TiO2/PdO-based eye-detectable fast-responding sensor to address H2 safety infrastructure: Unveiling the colour change mechanism and active sites

Deployment of hydrogen-based infrastructure is impeded by the difficulty of real-time detection of hydrogen leaks. To address this issue, a TiO 2 /PdO composite chemochromic hydrogen sensor is optimized by tuning TiO 2 particle size and Pd precursor concentration to achieve rapid, highly sensitive, eye-readable hydrogen detection. The optimized sensor exhibits an eye-readable colour change within 4 s at 4 vol% hydrogen in nitrogen, corresponding to the lower flammability limit of hydrogen, making it suitable for real-time leak detection. Through systematic investigations, correlations between hydrogen concentration, catalyst loading, magnitude of colour change, and response time are established. A maximum colour difference of ΔE = 28.86 is achieved by the optimized sensor in pure hydrogen. Spectroscopy and microscopy studies revealed that Ti–Pd ground-state interactions drive hydrogen adsorption and the optoelectronic changes responsible for the colour response, providing design guidelines for the development of rapid chemochromic hydrogen sensors.