  Hydrogen detection in a reliable, fast, and cost-effective manner is a
prerequisite for the large-scale implementation of hydrogen in a green economy.
We present thin film Ta$_{1-y}$Pd$_y$ as effective optical sensing materials
with extremely wide sensing ranges covering at least seven orders of magnitude
in hydrogen pressure. Nanoconfinement of the Ta$_{1-y}$Pd$_y$ layer suppresses
the first-order phase transitions present in bulk and ensures a sensing
response free of any hysteresis. Unlike other sensing materials,
Ta$_{1-y}$Pd$_y$ features the special property that the sensing range can be
easily tuned by varying the Pd concentration without a reduction of the
sensitivity of the sensing material. Combined with a suitable capping layer,
sub-second response times can be achieved even at room temperature, faster than
any other known thin-film hydrogen sensor.
