Covalent Organic Framework Catalyzed Amide Synthesis Directly from Alcohol Under Red Light Excitation.

The dehydrogenative coupling of alcohols and amines to form amide bonds is typically catalysed by homogeneous transition metal catalysts at high temperatures ranging from 130-140 °C. In our pursuit of an efficient and recyclable photocatalyst capable of conducting this transformation at room temperature, we report herein a COF-mediated dehydrogenative synthesis. The TTT-DHTD COF was strategically designed to incorporate a high density of functional units, specifically dithiophenedione, to trap photogenerated electrons and effectively facilitate hydrogen atom abstraction reactions. The photoactive TTT-DHTD COF, synthesized using solvothermal methods showed high crystallinity and moderate surface area, providing an ideal platform for heterogeneous amide synthesis.  Light absorption by the COF across the entire visible range, narrow band gap, and valence band position make it well-suited for the efficient generation of excitons necessary for targeted dehydrogenation. Utilizing red light irradiation and employing extremely low loading of the COF, we have successfully prepared a wide range of amides, including challenging secondary amides, in good to excellent yields. The substrate's functional group tolerance, very mild reaction conditions, and the catalyst's significant recyclability represent substantial advancements over prior methodologies.

Hydrogen Evolution in Neutral Media by Differential Intermediate Binding at Charge-Modulated Sites of a Bimetallic Alloy Electrocatalyst.

The energy barrier to dissociate neutral water has been lowered by the differential intermediate binding on the charge-modulated metal centers of Co85Mo15 sheets supported on Ni-foam (NF), where the overpotential for hydrogen evolution reaction (HER) in 1 M phosphate buffer solution (PBS) is only 50±9 mV at -10 mA cm-2. It has a turnover frequency (TOF) of 0.18 s-1, mass activity of 13.2 A g-1 at -200 mV vs. reversible hydrogen electrode (RHE), and produces 16 ml H2 h-1 at -300 mV vs. RHE, more than double that of 20 % Pt/C. The Moδ+ and Coδ- sites adsorb OH*, and H*, respectively, and the electron injection from Co to H-O-H cleaves the O-H bond to form the Mo-OH* intermediate. Operando spectral analyses indicate a weak H-bonded network for facilitating the H2O*/OH* transport, and a potential-induced reversal of the charge density from Co to the more electronegative Mo, because of the electron withdrawing Co-H* and Mo-OH* species. Co85Mo15/NF can also drive the complete electrolysis of neutral water at only 1.73 V (10 mA cm-2). In alkaline, and acidic media, it demonstrates a Pt-like HER activity, accomplishing -1000 mA cm-2 at overpotentials of 161±7, and 175±22 mV, respectively.

Urea Production on Metal-Free Dual Silicon Doped C9 N4 Nanosheet Under Ambient Conditions by Electrocatalysis: A First Principles Study.

The development of cheap, eco-friendly electrocatalysts for urea synthesis which avoids the traditional nitrogen reduction to form ammonia, is very important to meet our growing demand for urea. Herein, based on density functional theory, we propose a novel electrocatalyst (dual Si doped C9 N4 nanosheet) composed of totally environmentally benign non-metal earth abundant elements, which is able to adsorb N2 and CO2 together. Reduction of CO2 to CO happens, which is then inserted into activated N-N bond, and it produces *N(CO)N intermediate, which is the crucial step for urea formation. Eventually following several proton coupled electron transfer processes, urea is formed under ambient conditions. The limiting potential value for urea formation is found to be lower than that of NH3 formation and HER (hydrogen evolution reaction). Moreover, the faradaic efficiency of our proposed catalyst system is 100 % for urea formation, which suggests greater selectivity of urea formation over other competitive reactions.

Boosting photo-assisted efficient electrochemical CO2 reduction reaction on transition metal single-atom catalysts supported on the C6N6 nanosheet.

CO2 reduction to value-added chemicals turns out to be a promising and efficient approach to resolve the increasing energy crisis and global warming. However, the catalytic efficiency of CO2 reduction reaction (CO2RR) to form C1 products (CO, HCOOH, CH3OH, CH4) needs to be quite efficient. Herein with the help of density functional theory, CO2RR towards C1 products was investigated on a transition metal (TM = Fe, Co, Ni) embedded C6N6 framework. The stable geometry of the catalysts, CO2 adsorption configurations, and CO2RR mechanisms were systematically studied for all the systems considered. The possible different adsorption configurations and adsorption energy calculations indicated that CO2 could be chemically adsorbed on the Co@C6N6 system. On the other hand, physical adsorption of CO2 is more preferable on Fe@C6N6 and Ni@C6N6 systems. As a competitive reaction, hydrogen evolution reaction (HER) was investigated and the systems were found to show more selectivity for CO2RR than for HER. OCHO formation turned out to be more favorable than COOH formation as initial protonation intermediates for CO2RR on the TM@C6N6 systems. The present work demonstrates that the Co@C6N6 catalyst can favor the electrocatalytic CO2RR among all systems. In addition, the photocatalytic activity of the systems was also investigated. The systems are found to be active for photoreduction of CO2 to CH3OH and CH4 in the presence of reducing agents such as H2 and H2O as they possess appropriate absorption spectrum in the visible region as well as suitable band edge positions. These findings open a way for designing single atom catalysts for important catalytic reactions.

