Search

The construction of hydrophobic nanochannel with hydrophilic sites for bionic devices to proximally mimick real bio-system is still challenging. Taking the advantages of MOF chemistry, a highly oriented CuTCPP thin film has been successfully reconstructed with ultra-thin nanosheets to produce abundant two-dimensional interstitial hydrophobic nanochannels with hydrophilic sites. Different from the classical active-layer material with proton transport in bulk, CuTCPP thin film represents a new type of active-layer with proton transport in nanochannel for bionic proton field-effect transistor (H+ -FETs). The resultant device can reversibly modulate the proton transport by varying the voltage on its gate electrode. Meanwhile, it shows the highest proton mobility of ≈9.5×10-3 cm2 V-1 s-1 and highest on-off ratio of 4.1 among all of the reported H+ -FETs. Our result demonstrates a powerful material design strategy for proximally mimicking the structure and properties of bio-systems and constructing bionic electrical devices.

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 hydrolysis of earth-abundant AlIII has implications in mineral mimicry, geochemistry and environmental chemistry. Third-order nonlinear optical (NLO) materials are important in modern chemistry due to their extensive optical applications. The assembly of AlIII ions with π-conjugated carboxylate ligands is carried out and the hydrolysis and NLO properties of the resultant material are studied. A series of Al32 -oxo clusters with hydrotalcite-like cores and π-conjugated shells are isolated. X-ray diffraction revealed boundary hydrolysis occurs at the equatorially unsaturated coordination sites of AlIII ions. Charge distribution analysis and DFT calculations support the proposed boundary substitution. The Al32 -oxo clusters possess a significant reverse saturable absorption (RSA) response with a minimal normalized transmittance up to 29 %, indicating they are suitable candidates for optical limiting (OL) materials. This work elucidates the hydrolysis of AlIII and provides insight into layered materials that also have strong boundary activity at the edges or corners.

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.

Many metal-organic cages (MOCs) and a few hydrogen-bonded organic cages (HOCs) have been investigated, but little is reported about cooperative self-assembly of MOCs and HOCs. Herein, we describe an unprecedented MOC&HOC co-crystal composed of tetrahedral Ti4 L6 (L=embonate) cages and in-situ-generated [(NH3 )4 (TIPA)4 ] (TIPA=tris(4-(1H-1,2,4-triazol-1-yl)phenyl)amine) cages. Chiral transfer is observed from the enantiopure Ti4 L6 cage to enantiopure [(NH3 )4 (TIPA)4 ] cage. Two homochiral supramolecular frameworks with opposite handedness (PTC-235(Δ) and PTC-235(Λ)) are formed. Such MOC&HOC co-crystal features high stability in water and other solvents, affording single-crystal-to-single-crystal transformation to trap CH3 CN molecules and identify disordered NH4 + cations. A tablet pressing method is developed to test the third-order nonlinear optical property of KBr-based PTC-235 thin film. Such a thin film exhibits an excellent optical limiting effect.

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.

Recently, carbon dioxide capture and conversion, along with hydrogen from renewable resources, provide an alternative approach to synthesis of useful fuels and chemicals. People are increasingly interested in developing innovative carbon dioxide hydrogenation catalysts, and the pace of progress in this area is accelerating. Accordingly, this perspective presents current state of the art and outlook in synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols through two leading hydrogenation mechanisms: methanol reaction and Fischer-Tropsch based carbon dioxide hydrogenation. The future research directions for developing new heterogeneous catalysts with transformational technologies, including 3D printing and artificial intelligence, are provided. Carbon dioxide (CO2) capture and conversion provide an alternative approach to synthesis of useful fuels and chemicals. Here, Ye et al. give a comprehensive perspective on the current state of the art and outlook of CO2 catalytic hydrogenation to the synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols.

In the work reported in this article, di(methylsulfonyl) ethane (DMSE) was examined as a neoteric S-related electrolyte additive to elevate LiCoO2/electrolyte interfacial stability at 3.0-4.5 V (compared to Li/Li+). DMSE, when added to the electrolyte, can significantly enhance the high-voltage performance of LiCoO2/graphite cells. Meanwhile, capacity retention increased from 20.8 to 66.5% after 100 cycles owing to the adjunction of 0.5 wt % DMSE to the electrolyte (carbonate solvents and lithium salt). The density functional theory calculation results indicate that DMSE has a greater highest occupied molecular orbital energy in contrast to ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Differential capacity versus voltage analysis and linear sweep voltammetry result indicate that DMSE is decomposed in preference to the electrolyte solvents. DMSE's effects are distinguished by electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, X-ray-diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The outcomes indicate that the enhanced cycling performance is attributed to the involvement of DMSE in the generation of a thinner film on LiCoO2, which results in lower interfacial impedance and it protects the electrolyte from decomposition at high voltage.

