Microscopic-Level Insights into P-O-Induced Strong Electronic Coupling Over Nickel Phosphide with Efficient Benzyl Alcohol Electrooxidation.

Electrooxidation of biomass into fine chemicals coupled with energy-saving hydrogen production for a zero-carbon economy holds great promise. Advanced anode catalysts determine the cell voltage and electrocatalytic efficiency greatly, further the rational design and optimization of their active site coordination remains a challenge. Herein, a phosphorus-oxygen terminals-rich species (Ni2 P-O-300) via an anion-assisted pyrolysis strategy is reported to induce strong electronic coupling and high valence state of active nickel sites over nickel phosphide. This ultimately facilitates the rapid yet in-situ formation of high-valence nickel with a high reaction activity under electrochemical conditions, and exhibits a low potential of 1.33 V vs. RHE at 10 mA cm-2 , exceeding most of reported transition metal-based catalysts. Advanced spectroscopy, theoretical calculations, and experiments reveal that the functional P-O species can induce the favorable local bonding configurations for electronic coupling, promoting the electron transfer from Ni to P and the adsorption of benzyl alcohol (BA). Finally, the hydrogen production efficiency and kinetic constant of BA electrooxidation by Ni2 P-O-300 are increased by 9- and 2.8- fold compared with the phosphorus-oxygen terminals-deficient catalysts (Ni2 P-O-500). This provides an anion-assisted pyrolysis strategy to modulate the electronic environment of the Ni site, enabling a guideline for Ni-based energy/catalysis systems.

A Ferricyanide Anion-Philic Interface Induced by Boron Species within Carbon Framework for Efficient Charge Storage in Supercapacitors.

Carbon materials with hierarchical porous structures hold great potential for redox electrolyte-enhanced supercapacitors. However, restricted by the intrinsic inert and nonpolar characteristics of carbon, the energy barrier of anchoring redox electrolytes on the pore walls is relatively high. As such, the redox process at the interface less occurs, and the rate of mass transfer is impaired, further leading to a poor electrochemical performance. Here, a ferricyanide anion-philic interface made of in situ inserted boron species into carbon rings is constructed for enhanced charge storage in supercapacitors. Profiting from the unique component-driven effects, the polar anchoring sites on the pore wall can be built to grasp the charged redox ferricyanide anion from the bulk electrolyte and promote the redox process; the dynamics process is fastened correspondingly. Especially, the boron atoms in BC2O and BCO2 units with higher positive natural bond orbital values in the carbon skeleton are pinpointed as intrinsic active sites to bind the negatively charged nitrogen atoms in the ferricyanide anion via electrostatic interaction, confirmed by density functional theoretical calculations. This will suppress the shuttle and diffusion effects of the ferricyanide anion from the surface of the electrode to the bulk electrolyte. Finally, the well-designed PC-3 with high content of BC2O and BCO2 units can reach 1099 F g-1 at 2 mV s-1, which is a more than 2-fold increase over boron-free units of carbon (428 F g-1). The work offers a novel version for designing high-performance carbon materials with unique yet reaction species-philic effects.

Role of excited-state hydrogen bonding in CO2 photoreduction catalyzed by sodium magnesium chlorophyll.

In this paper, we report a joint experimental and computational study to elaborate the mechanism for the photocatalytic CO2 reduction reaction (CO2RR). Experimental results indicate that the catalyst (sodium magnesium chlorophyll, MgChlNa2), which has a well-defined structure for calculation and understanding, can achieve the photoreduction of CO2 to CO only using water as a dispersant, without adding any photosensitizer or sacrificial agent. Subsequently, a series of structural models of the hydrogen-bonded complexes of the catalyst were constructed and outlined via utilizing density functional theory (DFT) calculations, including photophysical and photochemical processes. The results confirm that the rate-limiting step of the whole CO2RR was the intersystem crossing process. The electron and proton transfers involved in photophysical and photochemical processes are induced by hydrogen bonds in the excited states. The combination of experiments and calculations will provide an important reference for the design of high-efficiency photocatalysts in the photocatalytic CO2RR.

