Effect of Electric Field on Gas Hydrate Nucleation Kinetics: Evidence for the Enhanced Kinetics of Hydrate Nucleation by Negatively Charged Clay Surfaces

Natural gas hydrates are found widely in oceanic clay-rich sediments, where clay–water interactions have a profound effect on the formation behavior of gas hydrates. However, it remains unclear why and how natural gas hydrates are formed in clay-rich sediments in spite of factors that limit gas hydrate formation, such as small pore size and high salinity. Herein, we show that polarized water molecules on clay surfaces clearly promote gas hydrate nucleation kinetics. When water molecules were polarized with an electric field of 10⁴ V/m, gas hydrate nucleation occurred significantly faster with an induction time reduced by 5.8 times. Further, the presence of strongly polarized water layers at the water–gas interface hindered gas uptake and thus hydrate formation, when the electric field was applied prior to gas dissolution. Our findings expand our understanding of the formation habits of naturally occurring gas hydrates in clay-rich sedimentary deposits and provide insights into gas production from natural hydrate deposits

Evolution of Compressional Wave Velocity during CO₂ Hydrate Formation in Sediments

While the acoustic wave-based survey is considered to be one of the most effective and promising means for monitoring the behavior of particulate/discrete geomaterials, the P-wave velocity has scarcely been used to monitor the long-term behavior of CO₂ sequestered sediments or to understand the characteristics of CO₂ hydrate formation in sediments. Furthermore, there are still only limited reliable laboratory results quantifying the P-wave velocity change in sediments that results from CO₂ hydrate formation and accumulation processes. This study presents experimental measurements on the evolution of P-wave velocity as CO₂ hydrate saturation increases in unconsolidated sediment. The measured data are compared with the simple yet robust asymptotic Gassmann model to estimate CO₂ hydrate saturation (volume fraction of hydrate in pore space) in sediments. Given that in situ techniques to measure acoustic waves are well-established for the exploration of deep oceanic sediment, the methodology presented in this paper for estimating hydrate saturation is of potential significance in the monitoring of the long-term behavior of CO₂ reservoirs after sequestration in deep marine sediments

Destabilization of Marine Gas Hydrate-Bearing Sediments Induced by a Hot Wellbore: A Numerical Approach

This study addresses a numerical approach for exploring how thermal change destabilizes marine gas hydrate-bearing sediments. The underlying physical processes of hydrate-bearing sediments, such as hydrate dissociation, self-preservation, pore pressure evolution, gas dissolution, and sediment volume expansion, are incorporated with the thermal conduction, pore fluid flow, and mechanical response of sediments. Two-dimensional numerical modeling is conducted using a verified finite difference method, in which a steady-state hot wellbore transfers heat to the surrounding hydrate-bearing sediments, resulting in dissociation of methane hydrate. During gas hydrate dissociation, excess pore fluid pressure is generated such that the sediments undergo plastic deformation in the dissociation region and uplift at the seafloor. Sediment stability in the early stage of heat transfer is governed by the intensity of the heat source and the thermal conductivity of the sediments with gas hydrates in place. Later on, excess pore fluid pressure diffusing from the dissociation region destabilizes the shallower overlying sediments. Case studies show that the stability of sediments experiencing thermal change is worsened by an increase in the intensity of the heat source and the initial hydrate saturation. In addition, a decrease in the permeability, initial free gas saturation, and sediment strength also decreases the stability of sediments. A considerable uplifting deformation of the overlying sediments and a sediment failure in a cylindrical or conical shape around a wellbore are observed when the factor-of-safety becomes less than one

Phosphorescent Sensor for Phosphorylated Peptides Based on an Iridium Complex

A bis­[(4,6-difluorophenyl)­pyridinato-<i>N</i>,<i>C</i>^2′]­iridium­(III) picolinate (FIrpic) derivative coupled with bis­(Zn²⁺–dipicolylamine) (ZnDPA) was developed as a sensor (<b>1</b>) for phosphorylated peptides, which are related to many cellular mechanisms. As a control, a fluorescent sensor (<b>2</b>) based on anthracene coupled to ZnDPA was also prepared. When the total negative charge on the phosphorylated peptides was changed to −2, −4, and −6, the emission intensity of sensor <b>1</b> gradually increased by factors of up to 7, 11, and 16, respectively. In contrast, there was little change in the emission intensity of sensor <b>1</b> upon the addition of a neutral phosphorylated peptide, non-phosphorylated peptides, or various anions such as CO₃^2–, NO₃^–, SO₄^2–, phosphate, azide, and pyrophosphate. Furthermore, sensor <b>1</b> could be used to visually discriminate between phosphorylated peptides and adenosine triphosphate in aqueous solution under a UV–vis lamp, unlike fluorescent sensor <b>2</b>. This enhanced luminance of phosphorescent sensor <b>1</b> upon binding to a phosphorylated peptide is attributed to a reduction in the repulsion between the Zn²⁺ ions due to the phenoxy anion, its strong metal-to-ligand charge transfer character, and a reduction in self-quenching

