Energy & Fuels最新文献

The acid production reaction between CO₂ and water in rocks changes the pore structure, thereby altering the rock mechanical properties. To ensure the safety of CO₂ storage, it is critical to identify the rock damage mechanisms, clarify the variation patterns of mechanical properties under damage conditions, and investigate the flow characteristics of two-phase CO₂-water systems under complex mixed-wettability. This study established a constant-temperature and -pressure multiphase CO₂-rock immersion experimental system. Additionally, a comprehensive experimental procedure integrating CO₂ immersion, CT imaging, and uniaxial compression was designed. A comparative study revealed that reactions involving gaseous CO₂ and ScCO₂ with water increased the core porosity by 1.2% and 2.9%, respectively. During the immersion period, gaseous CO₂ accumulated on the upper section of the rock, causing a sharp increase in the surface porosity of the upper section (Δϕ = 0.9%). By contrast, ScCO₂ accumulated on the middle section, causing a substantial increase in the surface porosity of the middle part (Δϕ = 2.8%). After the CO₂ saturation in different phase states, the pore connectivity of the core was enhanced. When exposed to gaseous CO₂, some isolated micropores became interconnected, thereby increasing connected porosity from 13.0 to 13.9%. When exposed to ScCO₂, the connected porosity increased from 11.3 to 11.7%. Under damage conditions, the primary factors contributing to the deterioration of mechanical properties were the expansion of the pore volume and the increase in the number of connected pores. Compared to gaseous CO₂, ScCO₂ generated stronger carbonic acid upon reaction with water. After the acidification reaction, the number of both interconnected and isolated pores within the core increased, leading to considerable changes in the mechanical properties. Specifically, the compressive strength and elastic modulus decreased by 19.08 and 16.2%, respectively, and the Poisson’s ratio increased by 26.9%. Under the single-phase wettability, the displacement efficiencies of gaseous CO₂ and ScCO₂ were enhanced under weak and strong wettability conditions, respectively. The displacement efficiencies of gaseous CO₂ and ScCO₂ under complex mixed-wettability decreased by 5.7 and 15.3%, respectively, compared with those observed under single-phase wettability. Therefore, neglecting the complex mixed-wettability of pore wall surface often leads to the overestimation of displacement efficiency.

Thermal decomposition of iron carbonate in the steel industry is one of the major sources of industrial CO₂ emissions. Hydrogenation of iron carbonate using renewable-driven green hydrogen (H₂) serves a transformative strategy for in situ CO₂ utilization by coupling iron production. In this study, we focus on the hydrogenation behavior of various iron carbonates in a fluidized bed using siderite as the raw material, as well as on the room-temperature pyrophoricity of the resulting reduced iron as a fundamental step related to iron-based zero-carbon fuel applications. The effects of siderite type, reaction atmosphere, and hydrogenation temperature during the hydrogenation process on the distribution of resulting gaseous products are systematically investigated using a thermogravimetric analyzer (TGA) and a fluidized bed reactor. Hydrogenation reduced the starting decomposition temperature of siderites by 50–100 °C and increased the decomposition rate. At temperatures below 400 °C, CO was mainly derived from the direct hydrogenation of siderite, and its yield increased with hydrogenation temperature. CH₄ was entirely generated from the direct hydrogenation of siderite, with its yield peaked at 400–450 °C. Metallic iron was the primary iron phase after hydrogenation of siderite. At temperatures above 450 °C, metallic iron exhibited catalytic effects on the reverse water-gas shift (RWGS) reaction of CO₂. At room temperature, metallic iron was highly reactive and quickly oxidized by O₂, leading to pyrophoricity. The peak temperatures during the pyrophoricity process were primarily influenced by the porous structure after hydrogenation and the O₂ concentration. Meanwhile, microexplosions were observed during the pyrophoricity process.

