The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) constitute the two main processes in electrochemical water splitting to produce high-purity hydrogen and oxygen as alternatives to fossil fuel. Catalysts are crucial to high-efficiency conversion of water to hydrogen and oxygen. Although transition metal nitrides (TMNs) are promising HER and OER catalysts due to the unique electronic structure and high electrical conductivity, single-phase nitrides have inferior activity compared to Pt-group metals because of the unsatisfactory metal–hydrogen (M–H) bonding strength. TMNs-based composites in combination with other metals, carbon materials, and metallic compounds have been demonstrated to possess improved catalytic properties because the modified electronic structure leads to balanced M–H bonding strength, synergistic effects, and improved electrochemical stability. Herein, recent progress pertaining to TMNs is reviewed from the perspective of advanced catalysts for electrochemical water splitting. The challenges and future opportunities confronting TMNs-based catalysts are also discussed.

Recent progress of transition metal nitrides for efficient electrocatalytic water splitting

High temperature solid-lubricating materials: A review

Refractory high entropy alloys (RHEAs) have been proven to have excellent mechanical properties with a potential use as protective thin films. However, the combination of high hardness with low friction and wear is a major challenge in the design of RHEA films. In this study, we show that NbMoWTa/Ag self-lubricating multilayered films give a remarkable reduction in friction and at same time maintain high hardness. Interestingly, it is found that the bcc superlattice dominates in both NbMoWTa and Ag layers and the interfaces become coherent when the individual layer thickness h is reduced below 10 nm. The film properties are then strongly dependent on h ranging from 100 to 2.5 nm, and the most promising properties are obtained when the interface structure transforms from incoherent to coherent one. Especially, the multilayer with h = 2.5 nm exhibits superior tribological performance over monolithic NbMoWTa due to the significant coherent strengthening along with the self-lubricating ability in the multilayer. This tailored phase transition and coherent structure between the matrix and lubrication phases can also provide an optimal wear rate-coefficient of friction combination, which is higher than most of the Ag-containing self-lubricating films. The current work might open a new route toward the development of innovative self-lubricating RHEA films with excellent tribological properties.

Design and Characterization of Self-Lubricating Refractory High Entropy Alloy-Based Multilayered Films.

The influence of Ag contents on the microstructure, mechanical and tribological properties of ZrN-Ag films

Friction and wear behavior of TiN films against ceramic and steel balls

Microstructure, mechanical and tribological properties of TiN-Ag films deposited by reactive magnetron sputtering

Crystal structure and tribological properties of ZrAlMoN composite films deposited by magnetron sputtering

Composite Nb-V-C-N films with different carbon content were synthesized using reactive magnetron sputtering system, and the influence of carbon on the microstructure, mechanical, and tribological properties of niobium vanadium nitride films was investigated. The films with carbon content below 9.1 at. % exhibited a two-phase of solid solution face-centered cubic (fcc) (NbV)(CN) and hexagonal close-packed (hcp) (NbV)2(CN); increasing the carbon content further induced the formation of amorphous carbon and CNx, and the films consist of fcc-(NbV)(CN), hcp-(NbV)2(CN), amorphous carbon, and CNx. Solid solution strengthening and the heterostructure led to an increase in hardness to ∼32 GPa at 9.1 at. % carbon. A further increase in carbon content led to a gradual decrease in hardness due to the formation of soft amorphous phases of carbon and CNx. The tribological properties of the films against alumina counterpart at room temperature were significantly influenced by the carbon content. The incorporation of carbon into the films decreased the average friction coefficient (μ) from ∼0.61 at 0 at. % carbon to ∼0.25 at 21.6 at. % carbon. As the carbon content increased, the wear rate first dropped from ∼2.6 × 10−8 mm3/(N mm) at 0 at. % carbon to ∼1.2 × 10−8 mm3/(N mm) at 9.1 at. % carbon, and then rose gradually to ∼8.7 × 10−7 mm3/(N mm) at 21.6 at. % carbon.Composite Nb-V-C-N films with different carbon content were synthesized using reactive magnetron sputtering system, and the influence of carbon on the microstructure, mechanical, and tribological properties of niobium vanadium nitride films was investigated. The films with carbon content below 9.1 at. % exhibited a two-phase of solid solution face-centered cubic (fcc) (NbV)(CN) and hexagonal close-packed (hcp) (NbV)2(CN); increasing the carbon content further induced the formation of amorphous carbon and CNx, and the films consist of fcc-(NbV)(CN), hcp-(NbV)2(CN), amorphous carbon, and CNx. Solid solution strengthening and the heterostructure led to an increase in hardness to ∼32 GPa at 9.1 at. % carbon. A further increase in carbon content led to a gradual decrease in hardness due to the formation of soft amorphous phases of carbon and CNx. The tribological properties of the films against alumina counterpart at room temperature were significantly influenced by the carbon content. The incorporation of car...

Dian Yu

Papers

Microstructure, mechanical and tribological properties of TiN-Ag films deposited by reactive magnetron sputtering

The influence of Ag contents on the microstructure, mechanical and tribological properties of ZrN-Ag films

Crystal structure and tribological properties of ZrAlMoN composite films deposited by magnetron sputtering

Microstructure, mechanical, and tribological properties of niobium vanadium carbon nitride films

The role of copper incorporation on the microstructure, mechanical and tribological properties of TiBN-Cu films by reactive magnetron sputtering