Control and Monitoring of Dye Distribution in Mesoporous TiO₂ Film for Improving Photovoltaic Performance

Dye distribution in a mesoporous TiO₂ film is a key factor in the performance of dye-sensitized solar cells, but there has been little research on it. Here we report even dye distribution within the porous TiO₂ film achieved by a physical driving force of gas flow. Gas-assisted dye arrangement, gas bubbling soaking (GBS), significantly accelerates the dye infiltration compared to conventional overnight soaking (OS). As a demonstration, we investigated the time-dependent dye infiltration using plasmon sensors. GBS produces an even vertical dispersion throughout the film, as illustrated by time-of-flight secondary ion mass spectrometry depth profiles. For devices using a 7-μm-thick active layer and a ruthenium-based dye (N719), only 15 min of GBS treatment produced better power conversion efficiency (PCE) than the optimal result from OS treatment (15 h), despite a lower dye capacity. Dual-GBS treatment (20 min for N719 and 10 min for YD2, a porphyrin dye) produced the best PCE (9.0%) in the device, which was ∼17% higher than that treated with dual-OS (10 h for N719 and 5 h for YD2). Such improvements are associated with reduced dye-free sites inside the porous TiO₂ film after GBS treatment, leading to faster charge transport and slower charge loss

Strategy for Improved Photoconversion Efficiency in Thin Photoelectrode Films by Controlling π‑Spacer Dihedral Angle

Benzo­[<i>c</i>]­[1,2,5]­thiadiazole (BT) has been used in dye-sensitized solar cells (DSCs) for its light-harvesting abilities. However, as a strongly electron deficient unit, BT causes rapid back electron transfer (BET), which in turn lowers the photoconversion efficiency (PCE) of devices. Herein, we report a powerful strategy for retarding BET by controlling both the photoelectrode thickness and π-spacer dihedral angle. To achieve this, we introduced planar (<b>BT-T</b>) or twisted π-spacers (<b>BT-P</b>, <b>BT-MP</b>, and <b>BT-HT</b>) between BT units and anchoring groups and used different photoelectrode thicknesses between 1.8 and 10 μm. Computational and experimental results show that twisted π-spacers were more efficient at retarding BET than the planar π-spacer. However, BET was found to be less important than expected, and light harvesting efficiency (LHE) played a critical role as the thickness of the photoelectrode decreased because charge collection efficiency was enhanced. The planar dye <b>BT-T</b> obtained the highest LHE, this value remained unusually high even in 1.8 μm photoelectrodes. As a result, <b>BT-T</b> gave a PCE of 6.5% (<i>J</i>_sc = 13.56 mA/cm², <i>V</i>_oc = 0.67 V, and FF = 0.72) in thin 1.8 μm photoelectrodes with 3.5 μm scattering layers, which represented a roughly 40% enhancement compared to the PCE in 10 μm photoelectrodes (4.76%). Overall, these results provide a novel approach to achieving ultrathin and highly efficient flexible DSCs

Influence of the Lithium-Ion Concentration in Electrolytes on the Performance of Dye-Sensitized Photorechargeable Batteries

Dye-sensitized photorechargeable batteries (DSPBs) have recently gained attention for realizing energy recycling systems under dim light conditions. However, their performance under high storage efficiency (i.e., the capacity charged within a limited time) for practical application remains to be evaluated. Herein, we varied the lithium (Li)-ion concentration, which plays a dual role as energy charging and storage components, to obtain the optimized energy density of DSPBs. Electrochemical studies showed that the Li-ion concentration strongly affected the resistance characteristics of DSPBs. In particular, increasing the Li-ion concentration improved the output capacity and decreased the output voltage. Consequently, the energy density of the finely optimized DSPB improved from 8.73 to 12.64 mWh/cm3 when irradiated by a 1000-lx indoor light-emitting-diode lamp. These findings on the effects of Li-ion concentrations in electrolytes on the performance of DSPBs represent a step forward in realizing the practical application of DSPBs