Energy & Fuels最新文献

Deep saline aquifers are promising locations for carbon sequestration, but the impact of the CO₂ injection rate on rock properties requires careful investigation. This study examines the effects of CO₂-saturated brine injection on limestone, specifically analyzing how the injection rate influences wormhole formation and subsequent changes in petrophysical and geomechanical properties. Various injection rates were employed to investigate the impact of the injection rate, ranging from 0.25 to 5 cm³/min, for the coreflooding experiments. Before and after coreflooding, the Young’s modulus (YM) and Poisson’s ratio of the samples were measured at various confining pressures. Additionally, the porosity and the permeability of the treated samples were assessed. A micro-CT scan was employed to visualize the generated wormholes and quantify their volumes to calculate the Damkohler number. Our study revealed that among the five tested injection rates 1 cm³/min resulted in the lowest pore volumes to breakthrough (PVBT). We employed the Buijse and Glasbergen model, curve-fitting our data to determine the optimum velocity for CO₂-saturated brine, which was found to be 0.4 cm/min (equivalent to an injection rate of 0.75 cm³/min). All samples showed a noticeable change in rock YM, with the rock exposed to a 5 cm³/min injection rate showing the least reduction. Furthermore, our experiments revealed that conventional methods for determining the optimum conditions for wormhole formation, such as the Buijse and Glasbergen model and the generalized curve using the Damkohler number, are insufficient for accurately predicting wormhole formation in CO₂-saturated brine. The experiments demonstrated a significant deviation from the expected behavior in terms of the generalized curve. Additionally, the Buijse and Glasbergen model overestimated PVBT at interstitial velocities lower than the predicted optimum. These findings underscore the need for alternative approaches to accurately predict wormholing phenomena, specifically in CO₂ storage applications, where the brine is saturated with CO₂.

The electrochemical carbon dioxide reduction (CO^₂r) reaction offers a viable method for converting waste carbon dioxide into valuable products. Gas diffusion electrodes (GDEs) are crucial for meeting the high current density demands associated with the upscaling of CO₂r. In this research, we investigated how the microstructure of the catalytic layer in a Bi-based GDE and the catalyst nanostructure can be modified by altering the electrodeposition duty cycle. Furthermore, we explored how the microstructure influences the key performance indicators of the GDE. The outcomes demonstrated that decreasing the duty cycle of pulsed electrodeposition enhances the catalyst dispersibility within the three-dimensional catalytic layer, thereby improving catalytic performance. Additionally, reducing the duty cycle increased the nucleation site density, leading to smaller catalysts and denser catalytic sites, further enhancing the catalytic performance. By employing a Sustainion ionomer and a 60–80 μm thick catalytic layer, we achieved a current density exceeding −210 mA/cm² (at −1.0 V vs RHE) with 100% Faradaic efficiency for formate in a semi-batch testing bed. This research provides novel insights into catalytic layer design and offers a strategy to modify it to meet the stringent industrial benchmarks.

The impact of hydrophilic and hydrophobic surfaces and their confined space on the nucleation and growth of gas hydrates is an important topic in hydrate formation research. This study employed molecular dynamics simulations to investigate the nucleation and growth mechanisms of methane hydrate (MH) within the confined space between graphene and mica. The results demonstrate that MH formation is influenced by the methane mole fraction and the pore size of the graphene-mica nanochannel. Higher methane mole fractions led to an increased number of MH cages. Methane molecules were adsorbed onto the graphene surface, while the water molecules accumulated on the mica surface due to the hydration properties of K⁺ cations. Furthermore, methane cannot penetrate the hydrated structures of K⁺ on the mica surface, leading to the formation of stable MH cages in the central region of the graphene-mica nanochannel. This study reveals the nucleation and growth mechanisms of MH within the confined space formed by graphene and the mica surface. These findings are significant for advancing the understanding and control of gas hydrate formation on hydrophilic and hydrophobic surfaces.

