Electrocatalytic Performance of 2D Monolayer WSeTe Janus Transition Metal Dichalcogenide for Highly Efficient H2 Evolution Reaction.

Nowadays, the development of clean and green energy sources is the priority interest of research due to increasing global energy demand and extensive usage of fossil fuels, which create pollutants. Hydrogen has the highest energy density by weight among all chemical fuels. For the commercial-scale production of hydrogen, water electrolysis is the best method, which requires an efficient, cost-effective, and earth-abundant electrocatalyst. Recent studies have shown that the 2D Janus transition metal dichalcogenides (JTMDs) are promising materials for use as electrocatalysts and are highly effective for electrocatalytic H2 evolution reaction (HER). Here, we report a 2D monolayer WSeTe JTMD, which is highly effective toward HER. We have studied the electronic properties of 2D monolayer WSeTe JTMD using the periodic hybrid DFT-D method, and a direct electronic band gap of 2.39 eV was obtained. We have explored the HER pathways, mechanisms, and intermediates, including various transition state (TS) structures (Volmer TS, i.e., H*-migration TS, Heyrovsky TS, and Tafel TS) using a molecular cluster model of the subject JTMD noted as W10Se9Te12. The present calculations reveal that the 2D monolayer WSeTe JTMD is a potential electrocatalyst for HER. It has the lowest energy barriers for all the TSs among other TMDs. It has been shown that the Heyrovsky energy barrier (= 8.72 kcal mol-1) in the case of the Volmer-Heyrovsky mechanism is larger than the Tafel energy barrier (= 3.27 kcal mol-1) in the Volmer-Tafel mechanism. Hence, our present study suggests that the formation of H2 is energetically more favorable via the Volmer-Tafel mechanism. This study helps to shed light on the rational design of 2D single-layer JTMD, which is highly effective toward HER, and we expect that the present work can be further extended to other JTMDs to find out the improved electrocatalytic performance.

Sonication-Induced Boladipeptide-Based Metallogel as an Efficient Electrocatalyst for the Oxygen Evolution Reaction.

Bioinspired, self-assembled hybrid materials show great potential in the field of energy conversion. Here, we have prepared a sonication-induced boladipeptide (HO-YF-AA-FY-OH (PBFY); AA = Adipic acid, F = l-phenylalanine, and Y = l-tyrosine) and an anchored, self-assembled nickel-based coordinated polymeric nanohybrid hydrogel (Ni-PBFY). The morphological studies of hydrogels PBFY and Ni-PBFY exhibit nanofibrillar network structures. XPS analysis has been used to study the self-assembled coordinated polymeric hydrogel Ni-PBFY-3, with the aim of identifying its chemical makeup and electronic state. XANES and EXAFS analyses have been used to examine the local electronic structure and coordination environment of Ni-PBFY-3. The xerogel of Ni-PBFY was used to fabricate the electrodes and is utilized in the OER (oxygen evolution reaction). The native hydrogel (PBFY) contains a gelator boladipeptide of 15.33 mg (20 mmol L-1) in a final volume of 1 mL. The metallo-hydrogel (Ni-PBFY-3) is prepared by combining 15.33 mg (20 mmol L-1) of boladipeptide (PBFY) with 3 mg (13 mmol L-1) of NiCl2·6H2O metal in a final volume of 1 mL. It displays an ultralow Tafel slope of 74 mV dec-1 and a lower overpotential of 164 mV at a 10 mA cm-2 current density in a 1 M KOH electrolyte, compared to other electrocatalysts under the same experimental conditions. Furthermore, the Ni-PBFY-3 electrocatalyst has been witnessed to be highly stable during 100 h of chronopotentiometry performance. To explore the OER mechanism in an alkaline medium, a theoretical calculation was carried out by employing the first-principles-based density functional theory (DFT) method. The computed results obtained by the DFT method further confirm that the Ni-PBFY-3 electrocatalyst has a high intrinsic activity toward the OER, and the value of overpotential obtained from the present experiment agrees well with the computed value of the overpotential. The biomolecule-assisted electrocatalytic results provide a new approach for designing efficient electrocatalysts, which could have significant implications in the field of green energy conversion.

