials properties including electrical conductivity and resonant frequency.After one year of thermal treatment, the resonance frequency of CTGS resonators from different crystal sources is found to decrease by no more than 0.4 %. Thus, the applicability of CTGS as a piezoelectric resonator that operates for long periods at extreme temperatures, such as a resonant nanobalance, is demonstrated.Application examples to be presented include resonant nanobalances for in-situ monitoring of non-stoichiometry and phase transformations in thin films during growth at high temperatures. In this context, the key application properties of the sensors at high temperatures, such as mass sensitivity and resolution, are discussed. As an application example, the attached figure shows the oxygen non-stoichiometry x of thin praseodymium-cerium oxide films (Pr0.1Ce0.9O2-x) at 700 °C as a function of oxygen partial pressure determined by LGS and CTGS nanobalances, which agrees very well with literature data (chemical capacitance: D. Chen et al., Chem. Mater. 2014, 26, 22, 6622–6627). Figure 1

Electrical Conductivity and Electrochemical Performance of Pr Doped Ceria

PCO (Praseodymium Cerium Oxide) solid solution (0-50% PrOx) has been prepared by the conventional solid-state ceramic processing route using CeO2 and PrOx powders in the desired stoichiometry and sintering at 1500°C in air. Synthesized powder has been characterized for phase chemistry and lattice structure. Electrochemical characteristics of the synthesized powder has been examined using electrochemical impedance spectroscopy. The observed increase in the electrical conductivity of PCO are associated with increased concentration of oxygen vacancies created by the replacement of Ce4+ ions with Pr+3 ions. The addition of PrOx also lowered the polarization and ohmic losses.

Measurement and control of oxygen non-stoichiometry in praseodymium-cerium oxide thin films by coulometric titration

Measurement and control of oxygen non-stoichiometry in praseodymium-cerium oxide thin films by coulometric titration

Sorption cryogenic cooling: Fundamentals, progress, and outlook

Sorption cryocoolers are of great interest for cooling vibration-sensitive instruments due to their nature of no vibration. This review presents the basic principle and brief developments of sorption cryocoolers, and discusses the measures improving their performance. At present, activated carbon is the main adsorbent for physisorption cryocoolers that can produce cooling at the temperatures ranging from 185 K to 4.5 K with Joule-Thomson (JT) cryocoolers and sub-kelvin cooling with evaporative cryocoolers. Metal hydride, manganese nitride and praseodymium cerium oxide are the main absorbents for chemisorption JT cryocoolers that can achieve 20 K, 75 K and 80 K using hydrogen, nitrogen and oxygen gases as working fluids, respectively. The sorption cryocoolers have the potential life-times for more than 15 years, and the life-times of physisorption JT cryocoolers are mainly determined by the only moving parts-check valves, whereas the life-times of chemisorption JT cryocoolers are affected by both check valves and sorbent stability. However, the efficiencies of sorption cryocoolers are still lower than mechanical cryocoolers. To realize the comparable efficiencies as mechanical cryocoolers, more efficient sorbents are required. Besides, there is plenty of room for efficiency improvement through the optimization of the compression cycle and key components related to sorption cryocoolers. This review aims to provide a reference for researchers interested in sorption cryocoolers for both space-based and ground-based applications and to identify the potential directions on this topic.

Chemical expansion of praseodymium-cerium oxide films at high temperatures by laser doppler vibrometry

The chemical expansion of Pr0.1Ce0.9O2−δ (PCO) films was determined as function of oxygen activity at 720 °C by laser Doppler vibrometry (LDV) in combination with previously reported chemical capacitance studies that provided relevant oxygen nonstoichiometry δ data. The LDV method enabled detection of nanometer displacements, provided that displacement frequencies were above 1 Hz. The PCO films were deposited on yttrium stabilized zirconia (YSZ) substrates operated in the electrochemical oxygen pump mode at 720 °C to periodically adjust the oxygen activity within the PCO film. The potential across the YSZ was varied between 0 and 0.3 V, corresponding to oxygen partial pressures of about 0.2 bar and 10−7 bar, respectively. The electrochemically induced expansion/contraction of the PCO film was observed to induce deflection in both film and substrate, as clearly demonstrated by scanning the sample surface by the LDV. A maximum displacement of about 18 nm at the center of the substrate plate was found during application of a periodic 1 Hz pumping voltage. A much lower displacement, on the order of 1 nm, was obtained when a pin-type sample support was applied, characteristic of chemical expansion of the film itself. These data were used to discuss correlations with similar recent data obtained by monitoring displacements of the PCO/YSZ sandwich structure with the aid of a specially modified nanoindenter.

