Impact of Surface Chemistry on Emulsion-Electrode Interactions and Electron-Transfer Kinetics in the Single-Entity Electrochemistry.

Single-entity electrochemistry (SEE) provides powerful means to track a single particle, single cell, and even single molecule from the nano to microscale. The electrode serves as not only the detector of collision but also the surface supplier in SEE, and the fundamental understanding of the electrode surface chemistry on the dynamic particle-electrode interactions and electrochemical responses of a single particle still remains unexplored, particularly for soft particles. Herein, dynamic interactions of microemulsions and the interaction-controlled electron-transfer (ET) kinetics are studied employing SEE and fluorescence spectroscopy. The o/w-type nitrobenzene emulsions were prepared with the surfactant-type room temperature ionic liquids (RTILs). Biased the electrode potential for the reduction of 7,7,8,8-tetracyanoquinodimethane within emulsions, it is surprising to see the distinct collision current signals on the carbon fiber ultramicroelectrode (C UME) and Au ultramicroelectrode (Au UME) in the late stage of chronoamperometric measurements. Theoretical understanding was made to determine the ET kinetics behind the disparate current signals. It is believed that the electrode surface chemistry, i.e., the surface energy, has a great influence on the dynamic emulsion-electrode interactions and ET kinetics. On the hydrophilic surface of Au UME, emulsions tend to decompose/detach from the electrode surface immediately after colliding. In contrast, on the lipophilic surface of C UME with lower surface energy, a layer of oil phase accumulated by the coalescence of emulsions and the migration of the precedent colliding emulsions, which would serve as a barrier to block ET via tunneling as manifested by the gradual slowdown of ET rate and the reduced collision frequency in the late stage of measurement. The impacts of the emulsion size and amphiphilicity of RTILs on the C UME-emulsion interactions and ET kinetics were also investigated.

Pharmacodynamic study of chitosan in combination with salvianolic acid B in the treatment of CC14 -induced liver fibrosis in mice.

Liver fibrosis is a chronic liver lesion caused by excessive deposition of the extracellular matrix after liver damage, resulting in fibrous scarring of liver tissue. The progression of liver fibrosis is partially influenced by the gut microbiota. Chitosan can play a therapeutic role in liver fibrosis by regulating the gut microbiota based on the 'gut-liver axis' theory. Salvianolic acid B can inhibit the development of liver fibrosis by inhibiting the activation of hepatic stellate cells and reducing the production of extracellular matrix. In this study, the therapeutic effect of chitosan in combination with salvianolic acid B on liver fibrosis was investigated in a mouse liver fibrosis model. The results showed that the combination of chitosan and salvianolic acid B was better than the drug alone, improving AST/ALT levels and reducing the expression of α-SAM, COL I, IL-6 and other related genes. It improved the structure of gut microbiota and increased the abundance of beneficial bacteria such as Lactobacillus. The above results could provide new ideas for the clinical treatment of liver fibrosis.

Kinetic Study of Hydrogen Evolution Reaction over Strained MoS2 with Sulfur Vacancies Using Scanning Electrochemical Microscopy.

Molybdenum disulfide (MoS2), with its active edge sites, is a proposed alternative to platinum for catalyzing the hydrogen evolution reaction (HER). Recently, the inert basal plane of MoS2 was successfully activated and optimized with excellent intrinsic HER activity by creating and further straining sulfur (S) vacancies. Nevertheless, little is known about the HER kinetics of those S vacancies and the additional effects from elastic tensile strain. Herein, scanning electrochemical microscopy was used to determine the HER kinetic data for both unstrained S vacancies (formal potential Ev0 = −0.53 VAg/AgCl, electron-transfer coefficient αv = 0.4, electron-transfer rate constant kv0 = 2.3 × 10(­4) cm/s) and strained S vacancies (Esv0= −0.53 VAg/AgCl, αsv = 0.4, ksv0 = 1.0 × 10(­3) cm/s) on the basal plane of MoS2 monolayers, and the strained S vacancy has an electron-transfer rate 4 times higher than that of the unstrained S vacancy. This study provides a general platform for measuring the kinetics of two-dimensional material-based catalysts.

