Energy Density Of Fuels Research Articles

The influence of acetone and isopropanol crossover on the direct isopropanol fuel cell

Liquid organic hydrogen carriers (LOHC) offer a promising option to store and release hydrogen on demand within existing infrastructure. The direct isopropanol fuel cell (DIFC) uses the electrochemical acetone/isopropanol LOHC couple and combines the advantages of high fuel energy density at ambient conditions with CO2-free direct electricity production. Like other alcohol fuel cells, the DIFC combines two kinetically slow reactions, the isopropanol oxidation reaction (IOR) and the oxygen reduction reaction (ORR), requiring considerable overpotentials to drive the reactions. Accordingly, deconvoluting kinetic characteristics in the full cell is difficult. Therefore, this work uses the electrolytic electrochemical dehydrogenation unit (EDU), consisting of the IOR and the kinetically fast hydrogen evolution reaction in acidic media. This EDU then serves as an IOR full-cell model to get insights on the DIFC. Correspondingly, the demonstrated work is a comparison study investigating in-house fabricated catalyst-coated membrane electrode assemblies as hydrogen fuel cells, DIFC, and EDU. It investigates characteristic features of the DIFC and demonstrates how the acetone and isopropanol crossover affect the cathode of the DIFC.

Spray combustion characteristics of boron slurry fuel in high particle loading conditions

Enhancing the energy density of hydrocarbon fuels is indeed crucial, especially in the context of addressing energy needs. Incorporating energetic particles as additives into conventional liquid fuels garners increased attention due to its potential to enhance energy density. Due to its high energy potential, boron is the most promising additive in several energetic particles. However, the study focusing on the boron-loaded slurry fuels are limited. Therefore, the present work focuses on the effect of boron loading on the spray combustion of boron-loaded slurry fuel, especially at higher loadings (10%, 20% & 30% boron + Jet A-1 fuel) using a swirl-stabilized spray combustor. The research scrutinizes the feed and exhaust particles' surface morphology, chemical composition and active boron content through diverse particle characterization techniques. Furthermore, the study investigates the influence of boron loading on the combustion characteristics of slurry fuel using methods such as colour flame imaging, spectroscopy, and BO2* Chemiluminescence imaging. The impact of boron loading on the positive thermal contribution of the slurry was examined by analyzing temperature measurements at various locations within the combustor. The BO2* chemiluminescence imaging and spectroscopy results indicate that the intensity of BO2 emission increases with a rise in particle loading. The temperature results reveal an increase in temperature compared to pure Jet A-1 for all the boron-loaded cases. In particular, JB10 and JB20 achieved nearly 90% and 85% of the theoretical temperature increase. The diffractogram and thermogravimetric results of the burnt particles collected show that the particles were burnt thoroughly for the boron-loaded cases.

Study on the combustion characteristics and reaction mechanism of aluminum/alcohol-based nanofluid fuel

Enhancing the volumetric energy density of fuels is a crucial approach in the exploration of efficient energy sources. As a commonly used high-energy additive, Aluminum nanoparticles (Al NPs) holds broad application prospects. This study delves into the effects of Al NPs on the combustion characteristics of methanol and ethanol fuels through in-depth analysis of single droplet combustion and spray combustion experiments involving alcohol-based nanofluid fuels. The experiments revealed that adding Al NPs significantly enhances fuel combustion efficiency, shortening both the combustion life and ignition delay time. Spray combustion tests demonstrated that adding 2 wt% Al NPs increased the maximum and average flame propagation speeds of ethanol fuel spray by 48.93 % and 47.94 %, respectively, while the maximum explosion pressure rose from 0.66MPa to 0.83MPa, with a reduced time to reach peak explosion pressure by 106ms. Based on the SEM and XRD characterization results of the combustion residues and the analysis of flame morphology, a physical model of the alcohol-based nanofluid fuel spray combustion flame was established. Numerical simulations of the gas-phase kinetics model showed that the generation rates of radicals such as H, O, and OH were significantly increased with the addition of Al NPs, intensifying the combustion reaction. The findings provide a theoretical basis for future fuel design and combustion performance optimization.

