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

利用原位拉曼显微镜对碳在固体氧化物燃料电池燃料电极上的沉积及其电化学氧化进行了研究，得到了以下结果。我们研制了一种专门用于光学显微镜和拉曼显微镜下高温电化学测试的样品加热台。在工作台上安装了两个独立的腔室，这使得样品电解液颗粒可以放置在燃气和空气下。通过使用加热阶段，可以在热力学控制的气氛下观察电极/电解液体系中的碳沉积过程。采用电化学测量和气体分析相结合的方法研究了甲烷的电化学氧化过程。发现甲烷的氧化不是直接进行的，而是通过电极上的局部水蒸气重整过程进行的。在氧化钇稳定的氧化锆电解液小球上制备了铂和镍模型电极。在甲烷和液化石油气(LPG、正丁烷)条件下，对碳沉积进行了微观观察，并对沉积碳进行了表征。在液化气作用下的铂电极上，观察到两个拉曼峰，分别为“D带”和“G带”，分别代表无序碳和石墨的沉积。随着电极表面颜色的变化，光学显微镜也能观察到碳的沉积。光学显微镜观察表明，碳在电极上沉积并不均匀，而是从第一个碳沉积的位置逐渐膨胀。另一方面，在甲烷燃料下的镍电极上，拉曼光谱只发现了石墨。沉积的石墨很难通过电解液向电解液中注入氧气来去除。

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.