Synergistic Niobium Doped Two-Dimensional Zirconium Diselenide: An Efficient Electrocatalyst for O2 Reduction Reaction.

The development of high-activity and low-price cathodic catalysts to facilitate the electrochemically sluggish O2 reduction reaction (ORR) is very important to achieve the commercial application of fuel cells. Here, we have investigated the electrocatalytic activity of the two-dimensional single-layer Nb-doped zirconium diselenide (2D Nb-ZrSe2) toward ORR by employing the dispersion corrected density functional theory (DFT-D) method. Through our study, we computed structural properties, electronic properties, and energetics of the 2D Nb-ZrSe2 and ORR intermediates to analyze the electrocatalytic performance of 2D Nb-ZrSe2. The electronic property calculations depict that the 2D monolayer ZrSe2 has a large band gap of 1.48 eV, which is not favorable for the ORR mechanism. After the doping of Nb, the electronic band gap vanishes, and 2D Nb-ZrSe2 acts as a conductor. We studied both the dissociative and the associative pathways through which the ORR can proceed to reduce the oxygen molecule (O2). Our results show that the more favorable path for O2 reduction on the surface of the 2D Nb-ZrSe2 is the 4e- associative path. The detailed ORR mechanisms (both associated and dissociative) have been explored by computing the changes in Gibbs free energy (ΔG). All of the ORR reaction intermediate steps are thermodynamically stable and energetically favorable. The free energy profile for the associative path shows the downhill behavior of the free energy vs the reaction steps, suggesting that all ORR intermediate structures are catalytically active for the 4e- associative path and a high 4e- reduction pathway selectivity. Therefore, 2D Nb-ZrSe2 is a promising catalyst for the ORR, which can be used as an alternative ORR catalyst compared to expensive platinum (Pt).

Illuminating the Role of Mo Defective 2D Monolayer MoTe2 toward Highly Efficient Electrocatalytic O2 Reduction Reaction.

The fuel cell is one of the solutions to current energy problems as it comes under green and renewable energy technology. The primary limitation of a fuel cell lies in the relatively slow rate of oxygen reduction reactions (ORR) that take place on the cathode, and this is an all-important reaction. An efficient electrocatalyst provides the advancement of green energy-based fuel cell technology, and it can speed up the ORR process. The present work provides the study of non-noble metal-based electrocatalyst for ORR. We have computationally designed a 3 × 3 supercell model of metal defective (Mo-defective) MoTe2 transition metal dichalcogenide (TMD) material to study its electrocatalytic activity toward ORR. This work provides a comprehensive analysis of all reaction intermediates that play a role in ORR on the surfaces of metal-deficient MoTe2. The first-principles-based dispersion-corrected density functional theory (in short DFT-D) method was implemented to analyze the reaction-free energies (ΔG) for each ORR reaction step. The present study indicates that the ORR on the surface of metal-defective MoTe2 follows the 4e- transfer mechanism. This study suggests that the 2D Mo-defective MoTe2 TMD has the potential to be an effective ORR electrocatalyst in fuel cells.

Relativistic quantum calculations to understand the contribution of f-type atomic orbitals and chemical bonding of actinides with organic ligands.

The nuclear waste problem is one of the main interests of rare earth and actinide element chemistry. Studies of actinide-containing compounds are at the frontier of the applications of current theoretical methods due to the need to consider relativistic effects and approximations to the Dirac equation in them. Here, we employ four-component relativistic quantum calculations and scalar approximations to understand the contribution of f-type atomic orbitals in the chemical bonding of actinides (Ac) to organic ligands. We studied the relativistic quantum structure of an isostructural family made of Plutonium (Pu), Americium (Am), Californium (Cf), and Berkelium (Bk) atoms with the redox-active model ligand DOPO (2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate). Crystallographic structures were available to validate our calculations for all mentioned elements except for Cf. In short, state-of-the-art relativistic calculations were performed at different levels of theory to investigate the influence of relativistic and electron correlation effects on geometrical structures and bonding energies of Ac-DOPO3 complexes (Ac = Pu, Am, Cf, and Bk): (1) the scalar (sc) and spin-orbit (so) relativistic zeroth order regular approximation (ZORA) within the hybrid density functional theory (DFT) and (2) the four-component Dirac equation with both the Dirac-Hartree-Fock (4c-DHF) and Lévy-Leblond (LL) Hamiltonians. We show that sr- and so-ZORA-DFT could be used as efficient theoretical models to first approximate the geometry and electronic properties of actinides which are difficult to synthesize or characterize, but knowing that the higher levels of theory, like the 4c-DHF, give closer results to experiments. We also performed spin-free 4c calculations of geometric parameters for the Americium and Berkelium compounds. To the best of our knowledge, this is the first time that these kinds of large actinide compounds (the largest contains 67 atoms and 421 electrons) have been studied with highly accurate four-component methods (all-electron calculations with 6131 basis functions for the largest compound). We show that relativistic effects play a key role in the contribution of f-type atomic orbitals to the frontier orbitals of Ac-DOPO3 complexes. The analysis of the results obtained applying different theoretical schemes to calculate bonding energies is also given.