Nonstoichiometry in Oxide Thin Films Operating under Anodic Conditions: A Chemical Capacitance Study of the Praseodymium–Cerium Oxide System

Nonstoichiometry in Oxide Thin Films Operating under Anodic Conditions: A Chemical Capacitance Study of the Praseodymium–Cerium Oxide System

Non-Stoichiometry in Oxide Thin Films Operating Under Anodic Conditions: A Chemical Capacitance Study of the Praseodymium-Cerium Oxide System

PrxCe1-xO2-δ can potentially serve as both cathode and anode in solid oxide fuel cells given that it exhibits significant mixed ionic-electronic conductivity (MIEC) under both cathodic and anodic conditions. While MIEC depends strongly on oxygen nonstoichiometry δ, there have been few ways to extract this information reliably and in situ, particularly for thin films. In this work, this is achieved by analysis of chemical capacitance values extracted from impedance spectroscopy data obtained on electrochemical cells of the form Pr0.1Ce0.9O2−δ/ Y0.16Zr0.84O1.92 / Pr0.1Ce0.9O2−δ operating at temperatures between 500 to 700 oC and over the pO2 range of 10-31-10-16 atm. The enthalpy of reduction for the Pr0.1Ce0.9O2−δ thin film is derived.

Defects and transport in PrxCe1−xO2−δ: Composition trends

Abstract

Praseodymium-cerium oxide thin film cathodes: Study of oxygen reduction reaction kinetics

Praseodymium-Cerium Oxide (PrxCe1-xO2−δ; PCO), a potential three way catalyst oxygen storage material and solid oxide fuel cell (SOFC) cathode, exhibits surprisingly high levels of oxygen nonstoichiometry, even under oxidizing (e.g. air) conditions, resulting in mixed ionic electronic conductivity (MIEC). In this study we examine the redox kinetics of dense PCO thin films using impedance spectroscopy, for x = 0.01, 0.10 and 0.20, over the temperature range of 550 to 670°C, and the oxygen partial pressure range of 10−4 to 1 atm O2. The electrode impedance was observed to be independent of electrode thickness and inversely proportional to electrode area, pointing to surface exchange rather than bulk diffusion limited kinetics. The large electrode capacitance (10−2F) was found to be consistent with an expected large electrochemically induced change in stoichiometry for x = 0.1 and x = 0.2 PCO. The PCO films showed surprisingly rapid oxygen exchange kinetics, comparable to other high performance SOFC cathode materials, from which values for the surface exchange coefficient, k q , were calculated. This study confirms the suitability of PCO as a model MIEC cathode material compatible with both zirconia and ceria based solid oxide electrolytes.

Electrical conductivity and defect equilibria of Pr0.1Ce0.9O2−δ

Praseodymium-cerium oxide (PCO) solid solutions exhibit mixed ionic electronic conductivity (MIEC) behavior in a relatively high and readily accessible oxygen partial pressure (P(O(2))) regime and as such serve as a model system for investigating the correlation between thermodynamic and kinetic properties and performance figures of merit in the areas of high temperature energy conversion, automotive control, and gas sensing applications. In this paper, we present measurements on the non-stoichiometry of Pr(0.1)Ce(0.9)O(2-δ) and develop a defect equilibria model to predict the dependence of the concentration of all the dominant charge carriers on temperature, P(O(2)), and Pr fraction. The predictive model is then employed to describe the measured electrical conductivity and oxygen nonstoichiometry whereby pre-exponentials and enthalpies of defect formation and migration are extracted.

Nonstoichiometry and Defect Chemistry in Praseodymium-Cerium Oxide

Praseodymium cerium oxide (Pr x Ce1 − xO2 − δ) is a mixed ionic-electronic conductor with high levels of nonstoichiometry under oxidizing conditions resulting from reduction of Pr4 + to Pr3 +. Coulometric titration measurements performed on (Pr x Ce1 − xO2 − δ) with x = 0.2 are generally consistent with those derived from electrical conductivity measurements. Nevertheless, a somewhat larger degree of nonstoichiometry measured via coulometric titration implies that non-charged defect species may be significant in the system.

