Carbon nanotubes (CNTs), which exhibit stable surfaces under acidic, neutral and alkaline solutions, provide an ideal platform for studying the nature of oxygen evolution reaction (OER) mechanisms at ...different pH. Here, OER on four types of pristine carbon nanotubes (CNTs) with walls from single-walled, double-walled, three-walled to multi-walled were studied in acid, neutral and alkaline conditions. Mechanism and kinetics study reveals that the OER on all CNTs is constrained by the water deprotonation in acid and neutral conditions,resulting in high Tafel slopes close to 240 mV dec−1, high overpotentials (0.7–1 V), and approaching zeroth-reaction-order to H+/OH−. The kinetics and mechanism shift at pH ∼9–10 due to competition discharge between H2O and OH−. The Tafel slopes decrease, and the reaction orders increase with the increase of OH− concentration. The higher kinetics and enhanced activities for CNTs with 2–4 walls support the proposed tunneling effect, highlighting the favourable electron transfer pathway between the outer wall and inner tubes. The finding will provide a new direction for designing highly efficient OER catalysts.
Concentration of electrolyte has significant effects on performances of rechargeable batteries. Previous studies mainly focused on concentrated electrolytes. So far, only several recipes on ...low‐concentration electrolytes were studied, performing enhanced performance in advanced rechargeable batteries. Here, based on common electrolyte components, a low‐concentration electrolyte composed of 0.2 M lithium hexafluorophosphate (LiPF6) solvated in fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) is employed for high‐voltage Li metal battery. The synergistic working mechanisms of introducing fluorine‐containing solvent in the solvated structure and low salt concentration effect are revealed, resulting in LiF‐rich, uniform, and robust solid electrolyte interphase layer and fewer unfavorable decomposition products. As a result, this low‐concentration electrolyte significantly enhances electrochemical performances of Li||Li symmetric cells and high‐voltage LiCoO2||Li batteries.
A low‐concentration electrolyte was employed in high‐voltage lithium metal batteries. The synergistic effects of fluorinated solvation shell and low salt concentration generated robust and LiF‐rich SEI and fewer unfavorable decomposition products. The excellent performance implies that the optimization of low concentration electrolytes is a successful solution for low‐cost and large‐scale electrolyte designs.
Expanded graphite has garnered considerable interest for potential applications in electrochemical energy storage due to its distinctive morphological and structural Li storage features. However, the ...present synthetic procedure of preparing expanded graphite is highly complex and yields low production. Herein, we demonstrate that an efficient microwave method can produce large-scale expanded graphite utilizing anthracite as a precursor. The designed expanded graphite exhibits a remarkably ordered graphitic structure and a unique morphology of porous layered gossamer nanosheets having a wider pore size distribution within the ranges of 3–70 nm and a practically huge specific surface area being 21.5 m2 g−1, which are beneficial for improving the conductivity of expanded graphite, inducing more active sites for electrochemical reactions and accelerating Li+ diffusion. Furthermore, the expanded graphite demonstrates a promising capacity utilization of 278.0 mAh g−1 and a stable Coulombic efficiency of 99.17% during 300 cycles at 0.2C when it is employed as lithium-ion batteries anode material. Hence, this study presents a promising method for the large-scale production of expanded graphite materials as anodes for lithium-ion battery by exploiting natural anthracite as the low-cost raw material.
•Expanded graphite was synthesized by microwave method utilizing anthracite as precursor.•The prepared expanded graphite demonstrated ordered graphitic structure and unique layered gossamer nanosheets.•The expanded graphite delivered a capacity of 278.0 mAh g−1 and 99.17% Coulombic efficiency.•Microwave method is suitable to achieve large-scale production of anode materials.
PtRu alloys have been recognized as the state-of-the-art catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, their applications in DMFCs are still less ...efficient in terms of both catalytic activity and durability. Rare earth (RE) metals have been recognized as attractive elements to tune the catalytic activity, while it is still a world-class challenge to synthesize well-dispersed Pt-RE alloys. Herein, we developed a novel hydrogen-assisted magnesiothermic reduction strategy to prepare a highly dispersed carbon-supported lutetium-doped PtRu catalyst with ultrafine nanoclusters and atomically dispersed Ru sites. The PtRuLu catalyst shows an outstanding high electrochemical surface area (ECSA) of 239.0 m2 gPt –1 and delivers an optimized MOR mass activity and specific activity of 632.5 mA mgPt –1 and 26 A cmPt –2 at 0.4 V vs saturated calomel electrode (SCE), which are 3.6 and 3.5 times of commercial PtRu-JM and an order higher than PtLu, respectively. These novel catalysts have been demonstrated in a high-temperature direct methanol fuel cell running in a temperature range of 180–240 °C, achieving a maximum power density of 314.3 mW cm–2. The AC-STEM imaging, in situ ATR-IR spectroscopy, and DFT calculations disclose that the high performance is resulted from the highly dispersed PtRuLu nanoclusters and the synergistic effect of the atomically dispersed Ru sites with PtRuLu nanoclusters, which significantly reduces the CO* intermediates coverage due to the promoted water activation to form the OH* to facilitate the CO* removal.
