Enhanced Free-Radical Generation on MoS2 /Pt by Light and Water Vapor Co-Activation for Selective CO Detection with High Sensitivity.

Semiconductor-based gas sensors hold great promise for effective carbon monoxide (CO) detection. However, boosting sensor response and selectivity remains a key priority in moist conditions. In this study, a composite material, Pt quantum dots decorated MoS2 nanosheets (MoS2 /Pt), is developed as a highly sensitive material for CO detection when facilitated with visible light. The MoS2 /Pt sensor shows a significantly improved response (87.4%) with impressive response/recovery kinetics (20 s/17 s), long-term stability (60 days), and good selectivity to CO at high humidity (≈60%). It is confirmed both experimentally and theoretically that the MoS2 /Pt surface lowers the activation energy to convert CO to CO2 via the free radicals induced by the synergy of photochemical effects and water vapor. As a result, the MoS2 /Pt surface promotes both CO response and selectivity, providing fundamental clues to improve room-temperature semiconductor-based sensors for gas detection under extreme conditions.

Effect of Current Density on Preparation and Properties of TF/ß-PbO2 in MSA Media.

The lead-based alloy and DSA anodes have drawbacks, such as poor corrosion resistance, easy peeling of coating, low electrocatalytic activity, and environmental pollution in electrode preparation processes. In this study, titanium foam/ß-PbO2 (TF/ß-PbO2) was prepared by electrodeposition in methanesulfonic acid (MSA) media. The current efficiency and the deposition rate were 89.7% and 5.36 v/(µm·min-1) at the best current density of 80 mA·cm-2, respectively. The TF/ß-PbO2 was characterized by electrochemical tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The cyclic voltammetry (CV) test shows that the anodic peak potential of the optimum TF/ß-PbO2 was as low as 2.135 V and anodic voltammetry charge was up to the maximum value of 3.564 × 10-2 C. The linear sweep voltammetry (LSV) test indicates that exchange current density of the optimum TF/ß-PbO2 reached the maximum value of 8.284 × 10-6 A·cm-2. CV and LSV tests indicate that the optimum TF/ß-PbO2 had a high electrocatalytic activity. Electrochemical impedance spectroscopy test Tafel polarization curves show that the optimum TF/ß-PbO2 had better corrosion resistance. The XRD test shows that the crystal was mainly ß-PbO2 of the optimum TF/ß-PbO2 surface and the current density affected the preferential growth of the crystal surface of PbO2. SEM tests show that grains of the optimum TF/ß-PbO2 coating prepared were tightly bound and uniform in size.

Compressive strain induced superior HER performance of nickel in alkaline solution.

The HER requires a highly efficient, cost-effective, and stable catalyst to adapt to the large-scale hydrogen industry. Nickel has been confirmed to be useful to drive the water splitting reaction, but the intrinsic performance remains unsatisfactory. In this work, nickel (EG-Ni) with compressive strain was prepared through a one-step electrochemical deposition strategy. It shows an outstanding enhancement for the HER, and it achieves a current density of 10 mA cm-2 at a low overpotential of 85.9 mV. A long-term durability test proves that the EG-Ni can tolerate a large current density of 100 mA cm-2, and the overpotential remains steady without dramatically increasing. Such a low overpotential and superior stability are attributed to the optimized adsorption energy on the catalyst surface, as evidenced by the downshifted position of the d-band center.

MXene/WS2 hybrids for visible-light-activated NO2 sensing at room temperature.

Optoelectronic gas sensors based on two-dimensional (2D) materials are touted as potential candidates for NO2 sensing at room temperature. However, most of the developed optoelectronic sensors to date are confined to the ultraviolet region with unsatisfactory performance. Herein, a room-temperature visible-light-activated optoelectronic NO2 sensor based on 2D/2D T3C2Tx/WS2 nanocomposites is presented. The T3C2Tx/WS2-based gas sensor exhibited fast response/recovery rate, full reversibility, long stability, good selectivity, and low detection limit (10 ppb). In addition to the efficient interfacial charge separation provided by 2D/2D heterostructures, the improvement of optoelectronic NO2 sensing performance was attributed to the visible-light-activation effects. This study provides a promising method to fabricate room-temperature high-performance gas sensors based on 2D nanomaterials.

Bottom-Up Construction of Active Sites in a Cu-N4-C Catalyst for Highly Efficient Oxygen Reduction Reaction.

Bottom-up construction of efficient active sites in transition metal-nitrogen-carbon (M-N-C) catalysts for oxygen reduction reaction (ORR) from single molecular building blocks remains one of the most difficult challenges. Herein, we report a bottom-up approach to produce a highly active Cu-N4-C catalyst with well-defined Cu-N4 coordination sites derived from a small molecular copper complex containing Cu-N4 moieties. The Cu-N4 moieties were found to be covalently integrated into graphene sheets to create the Cu-N4 active sites for ORR. Furthermore, the activity was boosted by tuning the structure of active sites. We find that the high ORR activity of the Cu-N4-C catalyst is related to the Cu-N4 center linked to edges of the graphene sheets, where the electronic structure of the Cu center has the right symmetry for the degenerate π* orbital of the O2 molecule. These findings point out the direction for the synthesis of the M-N-C catalysts at the molecular level.