Probing Substrate Diffusion in Interstitial MOF Chemistry with Kinetic Isotope Effects

<p>Metal-organic frameworks (MOFs) have garnered substantial interest as platforms for site-isolated catalysis. Efficient diffusion of small molecule substrates to interstitial lattice-confined catalyst sites is critical to leveraging unique opportunities of these materials as catalysts. Understanding the rate of substrate diffusion in MOFs is challenging and few <i>in situ </i>chemical tools are available to evaluate substrate diffusion during interstitial MOF chemistry. Here, we demonstrate nitrogen-atom transfer (NAT) from a lattice-confined Ru2 nitride to toluene to generate benzylamine. We use a comparison of the <i>intramolecular </i>deuterium kinetic isotope effect (KIE), determined for amination of a partially deuterated substrate, with the <i>intermolecular </i>KIE, determined by competitive amination of a mixture of perdeuterated and undeuterated substrates, to establish the relative rates of substrate diffusion and interstitial chemistry. We anticipate the developed KIE-based experiments will contribute to the development of porous materials for group-transfer catalysis</p

Fabrication of a Water-Stripped Free-Standing Silver Nanowire Network as the Top Electrode for Perovskite Solar Cells

Recently, there has been significant interest in inorganic–organic hybrid perovskite solar cells (PSCs) due to their excellent photovoltaic performance. However, the fabrication of PSCs’ top metallic electrodes using thermal evaporation in a vacuum atmosphere significantly increases the manufacturing cost and restricts large-scale production. In this study, we propose a water separation method for the fabrication of free-standing films of silver nanowires (AgNWs) that can be easily stripped by using water and laminated onto perovskite devices as top electrodes in an ambient atmosphere. The electrodes composed of long AgNWs exhibit superior electrical properties compared to those composed of shorter ones. We have identified that the reduced performance of PSCs with AgNW electrodes is mainly attributed to the high oxide content on the surface of AgNWs and the insufficient contact between the AgNW networks and hole transport layers. To resolve these issues, we employed sodium borohydride reduction and polyethoxysiloxane incorporation techniques. Through these treatments, PSCs with AgNW electrodes achieved a power conversion efficiency of 15.64%. This performance surpasses that reported in the literature for PSCs with AgNW electrodes, demonstrating the effectiveness of our approach

Fabrication of a Water-Stripped Free-Standing Silver Nanowire Network as the Top Electrode for Perovskite Solar Cells

Recently, there has been significant interest in inorganic–organic hybrid perovskite solar cells (PSCs) due to their excellent photovoltaic performance. However, the fabrication of PSCs’ top metallic electrodes using thermal evaporation in a vacuum atmosphere significantly increases the manufacturing cost and restricts large-scale production. In this study, we propose a water separation method for the fabrication of free-standing films of silver nanowires (AgNWs) that can be easily stripped by using water and laminated onto perovskite devices as top electrodes in an ambient atmosphere. The electrodes composed of long AgNWs exhibit superior electrical properties compared to those composed of shorter ones. We have identified that the reduced performance of PSCs with AgNW electrodes is mainly attributed to the high oxide content on the surface of AgNWs and the insufficient contact between the AgNW networks and hole transport layers. To resolve these issues, we employed sodium borohydride reduction and polyethoxysiloxane incorporation techniques. Through these treatments, PSCs with AgNW electrodes achieved a power conversion efficiency of 15.64%. This performance surpasses that reported in the literature for PSCs with AgNW electrodes, demonstrating the effectiveness of our approach

Functionalizing Biomaterials to Be an Efficient Proton-Exchange Membrane and Methanol Barrier for DMFCs

Biobased materials capable of transforming into selective proton-exchange composite membranes (PEMs) are highly favored for use in direct methanol fuel cells (DMFCs) because of their low cost and abundance. Here, a polysaccharide and a clay have been functionalized together to make a highly proton selective PEM. Use of chitosan and clay composites ensured limited methanol crossover and thereby high measured performance via efficient fuel convertibility. In this study, sulfonated natural nanocomposite PEMs made of chitosan and sodium–montmorillonite (CS-MMT) were characterized for their water swelling, proton conductivity and methanol permeability parameters. The CS-MMT membrane with a proton conductivity of 4.92 × 10^–2 S cm^–1 and a power density of 45 mW/cm² showed a measured methanol crossover current density (<i>J</i>) of <100 mA/cm². For higher methanol concentrations (4, 6 and 8 M), fuel loss was ∼4 times less in comparison with commercially successful PEMs, such as Nafion 117

