Development of conductive ceramics for NOx gas decomposition

本研究旨在通过在导电氧化物陶瓷上施加电场来控制NOx气体的吸附和分解行为，从而获得高可靠的NOx气敏和分解性能。N型导电Nd2CuO4陶瓷表现出由NO引起的电导降低和由NO2引起的电导增加。用X-射线光电子能谱分析了NOX吸附物的表面化学结合状态，确定了Nd2CuO4和La_2CuO_4；2-x&gt；BaxSrCu2O&lt；6-Delta&gt；为了证实外加电场对气体吸附和反应的影响，研究了在衬底电场作用下，SiO_2/Si衬底上SnO_2薄膜CO气体电导的变化。在衬底施加负偏压使SnO2的表观电导降低的情况下，证实了Co^+等正电荷物种的吸附被加速，O^-等负电荷物种的吸附被抑制。研究了Nd2CuO4/稳定化氧化锆铂元件在恒压(氧化物电极负偏压)下被NOx气体氧化后的电流变化。即使当两个电极暴露在相同的大气中时，也观察到NOx气体增加了直流氧离子电流，与环境氧分压无关。NOx和O2气体在氧化物电极上混合电位的变化是促进NOx分解和NOx敏感的直流离子电流的原因。这些结果表明，使用合适的氧化物材料作为电极，并施加外加偏压，可以控制NOx气体的吸附/解吸和分解。

This research aims to obtain high and reliable properties for NOx gas sensing and decomposition through controlling adsorption and decomposition behavior of NOx gas by applying electric field to conducting oxide ceramics. N-type conductive Nd_2CuO_4 ceramics showed a decrease of conductance by NO and an increase in conductance by NO_2 gas. Surface chemical binding states of NOX-adsorbates were analyzed with X-ray photoelectron spectroscopy, and different binding states for NO and NO_2 were confirmed for Nd_2CuO_4 and La_<2-x>Ba_xSrCu_2O_<6-delta>. In order to confirm effects of an external electric field on gas adsorption and reaction, changes in conductance by CO gas of SnO_2 thin film on SiO_2/Si substrate were examined under electric fields from the substrate. Acceleration of adsorption of positively-charged species like CO^+, and suppression of adsorption of negatively-charged species like O^- were confirmed under applying a minus bias from the substrate where apparent conductance of SnO_2 is lowered by the minus bias. Current changes of Nd_2CuO_4/stabilized zirconia/Pt element by NOx gas under a constant voltage (an negative bias to the oxide electrode) were examined. Even when two electrodes were exposed to a same atmosphere, increases in DC oxygen-ionic current by NOx gas, independent on ambient oxygen partial pressure, were observed. Changes in mixed potential by NOx and O_2 gases at the oxide electrode were found to be responsible for the enhancement of NOx decomposition and the NOx-sensitive DC ionic current. These results show that adsorption/desorption and decomposition of NOx gases could be controlled by using appropriate oxide material as an electrode and by applying an external bias.