Hydrogen has the potential to play a pivotal role in decarbonizing the energy sector. Electrochemical water splitting encompasses the hydrogen evolution reaction (HER) at the cathode utilizing platinum as a catalyst owing to its extraordinary performance. Nevertheless, low-cost, efficient, and stable electrocatalysts are required due to the high cost and scarcity of platinum. In the present study, a hydrothermally synthesized NiMoSe/Ti₃C₂T_x composite grown on activated carbon cloth (CC) has been investigated for its efficacy toward HER in an acidic medium (0.5 M H₂SO₄). Techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy have been incorporated to confirm and characterize the synthesis on CC. Consequently, the atomic ratio of Ni/Mo/Se/Ti has been determined as 1:2.78:3.12:1.06. Electrochemical characterization reveals an overpotential of 403 mV at −10 mA (η₁₀) as compared to 202 mV for commercial Pt/C (40%) and a Tafel slope of 33 mV dec^–1 as opposed to 28 mV dec^–1 for Pt/C. The use of MXene has a positive effect on the stability of the composite (49 mV increase in overpotential after 1000 cycles). Furthermore, a detailed economic and cradle-to-gate life cycle assessment has been done for the synthesized electrocatalyst, revealing a cost saving of 88.4% and a global warming potential of 0.15148 kg CO₂/(mg cm^–2). The synthesized electrocatalyst can thus be used as a cost-effective and efficient catalyst for electrochemical water splitting at the cathode.

To gain a deep understanding of the phase transition mechanisms of confined hydrocarbons, we first use the molecular dynamics simulations to model the phase transition process of hydrocarbons induced by temperature changes. The results show that the phase transition rates of confined hydrocarbons vary at different locations due to heterogeneous strength exerted by pore walls, which enables pure hydrocarbons to exhibit a multiphase coexistence state within the nanopores. Then, Grand Canonical Monte Carlo simulations were preformed to study the pore size effect and interfacial effect of n-pentane in nanopores. The pore size effect primarily influences the volume fraction of the adsorbed phase, while the interfacial effect regulates the density of the adsorption layers. This research provides theoretical insights into the phase behavior characteristic and phase transition mechanism of hydrocarbons in nanopores, which is significant for improving the recovery of shale oil and gas resources.

This study explores the catalytic properties of boron- and nitrogen-doped 585 extended line defects (585-ELD) in SiC monolayers for the CO₂ reduction reaction (CO₂RR). Using Density Functional Theory and ab initio Molecular Dynamics (AIMD) simulations, we analyze the stability, electronic structure, and adsorption characteristics of each doped defect. The results indicate that all doped systems, except for N–N, exhibit significant kinetic and thermodynamic stability, with midgap states that enhance electron availability and catalytic activity. Among the doped structures, the C–B ELD system uniquely balances CO₂ protonation and H₂ desorption, selectively favoring CO₂ reduction over hydrogen evolution. Calculated reaction free energies show that CH₄ formation is possible if the transition from H₂COH to CH₂ occurs, with a limiting potential (U_L) of 0.73 V, while strong interactions between H₂COH and the surface make CH₃OH formation energetically challenging. These findings position the C–B ELD SiC system as a promising candidate for efficient and selective CO₂ conversion, enabling the formation of valuable hydrocarbons and oxygenates through effective charge transfer and controlled reaction pathways.

The CH₄–CO₂ hydrate replacement exploitation method has gained high attention, but its low recovery efficiency hampers its application, and the reported limits of CH₄–CO₂ replacement vary greatly among different studies. This study introduces the concept of critical replacement thickness to quantify the exploitation limits of CH₄–CO₂ hydrate replacement, based on a series of CH₄–CO₂ replacement experiments conducted in a one-dimensional high-pressure reactor with well-defined hydrate-bearing sediments. Real-time hydrate composition analysis was employed to calculate the CH₄–CO₂ replacement limitation and critical replacement thickness at various stages of CO₂ flooding. The results show that during the initial stage, the replacement thickness is approximately 2–4 μm, while it decreases to 0.1–0.3 μm in the final stage. Additionally, the study systematically examines the impact of the hydrate particle size and fluid flow rate on CH₄ recovery and CO₂ sequestration. It is found that smaller particle sizes and higher flow rates significantly improve recovery efficiency, with CH₄ recovery increasing from 39.1 to 63.4% through optimization of these factors. Moreover, the mass transfer resistance created by the reformed CH₄–CO₂ hydrate film restricts the critical replacement thickness to no more than 7 μm for a particle size distribution of 0–250 μm without additional stimulation. The findings provide a clearer understanding of the factors influencing CH₄ recovery and offer insights into optimizing the replacement method for improved efficiency. These results contribute to the development of more effective strategies for the CH₄–CO₂ replacement exploitation in hydrate reservoirs.