Microscopic-Level Insights into Solvation Chemistry for Nonsolvating Diluents Enabling High-Voltage/Rate Aqueous Supercapacitors.

Localized "water-in-salt" (LWIS) electrolytes are promising candidates for the next generation of high-voltage aqueous electrolytes with low viscosity/salt beyond high-salt electrolytes. An effective yet high-function diluent mainly determines the properties of LWIS electrolytes, being a key issue. Herein, the donor number of solvents is identified to serve as a descriptor of interaction intensity between solvents and salts to screen the organic diluents having few impacts on the solvation microenvironment and intrinsic properties of the original high-salt electrolyte, further leading to the construction of a novel low-viscosity electrolyte with a low dosage of the LiNO3 salt and well-kept intrinsic Li+-NO3--H2O clusters. Nonsolvating diluents, especially acetonitrile (AN) that has never been reported previously, are presented with the capability of constructing a LWIS electrolyte with nonflammability, electrode-philic features, lower viscosity, decreased salt dosage, and a greatly enhanced ion diffusion coefficient by about 280 times. This strongly relies on a huge difference of about 5000 times in coordination and solubility between AN and H2O toward LiNO3 (0.05 vs 25 mol kgsolvent-1) and the moderate interaction between AN and H2O. Multi-spectroscopic techniques and molecular dynamics simulations uncover the solvation chemistry at the microscopic level and the interplay among cations, anions, and H2O without/with AN. The identified unique diluting and nonsolvating effects of AN reveal well-maintained cation-anion-H2O clusters and enhanced intermolecular hydrogen bonding between AN and H2O, further reinforcing the H2O stability and expanding the voltage window up to 3.28 V. This is a breakthrough that is far beyond high-viscosity/salt electrolytes for high-voltage and high-rate aqueous supercapacitors.

A Liquid-Liquid-Solid System to Manipulate the Cascade Reaction for Highly Selective Electrosynthesis of Aldehyde.

Electrocatalytic synthesis of aldehydes from alcohols exhibits unique superiorities as a promising technology, in which cascade reactions are involved. However, the cascade reactions are severely limited by the low selectivity resulting from the peroxidation of aldehydes in a traditional liquid-solid system. Herein, we report a novel liquid-liquid-solid system to regulate the selectivity of benzyl alcohol electrooxidation. The selectivity of benzaldehyde increases 200-fold from 0.4 % to 80.4 % compared with the liquid-solid system at a high current density of 136 mA cm-2 , which is the highest one up to date. In the tri-phase system, the benzaldehyde peroxidation is suppressed efficiently, with the conversion of benzaldehyde being decreased from 87.6 % to 3.8 %. The as-produced benzaldehyde can be in situ extracted to toluene phase and separated from the electrolyte to get purified benzaldehyde. This strategy provides an efficient way to efficiently enhance the selectivity of electrocatalytic cascade reactions.

Mismatching integration-enabled strains and defects engineering in LDH microstructure for high-rate and long-life charge storage.

Layered double hydroxides (LDH) have been extensively investigated for charge storage, however, their development is hampered by the sluggish reaction dynamics. Herein, triggered by mismatching integration of Mn sites, we configured wrinkled Mn/NiCo-LDH with strains and defects, where promoted mass & charge transport behaviors were realized. The well-tailored Mn/NiCo-LDH displays a capacity up to 518 C g-1 (1 A g-1), a remarkable rate performance (78%@100 A g-1) and a long cycle life (without capacity decay after 10,000 cycles). We clarified that the moderate electron transfer between the released Mn species and Co2+ serves as the pre-step, while the compressive strain induces structural deformation with promoted reaction dynamics. Theoretical and operando investigations further demonstrate that the Mn sites boost ion adsorption/transport and electron transfer, and the Mn-induced effect remains active after multiple charge/discharge processes. This contribution provides some insights for controllable structure design and modulation toward high-efficient energy storage.

