Hydrogen is a cornerstone of the emerging net-zero carbon economy, and its widespread deployment demands sensitive, stable, and scalable detection technologies. In this study, we present a comparative performance analysis of Fibre Bragg Grating (FBG) sensors coated with nanometre-thick metal hydride-forming layers—tantalum (Ta), tantalum-palladium alloy (Ta_0.88 Pd_0.12), palladium (Pd), and palladium-gold alloy (Pd _0.6 Au_0.4)—for optical hydrogen sensing. The integration of Ta and Ta _0.88 Pd_0.12, two tantalum-based metal hydrides, with FBG sensors is introduced here for the first time, offering a promising alternative to conventional Pd-based materials. All coatings were deposited via magnetron sputtering and tested under controlled hydrogen exposure across concentrations ranging from 0.001% to 100% H₂. The Ta-based FBGs exhibited outstanding performance, showing a remarkably linear relative wavelength shift over the full tested range (0.001% to 100% H₂), with sensitivity detectable down to 10 ppm—the lowest concentration achievable in the current setup. Both Ta and Ta_0.88 Pd_0.12 sensors exhibited fully reversible and hysteresis-free response characteristics, with rapid response and recovery. Among them, the Ta_0.88 Pd_0.12 sensor with a 100 nm coating demonstrated the highest logarithmic sensitivity of ∼9 pm/decade(%H₂), corresponding to a 9 pm wavelength shift for every tenfold increase in hydrogen concentration between 0.001% and 100% H₂. In contrast, Pd and Pd _0.6 Au_0.4 sensors showed degraded performance at low concentrations and greater signal hysteresis. These results underscore the potential of Ta and Ta _0.88 Pd_0.12 coatings as robust and high-performance alternatives to conventional Pd-based materials for next-generation distributed fibre-optic hydrogen sensing systems.

Hydrogen, a key component of a net-carbon free society, requires precise sensing solutions. This research focuses on the development of metal hydride-coated Fibre Bragg Grating (FBG) based hydrogen sensors, marking a significant step towards the realisation of multipoint hydrogen sensing systems - a growing demand in the industry. The performance of three FBG sensors coated with nanometre-thick tantalum, palladium, and palladium-gold hydrogen sensing metal thin films, deposited via magnetron sputtering, is presented. Among these, the novel tantalum sensor exhibited the best performance, achieving a minimum detection limit of 50 ppm and and an enhanced sensitivity below 0.1% H₂ levels at room temperature.

Optical hydrogen sensors have the power to reliably detect hydrogen in an inherently safe way, which is crucial to ensure safe operation and prevent emissions of hydrogen as an indirect greenhouse gas. These sensors rely on metal hydride material that can reversibly absorb hydrogen when it is present in the environment, and as a result, change their optical properties. To apply this technology along hydrogen infrastructure, in hydrogen-powered planes and other vehicles, it is crucial that these sensors can operate down to −60 °C, a challenge so far unaddressed. Here, it is showed that metal hydride hydrogen sensing materials can be used to detect hydrogen optically down to −60 °C in just a couple of seconds and across a hydrogen concentration range of 0.02–100% with a 1% change in transmission per order of magnitude change in hydrogen concentration. The in-situ X-ray diffraction and optical transmission measurements show that Ta, Ta₈₈Pd₁₂, Ta₈₈Ru₁₂, and Pd₆₀Au₄₀ can gradually, reversibly and hysteresis-free absorb hydrogen while providing sufficient optical contrast. Specifically, Ta₈₈Ru₁₂ possesses the largest optical contrast and the swiftest response down to 6 s at −60 °C. These results confirm the operational viability and foretell new applications of metal hydride hydrogen sensing in cold conditions.

The development of reliable hydrogen sensing materials for subzero environments is crucial for aviation, cryogenic storage, and hydrogen infrastructure applications. In this study, we investigate tetragonal β-tantalum (β-Ta) thin films at −60 °C to assess their potential for optical hydrogen sensing. In situ X-ray diffraction (XRD) measurements reveal a reversible lattice expansion upon hydrogen exposure, with β-Ta exhibiting a smaller volumetric expansion compared to α-Ta, indicating lower hydrogen solubility. Optical transmission measurements demonstrate a monotonic and fully reversible optical response across a range of hydrogen pressures, free of any hysteresis. However, β-Ta exhibits prolonged response times at low temperatures due to diffusion-limited kinetics, as confirmed by power-law response rate analysis and direct diffusion front measurements. Although β-Ta offers a temperature-independent resolution and structural robustness, its slower response time suggests the need for further microstructural optimizations to enhance hydrogen diffusion.