In-situ heteroatoms stabilization of zero-dimensional boron nanospheres for high-energy nanofluid fuels combustion enhancement

Since boron powder has the highest volume energy density, it has long been desired for use as fuel in aerospace and other fields. However, boron has poor ignition performance and low combustion efficiency due to uneven microstructure and oxide layers of boron. Here, we report a facile strategy to prepare zero-dimensional boron nanospheres from micrometer-scale amorphous boron through ultrasound-assisted in-situ stabilization of heteroatoms for inhibition of boron oxide layer by using hexachlorocyclotriphosphazene (HCCP) and 4,4′-sulfonyldiphenol (BPS) polycondensation and carbonization. The diameter of the obtained boron nanospheres was in the range of 500–800 nm, which is the smallest reported diameter of regular boron nanoparticles. The initial reaction temperature of CPZS@B-1.0 decreased from 791.1 to 641.7 °C, and the ignition delay time of 20 wt% CPZS@B-1.0/RP-3 nanofluid fuel decreased to 393 ms. The addition of CPZS@B promoted RP-3 oxidation at both low temperatures (<200 °C) and high temperatures (>200 °C) by in-situ FTIR analysis. Notably, the prepared zero-dimensional nano-boron exhibited removal of surface oxidation and complete combustion degree (from 42.06 % to 80.36 %). This work provides a new method for the preparation of nano-boron and a solution for increasing the fuel energy density of hydrocarbon fuels.

Comparative analysis of methane conversion: pyrolysis, dry and steam thermal plasma reforming

Methane reforming is gaining attention because of its potential to be converted into energy-dense fuels or high-value chemicals. In addition to the production of syngas (H2+CO), the utilization of CO2 can help reduce greenhouse gases. Water steam is typically used to increase the output of H2. This study evaluated the potential of thermal plasma technology to produce clean hydrogen, carbon monoxide, and carbon black from methane by applying a thermodynamic equilibrium model. A comparative analysis of three cases of methane processing (pyrolysis, dry reforming, and steam reforming) is presented to provide a comprehensive understanding of the potential of thermal plasma technology for methane conversion.

Toxicity of particles derived from combustion of Ethiopian traditional biomass fuels in human bronchial and macrophage-like cells

The combustion of traditional fuels in low-income countries, including those in sub-Saharan Africa, leads to extensive indoor particle exposure. Yet, the related health consequences in this context are understudied. This study aimed to evaluate the in vitro toxicity of combustion-derived particles relevant for Sub-Saharan household environments. Particles (< 2.5 µm) were collected using a high-volume sampler during combustion of traditional Ethiopian biomass fuels: cow dung, eucalyptus wood and eucalyptus charcoal. Diesel exhaust particles (DEP, NIST 2975) served as reference particles. The highest levels of particle-bound polycyclic aromatic hydrocarbons (PAHs) were found in wood (3219 ng/mg), followed by dung (618 ng/mg), charcoal (136 ng/mg) and DEP (118 ng/mg) (GC–MS). BEAS-2B bronchial epithelial cells and THP-1 derived macrophages were exposed to particle suspensions (1–150 µg/mL) for 24 h. All particles induced concentration-dependent genotoxicity (comet assay) but no pro-inflammatory cytokine release in epithelial cells, whereas dung and wood particles also induced concentration-dependent cytotoxicity (Alamar Blue). Only wood particles induced concentration-dependent cytotoxicity and genotoxicity in macrophage-like cells, while dung particles were unique at increasing secretion of pro-inflammatory cytokines (IL-6, IL-8, TNF-α). In summary, particles derived from combustion of less energy dense fuels like dung and wood had a higher PAH content and were more cytotoxic in epithelial cells. In addition, the least energy dense and cheapest fuel, dung, also induced pro-inflammatory effects in macrophage-like cells. These findings highlight the influence of fuel type on the toxic profile of the emitted particles and warrant further research to understand and mitigate health effects of indoor air pollution.

