In situ AP-XPS analysis of a Pt thin-film sensor for highly sensitive H2 detection

Probing Coordination Number of Single-Atom Catalysts by d-Band Center-Regulated Luminescence

It is essential to probe the coordination number (CN) because it is a crucial factor to ensure the catalytic capability of single-atom catalysts (SACs). Currently, synchrotron X-ray absorption spectroscopy (XAS) is widely used to measure the CN. However, the scarcity of synchrotron X-ray source and complicated data analysis restrict its wide applications in determining the CN of SACs. In this contribution, we have developed a d-band center-regulated acetone cataluminescence (CTL) probe for a rapid screening of the CN of Pt-SACs. It is disclosed that the CN-triggered CTL is attributed to the fact that the increased CN could induce the downward shift of d-band center position, which assists the acetone adsorption and promotes the subsequent catalytic reaction. In addition, the universality of the proposed acetone-CTL probe is verified by determining the CN of Fe-SACs. This work has opened a new avenue for exploring an alternative to synchrotron XAS for the determination of CN of SACs and even conventional metal catalysts through d-band center-regulated CTL.

Detection of PPB-Level H2S Concentrations in Exhaled Breath Using Au Nanosheet Sensors with Small Variability, High Selectivity, and Long-Term Stability

The continuous monitoring of hydrogen sulfide (H2S) in exhaled breath enables the detection of health issues such as halitosis and gastrointestinal problems. However, H2S sensors with high selectivity and parts per billion-level detection capability, which are essential for breath analysis, and facile fabrication processes for their integration with other devices are lacking. In this study, we demonstrated Au nanosheet H2S sensors with high selectivity, ppb-level detection capability, and high uniformity by optimizing their fabrication processes: (1) insertion of titanium nitride (TiN) as an adhesion layer to prevent Au agglomeration on the oxide substrate and (2) N2 annealing to improve nanosheet crystallinity. The fabricated Au nanosheets successfully detected H2S at concentrations as low as 5.6 ppb, and the estimated limit of detection was 0.5 ppb, which is superior to that of the human nose (8-13 ppb). In addition, the sensors detected H2S in the exhaled breath of simulated patients at concentrations as low as 175 ppb while showing high selectivity against interfering molecules, such as H2, alcohols, and humidity. Since Au nanosheets with uniform sensor characteristics enable easy device integration, the proposed sensor will be useful for facile health checkups based on breath analysis upon its integration into mobile devices.

Electrical Control of Spin Hall Effect in Pt by Hydrogen Ion Adsorption and Desorption

The manipulation of charge-to-spin current conversion and spin-orbit torque (SOT) is of great interest due to its profound physics and potential applications. Controlling the spin current through the electric field provides a perspective for highly efficient SOT devices. Here, we use H₂O-doped ionic liquid gating to realize the reversible and nonvolatile manipulation of the spin Hall effect of Pt, and the spin Hall angle can be modulated by 48% within an accessible gate voltage range. The increase in the spin Hall angle is demonstrated to be caused by the adsorption of hydrogen ions on the Pt surface and the consequent enhancement of the spin Hall conductivity under positive voltage. Furthermore, the enhancement of the spin Hall angle is beneficial to reduce the critical current density for driving the domain wall motion. These results supply a method for the dynamic control of the charge-to-spin current conversion, which will promote the development of spintronic devices driven by electric fields.

Origin of the High Selectivity of the Pt-Rh Thin-Film H2 Gas Sensor Studied by Operando Ambient-Pressure X-ray Photoelectron Spectroscopy at Working Conditions

The Pt-Rh thin-film sensors exhibit excellent sensitivity and selectivity for H₂ gas detection. Here, we studied the mechanism of highly selective detection of H₂ by the Pt-Rh thin-film sensors with ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) measurements at working conditions, which were paralleled with electric resistivity measurements. The elemental composition and chemical state of surface Pt and Rh drastically change depending on the background gas environments, which directly link to the sensor response. It is revealed that surface segregated Pt atoms accelerate dissociative adsorption of H₂, resulting in a reduction of the sensor surface and then a decrease of electric resistivity of the film, whereas a thin oxidized Rh layer blocks dissociation of the other reducing agent, that is, NH₃. This is supported from the adsorption energetics obtained by the density functional theory (DFT) calculations.

Simultaneous Detection of Mixed-Gas Components by Ionic-Gel Sensors with Multiple Electrodes

The sensing of gas components in a mixed gas is required for breath-based health monitoring and diagnosis. In this work, we report the simultaneous detection of mixed-gas components using a sensor consisting of [EMIM][BF₄]-based ionic gel with four electrodes made of Au, Pt, Rh, and Cr. The voltage between any given pair of electrodes depends on the gas molecules absorbed in the ionic gel and the elements the electrodes are made of. When the voltage signals between all pairs of electrodes were used, H₂, NH₃, and C₂H₅OH concentrations were simultaneously estimated by a neural-network-based inference. From molecular dynamics simulations, the origin of the voltage signal was attributed to the catalytically generated adsorbates on the electrodes.