Lattice Mismatch Guided Nickel-Indium Heterogeneous Alloy Electrocatalysts for Promoting the Alkaline Hydrogen Evolution.

The immiscibility of crystallographic facets in multi-metallic catalysts plays a key role in driving the green H2 production by water electrolysis. The lattice mismatch between tetragonal In and face-centered cubic (fcc) Ni is 14.9 % but the mismatch with hexagonal close-packed (hcp) Ni is 49.8 %. Hence, in a series of Ni-In heterogeneous alloys, In is selectively incorporated in the fcc Ni. The 18-20 nm Ni particles have 36 wt % fcc phase, which increases to 86 % after In incorporation. The charge transfer from In to Ni, stabilizes the Ni0 state and In develops a fractional positive charge that favors *OH adsorption. With only 5 at% In, 153 mL h-1 H2 is evolved at -385 mV with mass activity of 57.5 A g-1 at-400 mV, 200 h stability at -0.18 V versus reversible hydrogen electrode (RHE), and Pt-like activity at high current densities, due to the spontaneous water dissociation, lower activation energy barrier, optimal adsorption energy of OH- ions and the prevention of catalyst poisoning.

Anchoring boron on a covalent organic framework as an efficient single atom metal-free photo-electrocatalyst for nitrogen fixation: a first-principles analysis.

The production of ammonia in a sustainable cost-effective manner and ambient conditions is a very challenging task. Photo-/electrocatalytic nitrogen reduction (NRR) is a convenient way to produce NH3 for industrial applications. In this work, anchoring B atoms in Tp-bpy-COF is shown to effectively reduce N2 to NH3. By employing density functional theory, we demonstrated that N2 can be efficiently activated on the B center due to the synergistic effect of B-N. Meanwhile, we found that the NRR happens predominantly by the alternating path with a small limiting potential of 0.13 V. Moreover, the suitable band edge positions and broad visible light absorption zone result in B@Tp-bpy-COF acting as a promising photocatalyst. Our proposed catalytic system exhibits favorable formation energy and excellent structural stability during AIMD simulations, which suggest the feasibility of experimental synthesis. The system turns out to be highly selective toward the NRR compared to other competitive reactions. These findings may pave a new way for designing SACs on COFs for N2 fixation with high activity, which may also apply to other reactions.

Phenothiazine Embedded Dithiasmaragdyrins.

Two different types of novel phenothiazine-embedded dithiasmaragdyrins containing one phenothiazine ring, two thiophene rings and two pyrrole rings connected via three meso carbons and two direct bonds in the macrocyclic framework were synthesized over the sequence of synthetic steps starting with phenothiazine. Three examples of phenothiazine-embedded dithiasmaragdyrins were synthesized by condensing appropriate phenothiazine-based pentapyrrane with pentafluorobenzaldehyde and two examples of phenothiazine sulfone embedded dithiasmaragdyrins were synthesized by condensing phenothiazine-based diol with appropriate meso-aryl dipyrromethane under mild acid-catalysed conditions. 1D&2D NMR studies revealed that the thiophene rings adopted inverted orientation in phenothiazine sulfone embedded dithiasmaragdyrins whereas in phenothiazine-embedded dithiasmaragdyrins, the thiophene rings were in normal orientation. Both types of macrocycles exhibit nonaromatic absorption features and showed panchochromic absorption features in its neutral and protonated forms. The electrochemical studies indicated that the phenothiazine-embedded dithiasmaragdyrins were more electron-rich compared to phenothiazine sulfone embedded dithiasmaragdyrins. DFT studies revealed that both types of dithiasmaragdyrins exhibit significantly distorted structures and TD-DFT studies support the experimental observations.

High Ammonia Yield Rate from Dilute Nitrate Solutions Using a Cu(100)-Rich Foil: A Step Closer to Large-Scale Production.

The electrochemical reduction of nitrate (NO3-) ions to ammonia (NH3) provides an alternative method to eliminate harmful NO3- pollutants in water as well as to produce highly valuable NH3 chemicals. The NH3 yield rate however is still limited to the µmol h-1 cm-2 range when dealing with dilute NO3- concentrations found in waste streams. Copper (Cu) has attracted much attention because of its unique ability to effectively convert NO3- to NH3. We have reported a simple and scalable electrochemical method to produce a Cu foil having its surface covered with a porous Cu nanostructure enriched with (100) facets, which efficiently catalyzes NO3- to NH3. The Cu(100)-rich electrocatalyst showed a very high NH3 production rate of 1.1 mmol h-1 cm-2 in NO3- concentration as low as 14 mM NO3-, which is 4-5 times higher than the best-reported values. Increasing the NO3- concentration (140 mM) resulted in an NH3 production yield rate of 3.34 mmol h-1 cm-2. The durability test conducted for this catalyst foil in a flow cell system showed greater than 100 h stability with a Faradaic efficiency greater than 98%, demonstrating its potential to be used on an industrially relevant scale. Further, density functional theory (DFT) calculations have been performed to understand the better catalytic activity of Cu(100) compared to Cu(111) facets toward NO3-RR.

