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

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Green Energy & Environment 2023年第3期8卷 757-766页

作者： Wending Pan yifei Wang Holly y.H.Kwok dennis y.c.leung Department of Mechanical Engineering The University of Hong KongHong KongChina

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.

关键词： Al-air battery cotton-based Electrolyte pre-deposition capacity control Miniwatt electronics

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

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Journal of Materials Science & Technology 2022年第21期116卷 169-179页

作者： yingguang Zhang Muyan Wu yifei Wang Xiaolong Zhao dennis y.c.leung Department of Mechanical Engineering The University of Hong KongPokfulam RoadHong KongChina School of Mechanical Engineering and Automation Harbin Institute of TechnologyShenzhen 518000China

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.

关键词： Mesoporous ceO_(2) Manganese modification Scalable synthesis Photocatalysis VOcs abatement

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

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Journal of Environmental Sciences 2023年第12期134卷 55-64页

作者： Ruijie Xie Dongxue Lei Xiaowen Xie Ziyi Suo dennis y.c.leung Jianping cao Fang Ruimei Haibao Huang School of Environmental Science and Engineering Sun Yat-sen UniversityGuangzhou 510275China Department of Mechanical Engineering University of Hong KongHong Kong 999077China college of Environment and Resources Chongqing Technology and Business UniversityChongqing 400067China Scientific Research Academy of GuangXi Environmental Protection Nanning 530022China

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.

关键词： Volatile organic compounds(VOcs) Vacuum ultraviolet(VUV)photolysis Wet scrubbing process Toluene degradation Intermediates analysis

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

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Green Energy & Environment 2023年第4期8卷 1117-1127页

作者： yifei Wang Wending Pan Kee Wah Leong Shijing Luo Xiaolong Zhao dennis y.c.leung School of Mechanical Engineering and Automation Harbin Institute of TechnologyShenzhenChina Department of Mechanical Engineering The University of Hong KongHong KongChina

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.

关键词： Al-air battery Gel electrolyte Ethanol gel Al corrosion Polyethylene oxide

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

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Green Energy & Environment 2023年第5期8卷 1380-1388页

作者： yifei Wang Wending Pan Kee Wah Leong yingguang Zhang Xiaolong Zhao Shijing Luo dennis y.c.leung School of Mechanical Engineering and Automation Harbin Institute of TechnologyShenzhen518055China Department of Mechanical Engineering The University of Hong KongHong KongChina

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.

关键词： Al ion battery Aqueous electrolyte Water-in-salt Paper battery Flexible battery

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

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Journal of Materials Science & Technology 2023年第2期133卷 135-144页

作者： Xiaolong Zhao Xiaoping yi Wending Pan yifei Wang Shijing Luo yingguang Zhang Ruijie Xie dennis y.c.leung Department of Mechanical Engineering the University of Hong KongPokfulam RoadHong KongChina School of Energy and Environmental Engineering University of Science and Technology BeijingBeijing 100083China School of Mechanical Engineering and Automation Harbin Institute of TechnologyShenzhen 518055China

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.

关键词： UV light Oxygen doping charge transfer Graphitic carbon nitride cO_(2)reduction

Impacts of environmental factors on urban heating

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Journal of Environmental Sciences 2010年第12期22卷 1903-1909页

作者： Rizwan Ahmed Memon dennis y.c.leung Department of Mechanical Engineering Mehran University of Engineering & Technology Department of Mechanical Engineering The University of Hong Kong School of Energy and Environment City University of Hong Kong

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.

关键词： urban heat island urban cool island wind speed cloud cover

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

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Journal of Environmental Sciences 2008年第7期20卷 832-837页

作者： chun-Ho Liu dennis y.c.leung Department of Mechanical Engineering The University of Hong KongHong Kong.

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...

关键词： volatile organic compounds VOcs-to-NO_x ratio air quality vehicular emission chemistry box model

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

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Journal of Environmental Sciences 2012年第12期24卷 2091-2103页

作者： Nelson y.O.Tong dennis y.c.leung Department of Mechanical Engineering The University of Hong Kong

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.

关键词： photochemistry reactive pollutant dispersion building aspect ratio diurnal heating scenario wind speed urban streetcanyon