Aging-Responsive Phase Transition of VOOH to V10O24·nH2O vs Zn2+ Storage Performance as a Rechargeable Aqueous Zn-Ion Battery Cathode.

Vanadium oxyhydroxide has been recently investigated as a starting material to synthesize different phases of vanadium oxides by electrochemical or thermal conversion and has been used as an aqueous zinc-ion battery (AZIB) cathode. However, the low-valent vanadium oxides have poor phase stability under ambient conditions. So far, there is no study on understanding the phase evolution of such low-valent vanadium oxides and their effect on the electrochemical performance toward hosting the Zn2+ ions. The primary goal of the work is to develop a high-performance AZIB cathode, and the highlight of the current work is the insight into the auto-oxidation-induced phase transition of VOOH to V10O24·nH2O under ambient conditions and Zn2+ intercalation behavior thereon as an aqueous zinc-ion battery cathode. Herein, we demonstrate that hydrothermally synthesized VOOH undergoes a phase transition to V10O24·nH2O during both the electrochemical cycling and aerial aging over 38-45 days. However, continued aging till 150 days at room temperature in an open atmosphere exhibited an increased interlayer water content in the V10O24·nH2O, which was associated with a morphological change with different surface area/porosity characteristics and notably reduced charge transfer/diffusion resistance as an aqueous zinc-ion battery cathode. Although the fresh VOOH cathode had impressive specific capacity at rate performance, (326 mAh/g capacity at 0.1 A/g current and 104 mAh/g capacity at 4 A/g current) the cathode suffered from a continuous capacity decay. Interestingly, the aged VOOH electrodes showed gradually decreasing specific capacity with aging at low current and however followed the reverse order at high current. At a comparable specific power of ∼64-66 W/kg, the fresh VOOH and aged VOOH after 60, 120, and 150 days of aging showed the respective energy densities of 208.3, 281.2, 269.2, and 240.6 Wh/kg. Among all the VOOH materials, the 150 day-aged VOOH cathode exhibited the highest energy density at a power density beyond 1000 W/kg. Thanks to the improved kinetics, the 150 day-aged VOOH cathode delivered a considerable energy density of 39.7 Wh/kg with a high specific power of 4466 W/kg. Also, it showed excellent cycling performance with only 0.002% capacity loss per cycle over 20 300 cycles at 10 A/g.

Elucidating the oxygen reduction reaction mechanism on the surfaces of 2D monolayer CsPbBr3 perovskite.

