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Developing high‐performance electrocatalysts for urea production using CO2 and N2 holds great potential to mitigate environmental pollution and energy crisis. In this study, 26 kinds of quadruple TM2B2 ensembles supported on porous C2N monolayer are designed as the potential electrocatalysts, with the expectation to provide sufficient space for the co‐adsorption of CO2 and N2 and fulfill a synergistic effect of transition metal (TM) and boron atoms. Cr2B2@C2N is selected as the promising electrocatalyst with a record‐low limiting potential of −0.37 V (vs RHE) in the neutral environment, by using a three‐step screening strategy, i.e., stability of the catalyst, adsorption pattern of N2, and desorption of urea. With the help of artificial intelligence approaches, simple geometric and electronic descriptors are identified for the selectivity and activity of the electrocatalysts, which correlate strongly with the TM‐B distance and the number of d electrons and electronegativity of TM atoms. The geometric descriptor narrows the scope to the early‐TM‐containing systems while the electronic descriptor produces the Cr‐containing system. Results of this study provide a novel perspective to the electrochemical synthesis of urea that is useful to the rational design of effective electrocatalyst toward urea production. [ABSTRACT FROM AUTHOR]

Electrochemical NO reduction reaction (NORR) to NH3 emerges as a fascinating approach to achieve both the migration of NO pollutant and the green synthesis of NH3. In this contribution, within the framework of computational hydrogen model and constant-potential implicit solvent model, the NORR electrocatalyzed by a novel transition-metal-anchored SnOSe armchair nanotube (TM@SnOSe_ANT) was investigated using density functional theory calculations. Through the checking in terms of stability, activity, and selectivity, Sc- and Y@SnOSe_ANTs were screened out from the twenty-five candidates. Considering the effects of pH, solvent environment, as well as applied potential, only Sc@SnOSe_ANT is found to be most promising. The predicted surface area normalized capacitance is 11.4 µF/cm2, and the highest NORR performance can be achieved at the URHE of −0.58 V in the acid environment. The high activity originates from the mediate adsorption strength of OH. These findings add a new perspective that the nanotube can be served as a highly promising electrocatalyst towards NORR. [ABSTRACT FROM AUTHOR]

Developing high‐performance electrocatalysts for the CO2 reduction reaction (CO2RR) holds great potential to mitigate the depletion of fossil feedstocks and abate the emission of CO2. In this contribution, using density functional theory calculations, we systematically investigated the CO2RR performance catalyzed by TM2−B2 (TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) supported on a defective C3N monolayer (V‐C3N). Through the screening in terms of stability of catalyst, activity towards CO2 adsorption, and selectivity against hydrogen evolution reaction, Mn2−, Fe2−, Co2−, and Ni2−B2@V−C3N were demonstrated to be a highly promising CO2RR electrocatalyst. Due to quadruple active sites, these candidates can adsorb two or three CO2 molecules. Strikingly, different products, distributing from C1 to C2+, can be generated. The high activity originates from the synergistic effect of TM and B atoms, in which they serve as adsorption sites for the C‐ and O‐species, respectively. The high selectivity towards C2+ products at the Fe2−, and Ni2−B2 sites stems from moderate C adsorption strength but relatively weak O adsorption strength, in which a universal descriptor, that is, 0.6 ΔEC−0.4 ΔEO=−1.77 eV (ΔEC/ΔEO is the adsorption energy of C/O), was proposed. This work would offer a novel perspective for the design of high active electrocatalysts towards CO2RR and for the synthesis of C2+ compounds. [ABSTRACT FROM AUTHOR]