Tributyl borate (TBB) is studied as a protective additive that enhances the interfacial stability of a LiNi0.5Mn1.5O4 cathode/electrolyte at 5 V and 55 °C. Upon addition of 0.5 vol % TBB to the ele...

In recent years, organic–inorganic hybrid halide perovskites have attracted great attention. In view of the toxicity of lead, lead-free perovskites have been developed in order to obtain comparable or better photovoltaic performance than MAPbI3. In this study, the structural, electronic, and optical properties of pure and mixed perovskite systems were investigated by using density functional theory calculations. The results reveal that three Pb–Sn–Ge perovskites are predicted to preserve improved structural stabilities over MAPbI3. The band gaps of hybrid perovskites can be tuned by means of Sn–Ge doping. The band gap of MAPb0.50Sn0.25Ge0.25I3 is in the optimum range of 1.3–1.4 eV. Optical property analysis implies that MAPb0.50Sn0.25Ge0.25I3 possesses a comparable absorption ability in the visible light region compared with the MAPbI3 structure. In addition, the results indicate that MAPb0.50Sn0.25Ge0.25I3 with the highest power conversion efficieny of 23.65% can be chosen as a potential candidate for th...

The development of cost-effective, high-efficiency, and non-noble metal based electrocatalysts for oxygen evolution reaction (OER) is considered to be the most pivotal portion for electrochemical water splitting to generate renewable energy. Herein, well-aligned mesoporous CoFe2O4 thin film is first developed from surface epitaxial growth of oriented CoFe-based prussian blue analogue thin film (CoFe-PBA thin film) for efficient electrocatalytic OER. CoFe-PBA thin film with preferred [100] orientation is first prepared on the substrate surface by employing liquid phase epitaxial method without any structure-directing surfactants. After thermal pyrolysis, such CoFe-PBA thin film was transformed into well-aligned mesoporous CoFe2O4 thin film. Interestingly, the self-support CoFe2O4 thin film electrode with the mass loading of 1.6 mg cm−2 delivers an oxygen evolution current density of 10 mA cm−2 at an overpotential of 266 mV and exhibits durable stability in 1 M KOH aqueous solution. The remarkable and stable catalytic performance of the CoFe2O4 thin film can be mainly owing to the mesoporous structure of CoFe2O4, efficient charge/electron transfer, the numerous exposed active sites, and the well-structured configuration of the electrode. Hence, this work provides an effective paradigm for preparing binder-free, self-support, and low-cost spinel oxide electrocatalyst for efficient OER derived from surface epitaxial growth of oriented PBA thin film.

N-heterocyclic carbenes (NHCs) have attracted increasing attention on surface assembly due to their strong metal binding property, but an NHC-modified metal surface as a new growth platform to assemble other functional materials is still a challenge. Here, we report the preparation and chiral sensing properties of homochiral metal-organic framework thin films on carboxyl-containing NHC self-assembled monolayer-modified gold (Au(NHC)) substrates. By using a liquid-phase epitaxial layer-by-layer method, enantiopure [Cu2(cam)2dabco]n thin films with preferred [110] crystal orientation have been successfully grown on Au(NHC) surfaces. The results of electrochemical cyclic voltammetry and quartz crystal microbalance uptakes of (R)- and (S)-1-phenylethanol show that the chiral porous thin film on the robust Au(NHC) surface has good enantiomeric electrochemical recognition and enantioselective adsorption. The present work is a new step to develop metal-NHCs as surface platforms for the preparation of multifunctional thin films for sensing applications.

The material class of hybrid organic–inorganic halide perovskites has been rapidly progressed in the field of photovoltaic applications. However, this class of materials has limitations associated with its poor stability and toxicity of the lead element. Therefore, there is a strong desire to search for environmentally friendly perovskite materials without affecting the conversion efficiency. First-principles calculations have been employed to study thermodynamic stability, electronic, and optical properties of potential candidate lead-free perovskites. The results show that the ionization energy at the A-site can provide an explanation for the stabilities of hybrid perovskites. The bond lengths and bond angles are likely responsible for the discrepancy in the band gap. The results indicate that DAGeI3 has better stability and suitable band gap among Ge-based AGeI3 perovskites. It is observed that the Si-doped perovskites are energetically favorable. CsGe2/3Si1/3I3 can become the potential candidate for t...

