A novel and simple preparation of amine-modified γ-Fe2O3 nanoparticles is described. The presence of amine groups on the surface, instead of hydroxyl groups, will allow conjugation of biologically active molecules to the iron oxide nanoparticles without the need for a size increasing silica shell. Furthermore, the outer amine-layer increases the temperature of the γ-Fe2O3 to α-Fe2O3 structural transition in a similar way to previously reported cationic substitutions. This may suggest the formation of an oxide-nitride outer layer. Re-dispersion of the amine-modified γ-Fe2O3 nanoparticles led to the preparation of stable ferrofluids.
High temperature co-electrolysis of steam and carbon dioxide using a solid oxide cell (SOC) has been shown to be an efficient route to produce syngas (CO + H2), which can then be converted to synthetic fuel. Optimization of co-electrolysis requires detailed understanding of the complex reactions, transport processes and degradation mechanisms occurring in the SOC during operation. Thermal imaging, Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy are being developed to probe in-situ both the reactions occurring during operation and any associated changes within the structure of the electrodes and electrolyte. Here we discuss the challenges in designing experimental apparatus suitable for high temperature operation with optical spectroscopic access to the areas of the SOC that are of interest. In particular, issues with sealing, temperature gradients, signal strength and cell configuration are discussed and final designs are presented. Preliminary results obtained during co-electrolysis operation are also presented.
Solid oxide cells (SOCs) are highly efficient electrochemical energy conversion devices capable of operating in both fuel cell and electrolysis modes. The operating temperatures of SOCs (500 – 800 °C, for IT-SOCs) create opportunities for direct utilisation of a wide variety of reactants, including low-grade fuels such as biogas, however, in-situ characterisation of evolving electrode morphologies and compositions is challenging. The design of an optically accessible experimental setup is presented alongside methodology for obtaining and interpreting in-situ Raman spectroscopic measurements. Raman spectroscopy is a valuable analytical tool for in operando monitoring of both solid oxide electrolysis (SOEC) and fuel cells (SOFC). Molecular species adsorbed on the surface can be identified, thus providing direct insight into reaction intermediates, material phase transformations and the presence of contaminants and poisons, such as carbon, chromium, sulphur and silica. Raman spectroscopic evidence of carbon deposition during CO2 electrolysis is discussed.
Solid oxide electrolysis cell (SOEC) technology is a promising route for sustainable recycling of carbon dioxide and steam into synthetic fuels and commodity chemicals via syngas (H2+ CO) production. This technology is based on the reverse polarity of the prominent solid oxide fuel cell (SOFC) and commonly consists of a porous Ni/YSZ cathode, dense YSZ electrolyte and porous LSM/YSZ anode. High temperature co-electrolysis of CO2 and H2O is a complicated process and has not yet been fully understood. This is due to a number of reactions that take place simultaneously: water electrolysis, carbon dioxide electrolysis and the reverse water-gas shift reaction (rWGS CO2 + H2 ↔ CO + H2O). Other possible reactions driven by the equilibrium may include the Bosch reaction (CO + H2 ↔ C(s) + H2O) and Boudouard reaction (2CO ↔ CO2 + C(s)). Carbon deposition on the nickel-cermet surface of SOECs can severely degrade the performance of the cell by deactivating the reaction sites. Recent work by Tao et al. has shown that, at high current densities and conversion efficiencies of CO2 and H2O to CO and H2, carbon formation on the surface of Ni/YSZ fuel electrode is likely to occur [1]. SOECs are typically analyzed in-situ using electrochemical impedance spectroscopy and current-voltage characteristics and ex-situ using scanning electron microscopy to obtain information about cell’s surface topography and composition. However, these techniques are not able to provide conclusive information about the processes occurring during operation of the cell. In this work we aim to use in-situ Raman spectroscopy alongside traditional electrochemical techniques to probe the surface species of the SOEC electrodes for carbon impurities deposition and provide insight into the fundamental processes and reaction pathways that occur during high temperature (700 – 850 oC) co-electrolysis of CO2 and steam. In-situ Raman spectroscopy is also applied to characterize structural changes and material transformations during SOEC operation. The particular area of interest is the triple phase boundary (TPB), where the electrochemical reactions take place. Accessing the TPB is challenging due to high operation temperatures and the depth of laser penetration into the sample. The experimental setup with optical access for the Raman microscope will be discussed in detail as well as the correlation of in-situ spectroscopic data with the electrochemical information obtained from the SOECs. References [1] Tao Y., S. D. Ebbesen, and M. B. Mogensen, 2014, J. Electrochem. Soc. 161 (3), F337 – F343.
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