Facile Synthesis of Heterostructured MoS2-MoO3 Nanosheets with Active Electrocatalytic Sites for High-Performance Lithium-Sulfur Batteries.

In order to overcome the shuttling effect of soluble polysulfides in lithium-sulfur (Li-S) batteries, we have designed and synthesized a creative MoS2-MoO3/carbon shell (MoS2-MoO3/CS) composite by a H2O2-enabled oxidizing process under mild conditions, which is further used for separator modification. The MoS2-MoO3 heterostructures can conform to the CS morphology, forming two-dimensional nanosheets, and thus shorten the transport path of lithium ion and electrons. Based on our theoretical calculations and experiments, the heterostructures show strong surface affinity toward polysulfides and good catalytic activity to accelerate polysulfide conversion. Benefiting from the above merits, the Li-S battery with a MoS2-MoO3/CS modified separator exhibits good electrochemical performance: it delivers a high discharge capacity of 1531 mAh g-1 at 0.2 C; the initial capacity can be maintained by 92% after 600 cycles at 1 C, and the discharge capacity decay rate is only 0.0135% per cycle. Moreover, the MoS2-MoO3/CS battery still achieves good cycling stability with 78% capacity retention after 100 cycles at 0.2 C with a high sulfur loading of 5.9 mg cm-2. This work offers a facile design to construct the MoS2-MoO3 heterostructures for high-performance Li-S batteries, and may also improve one's understanding on the heterostructure contribution during polysulfide adsorption and conversion.

The role of thermodynamically stable configuration in enhancing crystallographic diffraction quality of flexible MOFs.

Single-crystal X-ray diffraction (SCXRD) is a widely used method for structural characterization. Generally, low temperature is of great significance for improving the crystallographic diffraction quality. Herein we observe that this practice is not always effective for flexible metal-organic frameworks (f-MOFs). An abnormal crystallography, that is, more diffraction spots at a high angle and better resolution of diffraction data as the temperature increases in the f-MOF (1-g), is observed. XRD results reveal that 1-g has a reversible anisotropic thermal expansion behavior with a record-high c-axial positive expansion coefficient of 1,401.8 × 10-6 K-1. Calculation results indicate that the framework of 1-g has a more stable thermodynamic configuration as the temperature increases. Such configuration has lower-frequency vibration and may play a key role in promoting higher Bragg diffraction quality at room temperature. This work is of great significance for how to obtain high-quality SCXRD diffraction data.

Recyclable and Magnetically Functionalized Metal-Organic Framework Catalyst: IL/Fe3O4@HKUST-1 for the Cycloaddition Reaction of CO2 with Epoxides.

A recyclable and magnetic nanocomposite catalyst (IL/Fe3O4@HKUST-1) was synthesized via grafting ionic liquid (IL) [AEMIm]BF4 into magnetically functionalized metal-organic framework Fe3O4@HKUST-1 in a water-ethanol media. The properties of IL/Fe3O4@HKUST-1 were fully characterized by powder X-ray diffraction, electron microscopy, Fourier-transform infrared spectroscopy, nitrogen adsorption-desorption, density-functional theory, and a magnetic property measurement system. IL/Fe3O4@HKUST-1 showed high activity in the solvent-free cycloaddition of CO2 with epoxides under mild conditions. Furthermore, the catalyst can be easily separated from the reaction mixture, and the recycled catalyst maintained high performance for several cycles. The synergistic effect of the Lewis acid and base sites in IL/Fe3O4@HKUST-1 contributes to its greater reactivity than individual IL or HKUST-1.

Recognition of Water-Induced Effects toward Enhanced Interaction between Catalyst and Reactant in Alcohol Oxidation.