Hybrid organic–inorganic halide perovskite solar cells have recently attracted much attention because of their highly efficient photovoltaic performance. However, perovskite solar cells suffer from intrinsic instabilities, which limit their commercial applications. In this study, we partially substituted the methyl-ammonium (MA) cation in MA lead iodide perovskite (MAPbI3) and investigated the geometric structures and electronic and optical properties by first-principles calculations to determine their thermodynamic stabilities and optical band gaps. The results suggest that substitution of the Az cation in the A-site can enhance the stability of the MA1−xAzxPbI3 system. However, the formation energies indicate that the MA1−xCyxPbI3 series is less stable. The estimated power conversion efficiency of MA0.50Az0.50PbI3 is 23.06%, which is higher than that of MAPbI3. Notably, MA1−xAzxPbI3 (0.50 < x < 0.75) is predicted to be a promising candidate for photovoltaic applications because it has the highest theoretical power conversion efficiency, which is attributed to its optimal band gap. These results suggest that an organic cation mixing strategy can be used to tune the stability, band gap, and photovoltaic performance of hybrid perovskites, which will be particularly useful for designing light-harvesting materials for perovskite solar cells.

Mixed-cation lead halide perovskites have emerged as a new class of promising photovoltaic materials for perovskite solar cells. Formamidinium (FA), methylammonium (MA), and Cs cations are widely studied in the field of mixed-cation hybrid halide perovskites. In this work, we have investigated ethylammonium (CH3CH2NH3, EA) as an alternative cation to explore the stabilities and electronic properties of mixed MA1−xEAxPbI3 perovskites. The results indicate that replacing MA with EA is a more effective way to improve the stabilities of the mixed MA1−xEAxPbI3 perovskites except for MA0.75EA0.25PbI3. The band gap of MA1-xEAxPbI3 slightly increases with x from 0.25 to 1.00, which is quite different from the MA–FA mixed-cation perovskites. The results indicate that the c axis distortion of the Pb–I–Pb bond angles can play a greater role in tuning the band gap. Moreover, the mixed MA1−xEAxPbI3 perovskites show comparable absorption abilities in the visible light region to the pure MAPbI3 structure. We hope that our study will be greatly helpful for further experiments to find more efficient perovskite materials in the future.

Lead-free hybrid perovskites have attracted great attention as environmentally friendly light absorber layers. In this work, we report on Te-based double perovskites A2TeI6 (A = Tl, K, NH4, Rb, Cs, CH3NH3, and CH(NH2)2) as potential candidates for optoelectronic applications. The structural stability and electronic and optical properties of these Te-based double perovskite materials are investigated by using first-principles calculations. These Te-based double perovskites exhibit good structural stability, tunable band gap, and strong optical absorption. These Te-based double perovskites show promising optoelectronic properties, and may be potential candidates for photovoltaic applications. Our calculated results can provide a deep insight into developing lead-free perovskite solar cells.

Perovskite photovoltaic materials are gaining significant attention due to their excellent photovoltaic properties. In this study, density functional theory calculations were performed to investigate the structure and electronic and optical properties of CsGeI3 under hydrostatic strain. The results show that the band gap of CsGeI3 can be tuned from 0.73 eV to 2.30 eV under different strain conditions. The results indicate that the change in the band gap under strain is likely to be determined by the Ge–I–Ge bond angle. Interestingly, the length of the short Ge–I bond remains unchanged, whereas that of the long Ge–I bond exhibits an evident increment with strain ranging from −4% to 4%. A suitable band gap (1.36 eV) of CsGeI3 can be obtained under a strain of −1%. Both the calculated elastic constants and the phonon spectrum imply that this structure is stable under the abovementioned condition. Bandgap narrowing induces a red shift of the light absorption spectrum of CsGeI3 by extending the onset light absorption edge. These results are important for understanding the effects of strain on the halide perovskites and guiding the experiments to improve the photovoltaic performance of the perovskite solar cells.

The reverse water gas shift (RWGS) reaction has attracted great attention in recent years. It is well-known that supported catalysts, especially single-atom catalysts (SACs), exhibit good catalytic activity in many reactions. Thus, we designed the single-atom catalyst (SAC) Cu@Mo2C(001) and the smallest copper cluster catalyst Cu4@Mo2C(001) for the RWGS reaction. In this study, density functional theory (DFT) calculations were used to explore the reaction mechanisms of the RWGS reaction on the surfaces of Cu@Mo2C(001) and Cu4@Mo2C(001). The dissociative adsorption of H2 on these two surfaces is barrier-free and highly exothermic, which is beneficial to the RWGS reaction. Importantly, three possible mechanisms—the COOH mechanism, HCOO mechanism, and redox mechanism—have been discussed. The results illustrated that the redox mechanism is the most feasible pathway among the Cu@Mo2C(001) and Cu4@Mo2C(001) surfaces. By comparing the activation barrier of the rate-limiting step of the redox mechanism on the two...

