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Chalcogenide perovskites have recently attracted enormous attention since they show promising optoelectronic properties and high stability for photovoltaic applications.

Confined metal clusters as sub-nanometer reactors for electrocatalytic N2 reduction reaction (eNRR) have received increasing attention due to the unique metal-metal interaction and higher activity than single-atom catalysts. Herein, the inspiration of the superior capacitance and unique microenvironment with regular surface cavities of the porous boron nitride (p-BN) nanosheets, we systematically studied the catalytic activity for NRR of transition-metal single-clusters in the triplet form (V3, Fe3, Mo3 and W3) confined in the surface cavities of the p-BN sheets by spin-polarized density functional theory (DFT) calculations. After a two-step screening strategy, Mo3@p-BN was found to have high catalytic activity and selectivity with a rather low limiting potential (–0.34 V) for the NRR. The anchored Mo3 single-cluster can be stably embedded on the surface cavities of the substrate preventing the diffusion of the active Mo atoms. More importantly, the Mo atoms in the Mo3 single-cluster would act as “cache” to accelerate electron transfer between active metal centers and nitrogen-containing intermediates via the intimate Mo-Mo interactions. The cooperation of Mo atoms can also provide a large number of occupied and unoccupied d orbitals to make the "donation–backdonation" mechanism more effective. This work not only provides a quite promising electrocatalyst for NRR, but also brings new insights into the rational design of triple-atom NRR catalysts.

MXenes have been considered as promising electrode materials for capacitive deionization (CDI). However, the availability of space for trapping and storing ions is usually inhibited in Mxene-based assemblies due to their special lamellar structure, which affects their desalination performance. Herein, a kind of N-doped Ti3C2Tx electrode with unique interconnected porous structure (N-3DM-S) are designed to improve the active site accessibility of the electrodes. The Ti3C2Tx shell layers with flaws are prepared on spherical sacrificial templates, which then lead to the formation of interconnected N-doped porous architecture upon the heat treatment under NH3 atmosphere. The interconnected porous feature improves the availability of electrode materials, while the doping of nitrogen further enhances the accessibility of electrode to electrolyte in addition to the chemical electrochemical properties. As a result, the as-obtained N-3DM-S samples with more valid surface active sites exhibit excellent CDI performance compared to the control samples with isolated pore structure and the ones without N-doping. Especially, the optimal CDI capacities of N-3DM-S electrodes can reach up to 53 ± 2 mg/g in NaCl aqueous of 5000 mg/L at 1.6V. Moreover, such N-3DM-S electrodes exhibit good regeneration stability as well, indicating their potential applications in the field of desalination.

The stability, elastic, electronic, and optical properties of AB2As2 (A = Ca, Sr; B = Mg, Zn, Cd) and their alloys with a trigonal CaAl2Si2-type structure are thoroughly examined for the first time based on the first-principles calculations.

The adsorption of carbon atom on Fe surface and in Fe subsurface with and without rare earth (La and Ce) substitution in the surface layer and subsurface layer was studied by first-principles calculations. The carbon atom is predicted to adsorb at hollow and long bridge site on Fe(100) and Fe(110), respectively. However, the carbon atom shifts to occupy preferentially hollow site on both Fe(100) and Fe(110) with rare earth atom doping at surface layer. The lower adsorption energies involved with stronger adsorption abilities were obtained for carbon atoms on Fe surface with rare earth doping at surface layer, which was determined by the electronic structure of the surface atoms. The La atom was pulled out the surface after carbon adsorption due to strong interaction of La–C, which is consistent with the more charge transfer. In the subsurface region, the carbon atom prefers to occupy at octahedral site with rare earth doping at surface layer in Fe slab. These strong adsorption energies of the carbon atoms on Fe surface and in Fe subsurface with rare earth pose relevant insights into the interaction between carbon and rare earth, which helps to understanding the influence mechanism of rare earth in carburizing.