Pickering emulsion stabilized by solid nanoparticles provides a diverse solvent microenvironment and enables to promote the phase transfer of reaction substrates/products in catalytic reactions, but the intrinsic role of solvent is still not clear. Herein, using benzyl alcohol (BA) as a model reactant, we demonstrate the nature of the water-promoted activity for alcohol oxidation over the Pd/MgAl-LDO catalyst. Depending on the water in the solvent, we observe different reactivities regarding the proportion of the water in the system. Kinetic isotope effects confirm the participation and positive effects of water for oxidation of BA. The water promotion effects are recognized and identified by the water vapor pulse adsorption coupled with temperature program desorption. Moreover, the adsorption behavior of BA or benzaldehyde at the interface of water and Pd/MgAl-LDO is also investigated by quasi-in-situ Raman spectroscopy. In addition, the mechanism of water-promoted alcohol oxidation is rationally proposed based on the Langmuir-Hinshelwood mechanism. The general applicability of the water promotion effects is further demonstrated over different supports and substrates, which well achieves excellent catalytic activity and selectivity in Pickering emulsion compared to that in the pure toluene system.

An insight into the reaction mechanism of CO2 photoreduction catalyzed by atomically dispersed Fe atoms supported on graphitic carbon nitride.

We report a combination of experimental and computational mechanistic studies for the photoreduction of CO2 to CO with water, catalyzed by single-atom Fe supported on graphitic carbon nitride (g-C3N4). Density functional theory (DFT) and time-dependent DFT (TDDFT) methods were utilized to explore the behavior of single-atom Fe in g-C3N4, which is of vital importance to the understanding of the CO2 reduction reaction (CO2RR) mechanism. The calculation results reveal that the rate-limiting step of the hydrogen-bonded complex in the absence of Fe atoms is the cleavage of C-O bonds in COOH radicals during the whole CO2RR, which includes the photophysical and photochemical processes. The presence of Fe atoms not only activated CO2 in the ground state and increased the rate constant of the limiting step in the photophysical process, but also functioned as the catalytic active center, lowering the reaction barrier of the C-O bond cleavage in COOH˙ in the photochemical process and resulting in improved photocatalytic activity. In addition, DFT calculations further demonstrated that the electron and proton transfer involved in the photophysical and photochemical processes is closely related to and induced by the hydrogen bonds in the excited state.

A C-S-C Linkage-Triggered Ultrahigh Nitrogen-Doped Carbon and the Identification of Active Site in Triiodide Reduction.

An efficient chemical synthesis route, with an aim of reaching an ultrahigh nitrogen (N)-doping level in carbon materials can provide a platform where the type and amount of N dopant can be tuned over a wide range. We propose a C-S-C linkage-triggered confined-pyrolysis strategy for the high-efficiency in situ N-doping into carbon matrix and an ultrahigh doping level up to 13.5 at %, which is close to the theoretical upper limit (15.2 at %) is realized at a high carbonization temperature of 1000 °C. The pyridinic N is dominant with a maximum percent of 48.7 %. By using I3 - reduction as an example, the resultant NCM-5 exhibits the best activity with a power conversion efficiency of 8.77 %. A pyridinic N site-dependent activity is demonstrated in which the amount of active sites increases with the increase of pyridinic N, and the carbon atom adjacent to electron-withdrawing pyridinic N at the armchair edge acts as the most favorable site for the adsorption of I2 .

Syntheses, structures, and photocatalytic properties of open-framework Ag-Sn-S compounds.

Four open-framework Ag-Sn-S compounds K2Ag2Sn2S6 (1); K2Ag2SnS4 (2); Rb2Ag2SnS4 (3); and Cs2Ag2SnS4 (4) have been synthesized using a solvothermal method. Compound 1 possesses a unique three-dimensional (3D) structure in which Ag+ ions are two-coordinated. Compounds 2-4 have the same layered structure in which Ag+ ions are tetrahedrally coordinated. Photocatalytic degradation properties of methylene blue have been investigated and compound 1 displays excellent photodegradation activities. The photoelectric response properties, optical properties, and theoretical calculations of these compounds have also been studied.

A Novel Single-Atom Electrocatalyst Ti1 /rGO for Efficient Cathodic Reduction in Hybrid Photovoltaics.