Developing efficient strategies to optimize the performance of electrocatalysts is essential for practical applications of electrochemical CO2 reduction, which, however, remains a great challenge. In this work, by means of density functional theory calculations, we report a surface defect-size engineering strategy to optimize the catalytic activity of two-dimensional SnSe2 nanosheets for CO2 reduction. Our results show that the basal plane of SnSe2 can be activated through the formation of an Se vacancy, where the CO2 can be efficiently captured and reduced into CH4 with a low limiting potential of −0.58 V. In addition, a structure–activity relationship has been established, which shows that the limiting potential can be further reduced by adopting external strain to tailor the Se vacancy to an optimal size. This work not only highlights a very promising catalyst for CO2 reduction but also provides an efficient way to tailor the catalysts to achieve enhanced activities and high selectivity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A multi-functional spintronic device based on 1,4,5,8-naphthalenetetracarboxylic diimide (NTCDI) was studied theoretically. • Remarkable NDR, spin filtering effect and spin rectification can be found in this model device. • An on/off ratio in the magnitude of 105 was achieved, enabling molecular switching. By using a combination of density functional theory (DFT) and nonequilibrium Green's function (NEGF) method, spin-resolved electronic transport behaviors of the device made of 1,4,5,8-naphthalenetetracarboxylic diimide (NTCDI) connected to two semi−infinite zigzag edged graphene nanoribbon (ZGNR) electrodes was analyzed theoretically. The results prove that the device has negative differential resistance (NDR) effect and perfect spin filtering effect under parallel (P) and anti-parallel (AP) structures, and there are a large spin rectification and perfect dual-spin filtering effect in AP configuration. Besides, by regulating the relative dihedral angle between the NTCDI molecule and ZGNR electrode planes, an on/off ratio in the magnitude of 105 was also achieved, enabling molecular switching. To further validate these characteristics, we analyzed the band structures, spin-resolved transmission spectra, and molecular orbitals' spatial distribution within the bias window. The proposed configuration with the intriguing properties enables its potential application in multi-functional nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Using density functional theory calculations, we systematically investigated the effects of numbers and types of transition metals (TM) on the magnetic property of SnSe2 bilayer nanosheet. Our results revealed that, when one TM is introduced into the interlayer, the magnetic moment induced by the Co and Ni is tiny while it is largely strengthened with the doping of V, Cr, Mn, and Fe. When two TMs are inserted into the interlayer, V and Cr make the system change into a weak antiferromagnetism (AFM) state while Mn-, Fe-, Co-doped systems display a weak ferromagnetism (FM) ground state. These FM states have the magnetic moments which double those of the one TM-doping systems. With the TM numbers further increasing to four, the robust AFM and FM features appear with the doping of Fe and Mn, respectively. Ni cannot induce any magnetism whatever the numbers of Ni are filling in. Interestingly, with the increase of the numbers of dopants, transitions from FM to AFM and AFM to FM are predicted to be realized on Fe-SnSe2 and Cr-SnSe2 systems, respectively. This kind of transition may be important for the applications in spintronic devices.ᅟ [ABSTRACT FROM AUTHOR]

