Hafnium - an optical hydrogen sensor spanning six orders in pressure
C. Boelsma (TU Delft - ChemE/Materials for Energy Conversion and Storage)
Lars Bannenberg (TU Delft - RST/Neutron and Positron Methods in Materials)
M. J. Van Setten (Katholieke Universiteit Leuven)
N. J. Steinke (Rutherford Appleton Laboratory)
A.A. van Well (TU Delft - RST/Neutron and Positron Methods in Materials)
B. Dam (TU Delft - ChemE/Materials for Energy Conversion and Storage)
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Abstract
Hydrogen detection is essential for its implementation as an energy vector. So far, palladium is considered to be the most effective hydrogen sensing material. Here we show that palladium-capped hafnium thin films show a highly reproducible change in optical transmission in response to a hydrogen exposure ranging over six orders of magnitude in pressure. The optical signal is hysteresis-free within this range, which includes a transition between two structural phases. A temperature change results in a uniform shift of the optical signal. This, to our knowledge unique, feature facilitates the sensor calibration and suggests a constant hydrogenation enthalpy. In addition, it suggests an anomalously steep increase of the entropy with the hydrogen/metal ratio that cannot be explained on the basis of a classical solid solution model. The optical behaviour as a function of its hydrogen content makes hafnium well-suited for use as a hydrogen detection material.
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