Electrochemical C-N Bond Formation within Boron Imidazolate Cages Featuring Single Copper Sites.

Electrocatalysis expands the ability to generate industrially relevant chemicals locally and on-demand with intermittent renewable energy, thereby improving grid resiliency and reducing supply logistics. Herein, we report the feasibility of using molecular copper boron-imidazolate cages, BIF-29(Cu), to enable coupling between the electroreduction reaction of CO (CORR) with NO reduction (NORR) to produce urea with high selectivity of 68.5% and activity of 424 μA cm.

CO Activation with Manganese Tricarbonyl Complexes through an H-Atom Responsive Benzimidazole Ligand.

Herein, we report the synthesis and characterization of two manganese tricarbonyl complexes, Mn (HL)(CO) Br (1 a-Br) and Mn (MeL)(CO) Br (1 b-Br) (where HL=2-(2'-pyridyl)benzimidazole; MeL=1-methyl-2-(2'-pyridy)benzimidazole) and assayed their electrocatalytic properties for CO reduction. A redox-active pyridine benzimidazole ancillary ligand in complex 1 a-Br displayed unique hydrogen atom transfer ability to facilitate electrocatalytic CO conversion at a markedly lower reduction potential than that observed for 1 b-Br. Notably, a one-electron reduction of 1 a-Br yields a structurally characterized H-bonded binuclear Mn(I) adduct (2 a') rather than the typically observed Mn(0)-Mn(0) dimer, suggesting a novel method for CO activation.

Raman scattering spectra of boron imidazolate frameworks containing different magnetic ions.

We present a Raman scattering spectroscopic study of boron imidazolate metal-organic frameworks (BIFs) with three different magnetic metal ions and one non-magnetic in a wide frequency range from 25 to 1700 cm-1, which covers local vibrations of the imidazolate linkers as well as collective lattice vibrations. We show that the spectral region above 800 cm-1 belongs to the local vibrations of the linkers, which have the same frequencies for the studied BIFs without any dependence on the structure of the BIFs and are easily interpreted based on the spectra of imidazolate linkers. In contrast, collective lattice vibrations, observed below 100 cm-1, show a distinction between cage and two-dimensional BIFs structures, with a weak dependence on the metal node.

Phosphate-functionalized Zirconium Metal-Organic Frameworks for Enhancing Lithium-Sulfur Battery Cycling.

Lithium-sulfur batteries are promising candidates for next-generation energy storage devices due to their outstanding theoretical energy density. However, they suffer from low sulfur utilization and poor cyclability, greatly limiting their practical implementation. Herein, we adopted a phosphate-functionalized zirconium metal-organic framework (Zr-MOF) as a sulfur host.

Tailored porous framework materials for advancing lithium-sulfur batteries.

Despite great promise as next-generation high-capacity energy storage devices, lithium-sulfur batteries still face technical challenges in long-term cyclability. With their porous structures and facile synthesis, metal-organic frameworks (MOFs) are tunable platforms for understanding polysulfide redox and can serve as effective sulfur hosts for lithium-sulfur batteries. This feature article describes our design strategies to tailor MOF properties such as polysulfide affinity, ionic conductivity, and porosity for promoting active material utilization and charge transport efficiency.

Guiding CORR Selectivity by Compositional Tuning in the Electrochemical Double Layer.

The electrochemical conversion of carbon dioxide to value-added chemicals provides an environmentally benign alternative to current industrial practices. However, current electrocatalytic systems for the CO reduction reaction (CORR) are not practical for industrialization, owing to poor specific product selectivity and/or limited activity. Interfacial engineering presents a versatile and effective method to direct CORR selectivity by fine-tuning the local chemical dynamics.

Chemical Sulfide Tethering Improves Low-Temperature Li-S Battery Cycling.

Demands for energy storage and delivery continue to rise worldwide, making it imperative that reliable performance is achievable in diverse climates. Lithium-sulfur (Li-S) batteries offer a promising alternative to lithium-ion batteries owing to their substantially higher specific capacity and energy density. However, improvements to Li-S systems are still needed in low-temperature environments where polysulfide clustering and solubility limitations prohibit complete charge/discharge cycles.