Charge generation and separation are two key issues in developing a high-efficiency semiconductor for the visible-light-driven photocatalysis. Here, we use the layered perovskite-type wide-gap semiconductor La2Ti2O7 (LTO) as a model to systematically explore the synergistic effect of doping (with sulfur or nitrogen) and heterojunction (with graphitic C3N4) on improving visible light absorption and photoexcited charge separation by means of density functional theory calculations. It is found that the anion (N or S) doping into the LTO(010) surface can not only shift the optical absorption edge to the visible region, but also creates some partially occupied or unoccupied states in the band gap that would facilitate the formation of recombination centers. For the purpose of promoting electron–hole separation, the (N or S-doped) LTO(010) surfaces were hybridized with the monolayer g-C3N4. Interestingly, we found that the (S-doped) LTO/g-C3N4 heterostructure forms a type-II heterojunction, with the valence ban...

Photo/electrochemical CO2 splitting is impeded by the low cost-effective catalysts for key reactions: CO2 reduction (CDRR) and water oxidation. A porous silicon and nitrogen co-doped carbon (SiNC) nanomaterial by a facile pyrolyzation was developed as a metal-free bifunctional electrocatalyst. CO2 -to-CO and oxygen evolution (OER) partial current density under neutral conditions were enhanced by two orders of magnitude in the Tafel regime on SiNC relative to single-doped comparisons beyond their specific area gap. The photovoltaic-driven CO2 splitting device with SiNC electrodes imitating photosynthesis yielded an overall solar-to-chemical efficiency of advanced 12.5 % (by multiplying energy efficiency of CO2 splitting cell and photovoltaic device) at only 650 mV overpotential. Mechanism studies suggested the elastic electron structure of -Si(O)-C-N- unit in SiNC as the highly active site for CDRR and OER simultaneously by lowering the free energy of CDRR and OER intermediates adsorption.

In order to probe into the roles of the promoters Pt, Ru and B in inhibiting the deactivation of Co catalysts in FTS reactions, the adsorption ability of neighboring surface C and subsurface C atom around the promoters (Pt, Ru and B), and the mechanisms of surface C diffusion, accumulation, hydrogenation and penetration are examined by density functional theory calculations over the promoters Pt, Ru and B-modified Co catalysts, as well as the pure Co catalysts. Our results clearly show that compared to Co catalysts, both PtCo and RuCo bimetallic catalysts promote surface C hydrogenation, and inhibit surface C diffusion, accumulation and penetration, and therefore the ability of resistance toward deactivation and the stability of Co-based catalysts are enhanced; the promoter B cannot effectively improve the ability of resistance toward deactivation. Thus, the sequence for resistance toward deactivation of Co-based catalyst is BCo

The electrochemical CO2 reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine-doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO2 -to-CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec-1 , outcompeting current metal-free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H2 on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine-doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO2 -to-CO conversion.

The quickly increasing demand for sustainable energy and materials requires researchers to develop highly efficient and stable catalytic materials for the hydrogenation of carbon–oxygen bonds into chemicals and fuels. Cu-based catalysts have been attracting tremendous attention in gas-phase catalytic reactions, such as the water-gas shift, CO oxidation and NOx reduction reactions. In particular, the C–O bond hydrogenation reaction is an economical and environmentally friendly way to produce alcohols. However, the instability of Cu-based catalysts has become a great challenge for industrial application. The majority of publications discuss the instability of Cu-based catalysts for reactions involving the hydrogenation of dimethyl oxalate, methyl acetate, furfural, or CO2 to alcohols. This review briefly summarizes the roots of Cu-based catalyst deactivation and introduces five strategies for improving their stability, as well as the evolution of copper species during preparation and reaction and a novel Cu-based catalyst technology.

