Advancing electrochemical nitrogen reduction: Efficacy of two-dimensional SiP layered structures with single-atom transition metal catalysts.

Researchers are interested in single-atom catalysts with atomically scattered metals relishing the enhanced electrocatalytic activity for nitrogen reduction and 100 % metal atom utilization. In this paper, we investigated 18 transition metals (TM) spanning 3d to 5d series as efficient nitrogen reduction reaction (NRR) catalysts on defective 2D SiPV layered structures through first-principles calculation. A systematic screening identified Mo@SiPV, Nb@SiPV, Ta@SiPV and W@SiPV as superior, demonstrating enhanced ammonia synthesis with significantly lower limiting potentials (-0.25, -0.45, -0.49 and -0.15 V, respectively), compared to the benchmark -0.87 eV for the defective SiP. In addition, the descriptor ΔG*N was introduced to establish the relationship between the different NRR intermediates, and the volcano plot of the limiting potentials were determined for their potential-determining steps (PDS). Remarkably, the limiting voltage of the NRR possesses a good linear relationship with the active center TM atom Ɛd, which is a reliable descriptor for predicting the limiting voltage. Furthermore, we verified the stability (using Ab Initio Molecular Dynamics - AIMD) and high selectivity (UL(NRR)-UL(HER) > -0.5 V) of these four catalysts in vacuum and solvent environments. This study systematically demonstrates the strong catalytic potential of 2D TM@SiPV(TM = Mo, Nb, Ta, W) single-atom catalysts for nitrogen reduction electrocatalysis.

A laser-induced zinc oxide/graphene photoelectrode for a photocurrent-polarity-switching photoelectrochemical biosensor with bipedal DNA walker amplification.

A photocurrent-polarity-switching photoelectrochemical (PEC) biosensor was developed for the ultrasensitive detection of tobramycin (TOB) through bipedal DNA walker amplification with hemin-induced photocurrent-polarity-switching using a laser-induced zinc oxide/graphene (ZnO/LIG) photoelectrode. Specifically, the ZnO/LIG photoelectrode was synthesized in situ by a laser direct writing (LDW) technique. In the presence of TOB, it reacted with HP1 and HP2 and the DNA walker response was activated to form a stable hemin/G-quadruplex. Furthermore, hemin induced a polarity shift in the photocurrent signal. The developed analytical platform exhibited excellent photoelectron transport performance of ZnO/LIG, the signal amplification effect of the DNA walker strategy, and the photocurrent-polarity-switching ability of hemin. Therefore, it demonstrated satisfying photocurrent responses to the target TOB within the working range of 20 nM-1.0 µM at a low detection limit of 5.43 nM. The PEC platform exhibited good stability, reproducibility, sufficient sensitivity and high selectivity for complex experimental samples. Moreover, the photocurrent-polarity-switching PEC biosensor improved the anti-interference ability and avoided false positives or negatives.

Coordination Engineering of Heteronuclear Fe-Mo Dual-Atom Catalyst for Promoted Electrocatalytic Nitrogen Fixation: A DFT Study.

Developing efficient nanostructured electrocatalysts for N2 reduction to NH3 under mild conditions remains a major challenge. The Fe-Mo cofactor serves as the archetypal active site in nitrogenase. Inspired by nitrogenase, we designed a series of heteronuclear dual-atom catalysts (DACs) labeled as FeMoN6-a Xa (a=1, 2, 3; X=B, C, O, S) anchored on the pore of g-C3 N4 to probe the impact of coordination on FeMo-catalyzed nitrogen fixation. The stability, reaction paths, activity, and selectivity of 12 different FeMoN6-a Xa DACs have been systematically studied using density functional theory. Of these, four DACs (FeMoN5 B1 , FeMoN5 O1 , FeMoN4 O2 , and FeMoN3 C3 ) displayed promising nitrogen reduction reaction (NRR) performance. Notably, FeMoN5 O1 stands out with an ultralow limiting potential of -0.11 V and high selectivity. Analysis of the density of states and charge/spin changes shows FeMoN5 O1 's high activity arises from optimal N2 binding on Fe initially and synergy of the FeMo dimer enabling protonation in NRR. This work contributes to the advancement of rational design for efficient NRR catalysts by regulating atomic coordination environments.