Structural sizing of a hydrogen tank for a commercial aircraft

To respond to the current climate crisis, hydrogen-powered aircraft are seen as a promising solution in the aviation sector to cut down CO 2 emissions. Hydrogen-fueled aircraft present however huge challenges, especially due to the complex storage of hydrogen. To achieve a reasonable fuel energy density for medium- to long-range missions, hydrogen must indeed be stored in liquid form in big and heavy pressurized tanks. Tank design must so be included in conceptual design, which now has an important impact on the aircraft. This study proposes a structural sizing methodology for a liquid hydrogen tank for a commercial aircraft. A parametric model of a cylindrical cryogenic tank placed at the back of the cabin in a conventional aircraft is created and sized to withstand pressure, bending, torsion and shear loads. The process integrates sizing standards for pressurized structures of the current CS-25 regulation in its methodology and remains general enough to consider both integral and non-integral tanks of any dimensions or materials. Initial analyses show a clear dependency of the tank’s performance as well as the optimal stiffening structure configuration on the design pressure.

Electrocatalytic CO2 reduction to formate by a cobalt phosphino-thiolate complex.

Electrochemical conversion of CO2 to value-added products serves as an attractive method to store renewable energy as energy-dense fuels. Selectivity in this type of conversion can be limited, often leading to the formation of side products such as H2. The activity of a cobalt phosphino-thiolate complex ([Co(triphos)(bdt)]+) towards the selective reduction of CO2 to formate is explored in this report. In the presence of H2O, selective production of formate (as high as 94%) is observed at overpotentials of 750 mV, displaying negligible current degradation during long-term electrolysis experiments ranging as long as 24 hours. Chemical reduction studies of [Co(triphos)(bdt)]+ indicates deligation of the apical phosphine moiety is likely before catalysis. Computational and experimental results suggest a metal-hydride pathway, indicating an ECEC based mechanism.

Energy aspects of automobile transport development

Problem. Improving automobile transport means increasing fuel economy and environmental indicators. Fuel, in a broad sense, means energy used to activate the car's power plant. Potential energy is dispersed in the earth’s interior, on its surface, in the atmospheric air, and even in space. Moreover, some of them exist in different substances. On the one hand, the efficiency of an energy product use is assessed by its energy intensity; on the other hand, it is evaluated by the costs of its production (transportation) and the quality of its transformation into a consumer type of energy. Special attention is paid to renewable and unlimited kinds of energy sources. Goal. The purpose of the study is a qualitative analysis of the road transport development direction from the standpoint of the alternative energy sources use, taking into account the factors that comprehensively determine the economic and environmental indicators at the stages of production and processing of fossil raw materials, production of power plants and conversion, transformation, and transportation of energy in the field of transport technologies. Methodology. The first direction consists of the adaptation (conversion) of the design of thermal internal combustion engines for alternative liquid or gaseous fuel types. The advantage of this approach is minimal costs for engine conversion and fuel production. The second approach involves using hybrid power plants, consisting of a main and auxiliary engine, an energy source or accumulator, an energy converter, and a braking recuperation system. The third direction is the use of non-traditional energy sources. Results. The directions of the development of power plants for motor vehicles related to the increase in the energy density of hydrocarbon fuels, the use of hybrid power plants, and the use of alternative energy sources have been determined. A qualitative assessment of the considered approaches is given. Originality. A comprehensive approach to evaluating the effectiveness of using alternative types of energy in road transport is considered in terms of energy, economic, and environmental indicators. Practical value. The obtained results can be regarded as recommendations when drawing up plans for the evolution of industries of fossil extraction and transformation of other energy resources, the development of motor vehicles, and transport infrastructure technologies, taking into account the natural and industrial potential of the country

