RESUMO
As the key half reaction of water-splitting electrolysis, the hydrogen evolution reaction (HER) that occurs at the cathode directly determines the overall efficiency of hydrogen production. To improve the efficiency of electrochemical water splitting for hydrogen generation, efficient and robust catalysts need to be developed. Strain engineering, which represents an effective and promising category of strategies, can regulate the electronic structures of catalysts by modulating the lattice strain and ultimately optimizing the HER dynamics. This work critically reviews the recent progress of strain engineering in HER and provides future perspectives for this area. The methods and characterization techniques are also introduced in detail. Hopefully this review can provide guidelines for the design and manufacturing of advanced catalysts for HER and other heterogeneous catalysis reactions such as chemical sensing, CO2 reduction and NH3 synthesis.
RESUMO
Electric field enhanced ultraviolet (UV)-induced nanoparticle colloid jet machining is proposed to improve the material removal efficiency of UV-induced nanoparticle colloid jet machining by applying an external electric field. The influences of TiO2nanoparticle concentration, applied electric field voltage and pH value for the photocatalytic activity of the polishing slurry was investigated by orthogonal experiments. Terephthalic acid (TPA) was used as a fluorescent molecular probe to reflect the relative concentration of hydroxyl radical groups (·OH) in polishing slurry, which directly affects the material removal rate in the UV-induced nanoparticle colloid jet machining process. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and x-ray photoelectron spectroscopy (XPS) were employed to inspect the interaction variations between the TiO2nanoparticles and the SiC workpiece surface. The SEM and XPS results exhibit that the external electric field can enhance the adsorption of TiO2nanoparticles on the SiC workpiece surface, which can create more interfacial reaction active centers in the polishing process. The FT-IR spectra results indicate that TiO2nanoparticles were chemically bonded to the SiC surface by oxygen-bridging atoms in Ti-O-Si bonds. The results of fixed-point polishing experiment show that due to the enhancement effect of external electric field on the photocatalytic activity of the polishing slurry, the material removal efficiency of electric field enhanced UV-induced nanoparticle colloid jet machining is 15% higher than that of UV-induced nanoparticle colloid jet machining, and is 28% higher than that of pure nanoparticle colloid jet machining. Atomic force microscope micromorphology show that an ultra-smooth SiC workpieces with surface roughness of Rms 0.84 nm (Ra 0.474 nm) has been obtained by electric field enhanced UV-induced nanoparticle colloid jet machining.
RESUMO
Ti-6Al-4V is widely used in various fields of modern industry, but it is difficult to obtain an ultra-smooth surface of Ti-6Al-4V due to its poor machinability. In this article, ultraviolet-induced (UV-induced) nanoparticle colloid jet machining was utilized to carry out ultra-precision polishing of Ti-6Al-4V to improve the surface quality. The results of infrared differential spectroscopy before and after polishing show that new chemical bonds such as Ti-O-Ti (Al-O-Ti and V-O-Ti) appear on the Ti-6Al-4V workpiece surface, which indicates that the material of Ti-6Al-4V workpiece is removed through the chemical interaction between TiO2 nanoparticles and workpiece surface in the process of UV-induced nanoparticle colloid jet machining. The comparison of metallographic structure of Ti-6Al-4V before and after polishing shows that the chemical activity and material removal rate of the primary α phase in Ti-6Al-4V is higher than that of the remnant ß phase in UV-induced nanoparticle colloid jet machining, which lead to the well-distributed nano-scale surface peaks and valleys at regular intervals on the polished Ti-6Al-4V workpiece surface. After polishing, the longitudinal residual stress on the surface of Ti-6Al-4V workpiece decreases from 75 MPa to 67 MPa and the transverse stress decreases from 13 MPa to 3 MPa. The surface roughness of Ti-6Al-4V workpiece is reduced from Sa 76.7 nm to Sa 2.87 nm by UV-induced nanoparticle colloid jet machining.
RESUMO
In this paper, ultraviolet (UV)-induced nanoparticle colloid jet machining is proposed to achieve ultrasmooth surface polishing by using the interaction between nanoparticles and the workpiece surface under the action of the ultraviolet field and the hydrodynamic pressure field. In the process of UV-induced nanoparticle colloid jet machining, the effects of photocatalysis on the interaction between nanoparticles and the workpiece surface need to be further studied in order to better understand the polishing process. This paper presents the interaction between TiO2 nanoparticles and a Si workpiece surface with and without ultraviolet irradiation. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) were applied to investigate the differences in the interaction of TiO2 nanoparticles with Si workpieces. The SEM and XPS results indicate that the photocatalysis of UV light can promote the interaction between TiO2 nanoparticles and a Si surface by creating more interfacial reaction active centers between the TiO2 nanoparticles and the Si workpiece. The FT-IR and XPS spectra show that TiO2 nanoparticles are chemically bonded to the Si workpiece by oxygen-bridging atoms in Ti-O-Si bonds. Due to the effects of photocatalysis, UV-induced nanoparticle colloid jet machining has a higher polishing efficiency than nanoparticle colloid jet machining with the same polishing parameters.