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Development of Cathode Catalysts for the Production of Synthesis Gas and Ammonia in Solid Oxide Electrolysis Cells

Deka, Dhruba Jyoti
http://rave.ohiolink.edu/etdc/view?acc_num=osu1588693027481087

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Solid oxide electrolyte cell (SOEC) is a promising renewable platform for facilitating reactions that involve removal or addition of oxide ions. The solid oxide electrolyte used in this type of reactor can transport oxide ions at elevated temperatures while being insulating to electron flow and impervious to diffusion of oxygen molecules. With suitable design of the electrode catalysts, reactions such as CO2 reduction, H2O reduction, and partial oxidation of hydrocarbons can be efficiently carried out in an SOEC. In this PhD work, cathode catalyst materials were designed for CO2 reduction, H2O reduction and NH3 production applications. For CO2 reduction, (La,Sr)xFeO3 perovskites with varying A-site occupancy were first tested as cathodes. A-site deficient cathode exhibited the highest Faradaic efficiency, whereas the A-site excess cathode exhibited the lowest Faradaic efficiency for CO production. It was found that Sr atoms segregated on the surface of the A-site excess cathode. SrO, being alkaline in nature, bind strongly to acidic CO2 forming a stable SrCO3, which consequently facilitates carbon formation. Due to such carbon formation, the A-site deficient perovskite was considered for further studies. B-site doping with Ni and Co was explored due to the proximity of these ions to Fe in the periodic table. The nickel and cobalt doped A-site deficient La0.7Sr0.2(Ni,Co,Fe)O3 perovskite demonstrated interesting performance during co-electrolysis of CO2 and H2O. While nickel - doping helped increasing the activity of the perovskite for H2O electrolysis, it reduced the activity for CO2 electrolysis. On the other hand, cobalt- doping decreased the activity for H2O electrolysis but increased the activity for CO2 electrolysis. As a result, by tuning the relative compositions of Ni and Co in the cathode, the H2/CO ratio in the produced synthesis gas could be controlled. In situ DRIFTS and in situ XANES were used to investigate the causes behind such observations. It was observed that under a reducing environment, the Ni-doped perovskite, La0.7Sr0.2Ni0.2Fe0.8O3, led to the formation of a Ruddlesden-Popper phase and metallic Ni nanoparticles, with the majority of the material still being in the perovskite structure. As shown by environmental TEM, the metal nanoparticles started forming at temperatures as low as 400 °C and continued forming with uniform dispersion at higher temperatures. These particles were strongly pinned to their position, giving them high thermal stability. The ability to adsorb CO2 and activity for CO2 reduction was found to be much higher for the exsolved system compared to the parent perovskite. Chapter 9 discusses the application of solid oxide electrolysis cells for the production of ammonia from N2 and H2O under atmospheric pressure. During the current study, a novel dual phase perovskite oxide- metal nitride (La0.7Sr0.2Ni0.2Fe0.8O3 - Fe3N) composite cathode catalyst was designed. The perovskite oxide phase carries out H2O reduction to form H2 while the metal nitride phase facilitates N2 activation; and these H2 and activated N2 then react to produce NH3. In summary, designing electrode catalysts is a major challenge behind the development of the aforementioned applications, and the current PhD work investigates possible solutions.
Umit S. Ozkan (Advisor)
403 p.
Chemical Engineering
solid oxide electrolysis cell, CO2 electrolysis, H2O electrolysis, NH3 production, perovskite, exsolution, nickel nanoparticles, NiFe alloy nanoparticles, composite electrodes, synthesis gas production

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Citations

  • Deka, D. J. (2020). Development of Cathode Catalysts for the Production of Synthesis Gas and Ammonia in Solid Oxide Electrolysis Cells [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1588693027481087

    APA Style (7th edition)

  • Deka, Dhruba Jyoti. Development of Cathode Catalysts for the Production of Synthesis Gas and Ammonia in Solid Oxide Electrolysis Cells. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1588693027481087.

    MLA Style (8th edition)

  • Deka, Dhruba Jyoti. "Development of Cathode Catalysts for the Production of Synthesis Gas and Ammonia in Solid Oxide Electrolysis Cells." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1588693027481087

    Chicago Manual of Style (17th edition)

osu1588693027481087
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