Fabrication of Cu-Single Atom Catalyst Supported on Unique 2D Graphdiyne Analogue-Based Porphyrin Metal Covalent Organic Frameworks for Carbon Dioxide Reduction Application

Excessive burning of fossil fuels for energy production has led to an exponential increase in CO2 concentrations in the atmosphere, which is the core of universal problems such as global warming and climate change. One of the new approaches to reducing CO2 emissions is to think of CO2 as a useful raw material and convert this compound into useful products. Moreover, electrocatalytic carbon dioxide reduction (eCO2R) can be conveniently utilized to establish a zero-emission carbon cycle and utilize this CO2 for energy-dense fuels and other chemical raw materials [1]. However, exploring novel catalysts is the ultimate need of the hour for an effective and efficient eCO2R.Heterogeneous single-atom catalysts (SAC) containing isolated metal species on an atomic level are gaining the increasing attention of the scientific community owing to their high metal utilization sites and superior catalytic properties[2]. The SACs are put into the full effect of catalysis by scattering it over conductive support. Therefore, in this work, the copper SACs are supported over a unique porphyrin-based graphdiyne (SAC-PG) with a π-conjugated structure (Figure 1). Graphdiyne possesses two acetylenic linkages between the aromatic rings and is responsible for not only displaying exceptional electronic conductivity but when coupled with the metalloporphyrin network provides numerous active sites for catalysis[3]. This SAC-PG analogue is achieved by a Glaser-Hay coupling reaction on Cu foam or foil. Moreover, SEM analysis is performed in combination with SEM-EDX and elemental mapping to investigate the morphology of the fabricated catalyst (Figure 2). In addition, this unique copper-based SAC-PG is evaluated as a catalyst for eCO2R in a customized H-cell with 0.1M/0.5M KHCO3 as an electrolyte and Pt as a counter electrode. Nafion 117 proton exchange membrane is used for separation between the cathodic and anodic compartments while an Ag/AgCl (3M KCl) was used as a reference electrode. Under these eCO2R conditions, the copper SAC-PG catalyst displayed extremely high current densities (32 – 75 mA/cm2) over a range of voltages (1.0-1.2 V vs RHE) and acceptable faradaic efficiencies for the carbon products (with maximum FE over 60% in total for all carbon products).In conclusion, a 2D metal covalent organic framework containing a repeating unit of Cu-porphyrin linked by butadiyne linkages was established. This unique structure showed effective CO2R catalysis due to its nanoporous structure, high electronic conductivity, and abundant metal cites utilization. Further optimization and constriction of these easily adjustable catalysts open up various possibilities of further exploration in the field of eCO2R. Acknowledgement: The author Zubair Masaud acknowledges support from the Norwegian Micro- and Nano-Fabrication Facility (NorFab, No. 245963/F50) The author Hao Huang acknowledges Marie Skłodowska-Curie Actions individual fellowship CarbonChem 101024758.

(Invited) Exploring Solar-Driven CO2 Reduction to C2+ Products

Use of solar irradiance to drive CO2 reduction (CO2R) holds great promise for the sustainable generation of energy-dense fuels and chemicals, especially as it relates well to carbon capture technology. Multicarbon (C2+) products (e.g., ethylene, ethanol, propanol) are particularly attractive because they have a large market size and can be further converted to higher molecular weight hydrocarbons fuels that have high volumetric and mass energy densities. Metallic copper (Cu) has the unique ability to catalyze CO2 to C2+ products with high faradaic efficiency; however, the product distribution of CO2R on Cu is potential and microenvironment dependent. In this talk, we will explore CO2R via different routes using both experiments and simulation. We will focus on obtaining C2+ products via tailoring the microenvironments including the use of ionomer films that are quite effective at the lower current densities that match against the solar irradiance. We will demonstrate how control of the local environment and dynamic operation provide metastable states of high pH and high CO2 concentration, thereby enabling high CO2R to C2+ production.In addition, for direct photoelectrochemical CO2R, there is an optimum cell design and operating photovoltage that is not at the maximum power point (unlike water splitting) due to the selectivity dependence on potential. Using a continuum model of PEC CO2R, we will explore the co-design of the photoelectrode bandgaps and device architecture for the generation of C2+ products. The simulation results demonstrate the critical importance of simultaneously engineering the photoelectrode and device design and operation in order to ensure the photovoltage and photocurrent from the photoelectrode enables operation at the optimum potential. Finally, for PEC CO2R, we will explore the use of metal-insulator-semiconductor (MIS) structures to obtain high rates of CO2R. This includes both theoretical and experimental investigations that elucidate the controlling phenomena and when coupled with the ionomer films provide high rates of direct PEC CO2R. Overall, the insights between the photoelectrode and device design is critical for the design of monolithic, unassisted PEC CO2R systems that yield high STC2+ efficiency.AcknowledgementsThis material is based partially on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266 and a University of California grant.