The realization of one-dimensional nanostructures or Ti3+ self-doping in TiO2 photocatalysts has proven to be an effective approach for significantly improving their photocatalytic performance. Herein, a series of nonstoichiometric anatase TiO2 nanorod films were deposited at 50-500 °C by a facile one-step magnetron sputtering method. The correlation between the microstructures and the photocatalytic H2 production abilities of the films was studied. It is found that, by increasing the deposition temperature, the as-sputtered TiO2 grains transformed from quasi-spherical to rod-like structures while the concentration of the Ti3+ species decreased gradually. Thus, by virtue of the collaboration between nanostructure engineering and defect engineering, the sample deposited at 300 °C showed a maximum H2 generation rate of 1874 μmol m-2 h-1, which was about 134 times higher than that of a Degussa P25 powder film (14 μmol m-2 h-1). Furthermore, the stoichiometric TiO2 shell formed on the surface of TiO2 nanograins protected the defective TiO2-x core from further oxidation, resulting in an excellent photocatalytic stability of the films. The possible film growth and photocatalytic reaction mechanisms over the Ti3+ doped TiO2 nanorod films have been investigated. Our work provides a facile route to fabricating a high-efficiency defect-based TiO2 or other transition metal oxide nanostructures with a controlled morphology for solar energy conversion.

Two-dimensional (2D) hydrogen evolution reaction (HER) electrocatalysts have attracted great attention due to their unique electronic properties and high activities. Recently, a new 2D monolayer material of MoSi2N4 has been successfully synthesized and its semiconducting property and excellent ambient stability have also been demonstrated (Science 2020, 369, 670). Here, a systematic screening of catalysts for HER among N- and Si-defective MoSi2N4-supported single non-precious transition metal (TM) and non-metal (NM) atom catalysts is performed by means of density functional theory (DFT) calculations. Interestingly, the single O/P/Fe/Nb atom doped N-(Si-) defective MoSi2N4 monolayer were found to possess excellent HER performance presenting a near-zero ΔGH, which is comparable to or even better than the state-of-the-art Pt-based materials. Moreover, the novel HER activities of some TM doped structures were explained by the “states filling” model. The energy level of the first available unoccupied states for accommodating hydrogen drops after the introduction of TM atom, which modulates the hydrogen binding strength. This work opens the door for the application of MoSi2N4 monolayer and other related 2D materials in the field of energy conversion.

We report for the first time the experimental realization of anatase TiO2 film comprised mainly of nanorods exposed with dominant {110} lateral surfaces growing on the quartz glass substrate. Based on microstructure and morphology analysis, it is found that, the average diameter of nanorods is less than 40 nm, which is favorable for the effective migration and separation of photogenerated carriers, while their lateral {110} facets contain abundant unsaturated 4c-Ti atoms which act as active sites for water splitting. The H2 generation rate by this bare anatase TiO2 nanorods film is 8.4 mmol g−1 h−1 under full-arc light irradiation without the assistance of metal cathode, bias or loading of co-catalyst, which is about three orders of magnitude higher than that of anatase TiO2 nanoparticles film, and even higher than the reported values of some noble metal loaded TiO2 photocatalysts. This work exemplifies that the controlled growth of photocatalysts with specified active facets and desired architectures is an effective strategy to achieve excellent photocatalytic properties.

MoS2, as a low-cost catalyst for hydrogen evolution reaction (HER), suffers from poor catalytic performance on the basal plane. Herein, by doping 19 main-group elements on the S-defective MoS2 nanosheet, the most promising MoS2-based catalysts for the HER are screened with high-throughput density functional theory (DFT) calculations. Remarkably, the doping of main-group elements except chalcogens can improve the activity of the MoS2 basal plane to a certain extent. The S-defective MoS2 monolayer doped with In/Ge atom (In3@MoS2 and Ge3@MoS2) show excellent HER performance, and their reaction barrier is even lower than that of commercial Pt/C catalyst. In In3@MoS2 and Ge3@MoS2, the In/Ge atoms act as electron donors to increase the unoccupied anti-bonding orbital, which enhances the interaction of In/Ge-H bonding. On the other hand, the unique co-existence of electron-depletion and electron-accumulation regions near In/Ge atoms enables the adsorption of free radical H to be moderate. Moreover, the In/Ge atoms also increase the conductivity of MoS2, especially the In atom brings a new impurity state near the Fermi level. This work presents a promising strategy for exploiting high-performance MoS2-based catalysts for HER, and would stimulate more researchers to optimize other two-dimensional materials by doping main-group elements for HER.