A theoretical exploration of the structural feature, mechanical, and optoelectronic properties of Au-based halide perovskites A2AuIAuIIIX6 (A = Rb, Cs; X = Cl, Br, I).

As a possible alternative to lead halide perovskites, inorganic mixed-valence Au-based halide perovskites have drawn much attention. In the current research, we have conducted comprehensive theoretical calculations to reveal the structural feature, thermodynamic and dynamic stability, mechanical behavior, optoelectronic properties, and photovoltaic performance of Au-based halide perovskites A2AuIAuIIIX6 (A = Rb, Cs; X = Cl, Br, I). The structural parameters of these compounds are carefully analyzed. Our calculations indicate that the thermodynamic, dynamic, and mechanical stability of monoclinic Rb2AuIAuIIIX6 and tetragonal Cs2AuIAuIIIX6 are ensured, and they are all ductile. The electronic band structure analysis shows that Rb2AuIAuIIII6 illustrates a direct-gap feature, while Rb2AuIAuIIIX6 (X = Cl, Br) and Cs2AuIAuIIIX6 (X = Cl, Br, I) are indirect-gap materials. The effect of A-site cation substitution on the optical band gaps of the Au-based halide perovskites is elucidated. Our results further suggest that Rb2AuIAuIIIX6 (X = Br, I) and Cs2AuIAuIIIX6 (X = Cl, Br, I) are more suitable for single-junction solar cells due to their suitable band gaps within 1.1-1.5 eV. Furthermore, four compounds A2AuIAuIIIX6 (A = Rb, Cs; X = Br, I) not only have high absorption coefficients in the visible region but also show excellent photovoltaic performance, especially for A2AuIAuIIII6 (A = Rb, Cs), whose efficiency can reach over 29% with a film thickness of 0.5 µm. Our study suggests that inorganic Au-based halide perovskites are potential alternatives for optoelectronic devices in solar cells.

Iron/cobalt/nickel regulation for efficient photocatalytic carbon dioxide reduction over phthalocyanine covalent organic frameworks.

Using solar photocatalytic CO2 reduction to produce high-value-added products is a promising solution to environmental problems caused by greenhouse gases. Metal phthalocyanine COFs possess a suitable band structure and strong light absorption ability, making them a promising candidate for photocatalytic CO2 reduction. However, the relationship between the electronic structure of these materials and photocatalytic properties, as well as the mechanism of photocatalytic CO2 reduction, is still unclear. Herein, the electronic structure of three MPc-TFPN-COFs (M = Ni, Co, Fe) and the reaction process of CO2 reduction to CO, HCOOH, HCHO and CH3OH were studied using DFT calculations. The calculated results demonstrate that these COFs have a good photo response to visible light and are new potential photocatalytic materials. Three COFs show different reaction mechanisms and selectivity in generating CO2 reduction products. NiPc-TFPN-COFs obtain CO through the reaction pathway of CO2 → COOH → CO, and the energy barrier of the rate-determining step is 2.82 eV. NiPc-TFPN-COFs and FePc-TFPN-COFs generate HCHO through CO2 → COOH → CO → CHO → HCHO, and the energy barrier of the rate step is 2.82 eV and 2.37 eV, respectively. Higher energies are required to produce HCOOH and CH3OH. This work is helping in understanding the mechanism of photocatalytic reduction of CO2 in metallophthalocyanine COFs.

Computational study of the fundamental properties of Zr-based chalcogenide perovskites for optoelectronics.

