Layered transition metal trichalcogenides MPX3 (M: transition metal; X: S, Se) demonstrate a wide spectrum of properties and are widely proposed as effective materials for the water splitting reactions. Among these materials, NiPX3 are the most promising ones because their electronic structures, band gaps and positions of the valence and conduction bands edges fit to the potentials characteristic for the oxygen and hydrogen evolution reactions. Here, first steps of a detailed theoretical description on the adsorption of water molecules on pristine and defected (chalcogen vacancies) surfaces of NiPX3 are presented and it is shown that in all cases a physisorption takes the place with adsorption energies do not exceeding −650 meV and water dissociative adsorption is unfavorable. This work provides a general description for water molecules interaction with MPX3 and can serve as a basis for further studies on more complicated water/MPX3 reactions.

The effect of vacancy and water adsorption on the electronic structure of semiconducting 2D trichalcogenide material CrPX 3 (X: S, Se) is studied using state-of-the-art density functional theory (DFT) approach. It is found that chalcogen vacancies play a minor role on the electronic structure of CrPX 3 in the vicinity of the Fermi level leading to the slightly reduced band gap for these materials, however, inducing strongly localised defect states which are placed in the energy gap formed by the valence band states. Our DFT calculations show that the interaction of water molecules with CrPX 3, pristine and defective, can be described as physisorption and the adsorption energy for H2O is insensitive to the difference between pristine and chalcogen-defective surface of trichalcogenide material. These results are the first steps for the theoretical description of the ambient molecules interaction with 2D semiconducting CrPX 3 material, that is important for its future experimental studies and possible applications.

Nanostructured metal oxide semiconductors have received great attention used as the chemiresistive layer of gas sensor to detect the volatile organic compound recently. As indispensable complementary parts for dominative n-type semiconductors, the p-type metal oxides based gas sensors fail to be studied sufficiently, which hampers their practical applications. In this work, the p-type delafossite CuCrO2 nanoparticles were synthesized, characterized, and tested for gas sensing, followed by the first principles calculations to simulate the generation of chemiresistive signal. The hydrothermal synthesis time of CuCrO2 nanoparticles is optimized as 24 h with a higher proportion of oxygen vacancies but a smaller size, which is confirmed by the microscopy and spectrum characterization and allows for a prevailing gas sensitivity. Meanwhile, this CuCrO2 gas sensor is proven to perform a higher selectivity to n-propanol and a low detection limit of 1 ppm. The adsorption sites and charge variations of dehydrogenation at the gas-solid interface predicted by the theoretical analysis are claimed to be crucial to such selectivity. It is an innovative approach to understand the chemiresistive gas sensing by evaluating the preference of charge transfer between the sensor and target gaseous molecule, which provides a new route to precisely design and develop the advanced sensing devices for the diverse applications.

Because of the special layered structure and catalytic properties, delafossite CuCrO2 has been extensively studied and can obtain outstanding performance by noble metal coupling. In this work, the Ag-decorated CuCrO2 hybridizations have been elaborated by a thermal evaporation method. Surface morphology characterization and chemical state analysis were combined to indicate that the isolated island distribution of Ag nanoclusters and the generation of a divalent copper ion may result in an improvement in the gas response toward 100 ppm volatile organic compounds, such as formaldehyde (38.7%), methanol (56.8%), and acetone (76.3%). First-principle calculations were carried out to demonstrate the sensing mechanism of the Ag-decorated CuCrO2, where the remarkable change in geometry and electronic structure provided the active interface and noble metal catalysis effect promoting the target gas adsorption and reaction process. Therefore, in this work, we propose that the thermal evaporation can be utilized to act as a controllable modification method to construct nanostructure gas sensors, and the fundamental enhancement mechanism is useful to guide the design of efficient delafossite-based composite catalysts.