Electrocatalytic nitrogen reduction reaction (eNRR) is a promising method for the sustainable production of ammonia as an alternative to the traditional energy-intensive Haber-Bosch process. In this work, an efficient strategy by atomic spin regulation to promote NRR through Fe-transition metal (TM) hybrid heteronuclear dual-atom catalysts has been studied. By means of DFT computations, the stability, activity, and selectivity of 30 kinds of Fe-based dual-atoms anchored on N-doped porous graphene are systematically investigated to evaluate their catalytic performance. Fe/MoNC is screened as an excellent NRR catalyst with the limiting potentials of 0.63 V, and also suppresses HER. In the Fe/MoNC, the neighboring Fe atom regulates the spin state of the Mo center in MoN

Considerable efforts have been made to enhance the hydrogen evolution reaction (HER) catalytic performance of Janus MoSSe monolayer, which have been considered to be a promising candidate due to the unique asymmetry structure. However, the activation effect remains non-optimal for the inert Janus MoSSe basal plane at present. Herein, a train of transition metal (TM) atoms were anchored on the S-/Se-/Mo-defective MoSSe basal plane to screen effective TM single-atom catalysts for HER through density functional theory (DFT) computations. Interestingly, the single Co atom anchored on Mo-defective MoSSe and the single Zn or Cd atom anchored on S-defective MoSSe were judged to possess excellent HER performance yielding a near-zero ΔGH (ΔGH = −0.050, −0.095, −0.098 eV, respectively), which is comparable to the optimized Pt-SACs. The enhanced HER activity is attributed to the doping of TM atoms (Co, Zn and Cd) which improves the conductivity of the original MoSSe and offers unoccupied states near the Fermi level decreasing the energy barrier of electrons transfer between H and TMs@MoSSe surface. In addition, the change of unoccupied antibonding states of active atoms leads to appropriate interaction between the active sites and H. The hybridization between H-s orbital and the TMs@MoSSe systems around the Fermi level also suggests the formation of stable bonding-antibonding hydrogen adsorption states. This work reveals an effective way of activating MoSSe basal plane for HER.

The vital role of the spin polarization in the electrocatalytic N2 reduction reaction (eNRR) stimulates us to explore the potential of the newly discovered two-dimensional (2D) vdW ferromagnetic materials as NRR electrocatalysts. Here, using density functional theory (DFT) computations, we report the first theoretical prediction that the single-layer defective Fe3GeTe2 acts as a 2D ferromagnetic material toward the NRR with outstanding electrocatalytic activity and high selectivity. Notably, all six hydrogenation steps are exothermic and spontaneous. The highly centralized spin-polarization on the exposed Fe4 center in defective Fe3GeTe2 leads to strong backdonation and substantial activation of the NN triple bond. Moreover, the metallic character of the defective Fe3GeTe2 ensures high-speed transport of carriers. This work not only provides a quite promising electrocatalyst for the NRR but also promotes the application of emerging 2D ferromagnets in the field of energy conversion.

Developing light-harvesting materials with broad spectral response is of fundamental importance in full-spectrum solar energy conversion. We found that, when a series of earth-abundant metal (Cu, Co, Ni and Fe) salts are dissolved in coordinating solvents uniformly dispersed nanodots (NDs) are formed rather than fully dissolving as molecular species. The previously unrecognized formation of this condensed state is ascribed to spontaneous aggregation of molecular transition-metal-complexes (TMCs) via weak intermolecular interactions, which results in redshifted and broadened absorption into the NIR region (200-1100 nm). Typical photoredox reactions, such as carbonylation and oxidative dehydrogenation, well demonstrate the feasibility of efficient utilization of NIR light (λ780 nm) by TMCs NDs. Our finding provides a conceptually new strategy for extending the absorption towards low energy photons in solar energy harvesting and conversion via photoredox transformations.