Atomically precise Ni 6 (SC 2 H 4 Ph) 12 nanoclusters (Ni 6 NCs) supported on g-C 3 N 4 nanosheets were constructed to enhance the photocatalytic hydrogen evolution performances. [Display omitted] Much effort has been devoted to improving the photocatalytic capacity of graphitic carbon nitride (g-C 3 N 4). In this paper, we reported the successful synthesis of a hybrid photocatalyst with superb photocatalytic hydrogen production activity through decorating atomically precise Ni 6 (SC 2 H 4 Ph) 12 nanoclusters on g-C 3 N 4 nanosheets (labeled as Ni 6 /g-C 3 N 4) at room temperature. Zeta potential experiments demonstrated that the electrostatic interaction between Ni 6 and g-C 3 N 4 led to the formation of Ni 6 /g-C 3 N 4. The photocatalytic measurements revealed that the 5 %-Ni 6 /g-C 3 N 4 prepared with the original mass ratio of m(Ni 6)/m(g-C 3 N 4) = 1/20 exhibited the strongest hydrogen production activity. In the system with triethanolamine (TEOA) as the sacrifice agent, the visible-light hydrogen production rate reached up to 5.87 mmol h−1 g−1, approximately 290 times higher than that of pure g-C 3 N 4 (0.02 mmol h−1 g−1). Density functional theory (DFT) calculations testified that the above significant enhancement of photocatalytic hydrogen evolution of the hybrid photocatalyst arose from the photogenerated electrons transfer from Ni 6 to g-C 3 N 4. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed to predicted the physical properties and property-guided potential applications of group IV-V compound MX 2 (M = Si, Ge, Sn; X= N, P, As) and its Janus structure MXY (X ≠ Y). [Display omitted] • 8 out of 18 monolayers from group IV-V compound MX 2 are demonstrated to be thermodynamically, dynamically, and mechanically stable. • The screened 2D materials have suitable band edge positions, excellent solar absorption, moderate exciton binding energies, and fair light conversion rates. • The calculated piezoelectric coefficients d 11 for the MX 2 and MXY monolayers are in the range from 8.0 to 26.9 pm/V. • The property-guided potential applications in water splitting are thoroughly examined. Using first-principles calculations, we predicted the physical properties and property-guided potential applications of group IV-V compound MX 2 (M = Si, Ge, Sn; X = N, P, As) and its Janus structure MXY (X ≠ Y), which are isostructural to the synthesized compound SiP 2. We demonstrated that 8 out of 18 monolayers are stable in thermodynamics, dynamics, and mechanics. Electronic calculations showed that these monolayers are semiconducting with optimal bandgaps ranging from 0.99 to 2.33 eV. The calculated piezoelectric coefficients d 11 for the MX 2 and MXY monolayers are in the range from 8.0 to 26.9 pm/V. Moreover, our results showed that these 2D materials have suitable band edge positions, excellent solar absorption, moderate exciton binding energies, and fair light conversion rates, rendering them potential application in photocatalytic water splitting. Our results may be instructive for the design, synthesis, and applications of group IV-V compounds for the future electronic, optoelectronic devices, and hydrogen producing materials. [ABSTRACT FROM AUTHOR]

The red phosphor Sr 2 Si 5 N 8 :Eu 2+ exhibits a significant emission redshift with increasing Eu concentration, but the reason remains controversial. Here, we investigate energetic, mechanical, and electronic properties of Sr 2 Si 5 N 8 :Eu 2+ by using density-functional theory (DFT) approaches with the periodic supercell model. Total-energy calculations for Sr 2− x Eu x Si 5 N 8 ( x =0.028, 0.125, 0.5) supercells reveal that Eu 2+ ions occupy the two distinct Sr1 and Sr2 sites with almost equal preference, with a nearly even distribution of Eu 2+ on the two Sr sites, irrespective of the doping concentration. Calculations for the Debye temperature and electronic properties show that, with increasing Eu Sr1 or Eu Sr2 content, the structural rigidity decreases gradually and the occupied 5d state in the excited Eu 2+ (4f 6 5d 1 ) ion becomes more delocalized, which may result in an enlarged Stokes shift of the 5d→4f emission and thus its redshift as observed experimentally. [ABSTRACT FROM AUTHOR]

Density functional theory calculation were performed to check the possibilities of two-dimensional M 4 X 9 s (M = Ge, Se; X = S, Se, Te) as the platform for photocatalytic water splitting. [Display omitted] • The reported Ge 4 Se 9 was not active toward water splitting because of the unfavorable thermodynamics of HER and OER. • The expanded 2D M 4 X 9 series (M = Ge, Sn; X = S, Se, Te) were found to be stable in thermodynamics, thermotics, and mechanics. • The 2D M 4 X 9 series were also not the ideal candidates for water splitting, although some of them show a certain OER activity. • Ge 4 S 9 and Sn 4 S 9 have negative Poisson's ratios. By means of first-principles calculations, we systematically evaluated the possibilities of M 4 X 9 s (M = Ge, Sn; X = S, Se, Te) as the platform for photocatalytic water splitting by checking their stabilities, electronic and optical properties, carrier properties, and the free energy changes of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It was found that all the studied monolayers are stable. From the viewpoints of electronic and optical properties, the facts of suitable band gaps and band edge positions as well as good optical absorption meet with the fundamental requirements for a qualified photocatalyst toward overall water splitting. However, from the viewpoints of carrier mobility and carrier location, the electron mobilities are in moderate quantity whereas the hole mobilities are in single digits, and only Te-based materials have the feature of carrier separation, which are indicative of a low application prospect as the photocatalysts. Additionally, thermodynamic calculations clearly show that the external potential provided by the light-induced electrons and holes are insufficient to drive the HER and OER, respectively; thus, the M 4 X 9 s monolayers are not the ideal candidates for water splitting. Our results offer clear information and guidance of these novel M 4 X 9 s for the application in water splitting. [ABSTRACT FROM AUTHOR]