Transition from Dion-Jacobson hybrid layered double perovskites to 1D perovskites for ultraviolet to visible photodetection.

New perovskite phases having diverse optoelectronic properties are the need of the hour. We present five variations of R2AgM(iii)X8, where R = NH3C4H8NH3 (4N4) or NH3C6H12NH3 (6N6); M(iii) = Bi3+ or Sb3+; and X = Br- or I-, by tuning the composition of (4N4)2AgBiBr8, a structurally rich hybrid layered double perovskite (HLDP). (4N4)2AgBiBr8, (4N4)2AgSbBr8, and (6N6)2AgBiBr8 crystallize as Dion-Jacobson (DJ) HLDPs, whereas 1D (6N6)SbBr5, (4N4)-BiI and (4N4)-SbI have trans-connected chains by corner-shared octahedra. Ag+ stays out of the 1D lattice either when SbBr63- distortion is high or if Ag+ needs to octahedrally coordinate with I-. Band structure calculations show a direct bandgap for all the bromide phases except (6N6)2AgBiBr8. (4N4)2AgBiBr8 with lower octahedral tilt shows a maximum UV responsivity of 18.8 ± 0.2 A W-1 and external quantum efficiency (EQE) of 6360 ± 58%, at 2.5 V. When self-powered (0 V), (4N4)-SbI has the best responsivity of 11.7 ± 0.2 mA W-1 under 485 nm visible light, with fast photoresponse ≤100 ms.

Inverse 'intra-lattice' charge transfer in nickel-molybdenum dual electrocatalysts regulated by under-coordinating the molybdenum center.

The prevalence of intermetallic charge transfer is a marvel for fine-tuning the electronic structure of active centers in electrocatalysts. Although Pauling electronegativity is the primary deciding factor for the direction of charge transfer, we report an unorthodox intra-lattice 'inverse' charge transfer from Mo to Ni in two systems, Ni73Mo alloy electrodeposited on Cu nanowires and NiMo-hydroxide (Ni : Mo = 5 : 1) on Ni foam. The inverse charge transfer deciphered by X-ray absorption fine structure studies and X-ray photoelectron spectroscopy has been understood by the Bader charge and projected density of state analyses. The undercoordinated Mo-center pushes the Mo 4d-orbitals close to the Fermi energy in the valence band region while Ni 3d-orbitals lie in the conduction band. Since electrons are donated from the electron-rich Mo-center to the electron-poor Ni-center, the inverse charge transfer effect navigates the Mo-center to become positively charged and vice versa. The reverse charge distribution in Ni73Mo accelerates the electrochemical hydrogen evolution reaction in alkaline and acidic media with 0.35 and 0.07 s-1 turnover frequency at -33 ± 10 and -54 ± 8 mV versus the reversible hydrogen electrode, respectively. The corresponding mass activities are 10.5 ± 2 and 2.9 ± 0.3 A g-1 at 100, and 54 mV overpotential, respectively. Anodic potential oxidizes the Ni-center of NiMo-hydroxide for alkaline water oxidation with 0.43 O2 s-1 turnover frequency at 290 mV overpotential. This extremely durable homologous couple achieves water and urea splitting with cell voltages of 1.48 ± 0.02 and 1.32 ± 0.02 V, respectively, at 10 mA cm-2.

Computational Insight into TM-N x Embedded Graphene Bifunctional Electrocatalysts for Oxygen Evolution and Reduction Reactions.

Due to the energy crisis, development of bifunctional electrocatalysts for both oxygen evolution and reduction reactions is highly demanding. In this study, we have systematically investigated the bifunctional activity of metal (Co/Rh/Ir) and N co-doped graphene systems with varying N-dopant concentrations (TM-N x @G, x = 0, 2, 4) using first-principles calculations. Charge transfer from the metal sites to the adsorbed intermediates and the adsorption free energy of the intermediates play important roles to help understand the potential-determining step and overpotential values for oxygen evolution reaction (OER)/oxygen reduction reaction (ORR). A dual volcano plot for all the systems using a common descriptor ΔG OH* has been constructed. We find that the systems having ΔG OH* values in the range of 0.40-0.70 eV can act as bifunctional electrocatalysts. Our study not only highlights the importance of metal and non-metal co-doped graphene as bifunctional catalysts but also can serve as a promising strategy for the design of efficient OER/ORR electrocatalysts.

Regioselective ring-opening of epoxides towards Markovnikov alcohols: a metal-free catalytic approach using abnormal N-heterocyclic carbene.

Herein we report the first metal-free regioselective Markovnikov ring-opening of epoxides (selectivity up to 99%) using an abnormal N-heterocyclic carbene (aNHC) to yield secondary alcohols. DFT calculations and X-ray crystallography suggest that the Markovnikov selectivity originates from the high nucleophilicity and steric factors associated with the aNHC.