skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Chemical Stability of BaMg 0.33 Nb 0.67-X Fe x O 3-δ in High Temperature Methane Conversion Environments
Doped perovskite metal oxide catalysts of the form A(BxM1-x)O3-δhave been instrumental in the development of solid oxide electrolyzers/fuel cells. In addition, this material class has also been demonstrated to be effective as a heterogeneous catalyst. Co-doped barium niobate perovskites have shown remarkable stability in highly acidic CO2sensing measurements/environments (1). However, the reason for their chemical stability is not well understood. Doping with transition metal cations for B site cations often leads to exsolution under reducing conditions. Many perovskites used for the oxidative coupling of methane (OCM) or the electrochemical oxidative coupling of methane (E-OCM) either lack long term stability, or catalytic activity within these highly reducing methane environments. The Mg and Fe co-doped barium niobate BaMg0.33Nb0.67-xFexO3-δshown activity in E-OCM reactors over long periods (2) (>100 hrs) with no iron metal exsolution observed by diffraction or STEM EDX measurements. In contrast, iron decorated BaMg0.33Nb0.67O3showed little C2 conversion activity.  more » « less
Award ID(s):
1828731 1647722
PAR ID:
10487371
Author(s) / Creator(s):
; ; ; ;
Publisher / Repository:
IOP Science
Date Published:
Journal Name:
ECS Transactions
Volume:
111
Issue:
6
ISSN:
1938-5862
Page Range / eLocation ID:
587 to 593
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, ChemCatChem)
    Abstract Oxidative coupling of methane (OCM) can be performed electrocatalytically by utilizing solid oxide cells, which provide a readily controlled oxygen supply through dense electrolytes. La0.7Sr0.2Ni0.2Fe0.8O3(LSNF) perovskite is an effective anode for OCM. Its surface characteristics and electrocatalytic activity can be improved by reduction and the resultant exsolution of bimetallic NiFe nanoparticles from its bulk. X‐ray diffraction (XRD) and environmental transmission electron microscopy proved that the evolution of hetero‐phases under reducing environment resulted in bimetallic NiFe nanoparticles being formed on the surface. A 36 % improvement in C2+hydrocarbon production rate was achieved due to the reduction of LSNF with the exsolved NiFe nanoparticles. Co‐feeding of H2O enhanced selective conversion of CH4resulting in the production rate of C2+hydrocarbons being increased by 56 %. Analysis of impedance spectra and in‐situ DRIFTS under a CH4+H2O atmosphere provided an understanding for the enhancement on the electrocatalytic OCM. 
    more » « less
  2. ; ; ; (, Journal of The Electrochemical Society)
    Direct conversion of methane into ethylene through the oxidative coupling of methane (OCM) is a technically important reaction. However, conventional co-fed fixed-bed OCM reactors still face serious challenges in conversion and selectivity. In this paper, we apply a finite element model to simulate OCM reaction in a plug-flow CO2/O2transport membrane (CTM) reactor with a directly captured CO2and O2mixture as a soft oxidizer. The CTM is made of three phases: molten carbonate, 20% Sm-doped CeO2, and LiNiO2. The membrane parameters are first validated by CO2/O2flux data obtained from CTM experiments. The OCM reaction is then simulated along the length of tubular plug-flow reactors filled with a La2O3-CaO-modified CeO2catalyst bed, while a mixture of CO2/O2is gradually added through the wall of the tubular membrane. A 12-step OCM kinetic mechanism is considered in the model for the catalyst bed and validated by data obtained from a co-fed fixed-bed reactor. The modeled results indicate a much-improved OCM performance by membrane reactor in terms of C2-yield and CH4conversion rate over the state-of-the-art, co-fed, fixed-bed reactor. The model further reveals that improved performance is fundamentally rooted in the gradual methane conversion with CO2/O2offered by the plug-flow membrane reactor. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; (, Journal of Materials Chemistry A)
    Electron doping in perovskites is an effective approach to design and tailor the structure and property of materials. In A 2 BB′O 6−δ -type double perovskites, B-site cation order can be tunable by A-site modification, potentially leading to significant effect on the oxygen nonstoichiometry of the compounds. La 3+ -doped Sr 2 FeMoO 6−δ (Sr 2−x La x FeMoO 6−δ , SLFM with 0 ≤ x ≤ 1) double perovskites have been designed and characterized systematically in this study as anode materials for solid oxide fuel cells. Rietveld refinement of powder X-ray diffraction reveals a crystalline symmetry transition of SLFM from tetragonal to orthorhombic with the increase of La content, driven by the extra electron onto the antibonding orbitals of e g and t 2g of Fe/Mo cations. An increase in Fe/Mo anti-site defect accompanies this phase transition. Solid oxide fuel cells incorporating the Sr 1.8 La 0.2 FeMoO 6−δ (SLFM2) anode demonstrate impressive power outputs and stable performance under direct CH 4 operation because of its altered electronic structure, desired oxygen vacancy concentration and enhanced reducibility. Density functional theory plus U correction calculations provide an insight into how La doping affects the Fe/Mo anti-site defects and consequently the oxygen transport dynamics. 
    more » « less
  4. ; ; ; ; (, Advanced Functional Materials)
    Abstract A traditional composite cathode for proton‐conducting solid oxide fuel cells (H‐SOFCs) is typically obtained by mixing cathode materials and proton conducting electrolyte of BaCe0.7Y0.2Zr0.1O3–δ(BZCY), providing chemical and thermal compatibility with the electrolyte. Here, a series of triple‐conducing and cobalt‐free iron‐based perovskites as cathodes for H‐SOFCs is reported. Specifically, BaCexFe1–xO3–δ(x = 0.36, 0.43, and 0.50) shows various contents of two single phase perovskites with an in situ heterojunction structure as well as triple conductivity by tailoring the Ce/Fe ratios. The cell performance with the optimized BaCe0.36Fe0.64O3–δ(BCF36) cathode composition reaches 1056 mW cm−2at 700 °C. Moreover, a record cell performance of 1525 mW cm−2at 700 °C is obtained by modifying the BCF36 cathode microstructure through a spraying method, demonstrating high promise with Co‐free cathodes for H‐SOFCs. 
    more » « less
  5. ; ; ; ; (, Dalton Transactions)
    The development of low-cost, highly efficient and stable electrocatalysts for the oxygen evolution reaction (OER) is of great significance for many promising energy storage and conversion applications, including metal–air batteries and water splitting technology. Here we report a layer-structured Ca 0.5 CoO 2 nanofibers composed of interconnected ultrathin nanoplates, synthesized using an electrospinning process. The OER activity of Ca 0.5 CoO 2 can be dramatically improved by iron doping, and the overpotential of Ca 0.5 Co 1− x Fe x O 2 ( x = 0.25) is only 346 mV at a current density of 10 mA cm −2 . The mass activity and intrinsic activity of Ca 0.5 Co 0.75 Fe 0.25 O 2 at 1.6 V are, respectively, ∼18.7 and ∼11.4 times higher than those of Ca 0.5 CoO 2 . Iron doping modifies the electronic structure of Ca 0.5 CoO 2 , resulting in partial oxidation of the surface cobalt and increased amount of highly oxidative species (O 2 2− /O 2 ). Consequently, Ca 0.5 Co 0.75 Fe 0.25 O 2 nanofibers with tuned electronic states have shown great potential as cost-effective and efficient electrocatalysts for OER. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email