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，并改善其在室温下的检测特性。由Pd/WO_3（双层薄膜）组成的传感器在室温下表现出良好的传感特性。Pd/MoO_3构成的传感器对低浓度氢气的检测响应速度快于Pd/WO_3。此外，Pd薄膜的透过率随其加氢而增加，这一现象可应用于新型的氢传感器。该传感器的优点是结构简单，对氢气的检测响应速度快。虽然较厚的钯膜具有较高的灵敏度，但其耐久性较低。此外，传感器显示的恢复率低于响应率。在Pd膜和玻璃基板之间插入W膜等缓冲层，有效抑制了表面形貌的变化，获得了较好的耐久性。反射率随氢脱附的变化表现出明显的三段式曲线特征，这是由于氢化钯的相变所致。传感器的回收率随氧分压的增大而增大，说明脱氢的决定速率步骤是氢在Pd氢化物表面的脱附成水反应，吸附的氧辅助了氢的脱附过程。研究发现，由于铂表面的成水速率高，极少量的铂负载在钯表面上，可以显著加快回收过程。此外，Pd/Y双层薄膜对低浓度氢也具有很高的灵敏度，对氢检测的响应速度也很快。

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.