Praseodymium-Cerium Oxide as a Surface-Effect Gas Sensor

The gas sensing behavior of praseodymium doped cerium oxide (PrxCe1 − xO2 or PCO) has been examined for 0–1000 ppm CO or H2 in a 10% O2 atmosphere at temperatures ranging from 250–350_∘C. Total conductivity as a function of temperature suggests that oxygen diffusion kinetics are slow below approximately 350_∘C. Devices with x = 0.05 and 0.10 show stable, n-type gas sensing response, while those with x = 0.20 exhibit significant drift in sensor output, presumably due to bulk oxygen migration. The response to CO is significantly stronger than that to H2 at 300_∘C, and at 350_∘C the response to H2 is nearly zero, resulting in a CO-selective gas sensing element. Suggestions for the source of selectivity in PCO are presented.

Electrical Conductivity in Praseodymium-Cerium Oxide

ABSTRACTThe electrical conductivity of PrxCe1-xO2-δ (PCO) for 0 ≤ × ≤ 0.20 was examined over a wide range of temperatures and oxygen partial pressures. A defect model based on multiple Pr valence states was found to be qualitatively consistent with the observed data. A unique pO2-dependent ionic conductivity is observed at high pO2 values in compositions containing low levels of Pr (0 ≤ × ≤ 0.01). In compositions containing higher amounts of Pr (0.05 ≤ × ≤ 0.20), formation of a Pr induced impurity band results in a significant electronic conductivity at high pO2 values.

Impedance and Mott-Schottky Analysis of a Pr0.15Ce0.85O2-x Solid Solution

ABSTRACTThe semiconductor properties of a praseodymium-cerium oxide solid solution with composition Pr0.15Ce0.85O2-x (PCO) were investigated by d.c. current-voltage and bias-dependent impedance measurements in aqueous solution. The solution data were compared with impedance values of dry cells in air. A Mott-Schottky analysis of the PCO-solution interface capacitance showed p-type semi conductivity, a flat-band potential Efb = (2.0 ± 0.1) V/NHE and an ionized acceptor density NA = 3 10 cm-3. Using these data, an electron hole mobility μh ∼ 10-5 cm2 V-1 s-1 was calculated pointing to a small polaron conduction mechanism with a hopping energy (Eh = 0.4 eV).

Nonstoichiometry and relaxation kinetics of nanocrystalline mixed praseodymium–Cerium oxide Pr 0·7Ce 0·3O 2−x

The oxygen deficiency and kinetics of oxygen uptake and release of nanocrystalline mixed praseodymium–cerium oxide with composition Pr 0·7Ce 0·3O 2−x were investigated by combining coulometric titration and potentiometric measurements using stabilised zirconia oxygen concentration cells. The P(O 2) versus composition isotherms indicate a two-phase region at high P(O 2) [P(O 2)>0·1 bar at 560°C] and a single-phase region at lower P(O 2). The oxygen pressure dependence in the homogeneous region can be described by a power law with an exponent (−1/6), in accordance with doubly charged oxygen vacancies as majority defects. The enthalpy of reduction amounts to (2·9±0·3) eV. The chemical diffusion coefficients are of the order of 10 −6 cm 2 s −1 at 640°C with an activation energy of ≈0·3 eV. The low activation energy for diffusion may be related to the high density of interface sites in the nanocrystalline material.

The effective thermal conductivity an adsorbent: Praseodymium cerium oxide

The results of an experimental study to determine the effective thermal conductivity of praseodymium cerium oxide are reported in this paper. Praseodymium cerium oxide is an adsorbent used in the development of adsorption compressors for spaceborne refrigeration systems. A guarded-hot-plate apparatus was built for this study. Measurements were carried out for mean temperatures ranging from 300 to 600 °C under a vacuum of 10 −5 torr. For the temperature range studied, the effective thermal conductivity increased from 0.14 to 0.76 W/m °C with increasing temperature, while displaying a cubic temperature dependency.