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Photosplitting water for H 2 production is a promising, sustainable approach for solar-to-chemical energy conversion. However, developing low-cost, high efficient and stable photocatalysts remains the major challenge. Here we report a composite photocatalyst consisting of FeP nanoparticles and CdS nanocrystals (FeP/CdS) for photogenerating H 2 in aqueous lactic acid solution under visible light irradiation. Experimental results demonstrate that the photocatalyst is highly active with a H 2 -evolution rate of 202000 μmol h −1 g −1 for the first 5 h (106000 μmol h −1 g −1 under natural solar irradiation), which is the best H 2 evolution activity, even 3-fold higher than the control in situ photo-deposited Pt/CdS system and the corresponding to an apparent quantum efficiency of over 35% at 520 nm. More important, we found that the system exhibited excellent stability and remained effective after more than 100 h in optimal conditions under visible light irradiation. A wide-ranging analysis verified that FeP effectively separates the photoexcited charge from CdS and showed that the dual active sites in FeP enhance the activity of FeP/CdS photocatalysts.

Localized surface plasmon resonance (LSPR) plays a significant role in the fields of photocatalysis and solar cells. It can not only broaden the spectral response range of materials, but also improve the separation probability of photo-generated electron-hole pairs through local field enhancement or hot electron injection. In this article, the LSPR effects of Au/TiO2 composite photocatalyst, with different sizes and shapes, have been simulated by the finite difference time domain (FDTD) method. The variation tendency of the resonance-absorption peaks and the intensity of enhanced local enhanced electric field were systematically compared and emphasized. When the location of Au nanosphere is gradually immersed into the TiO2 substrate, the local enhanced electric field of the boundary is gradually enhanced. When Au nanoshperes are covered by TiO2 at 100 nm depths, the local enhanced electric field intensities reach the maximum value. However, when Au nanorods are loaded on the surface of the TiO2 substrate, the intensity of the corresponding enhanced local enhanced electric field is the maximum. Au nanospheres produce two strong absorption peaks in the visible light region, which are induced by the LSPR effect and interband transitions between Au nanoparticles and the TiO2 substrate. For the LSPR resonance-absorption peaks, the corresponding position is red-shifted by about 100 nm, as the location of Au nanospheres are gradually immersed into the TiO2 substrate. On the other hand, the size change of the Au nanorods do not lead to a similar variation of the LSPR resonance-absorption peaks, except to change the length-diameter ratio. Meanwhile, the LSPR effects are obviously interfered with by the interband transitions between the Au nanorods and TiO2 substrate. At the end of this article, three photo-generated carrier separation mechanisms are proposed. Among them, the existence of direct electron transfer between Au nanoparticles and the TiO2 substrate leads to the enhanced local enhanced electric field at the boundaries, which is favorable for the improvement of photocatalytic performance of TiO2. These findings could explain the underlying mechanism of some experimental observations in published experimental works, and helpful to design highly efficient composite photocatalysts that contain noble metal co-catalyst nanoparticles.

As a potential and efficient photocatalyst, CuFeO2 has attracted increasing attention. However, the surface structures and properties of CuFeO2 have not been investigated in detail until now. In this work, the density functional theory calculations have been used to analyze the microstructures and electronic structures of low-index stoichiometric CuFeO2 surfaces. It is evident that atoms on the outermost surfaces with dangling bonds lead to the presence of surface states. The surface states at the valence band maximum and conduction band minimum facilitate the separation of photogenerated electron-hole pairs, in the cases of relaxed (012) and (110) surfaces. In contrast, the continuous surface states in the forbidden band increase the recombination of photogenerated electron-hole pairs, in the cases of relaxed (001), (100) and (101) surfaces. In all considered surfaces of CuFeO2, the relaxed (001) surface is the most stable, due to the minimum dangling bond density. According to the Wulff rule, the thermodynamic equilibrium shape of CuFeO2 is finally constructed. Among them, the {001} surface is the dominating exposed crystal facet (49.54%). These findings reveal the correlation between the surface microstructure and photocatalytic performance of CuFeO2 and provide further theoretical support for the subsequent development of more efficient CuFeO2-based photocatalysts.

