Study on Realization of Optical Hydrogen Sensor Operating at Room Temperature

本研究的目的是寻找用于光学氢传感器的薄膜材料，改善其室温检测特性。由Pd/WO_3（双层薄膜）构成的传感器在室温下表现出良好的传感特性。Pd/MoO_3比Pd/WO_3对低浓度氢气有更快的响应。此外，还发现Pd薄膜的透过率随氢化程度的增加而增加，这一现象可应用于新型氢传感器。该传感器的优点是结构简单，对氢气检测响应快。虽然较厚的Pd膜显示出较高的灵敏度，但其耐久性较低。此外，传感器指示的回收率低于响应率。在Pd膜和玻璃衬底之间插入W膜等缓冲层，有效抑制了表面形貌的变化，并获得了很好的耐久性。反射率随氢脱附的变化具有明显的三阶段曲线特征，这是由于Pd氢化物的相变所致。传感器的恢复速率随氧分压的增大而增大，表明脱氢反应的速率控制步骤是氢的脱附和Pd氢化物表面的水生成反应，吸附氧参与了氢的脱附过程。研究发现，由于Pt表面的高水生成速率，极少量的Pt负载在Pd表面上大大加速了回收过程。此外，由Pd/Y组成的双层薄膜被发现即使对于低浓度的氢也具有高灵敏度和对氢检测的快速响应。

The objective of this research was to search materials of thin film for optical hydrogen sensor and to improve its detection characteristics at room temperature. The sensor consisting of Pd/WO_3 (double-layered thin film) showed good sensing characteristics at room temperature. The sensor consisting of Pd/MoO_3 had faster response to detection of low concentration of hydrogen than that of Pd/WO_3. Moreover, it was found that the transmittance of Pd thin film increased with its hydrogenation and the phenomenon could be applied to a new hydrogen sensor. The strong points of the sensor are simple structure and fast response to hydrogen detection. Although thicker Pd film showed a higher sensitivity, it had a lower durability. Moreover, the sensor indicated lower recovery rate than response rate. The insertion of buffer layer such as W film between Pd film and glass substrate was effective in suppression of the surface morphology change and achieved a great durability. The change in reflectance with hydrogen desorption indicated distinctive characteristics with three-stage curve, which was due to thei phase transformation of Pd hydride. The recovery rate of the sensor increased with oxygen partial pressure, which suggested that the rate-determining step for dehydrogenation was hydrogen desorption with water forming reaction on Pd hydride surface, and adsorbed oxygen assisted the hydrogen desorption process. It was discovered that a very small quantity of Pt supported on Pd surface considerably accelerated the recovery process because of high water forming rate on Pt surface. Furthermore, double-layered thin film consisting of Pd/Y was found to indicate high sensitivity even for low concentration of hydrogen and fast response to hydrogen detection.