The mild and sustainable methods for C–H direct trifluoromethylation of (hetero)arenes without any base or strong oxidants are in extremely high demand. Here, we report that the photo-generated electron-hole pairs of classical semiconductors (CdS or g-C3N4) under visible light excitation are effective to drive C–H trifluoromethylation of (hetero)arenes with stable and inexpensive CF3SO2Na as the trifluoromethyl (TFM) source via radical pathway. Either CdS or g-C3N4 propagated reaction can efficiently transform CF3SO2Na to [rad]CF3 radical and further afford the desired benzotrifluoride derivatives in moderate to good yields. After visible light initiated photocatalytic process, the key elements (such as F, S and C) derived from the starting TFM source of CF3SO2Na exhibited differential chemical forms as compared to those in other oxidative reactions. The photogenerated electron was trapped by chemisorbed O2 on photocatalysts to form superoxide radical anion (O2[rad]−) which will further attack [rad]CF3 radical with the generation of inorganic product F− and CO2. This resulted in a low utilization efficiency of [rad]CF3 (3SO2Na served as the starting materials in inert atmosphere, the photoexcited electrons can be directed to reduce the nitro group to amino group rather than being trapped by O2. Meanwhile, the photogenerated holes oxidize SO2CF3− into [rad]CF3. Both the photogenerated electrons and holes were engaged in reductive and oxidative paths, respectively. The desired product, trifluoromethylated aniline, was obtained successfully via one-pot free-radical synthesis.

The visible-light-driven photocatalytic CO2 reduction with high efficiency is highly desirable but challenging. Herein, we present porphyrin-tetraphenylethene-based covalent organic frameworks (MP-TPE-COF, where M=H2, Co and Ni; TPE=4,4′,4″,4‴-(ethane-1,1,2,2-tetrayl) tetrabenzaldehyde; COF=covalent organic framework) as ideal platforms for understanding photocatalytic CO2 reduction at molecular level. Experimental and theoretical investigations have demonstrated crucial roles of metalloporphyrin units in selective adsorption, activation and conversion of CO2 as well as in the separation of charge carriers and electron transfer, thus allowing for flexible modulation of photocatalytic activity and selectivity. CoP-TPE-COF exhibits high CO evolution rate of 2,414 µmol g−1 h−1 with the selectivity of 61% over H2 generation under visible-light irradiation, while NiP-TPE-COF provides CO evolution rate of 525 µmol g−1 h−1 and 93% selectivity with superior durability. Moreover, the photocatalytic system is feasible for the simulated flue gas, which provides CO evolution rate of 386 µmol g−1 h−1 and selectivity of 77%. This work provides in-depth insight into the structure-activity relationships toward the activation and photoreduction of CO2.

Perovskite solar cells based on multiple cations have shown excellent optoelectronic properties with high power conversion efficiency. Herein, the structural, electronic, and optical properties of mixed-cation mixed-metal perovskites MA1–xCsxPb0.25Sn0.75I3 were studied by employing the first-principles calculations for the first time. Our calculated results reveal that these perovskite materials possess direct band gaps in the range of 1.0–1.3 eV. Moreover, these compounds show excellent photovoltaic performance in terms of strong optical absorption coefficients compared with MAPbI3. Particularly, they also exhibit good structural stability and decrement of lead content. These results demonstrated that mixed-cation mixed-metal perovskites may be potential candidates for high-efficiency light-absorbing materials.

The insufficient oxidation capacity, high carrier recombination rate and limited sunlight absorption seriously suppress the photocatalytic activity of pure g-C3N4. Using state-of-the-art hybrid density functional theory, we report an efficient method to tackle all aforementioned issues of g-C3N4 by metal-nonmetal (S and K) co-doping here. We find the adsorption of K atom on hollow site causes dynamic strain of g-C3N4. The S + K co-doping not only shifts the band edges downwards to achieve a much large overpotential of ca. 0.76 V, but also significantly extends the visible-light absorption threshold of g-C3N4. More importantly, the newly established channel between neighboring heptazine units in the doped structure is highly favorable for the separation of charge carriers. Our results help the design of high-performance visible-light-responsive g–C3N4–based photocatalyst for solar water splitting.

In recent years, double perovskites have attracted considerable attention as potential candidates for photovoltaic applications. However, most double perovskites are not suitable for single-junction solar cells due to their large band gaps (over 2.0 eV). In the present study, we have investigated the structural, mechanical, electronic and optical properties of the Cs2Te1−xTixI6 solid solutions using first-principles calculations based on density functional theory. These compounds exhibit good structural stability compared to CH3NH3PbI3. The results suggest that Cs2TeI6 is an indirect band gap semiconductor, and it can become a direct band gap semiconductor with the value of 1.09 eV when the doping concentration of Ti4+ is 0.50. Moreover, an ideal direct band gap of 1.31 eV is obtained for Cs2Te0.75Ti0.25I6. The calculated results indicate that all the structures are ductile materials except for Cs2Te0.50Ti0.50I6. Our results also show that these materials possess large absorption coefficients in the visible light region. Our work can provide a route to explore stable, environmentally friendly and high-efficiency light absorbers for use in optoelectronic applications.

