A general route via formamide condensation to prepare atomically dispersed metal-nitrogen-carbon electrocatalysts for energy technologies

Single-atom electrocatalysts (SAECs) have gained tremendous attention due to their unique active sites and strong metal–substrate interactions. However, the current synthesis of SAECs mostly relies on costly precursors and rigid synthetic conditions and often results in very low content of single-site metal atoms. Herein, we report an efficient synthesis method to prepare metal–nitrogen–carbon SAECs based on formamide condensation and carbonization, featuring a cost-effective general methodology for the mass production of SAECs with high loading of atomically dispersed metal sites. The products with metal inclusion were termed as formamide-converted metal–nitrogen–carbon (shortened as f-MNC) materials. Seven types of single-metallic f-MNC (Fe, Co, Ni, Mn, Zn, Mo and Ir), two bi-metallic (ZnFe and ZnCo) and one tri-metallic (ZnFeCo) SAECs were synthesized to demonstrate the generality of the methodology developed. Remarkably, these f-MNC SAECs can be coated onto various supports with an ultrathin layer as pyrolysis-free electrocatalysts, among which the carbon nanotube-supported f-FeNC and f-NiNC SAECs showed high performance for the O2 reduction reaction (ORR) and the CO2 reduction reaction (CO2RR), respectively. Furthermore, the pyrolysis products of supported f-MNC can still render isolated metallic sites with excellent activity, as exemplified by the bi-metallic f-FeCoNC SAEC, which exhibited outstanding ORR performance in both alkaline and acid electrolytes by delivering ∼70 and ∼20 mV higher half-wave potentials than that of commercial 20 wt% Pt/C, respectively. This work offers a feasible approach to design and manufacture SAECs with tuneable atomic metal components and high density of single-site metal loading, and thus may accelerate the deployment of SAECs for various energy technology applications

The Lewis Base-Catalyzed Silylation of AlcoholsA Mechanistic Analysis

Reaction rates for the base-catalyzed silylation of primary, secondary, and tertiary alcohols depend strongly on the choice of solvent and catalyst. The reactions are significantly faster in Lewis basic solvents such as dimethylformamide (DMF) compared with those in chloroform or dichloromethane (DCM). In DMF as the solvent, the reaction half-lives for the conversion of structurally similar primary, secondary, and tertiary alcohols vary in the ratio 404345:20232:1. The effects of added Lewis base catalysts such as 4-<i>N</i>,<i>N</i>-dimethylaminopyridine (DMAP) or 4-pyrrolidinopyridine (PPY) are much larger in apolar solvents than in DMF. The presence of an auxiliary base such as triethylamine is required in order to drive the reaction to full conversion

Preparation and Mechanism Insight of Nuclear Envelope-like Polymer Vesicles for Facile Loading of Biomacromolecules and Enhanced Biocatalytic Activity

The facile loading of sensitive and fragile biomacromolecules, such as glucose oxidase, hemoglobin, and ribonucleic acid (RNA), <i>via</i> synthetic vehicles directly in pure aqueous media is an important technical challenge. Inspired by the nucleus pore complex that connects the cell nucleus and the cytoplasm across the nuclear envelope, here we describe the development of a kind of polymeric nuclear envelope-like vesicle (NEV) to address this problem. The NEV is tailored to form the polymer pore complex (70 nm, similar to a nucleus pore complex) within the vesicle membrane based on nanophase segregation, which is confirmed <i>via</i> fluorescence spectrometry and dynamic light scattering (DLS) during self-assembly. This pH-triggered polymer pore complex can mediate the transportation of biomacromolecules across the vesicle membrane. Moreover, the NEVs facilitate the natural consecutive enzyme-catalyzed reactions <i>via</i> the H⁺ sponge effect. This simple strategy might also be extended for mimicking other synthetic cell organelles

Aluminated Derivatives of Porous Magadiite Heterostructures for Acid-Catalyzed <i>tert</i>-Butylation of Catechol

Novel porous magadiite/Al-magadiite heterostructures (PMH/PAMH) and aluminated derivatives of PMH (<i>x</i>Al-PMH, <i>x</i> = Al/Si in feeding) were fabricated upon two-dimensional interlayer cosurfactant-directing TEOS hydrolysis–condensation–polymerization from synthetic Na-magadiite/Na-[Al]­magadiite and postgrafting of Al into the interlayer silica framework of PMH from NaAlO₂ precursor, respectively. Characterization studies indicate that PMH and PAMH possess high surface area (SA), high thermal stability, and unique supermicro–mesoporous structure upon effective assembly of interlayer mesostructured silica and clay layers but weak Lewis acidity. The <i>x</i>Al-PMH (<i>x</i> = 0.2, 0.4) samples show successful incorporation of Al into interlayer mesostructure of PMH mainly in tetra-coordinated form, leading to greatly increased Lewis acidity and newly created Brønsted acidity together with well-kept layered supermicro-mesoporous porosity and reduced SA (>280 m²/g) while 0.6Al-PMH shows collapsed layers. 0.4Al-PMH exhibits the highest liquid-phase Friedel–Crafts <i>tert</i>-butylation activity of catechol with 93.4% conversion and 80.4% 4-<i>tert</i>-butylcatechol selectivity due to the strongest synergy between the surface acidity and supermicro–mesostructure

Electrophysiology of 4-AP induced epileptic activity.