Electrochemical Degradation of a Dicationic Rhenium Complex via Hoffman-Type Elimination.

Electrocatalytic reduction of carbon dioxide (CO) by transition-metal catalysts is an attractive means for storing renewably sourced electricity in chemical bonds. Metal coordination compounds represent highly tunable platforms ideal for studying the fundamental stepwise transformations of CO into its reduced products. However, metal complexes can decompose upon extended electrolysis and form chemically distinct molecular species or, in some cases, catalytically active electrode deposits.

Efficacy of Two Regimens for Colon Cleansing Using Polyethylene Glycol 4000: A Randomized Open Label Trial.

Aim: To compare effectiveness, safety and tolerance of two colon cleansing regimens using polyethylene glycol 4000 (PEG) in children.

Methods: Prospective, randomized, open clinical trial carried out in 129 children, 3 to 18 years old undergoing colonoscopy. Patients were randomized into two groups, 64 children received PEG with electrolyte (50 mL/kg) and oral bisacodyl (PEG+B group) or 65 other children received PEG with electrolyte (70 mL/kg) and glycerol enema (PEG+G group).

From Molecules to Porous Materials: Integrating Discrete Electrocatalytic Active Sites into Extended Frameworks.

Metal-organic and covalent-organic frameworks can serve as a bridge between the realms of homo- and heterogeneous catalytic systems. While there are numerous molecular complexes developed for electrocatalysis, homogeneous catalysts are hindered by slow catalyst diffusion, catalyst deactivation, and poor product yield. Heterogeneous catalysts can compensate for these shortcomings, yet they lack the synthetic and chemical tunability to promote rational design.

Non-Innocent Role of Porous Carbon Toward Enhancing C Products in the Electroreduction of Carbon Dioxide.

Selectivity for C-C coupled products remains a major challenge for electrochemical CO reduction. Herein, we report a facile method by modifying a Cu foil surface with a layer of porous carbon. The structure of carbon has a major influence on C and C product selectivity.

Graphene-Metal-Organic Framework Composite Sulfur Electrodes for Li-S Batteries with High Volumetric Capacity.

In an age of rapid acceleration toward next-generation energy storage technologies, lithium-sulfur (Li-S) batteries offer the desirable combination of low weight and high specific energy. Metal-organic frameworks (MOFs) have been recently studied as functionalizable platforms to improve Li-S battery performance. However, many MOF-enabled Li-S technologies are hindered by low capacity retention and poor long-term performance due to low electronic conductivity.

Reorganization of Interfacial Water by an Amphiphilic Cationic Surfactant Promotes CO Reduction.

The presence of cetyltrimethylammonium bromide (CTAB) near the surface of a Cu electrode promotes the electrochemical reduction of CO to fuels. CTAB increases the CO reduction rate by as much as 10× and decreased the HER rate by 4×, leading to ∼75% selectivity toward the reduction of CO. Surface enhanced infrared absorption spectroscopy (SEIRAS) was used to probe the effects of CTAB adsorption on the structure of interfacial water and CO reduction intermediates.

Electric Fields at Metal-Surfactant Interfaces: A Combined Vibrational Spectroscopy and Capacitance Study.

Surfactants modulate interfacial processes. In electrochemical CO reduction, cationic surfactants promote carbon product formation and suppress hydrogen evolution. The interfacial field produced by the surfactants affects the energetics of electrochemical intermediates, mandating their detailed understanding.

2D Oligosilyl Metal-Organic Frameworks as Multi-state Switchable Materials.

We report the synthesis of a set of 2D metal-organic frameworks (MOFs) constructed with organosilicon-based linkers. These oligosilyl MOFs feature linear Si Me (C H CO H) ligands (lin-Si , n=2, 4) connected by Cu paddlewheels. The stacking arrangement of the 2D sheets is dictated by van der Waals interactions and is tunable by solvent exchange, leading to reversible structural transformations between many crystalline and amorphous phases.

Lithium Thiophosphate Functionalized Zirconium MOFs for Li-S Batteries with Enhanced Rate Capabilities.

