Aluminum-air battery with cotton substrate:Controlling the discharge capacity by electrolyte pre-deposition

Conventional Al-air battery has many disadvantages for miniwatt applications,such as the complex water management,bulky electrolyte storage and potential leakage hazard.Moreover,the self-corrosion of Al anode continues even when the electrolyte flow is stopped,leading to great Al waste.To tackle these issues,an innovative cotton-based aluminum-air battery is developed in this study.Instead of flowing alkaline solution,cotton substrate pre-deposited with solid alkaline is used,together with a small water reservoir to continuously wet the cotton and dissolve the alkaline in-situ.In this manner,the battery can be mechanically recharged by replacing the cotton substrate and refilling the water reservoir,while the thick aluminum anode can be reused for tens of times until complete consumption.The cotton substrate shows excellent ability for the storage and transportation of alkaline electrolyte,leading to a high peak power density of 73 mW cm^(-2) and a high specific energy of 930 mW h g^(-1).Moreover,the battery discharge capacity is found to be linear to the loading of pre-deposited alkaline,so that it can be precisely controlled according to the mission profile to avoid Al waste.Finally,a two-cell battery pack with common water reservoir is developed,which can provide a voltage of 2.7 V and a power output of 223.8 mW.With further scaling-up and stacking,this cotton-based Al-air battery system with low cost and high energy density is very promising for recharging miniwatt electronics in the outdoor environment.

Solid-state Al-air battery with an ethanol gel electrolyte

Hydrogel electrolyte is especially suitable for solid-state Al-air batteries targeted for various portable applications, which may, however, lead to continuous Al corrosion during battery standby. To tackle this issue, an ethanol gel electrolyte is developed for Al-air battery for the first time in this work, by using KOH as solute and polyethylene oxide as gelling agent. The ethanol gel is found to effectively inhibit Al corrosion compared with the water gel counterpart, leading to stable Al storage. When assembled into an Al-air battery, the ethanol gel electrolyte achieves a much improved discharge lifetime and specific capacity, which are 5.3 and 4.1 times of the water gel electrolyte at 0.1 mA cm^(-2), respectively.By studying the gel properties, it is found that a lower ethanol purity can improve the battery power output, but at the price of decreased discharge efficiency. On the contrary, a higher polymer concentration will decrease the power output, but can bring extra benefit to the discharge efficiency. As for the gel thickness, a moderate value of 1 mm is preferred to balance the power output and energy efficiency. Finally, to cater the increasing market of flexible electronics, a flexible Al-air battery is developed by impregnating the ethanol gel into a paper substrate, which can function normally even under serious deformation or damage.

Paper-based aqueous Al ion battery with water-in-salt electrolyte

Low-cost,flexible and safe battery technology is the key to the widespread usage of wearable electronics,among which the aqueous Al ion battery with water-in-salt electrolyte is a promising candidate.In this work,a flexible aqueous Al ion battery is developed using cellulose paper as substrate.The water-in-salt electrolyte is stored inside the paper,while the electrodes are either printed or attached on the paper surface,leading to a lightweight and thin-film battery prototype.Currently,this battery can tolerate a charge and discharge rate as high as 4 A g^(-1) without losing its storage capacity.The charge voltage is around 2.2 V,while the discharge plateau of 1.6–1.8 V is among the highest in reported aqueous Al ion batteries,together with a high discharge specific capacity of~140 mAh g^(-1).However,due to the water electrolysis side reaction,the faradaic efficiency can only reach 85%with a cycle life of 250 due to the dry out of electrolyte.Benefited from using flexible materials and aqueous electrolyte,this paper-based Al ion battery can tolerate various deformations such as bending,rolling and even puncturing without losing its performance.When two single cells are connected in series,the battery pack can provide a charge voltage of 4.3 V and a discharge plateau as high as 3–3.6 V,which are very close to commercial Li ion batteries.Such a cheap,flexible and safe battery technology may be widely applied in low-cost and large-quantity applications,such as RFID tags,smart packages and wearable biosensors in the future.

Numerical study on the ozone formation inside street canyons using a chemistry box model

Tropospheric ozone is a secondary air pollutant produced in the presence of nitrogen oxides (NO_x),volatile organic compounds (VOCs),and solar radiation.In an urban environment,ground-level vehicular exhaust is the major anthropogenic source of ozone precursors.In the cases of street canyons,pollutant dilution is weakened by the surrounding buildings that creates localized high concentration of NO_x and VOCs,and thus leads to high potential of ozone formation.By considering the major physical and chemical p...

