Applying DRIFT Spectroscopy for High Temperature Electrochemical Cells-Lessons from SMOX Based Gas Sensors

In operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, the metal oxide sample is illuminated by the infrared beam, and the scattered (rather than transmitted) light is collected with appropriate optics for analysis. In addition to being better suited for operando methods, DRIFT spectroscopy has also been found to be more surface sensitive than other IR techniques suitable for powder samples, such as TIRS, ATR-IRS, and PM-IRRAS.(Roedel et al., 2008) DRIFT spectroscopy has allowed for significant gains in understanding the surface chemistry of semiconducting metal oxide (SMOX) based sensors to be made. Despite the potential usefulness in unravelling different surface mechanisms, ranging from the influence of humidity on the oxygen reduction reaction in fuel cell cathodes to insights about the anodic coking mechanisms when using hydrocarbon fuels, the use of DRIFTs for metal oxide electrochemical cells is still in its infancy, with only a handful of near operando studies being reported. (Cumming et al., 2015; Hauser et al., 2020; Tezel et al., 2022) One critical consideration is the potentially problematic intrinsic IR radiation of samples and the limited stability of cell materials at the high relevant operation temperatures. Nonetheless, using clever cooling systems that prevent the windows from overheating and intricate cell designs to allow for separate oxygen and fuel supply, Cumming et al. and more recently Hauser et al. were able to measure DRIFT spectra at elevated temperatures on cells. (Cumming et al., 2015; Hauser et al., 2020) In both cases, DRIFT spectra were depicted up to 600 ˚C without reports of significant errors due to radiation stemming from the sample. As a result, it is promising that through further optimization, DRIFT spectroscopy could become a useful tool for studying metal oxide based electrochemical systems. For the further optimization, lessons learned during the development of operando cells for SMOX based gases sensors are pertinent. Here a way forward for the optimization will be presented. Starting with practical aspects of DRIFT spectroscopy, e.g. need for precisely controlled room environments in non-evacuated systems or increased signal intensity through window optimization. Common artefacts will be shown, and avoidance strategies will be shown, e.g. ice bands that can be removed through detector evacuation. Additional considerations that are relevant specifically when working with metals oxides will be reviewed and the advantages of selecting the referencing method of Olinger and Griffiths over the traditionally used Kubelka-Munk will be elaborated.(Cumming et al., 2015; Jill M Olinger & Peter R Griffiths, 1988) The usefulness of using isotopically labelled gases to differentiate surface species, e.g. separate metal-oxygen groups from metal-hydroxides, will be discussed. Finally, the potential pitfalls of comparing different samples quantitatively will be highlighted. Overall, this presentation will provide a useful guideline for the future design of an operando DRIFT chamber for oxide based electrochemical cells. Bibliography Cumming, D. J., Tumilson, C., Taylor, S. F. R., Chansai, S., Call, A. v., Jacquemin, J., Hardacre, C., & Elder, R. H. (2015). Development of a diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) cell for the in situ analysis of co-electrolysis in a solid oxide cell. Faraday Discussions , 182 , 97–111. https://doi.org/10.1039/c5fd00030k Hauser, D., Nenning, A., Opitz, A. K., Klötzer, B., & Penner, S. (2020). Spectro-electrochemical setup for in situ and operando mechanistic studies on metal oxide electrode surfaces. Review of Scientific Instruments , 91 (8). https://doi.org/10.1063/5.0007435 Jill M Olinger, & Peter R Griffiths. (1988). Quantitative effects of an Absorbing Matrix on Near-Infrared Diffuse Reflectance Spectra. Anal. Chem. , 60 (21), 2427–2435. Roedel, E., Urakawa, A., Kureti, S., & Baiker, A. (2008). On the local sensitivity of different IR techniques: Ba species relevant in NOx storage-reduction. Physical Chemistry Chemical Physics , 10 (40), 6190–6198. https://doi.org/10.1039/b808529c Tezel, E., Guo, D., Whitten, A., Yarema, G., Freire, M., Denecke, R., McEwen, J.-S., & Nikolla, E. (2022). Elucidating the Role of B-Site Cations toward CO2 Reduction in Perovskite-Based Solid Oxide Electrolysis Cells . Journal of The Electrochemical Society , 169 (3), 034532. https://doi.org/10.1149/1945-7111/ac5e9b