The exploration of novel photocatalyst is one of the important directions of developing efficient photocatalysis technology. Delafossite CuCoO2 has unique crystal structure, suitable band gap and energy band edge, and excellent catalytic activity, which is a new photocatalyst well worth developing. However, the as-prepared CuCoO2 samples in literature often have the problems of containing impurity or secondary phases, non-stoichiometry, leading to some controversies about its fundamental physicochemical properties. Moreover, there is also insufficient understanding of the use of CuCoO2 as a novel photocatalyst. Herein, one-pot hydrothermal method was used to prepare stoichiometric delafossite CuCoO2 microcrystals (~ 3.65 μm) with high purity and single-phase. Then, its detailed fundamental physicochemical properties as photocatalyst are further provided by a series of experimental characterization and density functional theory calculations. The results show that delafossite CuCoO2 exhibit outstanding semi-metallic ferromagnetism, multiple electron transitions caused by various band gap types, multi band absorption and full spectrum absorption, and has appropriate band edge position, which can be applied to HER and OER of water splitting. The photocatalytic performance of CuCoO2 was systematically tested for the first time by photocatalytic degradation of tetracycline hydrochloride, photocatalytic water-splitting, and photocurrent measurement in PEC cell. Under visible light irradiation, the as-prepared CuCoO2 can degrade more than 90% of tetracycline hydrochloride within 4 h. Without sacrificial agent and cocatalyst, the shows the hydrogen and oxygen evolution rates from photocatalytic water-splitting of as-prepared CuCoO2 reached to 2.60 and 128.53 μmol/h g, respectively. In the three-electrode electrochemical cell with 1 M Na2SO4 electrolyte and zero-bias, the photocurrent density of CuCoO2 based photocathode reached to 20 μA/cm2. These findings prove that CuCoO2 has obvious advantages and great potential as a visible-light-driven photocatalyst.

As important functional materials, the electronic structure and physical properties of (GaAs)m(AlAs)n superlattices (SLs) have been extensively studied. However, due to limitations of computational methods and computational resources, it is sometimes difficult to thoroughly understand how and why the modification of their structural parameters affects their electronic structure and physical properties. In this article, a high-throughput study based on density functional theory calculations has been carried out to obtain detailed information and to further provide the underlying intrinsic mechanisms. The band gap variations of (GaAs)m(AlAs)n superlattices have been systematically investigated and summarized. They are very consistent with the available reported experimental measurements. Furthermore, the direct-to-indirect-gap transition of (GaAs)m(AlAs)n superlattices has been predicted and explained. For certain thicknesses of the GaAs well (m), the band gap value of (GaAs)m(AlAs)n SLs exponentially increases (increasing n), while for certain thicknesses of the AlAs barrier (n), the band gap value of (GaAs)m(AlAs)n SLs exponentially decreases (increasing m). In both cases, the band gap values converge to certain values. Furthermore, owing to the energy eigenvalues at different k-points showing different variation trends, (GaAs)m(AlAs)n SLs transform from a Γ-Γ direct band gap to Γ-M indirect band gap when the AlAs barrier is thick enough. The intrinsic reason for these variations is that the contributions and positions of the electronic states of the GaAs well and the AlAs barrier change under altered thickness conditions. Moreover, we have found that the binding energy can be used as a detector to estimate the band gap value in the design of (GaAs)m(AlAs)n devices. Our findings are useful for the design of novel (GaAs)m(AlAs)n superlattices-based optoelectronic devices.

Phase-change random access memory is regarded as the most promising candidate for storage class memory, which must be further improved by employing more competitive phase-change materials. In the present work, solid solutions combined with noble metals and Sb2Te3 were investigated by first-principles high-throughput calculations. The microstructures and properties of NMx(Sb2Te3)1−x (NM = noble metals) solid solutions are closely related to the compositions and solid solubility of NM composition. By changing the kind of NM composition, NMx(Sb2Te3)1−x solid solutions can present different properties, including transition temperature, short-range order, and thermal stability. The contributions of NM-nd states to electronic structures in Sb2(Te1−xNMx)3 solid solutions are much greater than Sb-5p and Te-5p states and even greater for (Sb1−xNMx)2Te3 solid solutions. Combining the results of energy, structure, stability, and electronic structure, (Sb1−xIrx)2Te3 solid solutions stand out as the best candidate for phase-change materials.