Mechanistic study of vacuum UV catalytic oxidation for toluene degradation over CeO_(2) nanorods

The present study specifically investigates vacuum ultraviolet (VUV) catalytic oxidation for toluene degradation over CeO_(2) nanorods.Synergetic effects of ultraviolet photocatalytic oxidation (UV-PCO) and ozone catalytic oxidation (OZCO) were manifested in the results of toluene removal and COx generation,while the combination of UV-PCO andOZCO (UV-OZCO) did not lead to improvement of mineralization.All the processes contribute to ozone decomposition,but no obvious synergetic effects of the different processes can be observed.Intermediate analysis results indicated that more toluene was oxidized into by-products,such as benzyl alcohol and benzaldehyde,by UV-OZCO rather than forming COx.Both hydroxyl radical (·OH) and superoxide radical (·O_(2)^(-)) were found in all the processes of the VUV-PCO-OZCO system(combination of VUV photolysis,UV-PCO,OZCO and UV-OZCO processes).In the UV-OZCO process,the formation of hydroxyl radical was promoted,while that of superoxide radical was impeded,resulting in lower mineralization level of toluene.The mechanistic study of toluene degradation over CeO_(2) nanorods in the VUV-PCO-OZCO system revealed that with the formation of·O_(2)^(-)and·OH,toluene is first oxidized to intermediates,followed by further ring–opening reaction and,finally,degradation into CO_(2) and H_(2)O.CeO_(2) nanorods function as both ozonation catalyst and photocatalyst,and the redox pair of Ce^(3+)and Ce^(4+)are interconvertible and can keep a balance.

UV light-induced oxygen doping in graphitic carbon nitride with suppressed deep trapping for enhancement in CO_(2) photoreduction activity

While photoreduction of CO_(2) to CH 4 is an effective means of producing value-added fuels,common pho-tocatalysts have poor activity and low selectivity in photocatalytic CO_(2)-reduction processes.Even though creating defects is an effective photocatalyst fabrication route to improve photocatalytic activity,there are some challenges with the facile photocatalyst synthesis method.In this work,an O element is in-troduced into a graphitic carbon nitride(CN)skeleton through a precursory ultraviolet light irradiation pretreatment to increase the visible light absorption and enhance the carrier density of this modified non-metal CN photocatalyst;the charge transfer dynamics thereof are also studied through electrochem-ical tests,photoluminescence spectroscopy,and nanosecond transient absorption.We verify that the op-timized sample exhibits lower charge recombination and a suppressed 84 ns electron-trapping lifetime,compared to the 103 ns electron-trapping lifetime of the CN counterpart,and thereby contributes to ro-bust detrapping and a fast transfer of active electrons.Through density functional theory calculations,we find that the improved light absorption and increased electron density are ascribed to O-element doping,which enhances the CO_(2) adsorption energy and improves the CO_(2)-to-CH 4 photoreduction activity;it be-comes 17 times higher than that of the bare CN,and the selectivity is 3.8 times higher than that of CN.Moreover,the optimized sample demonstrates excellent cyclic stability in a 24-hour cycle test.

Accelerated oxidation of VOCs via vacuum ultraviolet photolysis coupled with wet scrubbing process

Vacuum ultraviolet(VUV) photolysis is a facile method for volatile organic compounds(VOCs) elimination, but is greatly limited by the relatively low removal efficiency and the possible secondary pollution. To overcome above drawbacks, we developed an efficient method for VOCs elimination via VUV photolysis coupled with wet scrubbing process. In this coupled process, volatile toluene, a representative of VOCs, was oxidized by the gas-phase VUV photolysis, and then scrubbed into water for further oxidation by the liquid-phase VUV photolysis. More than 96% of toluene was efficiently removed by this coupled process, which was 2 times higher than that in the gas-phase VUV photolysis. This improvement was attributed to the synergistic effect between gas-phase and liquid-phase VUV photolysis. O3and HO·are the predomination reactive species for the toluene degradation in this coupled process, and the generation of O3in gas-phase VUV photolysis can efficiently enhance the HO·production in liquid-phase VUV photolysis. The result from in-situ proton transfer reaction ionization with mass analyzer(PTR-MS) further suggested that most intermediates were trapped by the wet scrubbing process and efficiently oxidized by the liquid-phase VUV photolysis, showing a high performance for controlling the secondary pollution. Furthermore, the result of stability test and the reuse of solution demonstrated that this coupled process has a highly stable and sustainable performance for toluene degradation. This study presents an environmentally benign and highly efficient VUV photolysis for gaseous VOCs removal in the wet scrubbing process.