All-inorganic double perovskites as promising photovoltaic materials have received great attention in recent years. In this work, the structural, mechanical, electronic, and optical properties of mixed-halide double perovskites Cs2TiI6−xBrx (x = 0, 2, 4, and 6) were studied by using first-principles calculations. The calculated lattice parameters of Cs2TiI6−xBrx agree well with the reported experimental values. The calculated results have confirmed that these compounds are thermodynamically stable. Moreover, these mixed-halide double perovskites can easily be converted into thin films based on their unique mechanical properties. The obtained band gaps of the Cs2TiI6−xBrx systems using the PBE+U method have better matched with the experimental values. When the Br content increases, the band gap of Cs2TiI6−xBrx increases gradually, which leads to a decreased optical performance in the visible light region. Based on a suitable direct band gap and strong absorption coefficient, Cs2TiI2Br4 is an ideal potential material for single-junction solar cells.

Selective photoreduction of CO2 into a given product is a great challenge but desirable. Inspired by natural photosynthesis occurring in hierarchical networks over non-precious molecular metal catalysts, we demonstrate an integration of single Ni sites into the hexagonal pores of polyimide covalent organic frameworks (PI-COFs) for selective photoreduction of CO2 to CO. The single Ni sites in the hexagonal pores of the COFs serve as active sites for CO2 activation and conversion, while the PI-COFs not only act as a photosensitizer to generate charge carriers but also exert a promoting effect on the selectivity. The optimized PI-COF with a triazine ring exhibits excellent activity and selectivity. A possible intra- and inter-molecular charge-transfer mechanism was proposed, in which the photogenerated electrons in PI-COFs are efficiently separated from the central ring to the diimide linkage, and then transferred to the single Ni active sites, as evidenced by theoretical calculations.

Molybdenum carbide (Mo2C) is one type of promising noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER), but the synthesis of highly crystalline Mo2C is usually accompanied by particle coarsening and/or carbon residues, resulting in low exposed active sites and decreased mass activity. Herein, we developed a metal–organic framework (MOF)-aided topotactic transformation strategy for the fabrication of N-doped porous Mo2C mesocrystals on carbon fiber paper (N–Mo2C/CFP). The optimized N–Mo2C/CFP requires the overpotentials of only 45, 80 and 37 mV to deliver the current density of 10 mA cm−2 in acidic, neutral and alkaline media, respectively. The pH-universal HER activities are competitive with those of commercial 20 wt% Pt/C. This work provides the advanced metal carbide mesocrystals as noble-metal-free electrocatalysts for HER in all pH ranges.

The effect of organic cation doping with aziridinium (Az+) on the material properties of CsPbI3 was investigated by applying first-principles calculations. The results showed that the phase stabili...

Capture and catalytic conversion of CO2 into value-added chemicals is a promising and sustainable approach to relieve global warming and the energy crisis. Nitrogen-rich porous organic polymers (POPs) are promising materials for CO2 capture and separation, but their application in the additive-free catalytic conversion of CO2 into cyclic carbonates is still a challenge. Herein, a nitrogen-rich click-based POP (CPP) was developed for the cycloaddition reaction of CO2 with epoxides in the absence of metal, solvents, and additives. The introduction of imidazolium-based ionic liquids on the CPP host backbone could modulate the porosity, CO2 adsorption/desorption, CO2 selectivity over N2 , and catalytic activity in the chemical transformation. A tentative catalytic pathway was proposed to account for the superior catalytic activity of the catalytic systems, in which the incorporated ionic liquid and porous properties of CPP synergistically contributed to the catalytic reaction. This study provides a platform to understand the cooperative effects of porous properties and nucleophilic anions on the cycloaddition reaction of CO2 with epoxides.

Inspired by the recent practical application of two-dimensional (2D) nanomaterials as gas sensors, catalysts, and materials for waste gas disposal, herein, the adsorption behaviors of environmental gas molecules, including NO, CO, O