Single-atom catalysts (SACs) are a frontier research topic in the catalysis community. Carbon materials decorated with atomically dispersed Ti are theoretically predicted with many attractive applications. However, such material has not been achieved so far. Herein, a Ti-based SAC, consisting of isolated Ti anchored by oxygen atoms on reduced graphene oxide (rGO) (termed as Ti1 /rGO), is successfully synthesized. The structure of Ti1 /rGO is characterized by high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure spectroscopy, being determined to have a five coordinated local structure TiO5 . When serving as non-Pt cathode material in dye-sensitized solar cells (DSCs), Ti1 /rGO exhibits high electrocatalytic activity toward the tri-iodide reduction reaction. The power conversion efficiency of DSCs based on Ti1 /rGO is comparable to that using conventional Pt cathode. The unique structure of TiO5 moieties and the crucial role of atomically dispersed Ti in Ti1 /rGO are well understood by experiments and density functional theory calculations. This emerging material shows potential applications in energy conversion and storage devices.

Discrimination of Various Amine Vapors by a Triemissive Metal-Organic Framework Composite via the Combination of a Three-Dimensional Ratiometric Approach and a Confinement-Induced Enhancement Effect.

Multiemissive sensors are being actively pursued, because of their ratiometric luminescent detection capabilities, which demonstrates better sensitivity and selectivity than conventional single-emission sensors. Herein, we present a trichromatic white-light-emitting metal-organic framework (MOF) composite (Z3) by simultaneously incorporating red/green-emitting Pt/Ru complex cations into porous blue-emitting bio-MOF-1 through post-synthetic modification. With the help of a three-dimensional (3-D) dual-ratiometric luminescence recognition method, and unique turn-on responses of the red emission toward amine compounds (ACs), including NH3 and aliphatic amines, via confinement-induced luminescence enhancement effect, Z3 can work as a dual-ratiometric luminescent sensor for discrimination of 7 out of 11 AC vapors. This work not only provides a new AC sensing mechanism (confinement effect) that can induce a "turn-on" response but also proves that the accuracy and selectivity of composite sensor can be greatly improved through the combination of 3-D recognition method and the confinement effect. Thus, it open up fresh opportunities to develop composite sensors with excellent sensing and differentiating ability.

FeNi Alloy Nanoparticles Encapsulated in Carbon Shells Supported on N-Doped Graphene-Like Carbon as Efficient and Stable Bifunctional Oxygen Electrocatalysts.

The development of cost-effective and durable oxygen electrocatalysts remains highly critical but challenging for energy conversion and storage devices. Herein, a novel FeNi alloy nanoparticle core encapsulated in carbon shells supported on a N-enriched graphene-like carbon matrix (denoted as FeNi@C/NG) was constructed by facile pyrolyzing the mixture of metal salts, glucose, and dicyandiamide. The in situ pyrolysis of dicyandiamide in the presence of glucose plays a significant effect on the fabrication of the porous FeNi@C/NG with a high content of doped N and large specific surface area. The optimized FeNi@C/NG catalyst displays not only a superior catalytic performance for the oxygen reduction reaction (ORR, with an onset potential of 1.0 V and half-wave potential of 0.84 V) and oxygen evolution reaction (OER, the potential at 10 mA cm-2 is 1.66 V) simultaneously in alkaline, but also outstanding long-term cycling durability. The excellent bifunctional ORR/OER electrocatalytic performance is ascribed to the synergism of the carbon shell and FeNi alloy core together with the high-content of nitrogen doped on the large specific surface area graphene-like carbon.

TD-DFT insights into the sensing potential of the luminescent covalent organic framework for indoor pollutant formaldehyde.

This paper investigates the sensitivity of the luminescent thieno[2,3-b]thiophene-based covalent organic framework (TT-COF) towards the formaldehyde using the density functional theory and time-dependent method. The hydrogen bonding dynamics is explored by comparison of geometries, electronic transition energies, binding energies, UV-vis, and infrared spectra. Frontier molecular orbitals examination, natural population analysis, and plotted electron density difference map describe the quenching process explicitly via electron density distribution. The MOMAP program illuminates the quenching owing to TT-COF-HCHO complex radiative rate constant. Furthermore, the S1-T1 energy gap describes the facilitation of the luminescence quenching through the intersystem crossing. Above all results elaborate the TT-COF's potential to detect the formaldehyde.