The oxygen reduction reaction (ORR) is an indispensable reaction in electrochemical energy converting systems such as fuel cells. Generally, reaction kinetics of the ORR is slow, and to speed it up, a practical electrocatalyst is needed. Pt-based catalysts are thermodynamically more appropriate, but due to their scarcity and high cost, they cannot be used on a commercial scale in industries. To search for non-noble metal catalysts, we have performed a theoretical study on the CsPbBr3 perovskite material as a potential candidate for the ORR. The 3D bulk crystal structure of CsPbBr3 shows a large electronic band gap (Eg) of around 2.95 eV and it cannot be used as an efficient electrocatalyst for the ORR. We have cleaved a (001) surface from the 3D CsPbBr3 perovskite and computationally designed a 2D monolayer slab structure of the CsPbBr3 material. The present study showed that the 2D monolayer structure of CsPbBr3 has a tiny band gap about 0.22 eV, and hence the 2D monolayer CsPbBr3 perovskite can be used as a cathode material for fuel cell applications. Special priority has been given to the 2D layered perovskite structure to gain insights into its ORR kinetics by employing the first principles-based density functional theory (DFT) method. This study reveals that the basal plane of the 2D CsPbBr3 perovskite exhibits excellent electrocatalytic activity toward the ORR with a four-electron reduction pathway selectivity. Both the dissociative and associative reaction mechanisms of the ORR on the surfaces of the 2D monolayer CsPbBr3 perovskite have been explored by computing the change in Gibb's free energy (ΔG). All the reaction intermediates studied here are thermodynamically favorable and the present study suggests that the ORR follows a 4e- transfer mechanism on the surface of 2D CsPbBr3 and the associative mechanism is favorable over the dissociative mechanism of the ORR. This study provides a theoretical basis for future application of 2D CsPbBr3 perovskite-based electrocatalysts for achieving an effective ORR, indicating that they are promising Pt-free candidates for fuel cell components.

Nanostructured Pt-doped 2D MoSe2: an efficient bifunctional electrocatalyst for both hydrogen evolution and oxygen reduction reactions.

Two-dimensional transition metal dichalcogenides (TMDs) are a new family of 2D materials with features that make them appealing for potential applications in nanomaterials science and engineering. Recently, these 2D TMDs have attracted significant research interest because of the abundant choice of materials with diverse and tunable electronic, optical, chemical, and electrocatalytic properties. Although, the edges of the 2D TMDs show excellent electrocatalytic performance, their basal plane (001) is inert, which hinders their industrial applications for electrocatalysis. Transition metal/chalcogen atom vacancies or doping with some other foreign atoms may be a remedy to activate the inert basal plane. Here, we have computationally designed 2D monolayer MoSe2 and studied its electronic properties with electrocatalytic activities. A Pt-atom has been doped in the pristine 2D MoSe2 (i.e., Pt-MoSe2) to activate the inert basal plane resulting in a zero band gap. This study reveals that the Pt-MoSe2 is an excellent bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) with the aid of first priciples-based hybrid density functional theory (DFT). The periodic hybrid DFT method has been applied to compute the electronic properties of both the pristine MoSe2 and Pt-MoSe2. To determine both the HER and ORR mechanisms on the surface of the Pt-MoSe2 material, non-periodic DFT calculation has been performed by considering a molecular Pt1-Mo9Se21 cluster model. The present study shows that the 2D Pt-MoSe2 follows the Volmer-Heyrovsky mechanism for the HER with energy barriers of about 9.29 kcal mol-1 and 10.55 kcal mol-1 during the H˙-migration and Heyrovsky reactions. The ORR is achieved by a four-electron transfer mechanism with the formation of two transition energy barriers of about 14.94 kcal mol-1 and 11.10 kcal mol-1, respectively. The lower energy barriers and high turnover frequency during the reactions expose that the Pt-MoSe2 can be adopted as an efficient bifunctional electrocatalyst for both the HER and ORR. The present studies demonstrate that the exceptional HER and ORR activity and stability performance shown by the MoSe2 electrocatalyst can be enhanced by Pt-doping, opening a promising concept for the sensible design of high-performance catalysts for H2 production and O2 reduction.

Pyrene-based fluorescent Ru(II)-arene complexes for significant biological applications: catalytic potential, DNA/protein binding, two photon cell imaging and in vitro cytotoxicity.

