[M(CO)4(2,2′-bipyridine)] (M = Cr, Mo, W) as efficient catalysts for electrochemical reduction of CO2 to CO at a gold electrode

Group 6 complexes of the type [M(CO)4(bpy)] (M=Cr, Mo, W) are capable of behaving as electrochemical catalysts for the reduction of CO2 at potentials less negative than those for the reduction of the radical anions [M(CO)4(bpy)].−. Cyclic voltammetric, chronoamperometric and UV/Vis/IR spectro-electrochemical data reveal that five-coordinate [M(CO)3(bpy)]2− are the active catalysts. The catalytic conversion is significantly more efficient in N-methyl-2-pyrrolidone (NMP) compared to tetrahydrofuran, which may reflect easier CO dissociation from 1e−-reduced [M(CO)4(bpy)].− in the former solvent, followed by second electron transfer. The catalytic cycle may also involve [M(CO)4(H-bpy)]− formed by protonation of [M(CO)3(bpy)]2−, especially in NMP. The strongly enhanced catalysis using an Au working electrode is remarkable, suggesting that surface interactions may play an important role, too

Functionalization of graphene at the organic/water interface

A simple method for the deposition of noble metal (Pd, Au) nanoparticles on a free-standing chemical vapour deposited graphene (CVD GR) monolayer is reported. The method consists of assembling the high purity CVD GR, by transfer from poly (methyl methacrylate) (PMMA), at the organic/water interface. Metal deposition can then proceed using either spontaneous or electrochemically-controlled processes. The resultant graphene-based metal nanoclusters are characterized using atomic force and electron microscopy techniques, and the location of the nanostructures underneath the graphene layer is determined from the position and the intensity changes of the Raman bands (D, G, 2D). This novel process for decoration of a single-layer graphene sheet with metal nanoparticles using liquid/liquid interfaces opens an alternative and useful way to prepare low dimensional carbon-based nanocomposites and electrode materials

The Modified Liquid‐Liquid Interface: The Effect of an Interfacial Layer of MoS 2 on Ion Transfer

From Wiley via Jisc Publications RouterHistory: received 2021-06-15, rev-recd 2021-08-08, pub-electronic 2021-10-28Article version: VoRPublication status: PublishedFunder: Ministry of Education, Saudi ArabiaFunder: EPSRC; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/R023034/1Abstract: MoS2 nanosheets have been assembled at the water|1,2‐dichlorobenzene (DCB) interface into uniform films, and the ion‐transfer properties investigated by voltammetry at the interface between immiscible electrolyte solutions. Remarkably, interfacial MoS2 films were found to enhance the simple and facilitated transfer of cationic species while restricting the transport of anionic species. The enhancement is attributed to a localised increase in the cationic concentration at the interface due to the adsorption onto the negatively charged surface of the exfoliated MoS2 nanosheets. Size‐selectivity for the cationic species was also recognized as a feature of such films. Characterisation of the interfacial film's structure revealed the inclusion of multiple emulsified droplets stabilised by MoS2, where the droplet number and size depend on the concentration of the MoS2 dispersion. Besides increasing the interfacial corrugation and area, the emulsified droplets are believed to influence the mass transport mechanism across the interface. Cyclic voltammetric measurements of saturated films suggested a capillary‐like structure of these films. While the capillaries/nanochannels allow them to have a degree of size‐selectivity that depends on the thickness/density of the film, they also affect the diffusion zones towards and away from the interface. Consequently, steady‐state conditions of mass transport similar to those found in solid‐state supported micro‐ITIES are observed in these nanofilms

Water friction in nanofluidic channels made from two-dimensional crystals.