It is a challenging process to recover oil from high-temperature and high-salinity (HTHS) heavy oil reservoirs because the viscosity of conventional polymers will be greatly reduced under HTHS conditions, and precipitation will easily occur. Temperature-resistant and calcium–magnesium-resistant (TR & CMR) polymers and TR & CMR surfactant–polymer (SP) flooding systems are being employed for oil recovery. To elucidate the mechanisms behind the enhanced oil recovery performance of these systems in such challenging environments and to investigate viable strategies for further improvement in oil recovery, this study examined the effectiveness of polymer flooding and SP flooding using a large three-dimensional (3D) flat-plate model. Following an evaluation of the properties of the polymer and surfactant employed in the experiment, large 3D flat-plate displacement oil experiments were conducted. Subsequently, the mechanism underlying the enhanced oil recovery from HTHS heavy-oil reservoirs achieved through the application of the TR & CMR polymer and TR & CMR SP flooding system was elucidated. The results showed that (1) The TR & CMR polymer exhibited a smaller molecular coil size, coupled with robust intermolecular association and cross-linking, significantly augmenting its capacity for viscosity enhancement. Furthermore, the incorporation of AMPS into the polymer enhanced its rigidity, thereby imparting it with excellent salt tolerance and high-temperature stability. The incorporation of the surfactant did not compromise the viscosity of the polymer, and the polymer and surfactant exhibited excellent compatibility. (2) In the process of TR & CMR polymer displacement, the water cut of the produced fluid was significantly reduced, the swept volume was effectively increased, and the recovery degree could be improved. Compared with water flooding, the water cut during polymer flooding decreased by 34.08%, the swept area increased by 28%, and the oil recovery increased by 11.67%. (3) Compared with water flooding, the water cut of the SP flooding system decreased by 46.28% during flooding, the swept area increased by 30%, and the recovery rate increased by 17.91%. Compared with polymer flooding, the oil recovery was further increased by 6.24%. SP flooding improved the oil washing efficiency, the remaining oil production degree was higher, and the remaining oil saturation was lower. The study can serve as an important basis for improving oil recovery from HTHS heavy-oil reservoirs.

The acid production reaction between CO₂ and water in rocks changes the pore structure, thereby altering the rock mechanical properties. To ensure the safety of CO₂ storage, it is critical to identify the rock damage mechanisms, clarify the variation patterns of mechanical properties under damage conditions, and investigate the flow characteristics of two-phase CO₂-water systems under complex mixed-wettability. This study established a constant-temperature and -pressure multiphase CO₂-rock immersion experimental system. Additionally, a comprehensive experimental procedure integrating CO₂ immersion, CT imaging, and uniaxial compression was designed. A comparative study revealed that reactions involving gaseous CO₂ and ScCO₂ with water increased the core porosity by 1.2% and 2.9%, respectively. During the immersion period, gaseous CO₂ accumulated on the upper section of the rock, causing a sharp increase in the surface porosity of the upper section (Δϕ = 0.9%). By contrast, ScCO₂ accumulated on the middle section, causing a substantial increase in the surface porosity of the middle part (Δϕ = 2.8%). After the CO₂ saturation in different phase states, the pore connectivity of the core was enhanced. When exposed to gaseous CO₂, some isolated micropores became interconnected, thereby increasing connected porosity from 13.0 to 13.9%. When exposed to ScCO₂, the connected porosity increased from 11.3 to 11.7%. Under damage conditions, the primary factors contributing to the deterioration of mechanical properties were the expansion of the pore volume and the increase in the number of connected pores. Compared to gaseous CO₂, ScCO₂ generated stronger carbonic acid upon reaction with water. After the acidification reaction, the number of both interconnected and isolated pores within the core increased, leading to considerable changes in the mechanical properties. Specifically, the compressive strength and elastic modulus decreased by 19.08 and 16.2%, respectively, and the Poisson’s ratio increased by 26.9%. Under the single-phase wettability, the displacement efficiencies of gaseous CO₂ and ScCO₂ were enhanced under weak and strong wettability conditions, respectively. The displacement efficiencies of gaseous CO₂ and ScCO₂ under complex mixed-wettability decreased by 5.7 and 15.3%, respectively, compared with those observed under single-phase wettability. Therefore, neglecting the complex mixed-wettability of pore wall surface often leads to the overestimation of displacement efficiency.

