Probing dissolved CO2(aq) in aqueous solutions for CO2 electro-reduction and storage

CO2 dissolved in aqueous solutions is of wide ranging importance from CO2 capture, storage and photo-/electro-reduction in the fight against global warming, to CO2 analysis in various liquids including natural waterbodies and consumer drinking products. Here we developed micro-scale infrared (IR) spectroscopy for in-situ dynamic monitoring and quantitating CO2(aq) in aqueous solutions with high time resolutions under various conditions including CO2 gas bubbling and high pressures. The quantized CO2(g) rotational state transitions were observed to quench when dissolved in water to form CO2(aq) solvated by water molecules, accompanied by increased H2O IR absorption. An accurate CO2 molar extinction coefficient ε was derived for in-situ CO2(aq) quantification up to 58 atm. For the first time, we directly measured CO2(aq) concentrations in electrolytes under CO2(g) bubbling and high pressure conditions. In KHCO3 electrolytes with CO2(aq) > ~ 1 M, CO2 electroreduction (CO2RR) to formate reaches > 98% Faradaic efficiencies on copper (Cu2O/Cu) based electrocatalyst. Further, we probed CO2 dissolution/desolvation kinetics important to energy and environmental applications dynamically, revealing large hysteresis and ultra-slow reversal of CO2(aq) supersaturation in water, with implications to CO2 capture, storage and supersaturation phenomena in natural water bodies.

Force Dependence of Proteins’ Transition State Position and the Bell–Evans Model

Single-molecule force spectroscopy has opened a new field of research in molecular biophysics and biochemistry. Pulling experiments on individual proteins permit us to monitor conformational transitions with high temporal resolution and measure their free energy landscape. The force–extension curves of single proteins often present large hysteresis, with unfolding forces that are higher than refolding ones. Therefore, the high energy of the transition state (TS) in these molecules precludes kinetic rates measurements in equilibrium hopping experiments. In irreversible pulling experiments, force-dependent kinetic rates measurements show a systematic discrepancy between the sum of the folding and unfolding TS distances derived by the kinetic Bell–Evans model and the full molecular extension predicted by elastic models. Here, we show that this discrepancy originates from the force-induced movement of TS. Specifically, we investigate the highly kinetically stable protein barnase, using pulling experiments and the Bell–Evans model to characterize the position of its kinetic barrier. Experimental results show that while the TS stays at a roughly constant distance relative to the native state, it shifts with force relative to the unfolded state. Interestingly, a conversion of the protein extension into amino acid units shows that the TS position follows the Leffler–Hammond postulate: the higher the force, the lower the number of unzipped amino acids relative to the native state. The results are compared with the quasi-reversible unfolding–folding of a short DNA hairpin.

Design and Performance Study of Clutch Disc Assembly of Wide-Angle, Large-Hysteresis, Multistage Damper

The clutch is an important component of the vehicle driveline system. One of its major functions is to attenuate or eliminate the torsional vibration and noise of the driveline system caused by the engine. Based on experiments of vibration damping under different vehicle conditions, the structure and functional principle of a clutch-driven disc assembly for a wide-angle, large-hysteresis, multistage damper is investigated in this study using an innovative combined approach. Furthermore, a systematic integration of key technologies, including wide-angle low-stiffness damping technology, large-hysteresis clutch technology, a novel split pre-damping structure technology, damping structure technology for component cushioning, and multistage damping structure technology, is proposed. The results show that the total torsional angle of the wide-angle large-hysteresis, multistage damper is more than twice that of the traditional clutch damper. The multistage damping design allows a better consideration of various damping requirements under different vehicle conditions, which can effectively address problems of severe idle vibrations and torsional resonance that occur under idled and accelerated conditions. Meanwhile, the use of a large-hysteresis structure and wear-resistant materials not only improves the vibration damping performance, but also prolongs the product service life, consequently resulting in multi-faceted optimization and innovative products.

Effects of Binder and Substrate Materials on the Performance and Reliability of Stretchable Nanocomposite Strain Sensors

In stretchable strain sensors, highly elastic elastomers such as polydimethylsiloxane (PDMS), Ecoflex, and polyurethane are commonly used for binder materials of the nanocomposite and substrates. However, the viscoelastic nature of the elastomers and the interfacial action between nanofillers and binders influence the critical sensor performances, such as repeatability, response, and hysteresis behavior. In this study, we developed a stretchable nanocomposite strain sensor composed of multiwalled carbon nanotubes and a silicone elastomer binder. The effects of binder and substrate materials on the repeatability, response, hysteresis behavior, and long-term endurance of the strain sensors were systematically investigated using stretching, bending, and repeated cyclic bending tests. Three different binder and substrate materials including PDMS, Ecoflex, and a mixture of PDMS/Ecoflex were tested. The stretchable strain sensors showed an excellent linearity and stretchability of more than 130%. Therefore, the long-term endurance of the strain sensors fabricated with Ecoflex binder should be improved. The strain sensors fabricated with Ecoflex binder showed a relatively large variation in electrical resistance during 10,000-cycle bending tests and repeatability errors at large bending angles. The strain sensors fabricated with PDMS binder showed repeatability errors at small bending angles and a slight response delay of 1 second. On the contrary, the strain sensors fabricated with a mixture of PDMS/Ecoflex binder showed excellent repeatability and response characteristics. The PDMS material showed hysteresis behavior; therefore, the strain sensors fabricated with PDMS binder on PDMS substrate exhibited a large hysteresis behavior in the first stretch–release cycle. It was found that the hysteresis behavior of the strain sensors was mainly dependent on substrate materials than on binder materials. The stretchable strain sensors made of the mixture of PDMS/Ecoflex exhibited excellent repeatability, response, hysteresis behavior, and excellent capability in detecting finger and wrist bending.