Ruthenium complexes are being studied extensively as anticancer drugs following the inclusion of NAMI-A and KP1019 in phase II clinical trials for the treatment of metastatic phase and primary tumors. Herein, we designed and synthesized four organometallic Ru(II)-arene complexes [Ru(η6-p-cymene)(L)Cl] (1), [Ru(η6-benzene)(L)Cl] (2), [Ru(η6-p-cymene)(L)N3] (3) and [Ru(η6-benzene)(L)N3] (4) [HL = (E)-N'-(pyren-1-ylmethylene)thiopene-2-carbohydrazide] that have anticancer, antimetastatic and two-photon cell imaging abilities. Moreover, in the transfer hydrogenation of NADH to NAD+, these compounds also display good catalytic activity. All the complexes, 1-4, are well characterized by spectroscopic techniques (NMR, mass, FTIR, UV-vis and fluorescence). The single crystal X-ray diffraction technique proved that the ligand L coordinates through an N,O-bidentate chelating fashion in the solid-state structures of complexes 1 and 2. The stability study of the complexes was performed through UV-visible spectroscopy. The cytotoxicities of all the complexes were screened through MTT assay and the results revealed that the complexes have potential anticancer activity against various cancerous cells (HeLa, MCF7 and A431). Studies with spectroscopic techniques revealed that complexes 1-4 exhibit strong interactions with biological molecules i.e. proteins (HSA and BSA) and CT-DNA. The density functional theory (DFT-D) method has been employed in the present study to know the interaction between DNA and complexes by calculating the HOMO and LUMO energy. A plausible mechanism for NADH oxidation has also been explored and the DFT calculations are found to be in accord with the experimental observation. Furthermore, we have investigated intracellular reactive oxygen species (ROS) generation capabilities in the MCF7 breast cancer cell line. The Hoechst/PI dual staining method confirmed the apoptosis mode of cell death. Meanwhile, complexes 1-4 show capabilities to prevent the metastasis phase of cancer cells by inhibiting cell migration.

Unveiling the role of 2D monolayer Mn-doped MoS2 material: toward an efficient electrocatalyst for H2 evolution reaction.

Two-dimensional (2D) monolayer pristine MoS2 transition metal dichalcogenide (TMD) is the most studied material because of its potential applications as nonprecious electrocatalyst for the hydrogen evolution reaction (HER). Previous studies have shown that the basal planes of 2D MoS2 are catalytically inert, and hence it cannot be used directly in desired applications such as electrochemical HER in industry. Here, we thoroughly studied a defect-engineered Mn-doped 2D monolayer MoS2 (Mn-MoS2) material, where Mn was doped in pristine MoS2 to activate its inert basal planes. Using the density functional theory (DFT) method, we performed rigorous inspection of the electronic structures and properties of the 2D monolayer Mn-MoS2 as a promising alternative to noble metal-free catalyst for effective HER. A periodic 2D slab of monolayer Mn-MoS2 was created to study the electronic properties (such as band gap, band structures and total density of states (DOS)) and the reaction pathways occurring on the surface of this material. The detailed HER mechanism was explored by creating an Mn1Mo9S21 non-periodic finite molecular cluster model system using the M06-L DFT method including solvation effects to determine the reaction barriers and kinetics. Our study revealed that the 2D Mn-MoS2 follows the most favorable Volmer-Heyrovsky reaction mechanism with a very low energy barrier during H2 evolution. It was found that the change in the free energy barrier (ΔG) during the H˙-migration (i.e., Volmer) and Heyrovsky reactions is about 10.34-10.79 kcal mol-1 (computed in the solvent phase), indicating that this material is an exceptional electrocatalyst for the HER. The Tafel slope (y) was lower in the case of the 2D monolayer Mn-MoS2 material due to the overlap of the s-orbital of hydrogen and d-orbitals of the Mn atoms in the HOMO and LUMO transition states (TS1 and TS2) of both the Volmer and Heyrovsky reaction steps, respectively. The better stabilization of the atomic orbitals in the HER rate-limiting step Heyrovsky TS2 is the key for reducing the reaction barrier, and thus the overall catalysis, indicating a better electrocatalytic performance for H2 evolution. This study focused on designing low-cost and efficient electrocatalysts for the HER using earth abundant transition metal dichalcogenides (TMDs) and decreasing the activation energy barriers by scrutinizing the kinetics of the reaction to achieve high reactivity.

Selective anticancer activities of ruthenium(II)-tetrazole complexes and their mechanistic insights.

