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The Volmer step in alkaline hydrogen evolution reactions (HERs), which supplies H* to the following steps by cleaving H–O–H bonds, is considered the rate-determining step of the overall reaction. The Volmer step involves water dissociation and adsorbed hydroxyl (*OH) desorption; Ru-based catalysts display a compelling water dissociation process in an alkaline HER. Unfortunately, the strong affinity of Ru for *OH blocks the active sites, resulting in unsatisfactory performance during HER processes. Hence, this study investigates a series of key descriptors (ΔG*H2O, ΔG*H–OH, ΔG*H, and ΔG*OH) of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt)–Ru/Mo2Ti2C3O2 to systematically explore the effects of bimetallic site interactions on the kinetics of the Volmer step. The results indicate that bimetallic catalysts effectively reduced the strong adsorption of *OH on Ru sites; especially, the NiRu diatomic state shows the highest electron-donating ability, which promoted the smooth migration of *OH from Ru sites to Ni sites. Therefore, Ru, Ni and MXenes are suitable to serve as water adsorption and dissociation sites, *OH desorption sites, and H2 release sites, respectively. Ultimately, NiRu/Mo2Ti2C3O2 promotes Volmer kinetics and has the potential to improve alkaline HERs. This work provides theoretical support for the construction of synergistic MXene-based diatomic catalysts and their wide application in the field of alkaline HERs. [ABSTRACT FROM AUTHOR]

The electrochemical hydrogen evolution reaction (HER) in alkaline media provides an environmentally friendly industrial application approach to replace traditional fossil energy. The search for efficient, low-cost, and durable active electrocatalysts is central to the development of this area. Transition metal carbides (MXenes) have been emerging as a new family of two-dimensional (2D) materials that have great potential in the HER. Herein, density functional theory calculations are performed to systematically explore the structural and electronic properties and alkaline HER performances of Mo-based MXenes, as well as the influence of species and the coordination environment of single atoms on the improvement of the electrocatalytic activity of Mo2Ti2C3O2. The results show that Mo-based MXenes (Mo2CO2, Mo2TiC2O2, and Mo2Ti2C3O2) exhibit excellent H binding ability, while slow water decomposition kinetics hinders their HER performance. Replacing the O-terminal of Mo2Ti2C3O2 with a Ru single-atom (RuS–Mo2Ti2C3O2) could promote the decomposition of water owing to the stronger electron-donating ability of the atomic state Ru. In addition, Ru could also improve the binding ability of the catalyst to H by adjusting the surface electron distribution. As a result, RuS–Mo2Ti2C3O2 exhibits excellent HER performance with a water decomposition potential barrier of 0.292 eV and a H adsorption Gibbs free energy of −0.041 eV. These explorations bring new prospects for single atoms supported on Mo-based MXenes in the alkaline hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

CdTe and related II–VI compound semiconductors have been widely utilized in the field of optoelectronic devices, detectors, solar cells and so on. As the surface treatment on the wafer involved in the device fabrication process has an important impact on its subsequent photoelectric performance, the investigations on the change in structures and properties of the wafer after different surface treatments, especially the formation of new phases at the surface, have important theoretical significance and practical application value. In this work, the surface morphology and microstructure of CdTe single crystal wafers after different chemical etching processes were investigated by atomic force microscopy (AFM), Raman spectroscopy and transmission electron microscopy (TEM). With the increase of etching time to 10 min, the surface gradually became smoother with a significantly reduced surface roughness from 61.4 nm to 30.5 nm. In addition, the I–V curves of Au/CdTe contact structure illustrate the optimized ohmic contact characteristics after chemical etching with the surface leakage current increasing from 4.723 × 10−10 A to 3.640 × 10−9 A when the etching time extends up to 10 min. TEM analysis on the chemical etched surface of CdTe confirms the formation of Cd2Te2O7 phase with two variants. The d-spacing of (100)CTO and twice that of {111}CdTe being similar is the main reason for the existence of low lattice mismatch and formation of coherent interface between Cd2Te2O7 and CdTe. Furthermore, the chemical etching process is also confirmed to remove the surface damage caused by mechanical polishing effectively by comparing the interface microstructures of Au/CdTe contacts without and after 10 min of chemical etching. The formation mechanism of Cd2Te2O7 and the structure model of Au/CdTe interface are also proposed based on the TEM results. [ABSTRACT FROM AUTHOR]

The heat induced self-welding of nanomaterials is an important method for the artificial design and synthesis of heterogeneous composite materials. The connection and growth of solid-state crystalline nanomaterials under heat treatment normally follow the oriented attachment growth mechanism. However, there is a lack of systematic research on the interface crystallography under such formation conditions, especially for crystals with relatively large structure differences. In this work, hydrothermally grown TiO2 (B) (TB) nanofibers are chosen as examples to investigate the welded interface structure and crystallography between the same and different TiO2 polymorphs. Through the manipulation of calcination temperature, TB–TB and TB–anatase (TA) self-welded nanofiber pairs can be firstly obtained. The transmission electron microscopy (TEM) results suggest that two TB nanofibers with the same {100} single crystal form (SCF) can be connected with the same orientation or by being rotated along the fiber growth direction for certain angles. In addition, the TB nanofibers with different SCFs can also be welded through the extension and growth of (010)TB. For TB–TA self-welded pairs, the welding direction is confirmed along the long axis direction of the fiber, which is different from that of TB–TB self-welded pairs. Moreover, it is proved that the TB nanofibers with both SCFs can be welded with TA, leading to the formation of two different interfaces with typical orientation relationships. Furthermore, fewer dislocations can be found in the welded pairs with the {100} SCF of TB, which is due to the similar distribution of the voids between TiO6 octahedra for TB and TA with the orientation relationships of [010]TB//[010]TA, [100]TB//[100]TA and [106]TB//[001]TA. For the self-welded cases between TA nanofibers, the mutual rotation along different axes followed by the attachment growth was considered to be the mechanism of different interface formations. The results of this work can provide useful experimental support for the controlled synthesis of heat induced self-welded metal-oxide nanofibers. [ABSTRACT FROM AUTHOR]

The Volmer step in alkaline hydrogen evolution reactions (HERs), which supplies H* to the following steps by cleaving H-O-H bonds, is considered the rate-determining step of the overall reaction. The Volmer step involves water dissociation and adsorbed hydroxyl (*OH) desorption; Ru-based catalysts display a compelling water dissociation process in an alkaline HER. Unfortunately, the strong affinity of Ru for *OH blocks the active sites, resulting in unsatisfactory performance during HER processes. Hence, this study investigates a series of key descriptors (Δ G *H 2 O , Δ G *H-OH , Δ G *H , and Δ G *OH ) of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, or Pt)-Ru/Mo 2 Ti 2 C 3 O 2 to systematically explore the effects of bimetallic site interactions on the kinetics of the Volmer step. The results indicate that bimetallic catalysts effectively reduced the strong adsorption of *OH on Ru sites; especially, the NiRu diatomic state shows the highest electron-donating ability, which promoted the smooth migration of *OH from Ru sites to Ni sites. Therefore, Ru, Ni and MXenes are suitable to serve as water adsorption and dissociation sites, *OH desorption sites, and H 2 release sites, respectively. Ultimately, NiRu/Mo 2 Ti 2 C 3 O 2 promotes Volmer kinetics and has the potential to improve alkaline HERs. This work provides theoretical support for the construction of synergistic MXene-based diatomic catalysts and their wide application in the field of alkaline HERs.