Tantalum–Palladium Ultrathin Resistance Hydrogen Sensor

Hydrogen sensors play a pivotal role in tomorrow's hydrogen economy, yet today's sensors cannot fulfill all needs. We rationally design resistive thin‐film hydrogen sensors based on tantalum alloys. The heart of the sensor is a tantalum‐based layer, that gradually absorbs hydrogen when exposed to hydrogen, which in turn results in a measurable change of the resistance. In situ x‐ray diffraction and x‐ray and neutron reflectometry show that nanoconfinement efficiently suppresses unwanted phase transitions present in bulk when the material is exposed to hydrogen and enables completely elastic expansion, yielding a stable, hysteresis‐free and long‐life sensor. Additionally, alloying is used to maximize the sensitivity of the sensor. The resulting sensor, combining a 5 nm sensing layer with a 4 nm adhesion layer, a 5 nm capping layer, and polymer protective layers, enables a low‐cost, reversible hydrogen sensor with a hysteresis‐free sensing range from ppb to 100% in anaerobic conditions at room temperature and sub‐second response‐times.