<p>Top: example of ictal discharges after the 4-AP injection. Middle: zoom on an ictal discharge. Bottom: expanded view of showing the onset of the discharge, the intermediate phase and the offset.</p

(a) Schematic of the confocal lifetime imaging system. Excitation light is provided by a laser diode (λ = 637nm, 170 mW maximum power, which is collimated by a convex lens (L1) and travels through the objective for illumination. It is focused onto the cranial window by a 10×magnification objective (Obj), which is directed to the specific points using galvanometric scanners (xy). Emitted phosphorescence light is separated from excitation light using a beam splitter (BS2) and filter (F) and detected with an avalanche photodiode (APD). The system is controlled by a computer through a data acquisition card (DAQ). (b) In vivo measurements of pO₂vs mean counts per millisecond as controlled by the diode laser power. Higher laser powers correlate with higher consumption of O₂ leading to a significant decrease of pO₂ estimates over time (seen in the first point when average counts exceed 10000). When limiting to 3000 average counts, no significant decrease in pO

<p>(a) Schematic of the confocal lifetime imaging system. Excitation light is provided by a laser diode (λ = 637nm, 170 mW maximum power, which is collimated by a convex lens (L1) and travels through the objective for illumination. It is focused onto the cranial window by a 10×magnification objective (Obj), which is directed to the specific points using galvanometric scanners (xy). Emitted phosphorescence light is separated from excitation light using a beam splitter (BS2) and filter (F) and detected with an avalanche photodiode (APD). The system is controlled by a computer through a data acquisition card (DAQ). (b) In vivo measurements of pO₂vs mean counts per millisecond as controlled by the diode laser power. Higher laser powers correlate with higher consumption of O₂ leading to a significant decrease of pO₂ estimates over time (seen in the first point when average counts exceed 10000). When limiting to 3000 average counts, no significant decrease in pO₂ could be measured over time. (c) Example of phosphorescence decay profiles under conditions where photo-consumption is negligible. Higher O₂ concentration causes more quenching of phosphorescence signal, and consequently a faster decay (red profile).</p

Measured pO₂ values during normoxia (color dots), overlaid with a grayscale angiogram of cortical pial tissue from an exposed window(with an artery shown by the red arrows).

<p>The size of scale bar is 0.2mm.</p

a) Correlation between initial dip (% change) and duration of epileptic activity. The line of linear fit was <i>y</i> = 0.74<i>x</i> − 4.35, R² = 0.81 (b) Statistical distribution of the slopes for all mice. M1 was the name of mouse and number in the bracket was the number of seizure that was calculated. The outliers were plotted with red plus sign. The average of goodness of fit (R2) was listed for each mouse.

<p>a) Correlation between initial dip (% change) and duration of epileptic activity. The line of linear fit was <i>y</i> = 0.74<i>x</i> − 4.35, R² = 0.81 (b) Statistical distribution of the slopes for all mice. M1 was the name of mouse and number in the bracket was the number of seizure that was calculated. The outliers were plotted with red plus sign. The average of goodness of fit (R2) was listed for each mouse.</p

(a) Grayscale angiogram of cortical pial tissue with points of interest (red dots). Scale bar size: 0.2mm (b) Corresponding temporal profiles of pO₂ measured while altering FiO₂. The gray segments denote the 10 minutes period during which FiO₂ was increased up to 40%.

<p>(a) Grayscale angiogram of cortical pial tissue with points of interest (red dots). Scale bar size: 0.2mm (b) Corresponding temporal profiles of pO₂ measured while altering FiO₂. The gray segments denote the 10 minutes period during which FiO₂ was increased up to 40%.</p

Obtained pO₂ values in tissue near the focus and surround.

<p>(a) Grayscale angiogram of cortical surface and locations for pO₂ measurement (red: focus; blue: surround). The artery was shown by the red arrows. Scale bar size: 0.2mm (b) Epileptic activity induced a transient dip in tissue pO₂ followed by an increase in pO₂ in the focus. A sustained increase in pO₂ was seen in the surround. The dashed vertical lines show the ictal onset (left) and offset (right). (c) Distribution of percent of initial dip at multiple locations (color dotted) during epileptic activity. The 4-AP injection site is shown by green circle. The artery was shown by the red arrows. Scale bar size: 0.2mm.</p