Mechanoelectrochemical catalysis of the effect of elastic strain on a platinum nanofilm for the ORR exerted by a shape memory alloy substrate.

Both the ligand effect and surface strain can affect the electrocatalytic reactivity. In that matter exists a need to be fundamentally understood; however, there is no effective strategy to isolate the strain effect in electrocatalytic systems. In this research we show how the elastic strain in a platinum nanofilm varies the catalytic activity for the oxygen reduction reaction, a key barrier to the wide applications of fuel cells. NiTi shape memory alloy was selected as the substrate to strain engineer the deposited Pt nanofilm in both compressively and tensilely strained states by taking advantage of the two-way shape memory effect for the first time. We demonstrate that compressive strain weakens the Pt surface adsorption and hence improves the ORR activity, which reflects in a 52% enhancement of the kinetic rate constant and a 27 mV positive shift of the half-wave potential for the compressively strained 5 nm Pt compared to the pristine Pt. Tensile strain has the opposite effect, which is in general agreement with the proposed d-band theory.

Suppressing photoinduced charge recombination at the BiVO4||NiOOH junction by sandwiching an oxygen vacancy layer for efficient photoelectrochemical water oxidation.

Nickel oxyhydroxide (NiOOH) is regarded as one of the promising cocatalysts to enhance the catalytic performance of photoanodes but suffers from serious interfacial charge-carrier recombination at the photoanode||NiOOH interface. In this work, surface-engineered BiVO4 photoanodes are fabricated by sandwiching an oxygen vacancy (Ovac) interlayer between BiVO4 and NiOOH. The surface Ovac interlayer is introduced on BiVO4 by a chemical reduction treatment using a mild reducing agent, sodium hypophosphite. The induced Ovac can alleviate the interfacial charge-carrier recombination at the BiVO4||NiOOH junction, resulting in efficient charge separation and transfer efficiencies, while an outer NiOOH layer is coated to prevent the Ovac layer from degradation. As a result, the as-prepared NiOOH-P-BiVO4 photoanode exhibits a high photocurrent density of 3.2 mA cm-2 at 1.23 V vs. RHE under the irradiation of 100 mW/cm2 AM 1.5G simulated sunlight, in comparison to those of bare BiVO4, P-BiVO4, and NiOOH-BiVO4 photoanodes (1.1, 2.1 and 2.3 mA cm-2, respectively). In addition to the superior photoactivity, the 5-h amperometric measurements illustrate improved stability of the surface-engineered NiOOH-P-BiVO4 photoanode. Our work showcases the feasibility of combining cocatalysts with Ovac, for improved photoactivity and stability of photoelectrodes.

Electrochemical observation of individual collision-blocking events of TX-100 nanomicelles: An accurate and universal approach for the critical micelle concentration determination of surfactants.

The electrochemical collision-blocking technique, equipped with the nanoelectrode of Pt was proposed for determination of the critical micelle concentration (CMC) of non-ionic surfactant TX-100. The approach was found on detection of individual collided nanomicelles in amperometric measurements of the oxidation of K4Fe(CN)6 varying the titrated concentration of TX-100 whereas the formed micelles above the CMC stick on the electrode surface during collision to locally block the flux of electroactive species and further to change the faradaic current. The step-like current transients observed in i-t curves have been demonstrated corresponding to electrochemical collision events of individual TX-100 micelles and micelle aggregates by 3D COMSOL simulations. The logarithm relations between the collision frequency of micelle(s) and the concentration of TX-100 were derived by regression analysis to give the corresponding values of CMC in salt solutions. Further, an 'ideal' CMC of TX-100 without influence of additional salts was estimated to be 0.194 mM using the McDevit-Long theory. The more accurate CMC determined in this work has shown less than the previously reported, mainly due to the detection limit for micelle as low as 0.41 fM. Also, we determined the second CMC of 1.21 mM as the first observation of the collision response of micelle aggregates during TX-100 titration. Owing to its analytical characteristics in single-particle tracking and material insensitivity, the approach we proposed is potentially to be a universal tool for accurate determination of CMC of surfactants, and also for studying the formation of polymer particles at a single-particle level, which is not easily accessible using conventional ensemble measurements.