Photoinduced transposed Paternò-Büchi reaction for effective synthesis of high-performance jet fuel

High-energy-density fuels are important for volume-limited aerospace vehicles, but the increase of the fuel energy density always leads to poor cryogenic performance. Herein, we investigated the transposed Paternò-Büchi reaction of biomass cyclic ketone and cyclic alkene to synthesize the new kind of alkyl-substituted polycyclic hydrocarbon fuels with high energy density and good cryogenic performance. The triplet-energy-quenching results and phosphorescent emission spectra reveal the sensitization mechanism of the reaction, including photosensitizer excitation, triplet-triplet energy transfer, cyclization and relaxation, and the possible reaction path was revealed by the DFT calculations. The reaction conditions of photosensitizer type and addition, molar ratio of substrates, reaction temperature and incident light intensity were optimized, with the target product yield achieving 65.5%. Moreover, the reaction dynamics of the reaction rate versus the light intensity is established. After hydrogenation deoxygenation reaction, three fuels with high density of 0.864-0.938 g·ml−1 and low freezing point of <−55 °C are obtained. This work provides a benign and effective approach to synthesize high-performance fuels.

Prediction of NOx emissions and pathways in premixed ammonia-hydrogen-air combustion using CFD-CRN methodology

Ammonia-hydrogen blends have gained significance as they are carbon-free energy-dense fuels. However, NOx emissions have been a significant concern. In this study, the emissions from the premixed combustion of 70/30VOL.% NH3/H2 blend is studied using the computational fluid dynamics (CFD)- chemical reactor network (CRN) approach. The velocity, temperature, and species field are first obtained using CFD, based on which, a network consisting of perfectly stirred reactors (PSR) and plug flow reactor (PFR) is constructed. Three mechanisms have been implemented in the CRN to predict the NO and N2O emissions. It is shown that the trend of NOx is correctly predicted by the CRN over a wide range of equivalence ratios (φ) of 0.65–1.2 as compared to the authors’ recently published experimental data. It is demonstrated that a single CRN (based on the CFD for a specific φ) can be run to cover the range of φ = 0.65 to 1.2 b y scaling the temperature input to each reactor of the CRN. To contrast the NO pathways at different φ, quantitative reaction pathway diagrams (QRPD) are constructed, and dominant production and consumption pathways of NO for lean and rich combustion are established. The shifts in reaction pathways with φ are noted and found to be governed by OH, O, and H radicals. Next, the effect of stoichiometry on these radicals is established. Finally, the experimental trend of high NO close to stoichiometric combustion and high N2O in very lean combustion along with their respective pathways are explained.

