mICROANALYSIS OF dEPOSITION AND ELECTROCHEMICAL oXIDATION OF cARBON ON AN eLECTROCHEMICAL SYSTEM UNDER hYDROCARBON gASES

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In-situ Raman microscope analysis was performed to investigate carbon deposition and its electrochemical oxidation on a fuel electrode of a solid oxide fuel cell, and the following results were obtained.1. We have developed a sample heating stage that was specially designed for high temperature electrochemical testing under optical microscope and Raman microscope. Two separate chambers were installed into the stage, which enabled a sample electrolyte pellet to be placed under fuel gas and air. By using the heating stage, it was possible to investigate observe carbon deposition processes at electrode/electrolyte system under a thermodynamically controlled atmospheres.2. Electrochemical oxidation process of methane was investigated by combined electrochemical measurements and gas analysis. It was found that oxidation of methane proceeds not directly but via local steam reforming processes on the electrode.3. Platinum and nickel model electrodes were fabricated on yttria stabilized zirconia electrolyte pellets. Microscopic observation of the carbon deposition, as well as the characterization of the deposited carbon were performed under methane and liquid petroleum gasses (LPG, n-butane). In the case of platinum electrode under LPG, two Raman bands called 'D-band' and 'G-band' were observed indicating the deposition of disordered carbon and graphite, respectively. The deposition of carbon can be observed also by optical microscope as color change of electrode surface. Optical microscope observation revealed that the carbon is deposited not uniformly on the electrode but expands gradually from the position where the first carbon is deposited. On the other hand, on a nickel electrode under methane fuel, only graphite was found by Raman spectroscopy. The deposited graphite was hard to be removed by electrochemical pumping of oxygen through the electrolyte.