Thermal decomposition of iron carbonate in the steel industry is one of the major sources of industrial CO₂ emissions. Hydrogenation of iron carbonate using renewable-driven green hydrogen (H₂) serves a transformative strategy for in situ CO₂ utilization by coupling iron production. In this study, we focus on the hydrogenation behavior of various iron carbonates in a fluidized bed using siderite as the raw material, as well as on the room-temperature pyrophoricity of the resulting reduced iron as a fundamental step related to iron-based zero-carbon fuel applications. The effects of siderite type, reaction atmosphere, and hydrogenation temperature during the hydrogenation process on the distribution of resulting gaseous products are systematically investigated using a thermogravimetric analyzer (TGA) and a fluidized bed reactor. Hydrogenation reduced the starting decomposition temperature of siderites by 50–100 °C and increased the decomposition rate. At temperatures below 400 °C, CO was mainly derived from the direct hydrogenation of siderite, and its yield increased with hydrogenation temperature. CH₄ was entirely generated from the direct hydrogenation of siderite, with its yield peaked at 400–450 °C. Metallic iron was the primary iron phase after hydrogenation of siderite. At temperatures above 450 °C, metallic iron exhibited catalytic effects on the reverse water-gas shift (RWGS) reaction of CO₂. At room temperature, metallic iron was highly reactive and quickly oxidized by O₂, leading to pyrophoricity. The peak temperatures during the pyrophoricity process were primarily influenced by the porous structure after hydrogenation and the O₂ concentration. Meanwhile, microexplosions were observed during the pyrophoricity process.

It is a challenging process to recover oil from high-temperature and high-salinity (HTHS) heavy oil reservoirs because the viscosity of conventional polymers will be greatly reduced under HTHS conditions, and precipitation will easily occur. Temperature-resistant and calcium–magnesium-resistant (TR & CMR) polymers and TR & CMR surfactant–polymer (SP) flooding systems are being employed for oil recovery. To elucidate the mechanisms behind the enhanced oil recovery performance of these systems in such challenging environments and to investigate viable strategies for further improvement in oil recovery, this study examined the effectiveness of polymer flooding and SP flooding using a large three-dimensional (3D) flat-plate model. Following an evaluation of the properties of the polymer and surfactant employed in the experiment, large 3D flat-plate displacement oil experiments were conducted. Subsequently, the mechanism underlying the enhanced oil recovery from HTHS heavy-oil reservoirs achieved through the application of the TR & CMR polymer and TR & CMR SP flooding system was elucidated. The results showed that (1) The TR & CMR polymer exhibited a smaller molecular coil size, coupled with robust intermolecular association and cross-linking, significantly augmenting its capacity for viscosity enhancement. Furthermore, the incorporation of AMPS into the polymer enhanced its rigidity, thereby imparting it with excellent salt tolerance and high-temperature stability. The incorporation of the surfactant did not compromise the viscosity of the polymer, and the polymer and surfactant exhibited excellent compatibility. (2) In the process of TR & CMR polymer displacement, the water cut of the produced fluid was significantly reduced, the swept volume was effectively increased, and the recovery degree could be improved. Compared with water flooding, the water cut during polymer flooding decreased by 34.08%, the swept area increased by 28%, and the oil recovery increased by 11.67%. (3) Compared with water flooding, the water cut of the SP flooding system decreased by 46.28% during flooding, the swept area increased by 30%, and the recovery rate increased by 17.91%. Compared with polymer flooding, the oil recovery was further increased by 6.24%. SP flooding improved the oil washing efficiency, the remaining oil production degree was higher, and the remaining oil saturation was lower. The study can serve as an important basis for improving oil recovery from HTHS heavy-oil reservoirs.

In this study, magnetite (Fe₃O₄)-based nanostructures were engineered in four different forms: pristine Fe₃O₄ (F), Cu-substituted Fe₃O₄ (FC), Fe₃O₄ incorporated with reduced graphene oxide (FR), and a ternary composite of Cu–Fe₃O₄ with rGO (FCR). The materials were obtained via a simple coprecipitation route and assessed for their suitability in supercapacitors, electrocatalytic water splitting, and hydrovoltaic energy harvesting. Extensive analyses, including structural, morphological, surface area (BET), chemical (XPS), and thermal studies, confirmed the successful formation and stability of the composites. Electrochemical testing of the symmetric FCR device revealed a specific capacitance of 193 F g^–1 with an energy density of 26.79 W h kg^–1 at 1 A g^–1. The device preserved 89.06% of its initial capacitance and exhibited 91.22% Coulombic efficiency after 8000 charge–discharge cycles, confirming its robust durability. In water-splitting studies, the FCR electrode showed excellent bifunctional activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), achieving low overpotentials of 94 mV and 228 mV, respectively. A complete water-splitting system based on FCR required only 1.672 V to drive 10 mA cm^–2 in an alkaline medium. Furthermore, hydrovoltaic evaluation demonstrated that FCR could generate an open-circuit voltage of 0.61 V and a short-circuit current of 0.6 μA. Collectively, these findings establish Cu–Fe₃O₄/rGO as a versatile multifunctional material with significant potential for integrated energy storage and conversion technologies.