Experimental and modeling study of the oxidation of fenchone, a high-energy density fuel-additive

Increasing fuel energy density constitutes a potential way to reduce engine exhaust carbon emission. Fenchone, a strained ring molecule, could be an interesting candidate. The present study investigates the oxidation of fenchone in a jet-stirred reactor at high pressure (10 atm) between 700 and 1180 K at constant fuel mole fraction and constant residence time of 0.1% and 0.7 s, respectively. Mole fraction profiles were obtained through sonic probe sampling, and analyzed by gas chromatography and Fourier transform infrared spectrometry. More than 30 species were identified and most of them were quantified. Also, a kinetic mechanism is developed in this study and tested against the present conditions showing good agreement. The present mechanism allows to illuminate the major reaction pathways involved in the decomposition routes of the fuel and its primary radicals as well as the formation pathways of the quantified intermediate species. During fenchone oxidation, the carbonyl group is mostly found in CO, CO2 and formaldehyde while heavier carbonyl species were identified at much lower quantities, indicating decarbonylation occurs early during the oxidation process. Aromatic compounds such as benzene and toluene are formed especially in rich conditions while some potential oxygenated pollutants like methacrolein and acetaldehyde were quantified as well.

Optimal performance assessment of intelligent controllers used in solar-powered electric vehicle

Introduction. Increasing vehicle numbers, coupled with their increased consumption of fossil fuels, have drawn great concern about their detrimental environmental impacts. Alternative energy sources have been the subject of extensive research and development. Due to its high energy density, zero emissions, and use of sustainable fuels, the battery is widely considered one of the most promising solutions for automobile applications. A major obstacle to its commercialization is the battery's high cost and low power density. Purpose. Implementing a control system is the primary objective of this work, which is employed to change the energy sources in hybrid energy storage system about the load applied to the drive. Novelty. To meet the control objective, a speed condition-based controller is designed by considering four separate math functions and is programmed based on different speed ranges. On the other hand, the conventional/intelligent controller is also considered to develop the switching signals related to the DC-DC converter’s output and applied the actual value. Methods. According to the proposed control strategy, the adopted speed condition based controller is a combined conventional/intelligent controller to meet the control object. Practical value. In this work, three different hybrid controllers adopted speed condition based controller with artificial neural network controller, adopted speed condition based controller with fuzzy logic controller, and adopted speed condition based controller with proportional-integral derivative controller are designed and applied separately and obtain the results at different load conditions in MATLAB/Simulink environment. Three hybrid controller’s execution is assessed based on time-domain specifications.

Synthesis and fuel properties of high-density and low-freezing-point asymmetric cycloalkyl adamantane

The exploration to increase the fuel energy density is stimulated by the payload and cruising range concerns in aerospace industry. The high-density fuels are always rationally designed for the advanced volume-limited aircrafts to fulfill more complicated missions. Alkyl adamantanes gradually become a prospective class of high-energy-density fuels. Herein, in this work, we reported an approach to synthesize asymmetric cyclopentyl adamantane via AlCl3-catalyzed alkylation of adamantane and cyclopentene with an attractive combination of a high density of 0.990 g/mL as well as a low freezing point of −30 °C. The obtained 1-cyclopentyl-adamantane was well designed with the cyclic substituent (enhance the density) and asymmetric structure (lower the freezing temperature). Subsequently, the comprehensive fuel performance of cyclopentyl adamantane, i.e., density, freezing point, low-temperature viscosity, heating value, and combustion properties were evaluated. It was shown that both density and combustion properties of cycloalkyl adamantane were superior to the typical high-density JP-10 fuel. In addition, the properties of binary fuel mixture (1-cyclopentyl-adamantane and JP-10) demonstrated that cyclopentyl adamantane could be used as a promising blendstock with conventional jet fuel to enhance the energy density and promote the combustion performance of the final fuel blends.

Transport Mediating Core-Shell Photocatalyst Architecture for Selective Alkane Oxidation.

The high activation barrier of the C-H bond in methane, combined with the high propensity of methanol and other liquid oxygenates toward overoxidation to CO2, have historically posed significant scientific and industrial challenges to the selective and direct conversion of methane to energy-dense fuels and chemical feedstocks. Here, we report a unique core-shell nanostructured photocatalyst, silica encapsulated TiO2 decorated with AuPd nanoparticles (TiO2@SiO2-AuPd), that prevents methanol overoxidation on its surface and possesses high selectivity and yield of oxygenates even at high UV intensity. This room-temperature approach achieves high selectivity for oxygenates (94.5%) with a total oxygenate yield of 15.4 mmol/gcat·h at 9.65 bar total pressure of CH4 and O2. The working principles of this core-shell photocatalyst were also systematically investigated. This design concept was further demonstrated to be generalizable for the selective oxidation of other alkanes.