In recent years, all-inorganic lead-free double perovskites as promising photovoltaic materials have received great attention. In this study, we have investigated the stability, electronic and optical properties of the pure and mixed halide Ti-based double perovskites. The calculated lattice parameters of the pure Ti-based double perovskites agree well with the available experimental values. These Ti-based double perovskites show good stability based on the calculations of their formation energies. The predicted band gaps of Cs2TiX6 (X = Cl, Br, I) within the GGA + U framework are in good agreement with their experimental values. Moreover, we find that the band gap increases slightly when inorganic cation changes from K to Rb and Cs in A2TiCl6. The electronic and optical properties can be tuned by changing the concentration of doping Cl. Cs2TiI2Cl4 has a suitable direct band gap with 1.60 eV, which is considered as an ideal candidate material for single-junction solar cells. Our study shows that the mixed halide Ti-based double perovskites can become nontoxic and environmentally stable materials with excellent optoelectronic properties for applications in perovskite solar cells.

Although numerous superior nonlinear optical (NLO) crystals for the UV-vis to the near-infrared (IR) region have been established, the development of an efficient NLO material capable of broadband second harmonic generation (SHG) in the mid-IR region is still a big challenge. In this work, we performed hybrid functional calculations to accurately assess the mid-IR NLO capabilities of a group of I3–V–VI4 compounds (with I = Ag or Cu, V = P or As, and VI = S or Se). The linear and nonlinear optical properties of these crystals were predicted and analyzed. This group of compounds display moderate optical anisotropy of refraction (0.1 > Δn > 0.03) to fulfill the phase-matching conditions. In particular, the static SHG coefficients of Cu3AsS4, Ag3PSe4 and Cu3PSe4 are predicted to be about twice that of the benchmark AgGaSe2. A detailed analysis of their precise electronic structures and local dipole moments suggests that it is the coupling of the large dipole moment vector of the constituent asymmetry [I–VI4] tetrahedron and the strong covalent character between V and VI ions that contributes to the large SHG response. These candidates would promote the development of the mid-IR NLO functional materials.

The oxygen evolution reaction (OER) is known to be the bottleneck of water-splitting. Ag3PO4 is a highly efficient visible light photocatalyst for dye degradation and water oxidation to O2, with a higher OER rate than BiVO4 and WO3. Despite extensive studies on Ag3PO4, the surface properties including surface electronic states, reaction sites and mechanisms of OER on Ag3PO4 surfaces are not clear at present. Herein, we reported a comparative first-principles density functional theory study of the bulk, surface properties and the mechanism of OER on the three primary low index facets of Ag3PO4: (100), (110) and (111). We revealed for the first time that the rate-limiting step of the OER on Ag3PO4 (100), (110) and (111) surfaces is the dehydrogenation of HO* (HO* → O* + H+ + e−), which is different from most reported metal oxides and nitrides like TiO2 and g-C3N4. The OER process on the (100) surface tends to proceed by following a different mechanism as that on the (110) and (111) surfaces. The illumination of the Ag3PO4 (100), (110), and (111) surfaces with solar light provides enough overpotential for the OER to proceed spontaneously. In particular, the free energy change of removal of the first proton from water on the Ag3PO4 (111) surface is much lower than that on (100) and (110) surfaces, giving an explanation for the experimentally observed higher catalytic activity of the (111) surface. The exposed phosphorus atoms on the Ag3PO4 (111) surface promote the dehydrogenation of H2O and suppress the formation of mid-gap states. Our results are profound for understanding the underlying mechanism of the photocatalytic water oxidation process occurring on Ag3PO4 surfaces, and serve as a foundation for developing new high-performance Ag3PO4 based photocatalysts for water splitting and organic contaminant decomposition.

The finding that transition metals on Mo2C-supported nanocatalysts are promising for water-gas shift (WGS) reactions at room temperature has generated much excitement. However, the progress achieved with computational chemistry in this area is far behind that of experimental studies. Accordingly, density functional theory (DFT) calculations have been used to design the catalytic activity center structure and study the stabilities and catalytic performances of transition metals doped on β-Mo2C(001) surfaces. A new catalyst that comprises atomically dispersed Pt over Mo2C was designed using DFT. The bimetallic Mo2C surfaces doped with single metal Pt exhibit catalytic activities similar to those of the Pt systems for WGS, while demonstrating the advantages of lower costs and higher thermal stabilities. Importantly, the Pt@Mo2C catalyst is more efficient than the pure Pt catalyst for H2 production under the same reaction conditions. Meanwhile, the density of active sites of Pt@Mo2C(001) for H2 production is considerably increased due to its highly dispersed Pt structure. Therefore, Mo and Pt can synergistically increase H2 production. These findings are significantly beneficial for establishing the relationship between the structure and characteristics of the catalyst, understanding the catalytic activities of single-atom catalysts, and gaining insight into the feasibility of developing substitutes for expensive noble metal catalysts.