Pyrolysis of Iron–Vitamin B9 As a Potential Nonprecious Metal Electrocatalyst for Oxygen Reduction Reaction

This study presents the performance of a carbon-black-supported pyrolyzed vitamin B9 (folic acid)-treated cathode catalyst (py-Fe-FA/C) in the oxygen reduction reaction (ORR) and proton exchange membrane fuel cell (PEMFC). Electrochemical ORR measurements revealed that using py-Fe-FA/C resulted in excellent ORR activity through the direct four-electron reduction pathway. The H₂–O₂ PEMFC with py-Fe-FA/C in the cathodic side produces a maximum power density of 330 mW cm^–2 with the 80 °C operation temperature and the 1 atm back pressure. X-ray photoelectron spectroscopy and <i>in situ</i> X-ray adsorption spectroscopy proved that the enhanced ORR activity was caused by the network structure of polyaromatic hydrocarbons, quaternary-type (graphitic) nitrogen, and the coordination structure of the py-Fe-FA/C, as confirmed by the ORR mechanism study using detailed XPS and <i>in situ</i> X-ray adsorption spectroscopy. Particularly, <i>in situ</i> X-ray adsorption spectroscopy elucidated the ORR mechanism of the py-Fe-FA/C

Ta₂O₅‑Nanoparticle-Modified Graphite Felt As a High-Performance Electrode for a Vanadium Redox Flow Battery

To increase the electrocatalytic activity of graphite felt (GF) electrodes in vanadium redox flow batteries (VRFBs) toward the VO₂⁺/VO²⁺ redox couple, we prepared a stable, high catalytic activity and uniformly distributed hexagonal Ta₂O₅ nanoparticles on the surface of GF by varying the Ta₂O₅ content. Scanning electron microscopy (SEM) revealed the amount and distribution uniformity of the electrocatalyst on the surface of GF. It was found that the optimum amount and uniformly immobilized Ta₂O₅ nanoparticles on the GF surface provided the active sites, enhanced hydrophilicity, and electrolyte accessibility, thus remarkably improved electrochemical performance of GF. In particular, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that the Ta₂O₅-GF nanocomposite electrode with a weight percentage of 0.75 wt % of Ta₂O₅ to GF exhibited the best electrochemical activity and reversibility toward the VO₂⁺/VO²⁺ redox reaction, when compared with the other electrodes. The corresponding energy efficiency was enhanced by ∼9% at a current density of 80 mA cm^–2, as compared with untreated GF. Furthermore, the charge–discharge stability test with a 0.75 wt % Ta₂O₅-GF electrode at 80 mA cm^–2 showed that, after 100 cycles, there was no obvious attenuation of efficiencies signifying the best stability of Ta₂O₅ nanoparticles, which strongly adhered on the GF surface

Highly Efficient Visible Light Photocatalytic Reduction of CO₂ to Hydrocarbon Fuels by Cu-Nanoparticle Decorated Graphene Oxide

The production of renewable solar fuel through CO₂ photoreduction, namely artificial photosynthesis, has gained tremendous attention in recent times due to the limited availability of fossil-fuel resources and global climate change caused by rising anthropogenic CO₂ in the atmosphere. In this study, graphene oxide (GO) decorated with copper nanoparticles (Cu-NPs), hereafter referred to as Cu/GO, has been used to enhance photocatalytic CO₂ reduction under visible-light. A rapid one-pot microwave process was used to prepare the Cu/GO hybrids with various Cu contents. The attributes of metallic copper nanoparticles (∼4–5 nm in size) in the GO hybrid are shown to significantly enhance the photocatalytic activity of GO, primarily through the suppression of electron–hole pair recombination, further reduction of GO’s bandgap, and modification of its work function. X-ray photoemission spectroscopy studies indicate a charge transfer from GO to Cu. A strong interaction is observed between the metal content of the Cu/GO hybrids and the rates of formation and selectivity of the products. A factor of greater than 60 times enhancement in CO₂ to fuel catalytic efficiency has been demonstrated using Cu/GO-2 (10 wt % Cu) compared with that using pristine GO