Combined operando IR/Raman spectroscopy applied to loaded metal-oxide gas sensors

金属氧化物半导体由于其对目标气体的高灵敏度且易于制造而被广泛用作气体传感器材料。它们的工作模式是基于半导体表面上气体分子的吸附而引起的电导率的变化。尽管该领域取得了相当大的进展，但仍然缺乏对气体传感过程的详细机械理解。具有更高选择性和灵敏度的气体传感器的合理开发关键取决于对其工作模式的透彻理解。为此，需要开发和应用新的实验方法。正如第一个资助期所示，操作拉曼光谱可以通过与操作紫外-可见光谱相结合，对金属氧化物半导体在操作过程中的操作模式进行新的机械洞察。然而，人们发现，这种方法在对技术相关的金属氧化物气体传感器（即负载有添加剂（例如贵金属）的材料）进行更深入的分析方面受到限制。该后续项目旨在阐明金属氧化物气体传感器中添加剂的工作模式，并开发一个集成的机制视图，包括金属氧化物、添加剂以及它们之间的相互作用。重点是负载金和铜的氧化铟和氧化铈气体传感器及其在乙醇 (EtOH) 和 CO 检测中的应用。为此，除了探索瞬态振动光谱方法和基于表面等离子体的拉曼增强的潜力之外，在气体传感器的背景下，操作拉曼光谱将首次与操作红外光谱在一个实验装置中相结合。这些机理研究将得到紫外-可见光和光电子光谱结果以及 DFT 计算振动带分配的支持。重点将放在传感器响应与光谱结果的相关性上，即吸附物的类型、添加剂的状态以及金属氧化物的氧化态。预计该机制很大程度上取决于气体环境和温度，因为两者都会对表面物质产生影响。为此，将在不同气体环境（即 N2、O2、N2/EtOH 和 O2/EtOH，以及 N2/CO 和 O2/CO）中进行 100°C 至 400°C 之间的详细温度依赖性研究。将通过 H2O 和 CO2 的存在来模拟现实条件。通过使用不同的金属氧化物（In2O3、CeO2）、添加剂（Au、Cu）和分析物（EtOH、CO），我们将探索所获得的结果可以推广到何种程度。

Metal oxide semiconductors have been commonly used as gas sensor materials due to their high sensitivity to target gases and their easy fabrication. Their mode of operation is based on changes of the electrical conductivity resulting from the adsorption of gas molecules on the surface of the semiconductor. Despite considerable progress in the field, a detailed mechanistic understanding of the gas sensing process is still missing. The rational development of gas sensors with increased selectivity and sensitivity will crucially depend on a thorough understanding of their mode of operation. To this end, the development and application of new experimental approaches is needed. As has been shown in the first funding period, operando Raman spectra allow for new mechanistic insight into the mode of operation of metal oxide semiconductors during operation, inter alia, by combination with operando UV-Vis spectra. It has been found, however, that this approach is limited regarding a more profound analysis of technically relevant metal oxide gas sensors, i.e., materials loaded with additives (e.g. noble metal).This follow-up project aims at elucidating the mode of operation of additives in metal oxide gas sensors and developing an integrated mechanistic view, including the metal oxide, the additive, as well as their mutual interplay. The focus is on Au- and Cu-loaded indium oxide and cerium oxide gas sensors and their application towards ethanol (EtOH) and CO detection. To this end, operando Raman spectroscopy will be combined with operando IR spectroscopy within one experimental setup for the first time in the context of gas sensors, besides exploring the potential of transient vibrational spectroscopic methods and surface plasmon-based Raman enhancements. These mechanistic studies will be supported by results from UV-Vis und photoelectron spectroscopy as well as by assignments of vibrational bands by DFT calculations.Emphasis will be put on the correlation of the sensor response with the spectroscopic results, i.e., the type of adsorbates, the state of the additive, as well as the oxidation state of the metal oxide. The mechanism is expected to depend strongly on the gas environment and temperature as both have an influence on the surface species. To this end, detailed temperature-dependent studies between 100°C and 400°C will be conducted in different gas environments, i.e., N2, O2, N2/EtOH and O2/EtOH, as well as N2/CO und O2/CO. Realistic conditions will be simulated by the presence of H2O and CO2. By using different metal oxides (In2O3, CeO2), additives (Au, Cu), and analytes (EtOH, CO) we will explore to which extent the results obtained can be generalised.