Concentration of electrolyte has significant effects on performances of rechargeable batteries. Previous studies mainly focused on concentrated electrolytes. So far, only several recipes on ...low‐concentration electrolytes were studied, performing enhanced performance in advanced rechargeable batteries. Here, based on common electrolyte components, a low‐concentration electrolyte composed of 0.2 M lithium hexafluorophosphate (LiPF6) solvated in fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC) is employed for high‐voltage Li metal battery. The synergistic working mechanisms of introducing fluorine‐containing solvent in the solvated structure and low salt concentration effect are revealed, resulting in LiF‐rich, uniform, and robust solid electrolyte interphase layer and fewer unfavorable decomposition products. As a result, this low‐concentration electrolyte significantly enhances electrochemical performances of Li||Li symmetric cells and high‐voltage LiCoO2||Li batteries.
A low‐concentration electrolyte was employed in high‐voltage lithium metal batteries. The synergistic effects of fluorinated solvation shell and low salt concentration generated robust and LiF‐rich SEI and fewer unfavorable decomposition products. The excellent performance implies that the optimization of low concentration electrolytes is a successful solution for low‐cost and large‐scale electrolyte designs.
The controllable design of low-cost oxygen electrocatalysts with outstanding activity and durability is a top priority for rechargeable metal–air batteries. Herein, a facile approach is proposed for ...obtaining hierarchically porous cobalt–nitrogen codoped carbon for reversible oxygen reduction and evolution reactions via the pyrolysis of Co/Zn bimetallic coordinated polymers with gradient Co:Zn ratio. The evaporation of Zn species during the pyrolysis process combined with the Kirkendall effect of Co species resulted in the formation of hierarchical porosity, which further creates highly accessible defective sites and improves multiscale mass transfer. The C-7Co93Zn catalyst with optimized defective Co–Nx and small-sized Co3O4 nanoparticles delivers an optimal bifunctional activity with a potential gap of 0.79 V for reversible oxygen reduction reaction (E1/2) and oxygen evolution reaction (Ej = 10). Moreover, it displays a superior power density of 122 mW cm−2 and long-term durability in a rechargeable Zn–air battery. Density functional theory calculations indicate that the defects adjacent to Co–Nx display improved electrocatalytic oxygen reduction with a smaller energy barrier. This work provides a facile method for optimizing the Co:Zn ratio towards the synthesis of bifunctional oxygen electrocatalyst derived from a class of bimetallic coordinated polymers resulting in hierarchically porous structure and defective cobalt-based active sites.
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•Rational design towards accessible defective active sites and multiscale mass transfer.•A novel bimetallic coordination polymer to prepare defective cobalt-based carbon.•Hierarchically porous cobalt-based carbon shows superior oxygen catalytic performance.•The sample is a promising candidate to replace noble metal-based catalyst in Zn–air battery.
•Kinetic models accurately predict the behavior of SARA fractions and gas production.•The use of stoichiometric coefficients is analyzed in detail.•During aquathermolysis, asphaltenes and resins are ...mainly converted to saturate fractions.•Sensitivity analysis guarantee the optimal values of calculated kinetic coefficients.
The aquathermolysis process is considered an efficient method to improve fluidity properties in-situ and increase the degree of oil extraction (recovery factor) from downhole hard-to-recover reserves. In this work, the effect of using stoichiometric coefficients during the kinetic modeling of the aquathermolysis process has been studied. The parameters of two kinetic models based on SARA fractions and gas production were determined. The estimation of kinetic coefficients was carried out through a series of numerical methods and statistical analysis to guarantee that the calculated values provide the lowest average absolute error with respect to experimental data. A series of aquathermolysis tests was carried out in a batch reactor in a temperature range of 250–300 °C and reaction times of 12–72 h. The results of both kinetic models are in good agreement with experimental data with an error lower than 5%.
A new kinetic model based on SARA (Saturates, Aromatics, Resins, Asphaltenes) fractions for the non-catalytic aquathermolysis of heavy crude oil is proposed. The aquathermolysis experiments were ...carried out with Ashal'cha heavy oil in batch reactor at different reaction times (12–72 h) and temperatures (250 and 300 °C). Different reactions in series and in parallel were considered in the model. The optimal values of estimated kinetic parameters were verified by sensitivity analysis. Residual analysis, parity plot, and average absolute error (less than 5%) demonstrated that the proposed kinetic model for the non-catalytic aquathermolysis of heavy crude oil fits well the experimental data.
•New reaction scheme for non-catalytic aquathermolysis of heavy crude oil based on SARA and gases yields.•Main reactions carried out are in series from asphaltenes to resins to aromatics and to saturates.•Increased gas formation at 300 °C mainly due to asphaltenes conversion.•Estimated kinetic parameters were ensured to have optimal values by sensitivity analysis.•Residual analysis, parity plot, and average absolute error less than 5% proved the good fit with experimental data.
