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  1. Free, publicly-accessible full text available June 1, 2025
  2. Free, publicly-accessible full text available May 1, 2025
  3. Perovskite materials are used for high temperature electrochemical applications such as solid oxide fuel cells (SOFC) and electrolyzers due to their tunable conductivity and catalytic activity. However, high temperature operation poses significant challenges in both fabrication and durable operation that is further complicated by the operating environment. We studied barium niobates with various A and B site dopants. These doped niobates showed enhanced thermochemical stability in SOFC relevant conditions and catalytic activity towards methane activation. The redox behavior of the Nb4+/5+couple seem to be at a key reason behind this redox stability while the size and electronegativity of the dopants affect the electrical properties. The chemical stability was analyzed by TGA measurements followed by analysis of the perovskite powders using PXRD measurements. Impedance measurements were utilized to analyze their electrical conductivity. Our results demonstrate doped barium niobates as a promising candidate for stable operation in high temperature electrochemical applications.

     
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  4. 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.

     
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  5. Abstract

    Efficient conversion of methane to value-added products such as olefins and aromatics has been in pursuit for the past few decades. The demand has increased further due to the recent discoveries of shale gas reserves. Oxidative and non-oxidative coupling of methane (OCM and NOCM) have been actively researched, although catalysts with commercially viable conversion rates are not yet available. Recently,$${{{{{{{\mathrm{Sr}}}}}}}}_2Fe_{1.5 + 0.075}Mo_{0.5}O_{6 - \delta }$$Sr2Fe1.5+0.075Mo0.5O6δ(SFMO-075Fe) has been reported to activate methane in an electrochemical OCM (EC-OCM) set up with a C2 selectivity of 82.2%1. However, alkaline earth metal-based materials are known to suffer chemical instability in carbon-rich environments. Hence, here we evaluated the chemical stability of SFMO in carbon-rich conditions with varying oxygen concentrations at temperatures relevant for EC-OCM. SFMO-075Fe showed good methane activation properties especially at low overpotentials but suffered poor chemical stability as observed via thermogravimetric, powder XRD, and XPS measurements where SrCO3was observed to be a major decomposition product along with SrMoO3and MoC. Nevertheless, our study demonstrates that electrochemical methods could be used to selectively activate methane towards partial oxidation products such as ethylene at low overpotentials while higher applied biases result in the complete oxidation of methane to carbon dioxide and water.

     
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