Effects of surface morphology changes on FTIR-ATR spectroscopy with compacted Sodium Alanate (NaAlH4) during cycling

The hydrogen content during ab-/desorption of complex metal hydrides can be monitored via FTIR-ATR spectroscopy. Through cycling, the surface morphology of the pellet sample may alter due to the various material changes (e.g., granularity, volume, composition) and contribute to the spectral changes in an undesirable way.Therefore, the desorption of the first reaction step of TiCl3-doped NaAlH4 compacts was investigated in terms of optical signal stability. It was found that optical signal degradation occurs with an increasing number of ab-/desorption cycles. Different hydrogen cycling procedures identified changes in temperature during cycling to further degrade the signal. Using SEM and SFM measurements, a roughening of the pellet surface was observed as an effect of cycling. For reliable optical monitoring, different approaches to ensure long-term signal-coupling have been applied and their benefits compared. Thereby, dimensional changes in the surface flatness were found to be the dominant factor controlling the optical signal quality.The experimental results allow a more adequate operation of the measurement method and may be relevant for similar optical sensing applications, especially for fuel level sensors needed for various solid-state hydrogen storage systems.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The hydrogen content during ab-/desorption of complex metal hydrides can be monitored via FTIR-ATR spectroscopy. Changes in the surface morphology of the pellet sample during cycling may affect the spectral changes and degrade the optical signal stability. Investigation of the desorption behavior of TiCl3-doped NaAlH4 compacts showed that optical signal degradation occurs with increasing ab-/desorption cycles, and temperature changes during cycling further contribute to the signal degradation. The roughening of the pellet surface observed through SEM and SFM measurements is attributed to cycling. Different approaches have been explored to ensure long-term signal coupling for reliable optical monitoring, and dimensional changes in surface flatness were identified as the primary factor controlling the optical signal quality. The findings have implications for the improvement of measurement methods and the development of fuel level sensors for solid-state hydrogen storage systems.