Chalcogenide perovskites have recently attracted enormous attention since they show promising optoelectronic properties and high stability for photovoltaic applications. Herein, the relative stability and photoactive properties of chalcogenide perovskites AZrX3 (A = Ca, Sr, Ba; X = S, Se) including the needle-like (α phase) and distorted perovskite (ß phase) structures are first revealed. The results show that the difference in the relative stability is large between the α and ß phases for both AZrS3 and AZrSe3. The fundamental direct-gap transition is only allowed for the ß phase, which is further confirmed by its optical properties. It is indicated that the suitable direct-gap energy of the α phase is not desirable for thin-film solar cells. Therefore, the stability, and mechanical, electronic, and optical properties of the distorted chalcogenide perovskites AZrS3-xSex (x = 0, 1, 2, 3) are mainly explored for the first time. The predicted direct band gaps of nine compounds AZrS3-xSex (x = 1-3) are in the ideal range of 1.3-1.7 eV. Most compounds have small effective masses, low exciton binding energies, and high optical absorption coefficients in the visible region. Moreover, the mechanical, thermodynamic, and dynamic stabilities are identified for these compounds. Our findings suggest that CaZrSe3, SrZrSe3, and BaZrSe3 are proposed to be the most promising candidates for photovoltaic applications owing to their promising properties.

Spin regulation for efficient electrocatalytic N2 reduction over diatomic Fe-Mo catalyst.

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 MoN4 from high-spin state (2.63 µB) to medium-spin state (0.74 µB), which can effectively relieve the strong overlapping between Mo 4d orbital with the NxHy intermediates, promote the desorption of reaction product, and eventually achieve a lower limiting potential. Interestingly, the archetype of the active center of nitrogenase is also a FeMo-cofactor, which is consistent with our screening results. The work may provide new insight into the mechanism of nitrogenase, and promote the rational design of efficient NRR catalysts by atomic spin regulation.

Data-driven generation of mixed X-anion perovskite properties.

Mixed X-anion perovskites, such as CsPbX3 (X = Cl, Br, or I), play an important role in photovoltaic applications. The massive disordered structures associated with mixed anions produce the need for property calculations. However, traditional density functional theory (DFT) computational tools are limited by their computational efficiency to generate the properties of a large number of structures quickly. Researchers have proposed supervised deep learning to forecast crystal properties. For such a supervised convolutional neural network (CNN), we introduce an adversarial loss function that allows for consistent or lower errors with a fewer samples. Meanwhile, we have trained parameterized quantum circuits (PQCs) of CNNs and auto-encoder networks for extracting structural representations. PQCs of deep learning, also named quantum deep learning or quantum machine learning, have been first applied in the research of perovskites and obtained an RMSE (root mean squared error) of less than 1 meV. Our work demonstrates that adversarial learning training mechanisms and PQC-based quantum deep learning will emerge for extensive and deep exploration of data-driven material formation prediction tasks.

Discovering the desirable physical properties of arsenic compounds AB2As2 and their alloys: a theoretical study.

In the current study, 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 optimized structural parameters are highly consistent with the experimental data. The dynamic stability of four alloys is demonstrated by computing their phonon spectra. All compounds are mechanically stable and brittle materials. The results imply that both CaMg2As2 and SrMg2As2 exhibit indirect band gaps at the Γ-M symmetry point, while AZn2As2 and ACd2As2 at the Γ point exhibit direct bandgap features. Moreover, the trend of band gap reduction (∼1 eV) is presented from AMg2As2 to ACd2As2. The allowed transition from an indirect band gap to a direct band gap is observed from AMg2As2 to A(Mg0.5B0.5)2As2. Four alloys display more suitable direct band gaps (1.2-1.5 eV) for potential optoelectronic applications. In addition, these compounds possess high carrier mobility. The analysis of various optical properties is discussed in detail. This finding demonstrates that some novel compounds can be potential candidates for possible optoelectronic devices.

Near-Infrared Light-Driven Photoredox Catalysis by Transition-Metal-Complex Nanodots.

