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

Abstract

Palladium (Pd) has been drawing increasing attention as a hydrogen (H 2 ) detecting material due to its highly selective sensitivity to H 2 . However, at H 2 concentrations above 2%, Pd undergoes an inevitable phase transition, causing undesirable electrical and mechanical alterations. In particular, nonlinear gas response (ΔR/R 0 ) that accompanies phase transition has been a great bottleneck for detecting H 2 in high concentrations, which is especially important as there is a risk of explosion over 4% H 2 . Here, we propose a phasetransition-inhibited Pd nanowire H 2 sensor that can detect up to 4% H 2 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 (ΔR/R 0 /[H 2 ] = 875%•bar −1 ) over a full range of H 2 concentrations (0.1−4%). Using the fabricated Pd sensors, we have successfully demonstrated a wireless sensor module that can detect H 2 with high linearity, notifying real-time H 2 leakage through remote communication. Overall, our work suggests a nanostructuring strategy for detecting H 2 with a phase-transition-inhibited pure Pd H 2 sensor with rigorous scientific exploration.

Pd Decoration with Synergistic High Oxygen Mobility Boosts Hydrogen Sensing Performance at Low Working Temperature on WO3 Nanosheet

“…Obviously, the reduction peak of the Pd-WO 3 -300 sample (729 °C) was much lower than those of WO 3 (758 °C), Pd-WO 3 -200 (757 °C), and Pd-WO 3 -400 (739 °C), revealing that strong interaction occurred between Pd and WO 3 . Typically, H 2 molecules can be easily dissociated into hydrogen atoms on the surface of Pd nanoparticles, and the adsorbed hydrogen atoms trended to diffuse into the interstitial octahedral sites in face-centered cubic (fcc) Pd crystal at low H 2 concentrations ([H 2 ] ≤ 1%) to form the α-PdH x . Notably, the formation of α-PdH x interrupts the transport of free electrons in Pd, leading to a higher resistance than Pd, and this transformation was reversible.…”

“…Typically, H 2 molecules can be easily dissociated into hydrogen atoms on the surface of Pd nanoparticles, and the adsorbed hydrogen atoms trended to diffuse into the interstitial octahedral sites in face-centered cubic (fcc) Pd crystal at low H 2 concentrations ([H 2 ] ≤ 1%) to form the α-PdH x . 35 Notably, the formation of α-PdH x interrupts the transport of free electrons in Pd, leading to a higher resistance than Pd, and this transformation was reversible. However, the release of hydrogen atoms in PdH x occurred at 160 °C in Pd-WO 3 -200 and Pd-WO 3 -400, demonstrating that hydrogen atoms can be stably adsorbed on the Pd surface.…”

“…Hence, versatile strategies such as synthesis of low-dimensional nanostructures, construction of heterojunctions, and noble metal decoration have been proposed to meet the demand of advanced H 2 sensing materials. Notably, the modification of MOS with palladium nanoparticles has attracted considerable attention due to their high affinity and selectivity to H 2 at low temperatures, and excellent sensing performance can be achieved after Pd decoration. − Particularly, Pd is highly chemically reactive to H 2 even at room temperature, and H 2 molecules adsorbed on the surface of Pd can be dissociated and diffused into the Pd lattice to form a hydride phase (PdH x ), accompanied by changes in sensing resistance, thus enhancing the sensing performance. − Rapid release of H atoms from PdH x at low temperatures to regenerate viable Pd sites is difficult, either by elevating the treating temperature or exposing to air to improve the release of H atoms, which greatly hinders its application at relatively low temperatures . Additionally, the metal oxide support also plays a crucial role in enhancing their sensing performance as it improves the dispersion of metal sites and creates the support-metal interfacial sites, which can greatly affect their electronic structure and surface properties .…”

Ultrafast (∼0.6 s), Robust, and Highly Linear Hydrogen Detection up to 10% Using Fully Suspended Pure Pd Nanowire

“…To selectively detect hydrogen, palladium (Pd) has been known as the most appealing sensing material due to its reversible reactivity to hydrogen, − forming palladium hydride (PdH x ). However, the fundamental issue in Pd associated with the phase transition of PdH x , depending on hydrogen concentration and catalytic property, has been a critical impediment to satisfy the requirements of a fast response time , as well as measurement range − and robustness. ,, Material-oriented approaches such as alloying with other metals − and Pd-based compounds − have been exploited to reduce activation energy to advance response speed, and the resulting PdAu , and PdTa nanoparticles were able to optically detect hydrogen with a subsecond response time. However, other required performances were not comprehensively investigated, and their optical transducing method, which has to be accompanied by bulky instruments to detect hydrogen, critically limits their essential ability to be conveniently utilized.…”

“…In this context, other methods were introduced to apply mechanical stress to Pd through structural optimization, avoiding material manipulation, to prevent the fundamental phase transition of PdH x. , However, such approaches are still insufficient in maintaining sensing characteristics up to 10% hydrogen and exhibit response times in the tens of seconds. Meanwhile, supplying heat to thermally activate Pd has been regarded as an effective strategy to improve the response rate without material engineering − by accelerating the hydrogen adsorption rate and thermodynamically inhibiting the phase transition of PdH x .…”