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

金属氧化物半导体由于对目标气体具有较高的灵敏度和易于制作等优点，被广泛用作气敏材料。它们的工作模式是基于气体分子在半导体表面吸附而引起的电导率的变化。尽管在这一领域取得了长足的进步，但对气体传感过程的详细机械理解仍然缺乏。提高选择性和灵敏度的气体传感器的合理开发将关键取决于对其操作模式的透彻了解。为此，需要开发和应用新的实验方法。正如第一个资助期所显示的那样，通过与Operando UV-Vis光谱相结合，Operando拉曼光谱使人们能够从新的机制上深入了解金属氧化物半导体在运行期间的运行模式。然而，人们发现，这种方法在对技术上相关的金属氧化物气体传感器进行更深入的分析时是有限的，即加载了添加剂(如贵金属)的材料。本后续项目旨在阐明添加剂在金属氧化物气体传感器中的作用模式，并开发包括金属氧化物、添加剂及其相互作用在内的综合力学观点。重点介绍了金和铜负载的氧化铟和氧化铈气体传感器及其在乙醇和一氧化碳检测中的应用。为此，除了探索瞬时振动光谱方法和基于表面等离子激元的拉曼增强技术的潜力外，还将首次在气体传感器的背景下，在一个实验装置中将OPANDO拉曼光谱与OPANDO IR光谱相结合。这些机理研究将得到UV-Vis和光电子能谱的结果以及DFT计算的振动带指定的支持，重点将放在传感器响应与光谱结果的关联上，即吸附物的类型、添加剂的状态以及金属氧化物的氧化状态。这一机理很大程度上取决于气体环境和温度，因为两者都对表面物种有影响。为此，将在不同的气体环境，即氮气、氧气、氮气/乙醇和氧气/乙醇以及氮气/一氧化碳和氧气/一氧化碳中，进行100°C至400°C之间随温度变化的详细研究。实际情况将通过H2O和CO2的存在来模拟。通过使用不同的金属氧化物(In_2O_3，CeO_2)、添加剂(Au，Cu)和分析物(EtO，CO)，我们将探索所获得的结果可以在多大程度上得到推广。

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.