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 (λ>780 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.

Adsorption Behavior of Environmental Gas Molecules on Pristine and Defective MoSi2N4: Possible Application as Highly Sensitive and Reusable Gas Sensors.

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, O2, CO2, NO2, H2O, H2S, and NH3, on the 2D pristine and defective MoSi2N4 (MSN) monolayers were systematically investigated using spin-polarized density functional theory (DFT) calculations. Our results reveal that all the gas molecules are physically adsorbed on the MSN surface with small charge transfer, but the electronic structures of NO, NO2, and O2 are obviously modified due to the in-gap states. The introduction of N vacancy on the MSN surface enhances the interaction between gas molecules and the substrate, especially for NO2 and O2. Interestingly, the adsorption type of NO and CO evolves from physisorption to chemisorption, which may be utilized in NO and CO catalytic reaction. Furthermore, the moderate adsorption strength and obvious changes in electronic properties of H2O and H2S on the defective MSN make them have promising prospects in highly sensitive and reusable gas sensors. This work offers several promising gas sensors based on the MSN monolayer and also provides a theoretical reference of other related 2D materials in the field of gas sensors, catalysts, and toxic gas disposal.

(Li,Na)SbS2 as a promising solar absorber material: A theoretical investigation.

NaSbS2 has been proposed as a novel photovoltaic material, but its band gap is not suitable for single-junction solar cells. In the present study, the systematic first-principles calculations were carried out to investigate the structural, mechanical, electronic and optical properties of ASbS2 (A = Li, Na, K) and Na1-xLixSbS2 solid solutions. These structures show good structural stability compared to CH3NH3PbI3. The results indicate that all the structures are indirect band gap semiconductors. The band gap of ASbS2 increases gradually when the alkali metal changes from Li to K. The band gap of NaSbS2 can be tuned by manipulating the amount of Li doping. The Na1-xLixSbS2 solid solutions have suitable band gaps for light-absorber semiconductors in solar cells. Moreover, the suitable band gap of NaSbS2 can be also obtained under moderate pressure. The mechanical properties of these materials are also analyzed, and the results indicate that they are brittle materials except for KSbS2. The optical absorption coefficients of these compounds are large over 10-5 cm-1 in the visible light region. We find that alloying can provide a feasible and effective approach for improving the photovoltaic performance of NaSbS2-based solar cells.

Carbon Dioxide Conversion Upgraded by Host-guest Cooperation between Nitrogen-Rich Covalent Organic Framework and Imidazolium-Based Ionic Polymer.

Invited for this month's cover are the groups of Rongjian Sa and Ruihu Wang at Minjiang University and the Chinese Academy of Sciences. The image shows how host-guest composite catalysts with task-specific components for the cycloaddition of CO2 with epoxides have been developed through integrating nitrogen-rich covalent organic framework and imidazolium-based ionic polymer. The Full Paper itself is available at 10.1002/cssc.202006158.

Integrating single Ni sites into biomimetic networks of covalent organic frameworks for selective photoreduction of CO2.

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.

Recent Advances on Metalloporphyrin-Based Materials for Visible-Light-Driven CO2 Reduction.

Photocatalytic CO2 reduction is a promising technology to mitigate environmental issue and the energy crisis. The four nitrogen atoms in the porphyrin ring can incorporate transition metals to form stable active sites for CO2 activation and photoreduction. Nevertheless, the photocatalytic efficiency of metalloporphyrins is still low due to the insufficient photoelectron injection to drive CO2 photoreduction upon visible light irradiation. To address this issue, considerable efforts have been made to introduce photosensitizers for constructing homogeneous or heterogeneous metalloporphyrin-based photocatalytic systems. In this Review, recent advances of metalloporphyrin-based materials for visible-light-driven CO2 reduction were summarized. The methods for the modulation of photosensitizing process at molecular level were presented for the promotion of photocatalytic performance. The mechanism of CO2 activation and photocatalytic conversion was illustrated. Better insight into the structure-activity relationship provides guidance to the design of metalloporphyrin-related photocatalytic systems.