Concentrating solar assisted biomass-to-fuel conversion through gasification: A review

Solar energy, the most abundant and exploitable renewable energy resource, is regarded as a major energy source for the future. Nevertheless, solar irradiation is characterized by relatively low energy density, intermittency and uneven distribution. Storage of solar energy for usage during non-solar times is required to match supply and demand rates in today’s society. In this context, the application of solar energy for converting into storable, transportable, and energy-dense fuels (i.e., solar fuels) is an attractive option, with the advantage of contributing to promoting the commercialization of solar power technologies. Solar assisted biomass gasification is a promising pathway to produce solar fuels. With concentrated solar energy providing reaction heat, carbonaceous materials can be converted to high grade syngas, which could be further synthesized into useful hydrocarbon fuels. In such process, solar energy is stored in a chemical form, with solar spectrum fully utilized. Compared with autothermal biomass gasification, the usage of high-flux concentrated solar radiation to drive endothermic gasification reactions improves energy efficiencies, saves biomass feedstocks, and is relatively free of combustion by-products. This review presents a comprehensive summary of solar assisted biomass gasification, including concentrating solar technology, fundamentals of solar biomass gasification, state-of-the-art solar gasifier designs, strategies for solar intermittence management, and downstream applications.

Application of functionalized carbon nanotubes as the cathode of nonaqueous lithium‑oxygen cells

Lithium‑oxygen cells have attracted the significant attention of researchers in recent years due to their extremely high energy density, comparable to the energy density of fossil fuels. However, because of the sluggish kinetics of discharge/charge reactions, the development of lithium‑oxygen technology has been largely limited. One way to tackle this problem is the development of an efficient catalyst for cathode materials that will exhibit high capacities, good rate capabilities, and sufficient stability. Due to their excellent electrochemical properties and controlled porous texture, carbon nanotubes (CNTs) have been one of the candidates for this application. Many methods have been proposed to improve their catalytic activity and, as a result, enhance the performance of lithium‑oxygen cells. These include transition metal coating, precious metal decorating, or heteroatom doping. This review provides an in-depth look at CNT functionalization methods and their impact on nonaqueous lithium‑oxygen cell performance.

Hydrothermal treatment: An efficient food waste disposal technology.

The quantities of food waste (FW) are increasing yearly. Proper disposal of FW is essential for reusing value-added products, environmental protection, and human health. Based on the typical characteristics of high moisture content and high organic content of FW, hydrothermal treatment (HTT), as a novel thermochemical treatment technology, plays unique effects in the disposal and utilization of FW. The HTT of FW has attracted more and more attention in recent years, however, there are few conclusive reviews about the progress of the HTT of FW. HTT is an excellent approach to converting energy-rich materials into energy-dense fuels and valuable chemicals. This process can handle biomass with relatively high moisture content and allows efficient heat integration. This mini-review presents the current knowledge of recent advances in HTT of FW. The effects of HTT temperature and duration on organic nutritional compositions (including carbohydrates, starch, lipids, protein, cellulose, hemicellulose, lignin, etc.) and physicochemical properties (including pH, elemental composition, functional groups, fuel properties, etc.) and structural properties of FW are evaluated. The compositions of FW can degrade during HTT so that the physical and chemical properties of FW can be changed. The application and economic analyses of HTT in FW are summarized. Finally, the analyses of challenges and future perspectives on HTT of FW have shown that industrial reactors should be built effectively, and techno-economic analysis, overall energy balance, and life cycle assessment of the HTT process are necessary. The mini-review offers new approaches and perspectives for the efficient reuse of food waste.