From Europe PMC via Jisc Publications RouterHistory: ppub 2021-05-01, epub 2021-05-25Publication status: PublishedFunder: European Research Council; Grant(s): 852674Membrane-based applications such as osmotic power generation, desalination and molecular separation would benefit from decreasing water friction in nanoscale channels. However, mechanisms that allow fast water flows are not fully understood yet. Here we report angstrom-scale capillaries made from atomically flat crystals and study the effect of confining walls' material on water friction. A massive difference is observed between channels made from isostructural graphite and hexagonal boron nitride, which is attributed to different electrostatic and chemical interactions at the solid-liquid interface. Using precision microgravimetry and ion streaming measurements, we evaluate the slip length, a measure of water friction, and investigate its possible links with electrical conductivity, wettability, surface charge and polarity of the confining walls. We also show that water friction can be controlled using hybrid capillaries with different slip lengths at opposing walls. The reported advances extend nanofluidics' toolkit for designing smart membranes and mimicking manifold machinery of biological channels

Electrochemical Interaction of Few-Layer Molybdenum Disulfide Composites vs Sodium: New Insights on the Reaction Mechanism

The direct observation of real time electrochemical processes is of great importance for fundamental research on battery materials. Here, we use electron paramagnetic resonance (EPR) spectroscopy to monitor the electrochemical reaction of sodium ions with few-layer MoS2 and its composite with carbon nanotubes (CNTs), thereby uncovering new details of the reaction mechanism. We propose that the sodiation reaction takes place initially in structural defects at the MoS2 surface that have been created during the synthetic process (ultrasonic exfoliation), leading to a decrease in the density of Mo5+ at low symmetry sites that can be related to the electrochemical irreversibility of the process. In the case of the few-layer MoS2/CNTs composite, we found metallic-type conduction behavior for the electrons associated with the Mo paramagnetic centers and improved electrochemical reversibility. The reversible nature of the EPR spectra implies that adsorption/desorption of Na+ ions occurs on the Mo5+ defects, or that they are neutralized during sodiation and subsequently created upon Na+ extraction. These effects help us to understand the higher capacities obtained in the exfoliated samples, as the sum of electrosorption of ions and faradaic effects, and support the suggestion of a different reaction mechanism in the few-layer chalcogenide, which is not exclusively an insertion process

Resolution of Lithium Deposition versus Intercalation of Graphite Anodes in Lithium Ion Batteries: An In Situ Electron Paramagnetic Resonance Study

From Wiley via Jisc Publications RouterHistory: received 2021-05-07, rev-recd 2021-07-02, pub-electronic 2021-08-13Article version: VoRPublication status: PublishedFunder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266; Grant(s): EP/R023034/1, NS/A000055/1, FIRG001 (EP/S003053/1)Abstract: In situ electrochemical electron paramagnetic resonance (EPR) spectroscopy is used to understand the mixed lithiation/deposition behavior on graphite anodes during the charging process. The conductivity, degree of lithiation, and the deposition process of the graphite are reflected by the EPR spectroscopic quality factor, the spin density, and the EPR spectral change, respectively. Classical over‐charging (normally associated with potentials ≤0 V vs. Li+/Li) are not required for Li metal deposition onto the graphite anode: Li deposition initiates at ca. +0.04 V (vs. Li+/Li) when the scan rate is lowered to 0.04 mV s−1. The inhibition of Li deposition by vinylene carbonate (VC) additive is highlighted by the EPR results during cycling, attributed to a more mechanically flexible and polymeric SEI layer with higher ionic conductivity. A safe cut‐off potential limit of +0.05 V for the anode is suggested for high rate cycling, confirmed by the EPR response over prolonged cycling

Effect of Salt Concentration in Water‐In‐Salt Electrolyte on Supercapacitor Applications

Electrical double‐layer supercapacitors offer numerous advantages in the context of energy storage; however, their widespread use is hindered by the high unit energy cost and low specific energy. Recently, water‐in‐salt (WIS) electrolytes have garnered interest for use in energy storage devices. Nevertheless, their direct application in high‐power devices is limited due to their high viscosity. In this study, we investigate the WIS Lithium bis(trifluoromethanesulfonyl)Imide (LiTFSI) electrolyte, revealing a high specific capacitance despite its elevated viscosity and restricted ionic conductivity. Our approach involves nuclear magnetic resonance (NMR) analysis alongside electrochemical analyses, highlighting the pronounced advantage of the WIS LiTFSI electrolyte over the WIS LiCl electrolyte at the molecular level. The NMR analysis shows that the LiTFSI electrolyte ions preferentially reside within the activated carbon pore network in the absence of an applied potential, in contrast to LiCl where the ions are more evenly distributed between the in‐pore and ex‐pore environments. This difference may contribute to the difference in capacitance between the two electrolytes observed during electrochemical cycling