In this study, magnetite (Fe₃O₄)-based nanostructures were engineered in four different forms: pristine Fe₃O₄ (F), Cu-substituted Fe₃O₄ (FC), Fe₃O₄ incorporated with reduced graphene oxide (FR), and a ternary composite of Cu–Fe₃O₄ with rGO (FCR). The materials were obtained via a simple coprecipitation route and assessed for their suitability in supercapacitors, electrocatalytic water splitting, and hydrovoltaic energy harvesting. Extensive analyses, including structural, morphological, surface area (BET), chemical (XPS), and thermal studies, confirmed the successful formation and stability of the composites. Electrochemical testing of the symmetric FCR device revealed a specific capacitance of 193 F g^–1 with an energy density of 26.79 W h kg^–1 at 1 A g^–1. The device preserved 89.06% of its initial capacitance and exhibited 91.22% Coulombic efficiency after 8000 charge–discharge cycles, confirming its robust durability. In water-splitting studies, the FCR electrode showed excellent bifunctional activity toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), achieving low overpotentials of 94 mV and 228 mV, respectively. A complete water-splitting system based on FCR required only 1.672 V to drive 10 mA cm^–2 in an alkaline medium. Furthermore, hydrovoltaic evaluation demonstrated that FCR could generate an open-circuit voltage of 0.61 V and a short-circuit current of 0.6 μA. Collectively, these findings establish Cu–Fe₃O₄/rGO as a versatile multifunctional material with significant potential for integrated energy storage and conversion technologies.

With the increase in the power density of proton exchange membrane fuel cells, the requirements for cell heat dissipation are also increasing. Raising the cell operating temperature to the boiling point temperature range (100–120 °C) can increase the temperature difference between the cells and the external environment, which is an effective method to enhance the cell heat dissipation capacity. However, a high temperature promotes the formation of peroxides on the surface of Pt catalysts and carbon supports, which react with each other to release carbon dioxide, causing carbon support corrosion. Carbon corrosion can exacerbate Pt degradation and reduce the fuel cell life. Therefore, taking into account the characteristics of a cross-temperature (C-T) fuel cell operating at high temperature, a Pt degradation model considering the carbon corrosion effect under dynamic loading conditions is constructed. In this model, the coupling effects of electrochemical dissolution/redeposition, Pt precipitation in the membrane, and Pt particle detachment/agglomeration are simultaneously considered, which can accurately describe the Pt degradation processes of normal-temperature (N-T) and C-T fuel cells under dynamic loading conditions. The characteristic parameters of Pt catalysts after degradation can also be obtained. Based on this model, this study found that the Pt degradation processes in N-T and C-T fuel cells are dominated by dissolution/redeposition and detachment/agglomeration, respectively. In addition, through the analysis of carbon corrosion dynamics, it was found that carbon corrosion mainly occurs during the rapid voltage change period, and the carbon corrosion rate is inversely proportional to the voltage change rate and the Pt particle size on the surface of the carbon support.

Coal electrolysis represents a paradigm shift from conventional high-emission applications by utilizing electrical current to decompose coal’s macromolecular structure into valuable chemical compounds. Despite technological advances, the relationship between particle size distribution and mechanistic pathways remains underexplored. This study systematically investigated particle size effects across three ranges (25–45, 45–75, and 75–106 μm) on charge consumption and structural evolution during repeated electrolysis cycles. Results demonstrated that 25–45 μm particles exhibited the highest charge consumption, indicating superior electrolysis performance. Ultimate analysis revealed increased carbon content and decreased oxygen content postelectrolysis across all sizes. Comprehensive characterization using Brunauer–Emmett–Teller (BET) surface area analysis, scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and solid-state ¹³C nuclear magnetic resonance (NMR) provided mechanistic insights into structural transformations. BET and SEM analyses confirmed significant surface modifications including increased surface area, enhanced pore volume, and surface crack development. Raman and XRD revealed increased graphitic character and crystallinity with reduced structural defects. FTIR and NMR spectroscopy demonstrated substantial transformations in aliphatic and aromatic carbon groups. The most pronounced structural changes occurred in smaller particles, establishing 25–45 μm as the optimal particle size range for coal electrolysis applications.