Wireless and Linear Hydrogen Detection up to 4% with High Sensitivity through Phase-Transition-Inhibited Pd Nanowires.

Palladium (Pd) has been drawing increasing attention as a hydrogen (H) detecting material due to its highly selective sensitivity to H. However, at H concentrations above 2%, Pd undergoes an inevitable phase transition, causing undesirable electrical and mechanical alterations. In particular, nonlinear gas response (Δ/) that accompanies phase transition has been a great bottleneck for detecting H in high concentrations, which is especially important as there is a risk of explosion over 4% H. Here, we propose a phase-transition-inhibited Pd nanowire H sensor that can detect up to 4% H with high linearity and high sensitivity. Based on the calculation of the change in free energy, we designed Pd nanowires that are highly adhered to the substrate to withstand the stress that leads to phase transition. We theoretically optimized the Pd nanowire dimensions using a finite element method simulation and then experimentally fabricated the proposed sensor by exploiting a developed nanofabrication method. The proposed sensor exhibits a high sensing linearity (98.9%) with high and stable sensitivity (Δ//[H] = 875%·bar) over a full range of H concentrations (0.1-4%). Using the fabricated Pd sensors, we have successfully demonstrated a wireless sensor module that can detect H with high linearity, notifying real-time H leakage through remote communication. Overall, our work suggests a nanostructuring strategy for detecting H with a phase-transition-inhibited pure Pd H sensor with rigorous scientific exploration.