Zirconium metal-organic frameworks (Zr-MOFs) are renowned for their extraordinary stability and versatile chemical tunability. Several Zr-MOFs demonstrate a tolerance for missing linker defects, which create "open sites" that can be used to bind guest molecules on the node cluster. Herein, we strategically utilize these sites to stabilize reactive lithium thiophosphate (LiPS) within the porous framework for targeted application in lithium-sulfur (Li-S) batteries.

Exploring ligand non-innocence of coordinatively-versatile diamidodipyrrinato cobalt complexes.

The non-innocence of diamidodipyrrin is explored in a series of cobaltous complexes with novel binding motifs. By varying the coordination modes, a reversible one-electron reduction is remarkably shifted by nearly 200 mV in a single metal-ligand platform. Our study illustrates a new strategy for modifying the redox activity of porphyrin-like scaffolds.

Lithiated Defect Sites in Zr Metal-Organic Framework for Enhanced Sulfur Utilization in Li-S Batteries.

Lithium sulfur (Li-S) battery technology is one of the most promising candidates for next-generation energy storage devices; however, it is still hindered by limited capacity yield and poor long-term stability. The complexity of these devices has hindered efforts to study electrochemical determinants of battery performance, impeding advancement of the field. Due to the ease of functionalization, metal-organic frameworks (MOFs) are unique platforms to explore such reactions, where integration of defects into the crystalline structure provides a convenient method for introducing synthetic handles.

Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells.

Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsHPO. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsHPO, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsHPO.

Visible-light photoredox catalysis: selective reduction of carbon dioxide to carbon monoxide by a nickel N-heterocyclic carbene-isoquinoline complex.

The solar-driven reduction of carbon dioxide to value-added chemical fuels is a longstanding challenge in the fields of catalysis, energy science, and green chemistry. In order to develop effective CO2 fixation, several key considerations must be balanced, including (1) catalyst selectivity for promoting CO2 reduction over competing hydrogen generation from proton reduction, (2) visible-light harvesting that matches the solar spectrum, and (3) the use of cheap and earth-abundant catalytic components. In this report, we present the synthesis and characterization of a new family of earth-abundant nickel complexes supported by N-heterocyclic carbene-amine ligands that exhibit high selectivity and activity for the electrocatalytic and photocatalytic conversion of CO2 to CO.

Complexes of earth-abundant metals for catalytic electrochemical hydrogen generation under aqueous conditions.

Growing global energy demands and climate change motivate the development of new renewable energy technologies. In this context, water splitting using sustainable energy sources has emerged as an attractive process for carbon-neutral fuel cycles. A key scientific challenge to achieving this overall goal is the invention of new catalysts for the reductive and oxidative conversions of water to hydrogen and oxygen, respectively.

Computational and experimental study of the mechanism of hydrogen generation from water by a molecular molybdenum-oxo electrocatalyst.

We investigate the mechanism for the electrocatalytic generation of hydrogen from water by the molecular molybdenum-oxo complex, [(PY5Me(2))MoO](2+) (PY5Me(2) = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine). Computational and experimental evidence suggests that the electrocatalysis consists of three distinct electrochemical reductions, which precede the onset of catalysis. Cyclic voltammetry studies indicate that the first two reductions are accompanied by protonations to afford the Mo-aqua complex, [(PY5Me(2))Mo(OH(2))](+).

Nickel N-heterocyclic carbene-pyridine complexes that exhibit selectivity for electrocatalytic reduction of carbon dioxide over water.

We report a homologous series of nickel(II) complexes supported by N-heterocyclic carbene-pyridine ((R)bimpy, R = Me, Et, Pr) ligands that exhibit high selectivity for reducing carbon dioxide over water under electrocatalytic conditions.

Diamidodipyrrins: versatile bipyrrolic ligands with multiple metal binding modes.

A straightforward, facile synthesis of diamidodipyrromethenes (diamidodipyrrins, DADP (R,R')) is presented. These tetradentate ligands readily form complexes with metal ions such as Ni (2+) and Cu (2+) and can adopt different binding modes with these metals. One version of the ligand (DADP (Ph, iPr )) has been structurally characterized in its "free base" form, as a HBr salt, and as the Ni (2+) and Cu (2+) complexes.