Ruthenium-based metallotherapeutics is an interesting alternative for platinum complexes acting as anticancer agents after the entry of KP1019, NAMI-A, and TLD1339 in clinical trials. Herein, we have synthesized three new arene ruthenium(II)-tetrazole complexes viz. [Ru2(η6-p-cymene)2(2-pytz)2Cl2] (1), [Ru2(η6-p-cymene)2(3-pytz)Cl3] (2), [Ru2(η6-p-cymene)2(4-pytz)Cl3] (3) [2-pytzH = 2-pyridyl tetrazole; 3-pytzH = 3-pyridyl tetrazole; 4-pytzH = 4-pyridyl tetrazole] which have been characterized by different analytical techniques. To aid the understanding of the complex formation, reactions of the arene ruthenium(II) dimer with tetrazoles were investigated using the first principles-based Density Functional Theory (DFT) B3LYP method. Electronic structures, equilibrium geometries of the reactants and products with the first-order saddle points, reactions mechanism, the changes of enthalpy (∆H) and free energy (∆G), chemical stability, and reaction barriers of the complexes were computed using the B3LYP DFT approach. The in vitro cytotoxicity of these complexes was investigated by MTT assay on different cancer cell lines which reveal complex 2 as the most significant cytotoxic agent toward the HeLa cell line. The complexes have also shown a strong binding affinity towards CT-DNA and albumin proteins (HSA and BSA) as analyzed through spectroscopic techniques. Investigation of the mechanism of cell death by complex 2 was further performed by various staining techniques, flow cytometry, and gene expression analysis by RT-PCR. Inhibition of cell migration study has been also revealed the possibility of complex 2 to act as a prospective anti-metastatic agent.

Rapidly Reversible Organic Crystalline Switch for Conversion of Heat into Mechanical Energy.

Solid-state thermoelastic behavior-a sudden exertion of an expansive or contractive physical force following a temperature change and phase transition in a solid-state compound-is rare in organic crystals, few are reversible systems, and most of these are limited to a dozen or so cycles before the crystal degrades or they reverse slowly over the course of many minutes or even hours. Comparable to thermosalience, wherein crystal phase changes induce energetic jumping, thermomorphism produces physical work via consistent and near-instantaneous predictable directional force. In this work, we show a fully reversible thermomorphic actuator that is stable at room temperature for multiple years and is capable of actuation for more than 200 cycles at near-ambient temperature. Specifically, the crystals shrink to 90% of their original length instantaneously upon heating beyond 45 °C and expand back to their original length upon cooling below 35 °C. Furthermore, the phase transition occurs instantaneously, with little obvious hysteresis, allowing us to create real-time actuating thermal fuses that cycle between on and off rapidly.

Mechanistic Insight for Targeting Biomolecules by Ruthenium(II) NSAID Complexes.

With the enormous progress in ruthenium complexes as promising anticancer agents after the entry of KP1019, KP1339, and NAMI-A in clinical trials, herein three arene ruthenium(II) NSAID (nonsteroidal anti-inflammatory drugs) complexes viz. [Ru(η6-p-cymene)(mef)Cl] (1), [Ru(η6-p-cymene)(flu)Cl] (2), and [Ru(η6-p-cymene)(dif)Cl] (3) are synthesized, characterized, and reported. Density functional theory (DFT) calculations were performed in support of the obtained experimental results by computing the equilibrium geometries, reactions pathways, relative Gibbs free energy, stability, and reactions barriers of the complexes. The present theoretical study shows that all the proposed structures of the complexes are energetically stable and favorable, and the results obtained are in close accordance with the experiment. Further, the in vitro cytotoxicity of the complexes was explored through MTT assay on MCF-7, Hela, A549, and HEK cell lines. It was found the complex 1 and 2 are significantly cytotoxic toward the MCF-7 cell line. These complexes have also shown a strong affinity toward CT-DNA and proteins (HSA and BSA) as analyzed through spectroscopic techniques. Further investigation of the mechanism of cell death of selected complexes was carried out by various staining, flow cytometry, and gene expression analysis obtained by RT-PCR.

Raman and electrical transport properties of few-layered arsenic-doped black phosphorus.