Preferential oxidation of the H2 impurity in CO streams is crucial for the catalytic conversion of CO into ethylene glycol. It is uncertain as to whether H2 can overthrow the dominance of CO and finally lead the reaction. Not only is this a typical research issue, but it is also extremely critical for practical applications. So far, no catalyst has shown selectivity higher than 50 % owing to competitive adsorption of CO. In this work, we report a PdClx-based catalyst that can readily overcome the challenge mentioned above. Over this catalyst, the selectivity of H2 oxidation is promoted by more than 40 % relative to that over the conventional Pd/Al2O3 catalyst and reaches a value of 87 %. The turnover frequency of undesired CO oxidation is inhibited by at least one order of magnitude. We found that the reconstructed palladium chloride was highly selective to this reaction by facile inhibition of the adsorption and oxidation of CO.

Development of nonprecious metal-based electrocatalysts with highly efficient oxygen reduction reaction (ORR) has increasingly attracted wide attention in energy conversion and storage systems. In this work, we stepwise grow cobalt chelated COF TpBpy (Co-TpBpy) on silica nanospheres to form core–shell SiO2@Co-TpBpy nanospheres. After calcination high temperatures and removing silica template, cobalt subnanoclusters dispersed in N-doped carbon (N/C) nanocages are obtained for ORR. As a result, the Co-TpBpy-800 nanocages exhibit highly efficient activity on electrocatalytic ORR with 0.831 V of half-wave potential and high stability. Moreover, DFT calculation verifies the resulting unique nanocages reveal an unconventional five-step ORR process in which it skips the intermediate OOH* because the oxygen dissociation and adsorption directly occur on the catalyst surface. The present work will help the development of highly-efficient nonprecious metal-based catalysts for various energy applications.

Recently, 2D ferromagnets have emerged as a hot research topic, especially after the exfoliation of monolayer ferromagnetic Fe3GeTe2 from its bulk structure (Nature 2018, 563, 94; Nat. Mater. 2018, 17, 778). In this work, we systematically report the adsorption behavior of CO, CO2, H2, H2O, NO, and O2 on the pristine and Te-deficient Fe3GeTe2 (FGT and d-FGT) monolayer using hybrid density functional theory. We find that the toxic gas molecules (CO and NO) and O2 molecular are chemically anchored at the surface of the pristine FGT, while the H2O, CO2, and H2 are physically associated with FGT. Interestingly, the introduction of Te deficiency would significantly enhance the covalent interactions between the substrate and the gas molecules, especially for CO2 and H2O, whose adsorption type has evolved from physisorption to chemisorption. Furthermore, the adsorption capacity of (d-)FGT to gas molecules is found to be stronger than that of the two well-studied 2D materials: MoS2 and MXenes. Meanwhile, the adsorption changes the electronic structure of (d-)FGT but does not change the metallicity of FGT. This work provides a valuable reference for the application of 2D metallic ferromagnetic materials in the field of catalysis, sensors, gas storage, and environmental remediation.

Cost-effective CO2 conversion to highly demanded fuels or chemicals is challenging. Accordingly, a nanostructured Ni/CeO2-SGM catalyst synthesized by a simple sol-gel method was developed to make progress in this area for CO2 methanation. CO2 conversion reached 80.5 % and the achieved CH4 selectivity was as high as 95.8 % even at a temperature as low as 250 oC under a high gas hourly space velocity of 40,000 mL·g−1·h−1 for 106 h over Ni/CeO2-SGM. The activity of Ni/CeO2-SGM is 2–48 times of the state-of-the-art Ni/CeO2 catalysts. It was found that the high-performance mainly results from a formate pathway via a *CHO intermediate along with the significant synergy of efficient dissociation of H2 by small nickel NPs and the strong adsorption and activation of CO2 by CeO2 support. The findings with the performance of nanostructured Ni/CeO2-SGM and the associated reaction mechanism, will be significantly beneficial to development of new generation of CO2 methanation catalysts.

LiB3O5 (LBO), although with high nonlinearity, is angular non-phase matched in deep ultraviolet second harmonic generation (SHG) processes due to its small birefringence. The structural configuration distortion is a promising way to improve the birefringence. By means of first principles computations, the effect of strain along the a, b and c-axes on the birefringence of LBO is systematically predicted in this work. We find that the birefringence can be effectively and considerably enhanced (to 0.075 at 266 nm) by applying a rather weak strain (0.42 GPa) along the c-axis. Such a strain-induced increase in the birefringence of LBO is favourable for extending the shortest wavelength that can be produced by means of the SHG process. The results indicate that strain-engineering is an effective strategy for enhancing birefringence, which behaves like a switch to control the generation of deeper coherent light output for some nonlinear optical crystals.