Bismuth oxyiodide (BiOI) is an important photoelectric functional material that has a wide range of applications. In particular, it can be used as a photocatalyst that shows photocatalytic activity under visible-light irradiation. The synthesis procedure and related photocatalytic performance of BiOI have been reported. However, some of its fundamental properties still need to be further investigated. In this article, density functional theory calculations were performed to investigate the crystal structure, electronic properties, and optical properties of BiOI. Furthermore, the relationship between the intrinsic properties and the photocatalytic performance of BiOI was investigated. Based on the calculated results of the band structure, density of states, and projected wave function, the molecular-orbital bonding structure of BiOI is proposed. As a semiconductor photocatalyst, BiOI shows slight optical anisotropy in the visible-light region, indicating that it can efficiently absorb visible light if the morphology of BiOI is controlled. After comparing several computational methods, it was found that the generalized-gradient approximation corrected for on-site Coulomb interactions (GGA + U) is a suitable computational method for large sized BiOI models (e.g., impurity doping, the surface, and the interface) because it can significantly reduce the computational time while maintaining calculation accuracy. Thus, this article not only provides an in-depth understanding of the fundamental properties of BiOI as a potential efficient photocatalyst driven by visible light, but it also suggests a suitable computational method to investigate these properties.

Six BiOX 1− x Y x (X, Y = F, Cl, Br and I) solid solutions have been systematically investigated by density functional theory calculations. BiOCl 1− x Br x , BiOBr 1− x I x and BiOCl 1− x I x solid solutions have very small bowing parameters; as such, some of their properties increase almost linearly with increasing x . For BiOF 1− x Y x solid solutions, the bowing parameters are very large and it is extremely difficult to fit the related calculated data by a single equation. Consequently, BiOX 1− x Y x (X, Y = Cl, Br and I) solid solutions are highly miscible, while BiOF 1− x Y x (Y = Cl, Br and I) solid solutions are partially miscible. In other words, BiOF 1− x Y x solid solutions have miscibility gaps or high miscibility temperature, resulting in phase separation and F/Y inhomogeneity. Comparison and analysis of the calculated results and the related physical–chemical properties with different halogen compositions indicates that the parameters of BiOX 1− x Y x solid solutions are determined by the differences of the physical–chemical properties of the two halogen compositions. In this way, the large deviation of some BiOX 1− x Y x solid solutions from Vegard’s law observed in experiments can be explained. Moreover, the composition ratio of BiOX 1− x Y x solid solutions can be measured or monitored using optical measurements.

Recently, chalcogenide phase-change materials have been widely applied in phase-change random access memory. However, the materials still have shortcomings of poor stability and low crystalline resistivity, causing high-power consumption, resistance drift, and short device life in phase-change random access memory. These do not meet the technical requirements and need to be modified. To improve Sb-Te systems alloy materials' properties and discover new phase-change materials, in this work, we construct 16 solid-solution systems based on SbTe (Sb1−xNMx)Te and Sb(Te1−xNMx) (NM = noble metals). We use a high-throughput computing method to calculate and analyze the underlying physical mechanism of solid-solution noble metal atoms' effects on improving the performance of phase-change materials. Based on the calculation results, we believe that the (Sb1−xNMx)Te solid solutions are more stable than Sb(Te1−xNMx). At the same time, the solid solution of the substituted Sb atom sites keeps the crystal structure symmetry improved structural stability. Furthermore, lone-pair electrons exist due to (Sb1−xNMx)Te keeping the SbTe’s unique layer structure, which confers a higher activity of the surrounding atoms. This is an essential determinant for keeping the phase-change properties. On the other hand, (Sb1−xNMx)Te solid solutions increase the band gap, leading to increased resistivity. Considering the structural stability and electrical properties, we believe that the (Sb1−xRux) and (Sb1−xPdx)Te systems can create new phase-change materials.