Study of ultramicroelectrode-based-measurement system for polymer electrolyte/electrocatalyst interface

通过制作一系列超微电极，构建了三电极体系难以应用的聚合物电解质膜/电催化剂层状结构的电化学测量系统。该系统使我们即使在高阻介质中也能成功地基于小电流诱导的小Ir降来评估界面电化学反应。此外，微阵列电极揭示了电催化过程的反应机理。为此，研制了聚合物电解质燃料电池(PEFC)电化学测试系统。主要研究成果总结如下。首先，制作了一个集成的超微电极，它包括工作微电极、反微电极和参考微电极在玻璃毛细管的尖端。以此为基础，测定了氢气和甲醇氧化的气相电化学反应。其次，采用交叉型微阵列电极，通过改变水与甲醇的混合比例，测量了聚合物电解质膜的离子电导率。这对于直接甲醇燃料电池(DMFC)的运行是有价值的。第三，利用交叉型微阵列电极，首次检测到了传统旋转环盘电极无法记录的甲醇氧化中间体。接下来，制作了一种多孔微电极，它的尖端有一个微腔来测量颗粒材料的电化学性质。这使得以粉末形式对电催化剂进行常规评估成为可能。最后，制作了一种末端具有聚合物电解质/电催化剂层状结构的多孔微环电极，用于对膜电极组件(MEA)进行电化学评价。总而言之。通过设计和制备新型的超微电极，聚合物电解质膜/电催化剂结构的电化学表征已经取得了很大的进展。

Electrochemical measurement system for polymer electrolyte membrane/electrocatalyst layered structure, where the three-electrode system was difficult to apply so far, has been constructed by creating a series of ultramicroelectrodes. The system successfully enabled us to evaluate the interfacial electrochemical reaction based on a small-current-induced small iR drop even in the high resistivity medium. In addition, microarray electrode revealed a reaction mechanism of the electrocatalytic process. Consequently, electrochemical measurement system for polymer electrolyte fuel cell (PEFC) has been developed. Main research results are summarized as follows. First, an integrated ultramicroelectrode has been fabricated which involves working, counter and reference microelectrodes at a tip of a glass capillary. By using this, the gas phase electrochemical reactions were measured for hydrogen and methanol oxidation. Second, ionic conductivity of polymer electrolyte membrane has been measured employing an interdigitated microarray electrode by changing a water:methanol mixture ratio. Which is worthwhile for an operation of direct methanol fuel cell (DMFC). Third, by utilizing the interdigitated microarray electrode, methanol oxidation intermediate, which could not recorded at a conventional rotating ring-disk electrode, has been detected for the first time. Next, a porous microelectrode has been made which has a microcavity at the tip to measure electrochemical properties of particulate materials. This allowed a conventional evaluation of electrocatalysts in a powder form. Finally, a porous microring electrode, which has polymer electrolyte/electrocatalyst layered structure at the tip, has been created for a purpose to appraise a membrane electrode assembly (MEA) electrochemically. In conclusion. By designing and fabricating novel ultramicroelectrodes, electrochemical characterization for polymer electrolyte membrane/electrocatalyst structure has been greatly progressed.