Mediating the backbone coplanarity and solubility of oligothiophenes, especially the head-to-head (HH) disubstituted bithiophene, to achieve an optically and electronically advantageous building block for organic semiconductor materials is a vital yet challenging task. On the other hand, exploring polymer solar cells (PSCs) processed from nonhalogenated solvents is necessary toward their large-scale applications. In this contribution, we develop a HH-type bithiophene analogue (TIPS-T2) by strategically applying the triisopropylsilylethynyl (TIPS) scaffold as the side chain. TIPS can serve to narrow optical band gaps, lower the highest occupied molecular orbital level, reduce intrachain steric hindrance, and guarantee sufficient solubility of the involving polymers. Upon alternating with difluorobenzotriazole (FTAZ) or benzodithiophene-4,8-dione (BDD) acceptor units, two polymers named PT4Si-FTAZ and PT4Si-BDD are synthesized. Encouragingly, non-fullerene PSCs incorporating PT4Si-FTAZ yield a power conversion efficiency of 6.79% when processed from an environment-friendly solvent of trimethylbenzene because of its promoted backbone planarity, as demonstrated by density functional theory, higher hole mobility, and superior film morphology. The results indicate that TIPS-T2 is a promising building block for constructing photovoltaic polymers, and our findings offer an avenue for the ingenious use of TIPS as functional side chains.

Fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2) are evaluated as hybrid functional additives to improve the electrochemical performance of SiC-based lithium-ion batteries. When added to the electrolyte, FEC + LiPO2F2 significantly enhance the performance of SiC/Li cells. The capacity retention increases from 28.5% to 76.2% after 200 cycles. The effects of FEC + LiPO2F2 are characterized by charge–discharge testing, electrochemical impedance spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. Combining the results of these analyses reveals that hybrid functional additives are beneficial for forming a uniform and thinner solid–electrolyte interface film on the SiC surface. The solid–electrolyte interface film derived from FEC + LiPO2F2 greatly inhibits particle pulverization and electrolyte decomposition, which play an important role in the performance of SiC-based cells.

We examined the potential catalytic role of the palladium chloride catalyst in CO oxidation using density functional theory and experimental investigations. The active plane of the palladium chloride catalyst is identified as (140). We found that the defective PdCl2(140) surface is able to facilitate the activation of O2 and subsequently promote the oxidation of CO. The most significant reaction channel, the Eley–Rideal mechanism (MER1), proceeds first by a peroxo-type (OOCO) intermediate formation, second by O adsorption with the first CO2 release, then by the second CO attraction and the second CO2 formation, and finally by the second CO2 desorption and restoration of the defective PdCl2(140) surface. The rate-determining step is the formation of the second CO2 in the whole catalytic cycle. Compared to the previously reported catalytic systems, the reaction activation barrier (0.54 eV) of CO oxidation in the PdCl2 catalyst is low, indicating PdCl2 as a potential high-performance catalyst for CO oxidation. The present results enrich our understanding of CO oxidation of Pd-based catalysts and provide a basis for fabricating Pd-based catalysts with high activity.

New metal-free carbon nanodot/carbon nitride (C3N4) nanocomposites have shown to exhibit high efficiency for photocatalytic solar water splitting. (J. Liu, et al., Science, 2015, 347, 970) However, the mechanism underlying the ultrahigh performance of these nanocomposites and consequently the possibilities for further improvements are not at present clear. In this work, we performed hybrid functional calculations and included long-range dispersion corrections to accurately characterize the interfacial electron coupling of the graphene quantum dot-graphitic carbon nitride composites (Gdot/g-C3N4). The results revealed that the band gap of Gdot/g-C3N4 could be engineered by changing the lateral size of Gdots. In particular, the C24H12/g-C3N4 composites present an ideal band gap of 1.92 eV to harvest a large part of solar light. More interestingly, a type-II heterojunction is formed at the interface of the Gdot/g-C3N4 composites, a desirable feature for enhanced photocatalytic activity. The charge redistribution at the interface leads to strong electron depletion above the Gdot sheet and electron accumulation below the g-C3N4 monolayer, potentially facilitating the separation of H2O oxidation and reduction reactions. Furthermore, we suggested that the photocatalytic performance of the Gdot/g-C3N4 nanocomposites can be further improved by decreasing the thickness of Gdots and tuning the size of Gdots.