Black phosphorus (b-P) is an allotrope of phosphorus whose properties have attracted great attention. In contrast to other 2D compounds, or pristine b-P, the properties of b-P alloys have yet to be explored. In this report, we present a detailed study on the Raman spectra and on the temperature dependence of the electrical transport properties of As-doped black phosphorus (b-AsP) for an As fraction x = 0.25. The observed complex Raman spectra were interpreted with the support of Density Functional Theory (DFT) calculations since each original mode splits in three due to P-P, P-As, and As-As bonds. Field-effect transistors (FET) fabricated from few-layered b-AsP exfoliated onto Si/SiO2 substrates exhibit hole-doped like conduction with a room temperature ON/OFF current ratio of ∼103 and an intrinsic field-effect mobility approaching ∼300 cm2 V-1 s-1 at 300 K which increases up to 600 cm2 V-1 s-1 at 100 K when measured via a 4-terminal method. Remarkably, these values are comparable to, or higher, than those initially reported for pristine b-P, indicating that this level of As doping is not detrimental to its transport properties. The ON to OFF current ratio is observed to increase up to 105 at 4 K. At high gate voltages b-AsP displays metallic behavior with the resistivity decreasing with decreasing temperature and saturating below T ∼100 K, indicating a gate-induced insulator to metal transition. Similarly to pristine b-P, its transport properties reveal a high anisotropy between armchair (AC) and zig-zag (ZZ) directions. Electronic band structure computed through periodic dispersion-corrected hybrid Density Functional Theory (DFT) indicate close proximity between the Fermi level and the top of the valence band(s) thus explaining its hole doped character. Our study shows that b-AsP has potential for optoelectronics applications that benefit from its anisotropic character and the ability to tune its band gap as a function of the number of layers and As content.

Intercalation of first row transition metals inside covalent-organic frameworks (COFs): a strategy to fine tune the electronic properties of porous crystalline materials.

Covalent-organic frameworks (COFs) have emerged as an important class of nano-porous crystalline materials with many potential applications. They are intriguing platforms for the design of porous skeletons with special functionality at the molecular level. However, despite their extraordinary structural tunability, it is difficult to control their electronic properties, thus hindering the potential implementation in electronic devices. A new family of nanoporous materials, COFs intercalated with first row transition metals, is proposed to address this fundamental drawback - the lack of electronic tunability. Using first-principles calculations, we designed 31 new COF materials in silico by intercalating all of the first row transition metals (TMs) with boroxine-linked and triazine-linked COFs: COF-TM-x (where TM = Sc-Zn and x = 3-5). We investigated their structure and electronic properties. Specifically, we predict that the band gap and density of states (DOS) of COFs can be controlled by intercalating first row transition metal atoms (TM: Sc-Zn) and fine tuned by the concentration of TMs. We also found that the d-subshell electron density of the TMs plays a main role in determining the electronic properties of the COFs. Thus intercalated-COFs provide a new strategy to control the electronic properties of materials within a porous network. This work opens up new avenues for the design of TM-intercalated materials with promising future applications in nanoporous electronic devices, where a high surface area coupled with fine-tuned electronic properties is desired.

Synthesis and Characterization of Tris-chelate Complexes for Understanding f-Orbital Bonding in Later Actinides.

An isostructural family of f-element compounds (Ce, Nd, Sm, Gd; Am, Bk, Cf) of the redox-active dioxophenoxazine ligand (DOPOq; DOPO = 2,4,6,8-tetra- tert-butyl-1-oxo-1 H-phenoxazin-9-olate) was prepared. This family, of the form M(DOPOq)3, represents the first nonaqueous isostructural series, including the later actinides berkelium and californium. The lanthanide derivatives were fully characterized using 1H NMR spectroscopy and SQUID magnetometry, while all species were structurally characterized by X-ray crystallography and electronic absorption spectroscopy. In order to probe the electronic structure of this new family, CASSCF calculations were performed and revealed these systems to be largely ionic in contrast to previous studies, where berkelium and californium typically have a small degree of covalent character. To validate the zeroth order regular approximation (ZORA) method, the same CASSCF analysis using experimental structures versus UDFT-ZORA optimized structures does not exhibit sizable changes in bonding patterns. This shows that UDFT-ZORA combined with CASSCF could be a useful first approximation to predict and investigate the structure and electronic properties of actinides and lanthanides that are difficult to synthesize or characterize.

Rotational dynamics of the organic bridging linkers in metal-organic frameworks and their substituent effects on the rotational energy barrier.