Inthe present work, geometric structures, electronic properties,and 4f → 5d transitions of γ-Ca2SiO4:Ce3ꘚⲦᨫ have been investigated by using first-principlescalculations. Four categories of typical substitutions (i.e., thedoping of the Ce3숫憢 the neighboring dopants/defectsand with the neighboring VO••,AlSi′, and VCa″) are taken intoaccount to simulate local environments of the Ce3隇᪵at two crystallographically different calcium sites in the γ-Ca2SiO4. Density functional theory (DFT) geometryoptimization calculations are first performed on the constructed supercellsto obtain the information about the local structures and preferredsites for the Ce3. On the basis of the optimized crystalstructures, the electronic properties of γ-Ca2SiO4:Ce3ꘚⲦᨫ are calculated with the Heyd–Scuseria–Ernzerhofscreened hybrid functional, and the energies and relative oscillatorstrengths of the 4f → 5d transitions of the Ce3檷 derived from the ab initioembedded clustercalculations at the CASSCF/CASPT2/RASSI-SO level. A satisfactory agreementwith the available experimental results is thus achieved. Moreover,the relationships between the dopants/defects and the electronic aswell as spectroscopic properties of γ-Ca2SiO4:Ce3ꘚⲦᨫ have been explored. Such informationis vital, not least for the design of Ce3+based phosphorsfor the white light-emitting diodes (w-LEDs) withexcellent performance. [ABSTRACT FROM AUTHOR]

Abstract: By combination of experiments and density functional theory calculations, we present a simple but effective “facet dependent binding and etching” strategy for non-enzymatic and non-aggregated colorimetric sensing of blood uric acid (UA), using unmodified Ag nanoprisms as the signal readout. In the absence of UA, the triangular Ag nanoprisms are etched alongside (110) facets by H2O2 and form round nanodiscs, and a more than 160nm surface plasmon resonance (SPR) blue shift is observed. Because of special affinity between UA and side facets of the Ag nanoprisms, pre-added UA can well protect the Ag nanoprisms from etching. Such protection effect can be used for well quantifying UA in the range of 10–3000nM, based on the inverse proportion of the SPR blue shift with the added analyte. Due to very thin plate morphology (5nm) and facet dependent binding/etching effects of the Ag nanoprisms, the sensing system has ultrahigh sensitivity. The detection limit is only 10nM, which is about 2 to 4 orders of magnitude lower than that of previous colorimetric sensing systems. In addition to accurate quantitation, the proposed strategy can conveniently discriminate the patient of hyperuricemia from normal person by naked eyes. So, the present simple, low-cost and visualized UA chemosensor has great potential in the applications for point-of-care diagnostics. [Copyright &y& Elsevier]

TheCe3+ions occupying the two crystallographicallydistinct Y3+sites both with C1point group symmetry in the X2-Y2SiO5(X2-YSO)crystal are discriminated by their spectroscopic properties calculatedwith ab initioapproaches and phenomenological modelanalyses. Density functional theory (DFT) calculations with the supercellapproach are performed to obtain the local structures of Ce3+, based on which the wave function-based embedded cluster calculationsat the CASSCF/CASPT2 level are carried out to derive the 4f →5d transition energies. From the ab initiocalculatedenergy levels and wave functions, the crystal-field parameters (CFPs)and the anisotropic g-factor tensors of Ce3+are extracted. The theoretical results agree well with availableexperimental data. The structural and spectroscopic properties forthe two types of Ce3+ions in X2-YSO are thus distinguishedin terms of the calculated local atomic structures, 4f → 5dtransition energies, and spectral parameters. [ABSTRACT FROM AUTHOR]