Tunable optoelectronic properties of a two-dimensional graphene/α-In2Se3/graphene-based ferroelectric semiconductor field-effect transistor

Two-dimensional (2D) materials are promising for future electronic and optoelectronic devices. In particular, 2D material-based photodetectors have been widely studied because of their excellent photodetection performance. Owing to its excellent electrical and optical characteristics, 2D indium selenide (α-In2Se3) is a good candidate for photodetection applications. In addition, α-In2Se3 samples, including atom-thick α-In2Se3 layers, present ferroelectric properties. Herein, we report the fabrication and electrical and optoelectronic properties of multilayered graphene (Gr)/α-In2Se3/Gr-based ferroelectric semiconductor field-effect transistors (FeS-FETs). Furthermore, we discuss the physical mechanisms affecting electronic and optoelectronic transport in the Gr/α-In2Se3/Gr heterostructure. Large hysteresis was observed in the transfer characteristic curves and it was attributed to the ferroelectric polarization of MTL α-In2Se3 and carrier trapping–detrapping effects. The optoelectronic performance of the fabricated FeS-FETs depended on the ferroelectric properties of α-In2Se3 and can be easily tuned to achieve the maximum photoresponsivity and specific detectivity of 10 AW-1 and 4.4 × 1012 cmHz1/2W-1, respectively.

Insight into formation propensity of pseudocircular DNA G-hairpins

We recently showed that Saccharomyces cerevisiae telomeric DNA can fold into an unprecedented pseudocircular G-hairpin (PGH) structure. However, the formation of PGHs in the context of extended sequences, which is a prerequisite for their function in vivo and their applications in biotechnology, has not been elucidated. Here, we show that despite its ‘circular’ nature, PGHs tolerate single-stranded (ss) protrusions. High-resolution NMR structure of a novel member of PGH family reveals the atomistic details on a junction between ssDNA and PGH unit. Identification of new sequences capable of folding into one of the two forms of PGH helped in defining minimal sequence requirements for their formation. Our time-resolved NMR data indicate a possibility that PGHs fold via a complex kinetic partitioning mechanism and suggests the existence of K+ ion-dependent PGH folding intermediates. The data not only provide an explanation of cation-type-dependent formation of PGHs, but also explain the unusually large hysteresis between PGH melting and annealing noted in our previous study. Our findings have important implications for DNA biology and nanotechnology. Overrepresentation of sequences able to form PGHs in the evolutionary-conserved regions of the human genome implies their functionally important biological role(s).

Resistance Switching Effect in Octahedral framework oxide

Resistive Random-Access Memories (ReRAM) are an alternative way to create new memory devices. This is physically possible due to the existence in the material, of two resistive states clearly discreditable, as a function of voltage value and polarity first parameter under control to pass from one state to another one. However, the mechanism of the resistance switching is not simple and is under debate. We present in the present chapter all the factors entering in the switching process in tetragonal tungsten bronze (TTB) type structure oxide thin films deposited by PLD technique onto MgO or STO substrates. Results show that GdK2Nb5O15 (GKN) thin films deposited on MgO and STO substrates are resistively switchable. It was found that the nature of the substrate strongly affects the resistance ratio: GKN on SRO/LSCO/MgO showed a large hysteresis compared to GKN on SRO/STO. Substrate effect and oxygen vacancy on resistance switching in GKN thin film were studied in the same experimental conditions. The study of resistance switching in the GKN/MgO and GKN/STO thin films has confirmed that for low voltages, below the threshold value of 1.3 V, the electric transport is dominated by the formation of a Schottky type barrier, which allows a minimum leakage current. Resistance switching in GKN is attributed to the oxygen vacancies migration which can be controlled by the substrate or the frequency sweep.

Excellent energy storage properties and stability of NaNbO3-Bi(Mg0.5Ta0.5)O3 ceramic by introducing (Bi0.5Na0.5)0.7Sr0.3TiO3

NaNbO3-based energy storage ceramics have the characteristics of high breakdown field strength (Eb) with large energy storage density (Wrec). However, due to the large hysteresis loss (Wloss) under high electric...