Effects of building aspect ratio,diurnal heating scenario,and wind speed on reactive pollutant dispersion in urban street canyons

A photochemistry coupled computational fluid dynamics （CFD） based numerical model has been developed to model the reactive pollutant dispersion within urban street canyons, particularly integrating the interrelationship among diurnal heating scenario （solar radiation affections in nighttime, daytime, and sun-rise/set）, wind speed, building aspect ratio （building-height-to-street-width）, and dispersion of reactive gases, specifically nitric oxide （NO）, nitrogen dioxide （NO2） and ozone （O3） such that a higher standard of air quality in metropolitan cities can be achieved. Validation has been done with both experimental and numerical results on flow and temperature fields in a street canyon with bottom heating, which justifies the accuracy of the current model. The model was applied to idealized street canyons of different aspect ratios from 0.5 to 8 with two different ambient wind speeds under different diurnal heating scenarios to estimate the influences of different aforementioned parameters on the chemical evolution of NO, NO2 and 03. Detailed analyses of vertical profiles of pollutant concentrations showed that different diurnal heating scenarios could substantially affect the reactive gases exchange between the street canyon and air aloft, followed by respective dispersion and reaction. Higher building aspect ratio and stronger ambient wind speed were revealed to be, in general, responsible for enhanced entrainment of 03 concentrations into the street canyons along windward walls under all diurnal heating scenarios. Comparatively, particular attention can be paid on the windward wall heating and nighttime uniform surface heating scenarios.

A novel Z-scheme CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst for degradation of Bisphenol A and hydrogen evolution and insight of the photocatalysis mechanism

CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst had been successfully fabricated through a one-step in-situ pyrolysis formation of 3D hollow CeO_(2)mesoporous nanospheres and 2D g-C_(3)N_(4)nanosheets together with simultaneous removal of carbon sphere templates after heat treatment.The sample shows high catalytic performances for photocatalytic hydrogen generation and photocatalytic oxidation of Bisphenol A(BPA)under visible light irradiation,and the catalytic degradation route of BPA was suggested by the degradation products determined by GC-MS.The enhancing catalytic activity was attributed to the effective interfacial charge migration and separation.Finally,it was proposed that the CeO_(2)/g-C_(3)N_(4)heterojunction photocatalyst could follow a more appropriate Z-scheme charge transfer mechanism,which was confirmed by the analysis of experiment and theoretical calculation results.

Computational fluid dynamics simulation of the wind flow over an airport terminal building

Turbulence in the wake generated by wind flow over buildings or obstacles may produce complex flow patterns in downstream areas.Examples include the recirculating flow and wind deficit areas behind an airport terminal building and their potential impacts on the aircraft landing on nearby runways.A computational fluid dynamics(CFD) simulation of the wind flow over an airport terminal building was performed in this study of the effect of the building wake on landing aircraft.Under normal meteorological conditions,the studied airport terminal building causes limited effects on landing aircraft because most of the aircraft have already landed before entering the turbulent wake region.By simulating the approach of a tropical cyclone,additional CFD sensitivity tests were performed to study the impacts of building wake under extreme meteorological conditions.It was found that,in a narrow range of prevalent wind directions with wind speeds larger than a certain threshold value,a substantial drop in wind speed(>3.6 m/s) along the glide path of aircraft was observed in the building wake.Our CFD results also showed that under the most critical situation,a drop in wind speed as large as 6.4 m/s occurred right at the touchdown point of landing aircraft on the runway,an effect which may have a significant impact on aircraft operations.This study indicated that a comprehensive analysis of the potential impacts of building wake on aircraft operations should be carried out for airport terminals and associated buildings in airfields to ensure safe aviation operation under all meteorological conditions and to facilitate implementation of precautionary measures.