Hexylammonium Iodide Derived Two-Dimensional Perovskite as Interfacial Passivation Layer in Efficient Two-Dimensional/Three-Dimensional Perovskite Solar Cells.

Defects locating within grain boundaries or on the film surface, especially organic cation vacancies and iodine vacancies, make the fabrication of perovskite solar cells (PSCs) with superior performance a challenge. Organic ammonium iodide is a promising candidate and has been frequently used to passivate these defects by forming two-dimensional (2D) perovskite. In this work, it is found that the chain length of organic ammonium iodide is a crucial factor on the defect passivation effect. Compared to butylammonium iodide, the hexylammonium iodide (HAI)-derived 2D perovskite is more efficient in decreasing interfacial defects, resulting in a notably enhanced photoluminescence lifetime and a more suppressed interfacial charge recombination process. As a consequence, the ultimate power conversion efficiency (PCE) has reached 20.62% (3D + HAI) as compared to 18.83% (3D). Moreover, the long-term durability of the corresponding PSCs against humidity and heat is simultaneously improved. This work once again demonstrates that the 2D/3D structure is promising for further improving the PCE and stability of PSCs.

Solvothermal Syntheses and Characterizations of Four Quaternary Copper Sulfides BaCu3MS4 (M = In, Ga) and BaCu2MS4 (M = Sn, Ge).

Hydro(solvo)thermal syntheses of quaternary copper sulfides containing alkaline earth metal ions remain a great challenge because of the low solubility of Cu-S compounds. Herein, a new facile solvothermal method was developed, and four quaternary copper sulfides, i.e., BaCu3InS4 (1), BaCu3GaS4 (2), BaCu2SnS4 (3), and BaCu2GeS4 (4), were prepared using excess sulfur as a mineralizer. Compound 1 possesses a novel three-dimensional (3D) anionic [Cu3InS4]2- framework constructed by an 8-membered ring of [Cu4S4] and [Cu2In2S4] alternatively. Compound 2 features a unique 3D anionic [Cu3GaS4]2- framework composed of [Cu3GaS10]n14n- anionic chains and 8-membered rings, in which [Cu4S4] and [Cu2Ga2S4] reside alternatively. Compounds 3 and 4 feature 3D anionic [Cu2MS4]2- (M = Sn, Ge) frameworks composed of CuS4 and MS4 tetrahedra with Ba2+ located in the channels. It is worth noting that different 3D Cu-S frameworks exist in the title crystal structures, in which main group ions are incorporated. This paper provides a new synthetic strategy for new quaternary sulfides.

Design Principles for Covalent Organic Frameworks to Achieve Strong Heteroatom-Synergistic Effect on Anchoring Polysulfides for Lithium-Sulfur Batteries.

The shuttle effect is still a notorious issue hindering commercial applications of lithium-sulfur batteries. Recently, covalent organic framework (COF) nanomaterials have been employed as cathode materials, especially because of their polar linkages, which can induce strong anchoring capacity to impede the shuttle of polysulfides. To investigate the structure-activity relationship between COF composition and anchoring performance, eight representative linkages composed of high-electronegativity elements are selected and constructed to be eight linkage-benzene-linkage COFs. Through the analyses of adsorption energy, charge transfer, atomic density of states, and so forth, the synergistic effect of O atoms in the secondary amine linkage and the "clamp" structure (N1-N2-C-O1) can both make significant contributions to improve the anchoring capacity on polysulfides. The promising effect of nucleophilic group branches is demonstrated. The solvent effect is also considered while selecting favorable COF scaffoldings in DME or DOL solvents. These results can provide helpful guidance for designing ideal cathode scaffoldings of lithium-sulfur batteries.