The polymer solar cells (PSCs) have received a lot of research attention owing to their commendable qualities. However, the insufficient photoelectric conversion efficiency restricts their application and popularization, among which the existing problems can be summarized as low optical absorption leading to low spectral utilization of the device and the charge transfer obstructed due to energy level mismatch. Therefore, broadening the light absorption range of the active layer and promoting carrier transmission are the keys to improving the device performance. We synthesized blue polyfluorene derivatives containing a phenoxazine unit (PF-PO) and introduced in a PSC system based on PM6:IT-4F blends to improve the absorbance and improve the exciton dissociation efficiency and balanced charge carrier mobility. The power conversion efficiency (PCE) of the device improved from 12.64% when undoped to 13.97% after doping with PF-PO. The short-circuit density (J_SC) is improved from 21.23 to 22.47 mA/cm², and the fill factor (FF) is improved from 70.31 to 73.16%, which is the main factor for the improvement of device efficiency. These findings suggest that incorporating doping into the device is a highly effective method for improving the photovoltaic performance of the material.

SO₂-resistance ability is critical for a catalyst since SO₂ usually coexists in polluted gas and results in catalyst deactivation. In this work, structural design and Ce modification methods are utilized to synthesize a Ce-modified TiO₂-wrapped V₂O₅ catalyst, and its performance is verified in the selective catalytic reduction of nitrogen oxide (SCR). As a result, the wrapped structure (Ti/V_S) and Ce modification (CeTi/V_S) not only increase the conversion but also enhance the SO₂-resistance ability. Under the same V amount and catalysis conditions, Ti/V_S reaches a removal rate of 60% at 250 °C, which is higher than that (55%) of the typical V-supported TiO₂ (V/Ti). The conversion of CeTi/V_S is further increased to 72%. After SO₂ deactivation, conversions follow the order of 25% (V/Ti) < 38% (Ti/V_S) < 52% (CeTi/V_S). In addition, SO₂ deactivation is easier to reduce in the two wrapped catalysts under thermal regeneration. After detailed characterizations of surface elements and SCR intermediates, the mechanism for the enhanced SO₂-resistance ability is revealed. In brief, SO₂-derived species on Ti/V_S are replaceable by nitrogen oxide, and Ce-combined SO₂ in CeTi/V_S functions as new sites for SCR. Besides, the two wrapped catalysts have larger specific surface areas than V/Ti. The main result of this work is devoted to understanding the structure–function relationship, which is also in favor of promoting catalyst application.

The conversion of ethylene (C₂H₄) with photocatalysis provides an alternative to traditional C₂H₄ conversion into acetaldehyde (CH₃CHO) processes in industrial production. Herein, low-temperature C₂H₄ oxidation is conducted on rutile (R)-TiO₂(110) under the third-harmonic (343 nm) and fourth-harmonic (257 nm) outputs of the laser. The results illustrate that both hole-trapped bridging oxygen (O_b^–) and Ti_5c bound oxygen adatom (O_Ti^–) are photoactive for C₂H₄ conversion. The former is strongly wavelength-dependent, which mainly induces C₂H₄ dehydrogenation into the C₂H₃^• radical, which follows an Eley–Rideal (E–R) type direct mechanism. Conversely, the latter induces two parallel reaction pathways to produce C₂H₂ via the elimination pathway and acetaldehyde (CH₃CHO) via the addition pathway. The latter pathway may undergo formation of oxometallacycle intermediates on the surface. These results not only achieve C₂H₄ direct conversion into useful partial oxidation products via photocatalysis but also further deepen the understanding of the nature of C–H activation.