Enhancing the Hydrogen-Sensing Performance of p-Type PdO by Modulating the Conduction Model

Abstract

The implementation of the p-type metal oxide semiconductor (MOS) in modern sensing systems requires a strategy to effectively enhance its inherent low response. However, for p-type MOS sensors, conventional methods such as catalyst nanoparticle (NP) decoration and grain size regulation do not work as effectively as they do for n-type MOS sensors, which is basically due to the fact that the p-type MOS adopts an unfavorable parallel conduction model. Herein, taking Au@PdO as an example, we demonstrate that the conduction model of the p-type MOS can be manipulated into the series conduction model by inserting a high-conductive metallic core into less-conductive p-type MOS NPs. This unique series conduction model makes the sensor response of Au@PdO nanoparticle arrays (NAs) very sensitive to the catalyst NP decoration as well as the change of structural parameters. For example, Au@PdO NAs demonstrate an ∼9000 times increase in sensor response when decorated with Pd NPs, whereas there is only ∼100 times increase for PdO NAs. This greatly improved response value outperforms all previously reported PdO-based (and most other p-type semiconductor-based) H2 sensors, which helps the obtained sensor to achieve an ultralow detection limit of ∼0.1 ppm at room temperature. Additionally, Au@PdO NAs inherit the high surface reactivity and gas adsorption property of p-type PdO. As a result, the as-prepared sensor exhibits high humidity-resistive property and excellent selectivity. This work provides a new strategy to significantly enhance the sensing performance of p-type gas sensors by manipulating their conduction model.

Controllable Fabrication of PdO‐PdAu Ternary Hollow Shells: Synergistic Acceleration of H2‐Sensing Speed via Morphology Regulation and Electronic Structure Modulation

“…Finally, the PdO-PdAu HSs were obtained by reduction of PdO-Au HSs in NaBH 4 solution for certain degree via controlling the reaction time. [21,25] A detailed characterization of samples obtained during each synthesize step can be found in Figures S1 and S2, Supporting Information.…”

Hydrogen-Induced Aggregation of Au@Pd Nanoparticles for Eye-Readable Plasmonic Hydrogen Sensors

“…The core–shell structure of Au@Pd NPs can be observed clearly in the high-resolution TEM image (Figure D). The interplanar spacing between the adjacent lattice fringes in the shell area is 0.224 nm, which corresponds to the (111) plane of Pd . Energy dispersive X-ray (EDX) elemental mapping (Figure E–G) shows that Au locates in the inner part of the nanoparticle, while Pd mainly appears at the surface, which also confirms the core–shell structure of Au@Pd NPs.…”

“…The interplanar spacing between the adjacent lattice fringes in the shell area is 0.224 nm, which corresponds to the (111) plane of Pd. 38 Energy dispersive X-ray (EDX) elemental mapping (Figure 2E−G) shows that Au locates in the inner part of the nanoparticle, while Pd mainly appears at the surface, which also confirms the core−shell structure of Au@Pd NPs. The self-assembly method adopted here does not involve any strong capping agents such as −SH and −NH 2 or surfactants that prevent the interaction between Pd and H 2 .…”

“…To figure out the reason for the irreversible optical response, XPS and XRD measurements were carried out to characterize the chemical states of Au@Pd (16/2) NAs. As shown in Figure A,B, the pristine Au@Pd NAs have Pd3d binding energies at 335.86 and 341.09 eV and Au4f binding energies at 84.38 and 88.00 eV, corresponding to the metallic state of the Pd shell and Au core. , After Au@Pd NAs are exposed to H 2 and then back to air, both Pd3d peaks and Au4f peaks shift slightly to lower binding energies by ∼0.3 eV. The decrease of binding energies may possibly be ascribed to the Au/Pd interdiffusion at the core–shell interface, and Pd and Au gain d and s/p electrons, respectively. ,− A similar phenomenon was also observed by Tang et al during the investigation of the hydrogen sensing performance of single Au@Pd NPs .…”

Ultrafast Metal Oxide Reduction at Pd/PdO2 Interface Enables One-Second Hydrogen Gas Detection Under Ambient Conditions

“…The Pd black/C sensor exhibited p-type semiconductor sensing behavior (Figure 3C), the same as other Pd/PdO sensors reported in the literature. 47,48 The XPS analysis revealed that the PdO content of Pd black did not change after exposure to 4% H2 (Figure S16, Table S6), indicating that H2 reduction of PdO is insignificant even in the presence of Pd 0 at room temperature. Thus far, our compositional study has shown that neither Pd/PdO nor PdO/PdO2 could effectively react with 4% H2 at room temperature to be reduced to Pd, supporting our hypothesis that Pd and PdO2 are responsible for the rapid reduction.…”