Low-cost and efficient Mn/CeO_(2) catalyst for photocatalytic VOCs degradation via scalable colloidal solution combustion synthesis method

Colloidal solution combustion synthesis(CSCS)is a simple and easy method for mass-production of crystalline nanomaterials with tunable pore structure.In this work,mesoporous Mn/CeO_(2) catalysts were fabricated via CSCS method coupled with a dip-coating process and used for photocatalytic oxidation(PCO)of toluene.Under vacuum ultraviolet(VUV)irradiation,a high toluene removal efficiency of about 92%was achieved with a toluene reaction rate of about 118μmol/g/h in a continuous flow reactor.A possible degradation pathway was proposed based on the analysis of intermediates by Fourier transform infrared photoluminescence spectra(FTIR)and GC-Mass.Hydrogen temperature-programmed reduction(H_(2)-TPR),Brunauer-Emmett-Teller(BET)surface areas,photoluminescence spectra(PL)spectra and X-ray photoelectron spectroscopy(XPS)were carried out to analyze physical and chemical properties of the catalysts.Compared with Mn_(x)Ce_(1-x)O_(2) catalysts synthesized by one step CSCS method,Mn/CeO_(2) has a higher photocatalytic activity,which is attributed to the presence of higher contents of Ce^(3+),Mn^(2+)and Mn^(3+)species.The presence of higher contents of these species plays a key role in the activity enhancement of toluene oxidation and ozone decomposition.This method is facile,efficient and scalable,and it may become a promising industrial application technology for catalyst synthesis in the near future.

Impacts of environmental factors on urban heating

This study investigated the impact of important environmental variables （i.e., wind speed, solar radiation and cloud cover） on urban heating. Meteorological parameters for fifteen years （from 1990 to 2005）, collected at a well developed and densely populated commercial area （Tsim Sha Tsui, Hong Kong）, were analyzed in details. Urban heat island intensity （UHII）, a well known indicator of urban heating, has been determined as the spatially averaged air-temperature difference between Tsim Sha Tsui and Ta Kwu Ling （a thinly populated rural area with lush vegetation）. Results showed that the UHII and cloud cover have increased by around 9.3% and 4%, respectively, whereas the wind speed and solar radiation have decreased by around 24% and 8.5%, respectively. The month of December experienced the highest UHII （10.2℃） but the lowest wind speed （2.6 m/sec） and cloud cover （3.8 oktas）. Conversely, the month of April observed the highest increases in the UHII （over 100%） and the highest decreases in wind speed （over 40 %） over fifteen years. Notably, the increases in the UHII and reductions in the wind speed were the highest during the night-time and early morning. Conversely, the intensity of solar radiation reduced while the intensity of urban cool island （UCII） increased during solar noon-time. Results demonstrated strong negative correlation between the UHII and wind speed （coefficient of determination, R^2 = 0.8） but no negative correlation between UCII and solar radiation attenuation. A possible negative correlation between UHII and cloud cover was investigated but could not be substantiated.

Non-aqueous Al-ion batteries:cathode materials and corresponding underlying ion storage mechanisms

Aluminum-ion batteries(AIBs)are recognized as one of the promising candidates for future energy stor-age devices due to their merits of cost-effectiveness,high voltage,and high-power operation.Many efforts have been devoted to the development of cathode materials,and the progress has been well summarized in this review paper.Moreover,in addition to materials,the intercalation mechanism also plays a key role in determining cell per-formance.Here,the research progress of cathode materials and corresponding ion intercalation mechanism in AIBs are summarized,including intercalation of AlCl_(4)-,intercala-tion of Al^(3+),and coordination of AlCl_(2)^(+)/AlCl^(2+).This minireview provides comprehensive guidance on the design of cathode materials for the development of high-performance AIBs.

GO-modified flexible polymer nanocomposites fabricated via 3D stereolithography

Graphene oxide(GO)induced enhancement of elastomer properties showed a great deal of potential in recent years,but it is still limited by the barrier of the complicated synthesis processes.Stereolithography(SLA),used in fabrication of thermosets and very recently in“flexible”polymers with elastomeric properties,presents itself as simple and user-friendly method for integration of GO into elastomers.In this work,it was first time demonstrated that GO loadings can be incorporated into commercial flexible photopolymer resins to successfully fabricate GO/elastomer nanocomposites via readily accessible,consumer-oriented SLA printer.The material properties of the resulting polymer was characterized and tested.The mechanical strength,stiffness,and the elongation of the resulting polymer decreased with the addition of GO.The thermal properties were also adversely affected upon the increase in the GO content based on differential scanning calorimetry and thermogravimetric analysis results.It was proposed that the GO agglomerates within the 3D printed composites,can result in significant change in both mechanical and thermal properties of the resulting nanocomposites.This study demonstrated the possibility for the development of the GO/elastomer nanocomposites after the optimization of the GO/“Hexible”photoreactive resin formulation for SLA with suitable annealing process of the composite in future.