Organic bridging linkers or ligands play an important role in gas and fuel storage, CO2 capture, and controlling the radical polymerization reactions in metal-organic frameworks (MOFs) nanochannels. The rotation of the linkers causes the expansion of the pore size and pore volume in MOFs. To understand the rotational behavior of organic linkers in MOFs and the substituent effects of the linkers, we investigated the equilibrium structure, stability, potential energy curves (PECs), and rotational energy barriers of the organic bridging linkers of a series of MOF model systems imposing three constrained imaginary planes. Both the dispersion-uncorrected and dispersion-corrected density functional theory (DFT and DFT-D i.e. B3LYP and B3LYP-D3) methods with the correlation consistent double-ζ quality basis sets have been applied to study the model MOF systems [Cu4(X)(Y)6(NH3)4] (where X = organic bridging linker, and Y = HCO2). The present study found that the structural parameters and rotational energy barrier of the model MOF containing 1,4-benzendicarboxylate (BDC) linker are in accord with previous experiments. This study reveals that rotational barriers significantly differ depending on the substituents of organic linkers, and the linker dynamical rotation provides information about the framework flexibility with various potential applications in porous materials science. Changing the linkers in the MOFs could be helpful for designing various new kinds of flexible MOFs which will have many important applications in gas storage and separation, catalysis, polymerization, sensing, etc.

Achieving Fast and Efficient K+ Intercalation on Ultrathin Graphene Electrodes Modified by a Li+ Based Solid-Electrolyte Interphase.

Advancing beyond Li-ion batteries requires translating the beneficial characteristics of Li+ electrodes to attractive, yet incipient, candidates such as those based on K+ intercalation. Here, we use ultrathin few-layer graphene (FLG) electrodes as a model interface to show a dramatic enhancement of K+ intercalation performance through a simple conditioning of the solid-electrolyte interphase (SEI) in a Li+ containing electrolyte. Unlike the substantial plating occurring in K+ containing electrolytes, we found that a Li+ based SEI enabled efficient K+ intercalation with discrete staging-type phase transitions observed via cyclic voltammetry at scan rates up to 100 mVs-1 and confirmed as ion-intercalation processes through in situ Raman spectroscopy. The resulting interface yielded fast charge-discharge rates up to ∼360C (1C is fully discharge in 1 h) and remarkable long-term cycling stability at 10C for 1000 cycles. This SEI promoted the transport of K+ as verified via mass spectrometric depth profiling. This work introduces a convenient strategy for improving the performance of ion intercalation electrodes toward a practical K-ion battery and FLG electrodes as a powerful analytical platform for evaluating fundamental aspects of ion intercalation.

Reaction mechanism of the selective reduction of CO2 to CO by a tetraaza [CoIIN4H]2+ complex in the presence of protons.

The tetraaza [CoIIN4H]2+ complex (1) is remarkable for its ability to selectively reduce CO2 to CO with 45% Faradaic efficiency and a CO to H2 ratio of 3 : 2. We employ density functional theory (DFT) to determine the reasons behind the unusual catalytic properties of 1 and the most likely mechanism for CO2 reduction. The selectivity for CO2 over proton reduction is explained by analyzing the catalyst's affinity for the possible ligands present under typical reaction conditions: acetonitrile, water, CO2, and bicarbonate. After reduction of the catalyst by two electrons, formation of [CoIN4H]+-CO2- is strongly favored. Based on thermodynamic and kinetic data, we establish that the only likely route for producing CO from here consists of a protonation step to yield [CoIN4H]+-CO2H, followed by reaction with CO2 to form [CoIIN4H]2+-CO and bicarbonate. This conclusion corroborates the idea of a direct role of CO2 as a Lewis acid to assist in C-O bond dissociation, a conjecture put forward by other authors to explain recent experimental observations. The pathway to formic acid is predicted to be forbidden by high activation barriers, in accordance with the products that are known to be generated by 1. Calculated physical observables such as standard reduction potentials and the turnover frequency for our proposed catalytic cycle are in agreement with available experimental data reported in the literature. The mechanism also makes a prediction that may be experimentally verified: that the rate of CO formation should increase linearly with the partial pressure of CO2.