Intrinsic electrocatalytic activity of a single IrOx nanoparticle towards oxygen evolution reaction.

Identifying the intrinsic electrocatalytic activity of an individual nanoparticle is challenging as traditional ensemble measurements only provide average activity over a large number of nanoparticles and may be greatly affected by the ensemble properties, irrelevant to the nanoparticle itself. Here, single-particle collision electrochemistry is used to investigate the electrocatalytic activity of a single IrOx nanoparticle towards the oxygen evolution reaction (OER). The collision frequency is linearly proportional to the nanoparticle concentration. The mean peak current and transferred charge, extracted from current spikes of the collision, present a similar potential dependence relevant to IrOx intrinsic activity. The turnover frequency (TOF) is determined as 1.55 × 102 O2 s-1, which is orders of magnitude larger than TOFs of the reported ensemble systems. In addition, the deactivation of a single IrOx nanoparticle is also explored based on a half-width analysis of current spikes. This versatilely applicable method provides new insights into the intrinsic performance of a single nanoparticle, which is essential to reveal the structure-activity relations of nanoscale materials for the rational design of advanced catalysts.

A New Reversible Phase Transformation of Intermetallic Ti3Sn.

Ti3Sn has received increasing attention as a high damping metallic material and as an anode material for rechargeable lithium-ion batteries. However, a heated dispute concerning the existence of solid state phase transformation of stoichiometric Ti3Sn impedes its development. Here, thermal-induced reversible phase transformation of Ti3Sn is demonstrated to happen at around 300 K by the means of in-situ variable-temperature X-ray diffraction (XRD) of Ti3Sn powder, which is also visible for bulk Ti3Sn on the thermal expansion curve by a turning at 330 K. The new phase's crystal structure of Ti3Sn is determined to be orthorhombic with a space group of Cmcm and the lattice parameters of a = 5.87 Å, b = 10.37 Å, c = 4.76 Å respectively, according to selected area electron diffraction patterns in transmission electron microscope (TEM) and XRD profiles. The hexagonal → orthorhombic phase transformation is calculated to be reasonable and consistent with thermodynamics theory. This work contributes to a growing knowledge of intermetallic Ti3Sn, which may provide fundamental insights into its damping mechanism.

Operando Synthesis of High-Curvature Copper Thin Films for CO2 Electroreduction.

As the sole metal that could reduce CO2 to substantial amounts of hydrocarbons, Cu plays an important role in electrochemical CO2 reduction, despite its low energy efficiency. Surface morphology modification is an effective method to improve its reaction activity and selectivity. Different from the pretreated modification method, in which the catalysts self-reconstruction process was ignored, we present operando synthesis by simultaneous electro-dissolution and electro-redeposition of copper during the CO2 electroreduction process. Through controlling the cathodic potential and CO2 flow rate, various high-curvature morphologies including microclusters, microspheres, nanoneedles, and nanowhiskers have been obtained, for which the real-time activity and product distribution is analyzed. The best CO2 electro-reduction activity and favored C2H4 generation activity, with around 10% faradic efficiency, can be realized through extensively distributed copper nanowhiskers synthesized under 40 mL/min flow rate and -2.1 V potential.

A transforming metal nanocomposite with large elastic strain, low modulus, and high strength.

Freestanding nanowires have ultrahigh elastic strain limits (4 to 7%) and yield strengths, but exploiting their intrinsic mechanical properties in bulk composites has proven to be difficult. We exploited the intrinsic mechanical properties of nanowires in a phase-transforming matrix based on the concept of elastic and transformation strain matching. By engineering the microstructure and residual stress to couple the true elasticity of Nb nanowires with the pseudoelasticity of a NiTi shape-memory alloy, we developed an in situ composite that possesses a large quasi-linear elastic strain of over 6%, a low Young's modulus of ~28 gigapascals, and a high yield strength of ~1.65 gigapascals. Our elastic strain-matching approach allows the exceptional mechanical properties of nanowires to be exploited in bulk materials.