Carbon Dioxide Conversion Upgraded by Host-guest Cooperation between Nitrogen-Rich Covalent Organic Framework and Imidazolium-Based Ionic Polymer.

The chemical conversion of CO2 into value-added chemicals is one promising approach for CO2 utilization. It is crucial to explore highly efficient catalysts containing task-specific components for CO2 fixation. Here, a host-guest catalytic system was developed by integrating nitrogen-rich covalent organic framework (TT-COF) and imidazolium-based ionic polymer (ImIP), which serve as hydrogen-bonding donor and nucleophilic agent, respectively, for cooperatively facilitating the activation of the epoxides and subsequent CO2 cycloaddition. The catalytic activity of the host-guest system was remarkably superior to those of ImIP, TT-COF, and their physical mixture. Furthermore, selective adsorption for CO2 over N2 rendered this catalytic system effective for the cycloaddition reaction of the simulated flue gas. The protocols for the unification of two catalytically active components provide new opportunities for the development of composite systems in multiple applications.

Stable lead-free perovskite solar cells: A first-principles investigation.

A suitable substitution of the lead element in lead-based halide perovskites is a feasible approach to explore lead-free perovskite material with excellent stability, tunable band gap, high optical absorption, and better photovoltaic performance. In this study, the toxic lead is replaced by mixing Ba/Si and Ba/Sn to develop environmentally friendly perovskite materials with excellent properties. MABa0.125Sn0.875I3 has shown evidently improved properties in terms of structural stability and suitable band gap, which indicates that MABa0.125Sn0.875I3 can become the most potential material for applications in single-junction solar cells. Moreover, MABa0.50Sn0.50I3 and MABa0.25Sn0.75I3 can be promising materials for the top cell in the tandem architecture due to their proper band gaps (1.70-1.80 eV). Moreover, the optical absorption coefficients of the proposed lead-free perovskites are stronger than that of MAPbI3 in the range of 500-800 nm. Our work can provide new insights into exploring lead-free perovskite solar cells with excellent stability and suitable band gap.

Mixed-Cation Mixed-Metal Halide Perovskites for Photovoltaic Applications: A Theoretical Study.

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-x Cs x Pb0.25Sn0.75I3 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.

Insight into the Improved Phase Stability of CsPbI3 from First-Principles Calculations.

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 stability is greatly improved by incorporating the organic cation Az+ at the A site of CsPbI3. However, the band gap of CsPbI3 is further enlarged from 1.76 to 2.27 eV when 12.5% of Az doping is used. The optical absorption coefficient of Cs0.875Az0.125PbI3 is also decreased in the visible light region. The reasons of the improved phase stability and the enlargement of band gap arising from the organic cation doping are revealed. Our calculated results can provide theoretical guidance for improving the phase stability of halide perovskites.

Exploring electronic and optical properties of Ge-based perovskites under strain: Insights from the first-principles calculations.

Organic-inorganic hybrid perovskites have attracted extensive attention as promising photovoltiac materials for high-efficiency solar cells. In this study, strain effects on the material properties of Ge-based perovskites are fully investigated by the first-principles calculations. The results indicate that the structural, mechanical, electronic and optical properties of CH3NH3GeX3 (X = Cl, Br, I) are sensitive to external modulations. The band gaps of three Ge-based halide perovskites are well predicted by using the HSE06 functional. By increasing the compressive strain, the band gaps of three compounds decrease. A suitable band gap (1.36 eV) of CH3NH3GeI3 can be obtained under a strain of -3%. Moreover, the calculated elastic constants further imply that this compound is stable under this condition. The relationship between the band gap variation and geometry change under the compressive strain is revealed. These results are useful for understanding the effects of strain on the material properties of semiconductors and guiding the experiments to improve photovoltaic performance of Ge-based perovskites.