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Photocatalyst fabrication process plays the central role in photocatalytic hydrogen (H 2) evolution reaction. Herein, we synthesize Na+ functionalized porous graphitic carbon nitride nanorods (Na-CNNR) via a facile one-pot calcination method. The morphology and size of Na-CNNR are controllable by changing the amount of sodium salt; both sodium salt and air are essential to the unique structure and oxygen doping. The obtained Na-CNNR contains abundant oxygen in the graphitic carbon nitride (CN) plane. The optimized Na20-CNNR (20 wt% Na 2 S 2 O 3 •5H 2 O to dicyanamide) photocatalyst exhibits a high surface area with enhanced visible light absorption. Besides, Na20-CNNR displays fast charge transfer and high carrier separation rate characterized by photoluminescence (PL) spectroscopy and electrochemical test. Through time-resolved transient absorption spectra analysis, the trapped unreactive electron accumulation can be highly restrained, favoring efficient active electron de-trapping and transfer. The optimized Na20-CNNR sample exhibits the highest photocatalytic H 2 evolution rate of 7.46 mmol/h/g under visible light irradiation (>400 nm, 100 mW/cm2), which is up to 85 times that of the bare CN and 27 times that of Na+ doped graphitic carbon nitride nanoparticles (Na20–CNNP). Meanwhile, the cyclability tests indicate that Na20-CNNR displays robust stability over 24 h. [Display omitted] • The Na and O Doped porous g-C 3 N 4 nanorod structure was obtained after washing with water without tedious treatment. • Sodium salt and air are essential for g-C 3 N 4 nanorod structure formation and oxygen doping. • Photogenerated electron transfer is highly improved from the picosecond level. • Na20-CNNR exhibits a highly improved photocatalytic H 2 evolution rate of 7460 μmol/h/g. [ABSTRACT FROM AUTHOR]

Highlights • Pure CeO 2 can achieve both photocatalysis and catalytic ozonation in VUV-PCO system. • High toluene removal, mineralization and ozone removal can be achieved by pure CeO 2. • Amount of Ce3+ plays a critical role in toluene removal. • Differences in photocatalytic activity were explained by electrochemical behaviors. Abstract Volatile organic compounds (VOCs) are one of the biggest concerns in the ambient environment that have attracted a great number of studies related to its remediation. Vacuum ultraviolet (VUV)-based photocatalytic oxidation (PCO) is a promising technology in controlling VOCs. CeO 2 is found to be a promising catalyst for the VUV-PCO technology possessing catalytic capacities in both the photocatalysis and ozonation processes. In this study, three typical kinds of pure CeO 2 with various nanostructures were synthesized and creatively applied for VUV-photocatalytic oxidation of toluene. Material characterizations, including BET, SEM, TEM, XRD, Raman, XPS, H 2 -TPR and DRS, were conducted to characterize different CeO 2 samples. Results indicated that synthetic CeO 2 samples have a much more remarkable enhancement in degrading toluene compared to commercial ones. Higher COx generation and mineralization rates were obtained with the use of all the synthetic CeO 2 samples. Compared to commercial CeO 2 , the synthetic samples have much better capacity towards removing ozone and the best activity in ozone decomposition was observed in CeO 2 Nanorods catalysts. Both the effects of photocatalysis and catalytic ozonation exist in all the CeO 2 catalysts. The amount of Ce3+ plays a critical role in both the catalytic activity of photocatalysis and ozonation that higher ratio of Ce3+ leads to better performance in toluene removal. The differences in photocatalytic activity were further explained by the results of electrochemical behaviors of different CeO 2 samples which showed varying responses to UV irradiation. [ABSTRACT FROM AUTHOR]

The optimized C-USTiO 2 photocatalysts on carbon cloth for a toluene degradation test at continuous toluene gas flow under LED light irradiation showed a superior toluene removal efficiency. • USTiO 2 with abundant active sites was obtained by a facile acid assisted solvent method. • Light absorption ability of C-USTiO 2 was promoted through a carbon doping process. • Photo-generated electrons and holes of C-USTiO 2 were separated efficiently. • Optimized C-USTiO 2 exhibited superior toluene removal rate and robust stability under visible LED light irradiation. Photocatalytic activity triggered by visible light from light emitting diode (LED) is highly restricted by limited active sites, poor light absorption, and sluggish photo-generated carrier separation of the photocatalysts. Particularly for continuous degradation reaction of volatile organic compounds (VOCs), confined contact between flowing air pollutant gas and photocatalysts renders the degradation ineffective within a transient retention period. Considering the restriction of photocatalytic reaction occurred on semiconductor surface, ultra-small TiO 2 (USTiO 2) nanoparticles were fabricated by a facile acid-assisted solvent method, which possess copious active sites. A simple heating process was further applied for carbon doping on USTiO 2 (C-USTiO 2) surface. As a result, the obtained C-USTiO 2 exhibited high visible light absorption, rich photo-generated carrier density, and its rapid carrier separation performance. In this study, optimized C-USTiO 2 photocatalyst was deposited on carbon cloth and tested for continuous toluene degradation under LED light irradiation. Results showed that the toluene removal efficiency can reach higher than 80% with high concentration of CO 2 generated and an excellent cycle stability of over 180 min. [ABSTRACT FROM AUTHOR]

In this work, a paper-based hydrogen fuel cell is developed without the need for hydrogen storage. Instead, an embedded aluminum foil inside the paper is utilized for in-situ hydrogen generation. The electrodes and current collectors are also deposited on the paper, leading to a lightweight, compact and flexible hydrogen fuel cell with an OCV reaching 0.93 V and a peak power density of 4 mW cm−2. Benefited from the impeded hydroxyl ion diffusion, the hydrogen generation rate is well controlled, leading to a high faradaic efficiency of 72%. In addition, the cell can be operated under different bending angles with negligible power loss. Furthermore, it can be conveniently stacked in the same piece of paper for higher voltage and power outputs. Such a novel fuel cell design is especially suitable for powering various flexible devices with small rated power. • A paper-based hydrogen fuel cell is developed with an OCV of 0.93 V. • The peak power density is 4 mW cm−2 and the maximum current density is 8 mA cm−2. • Faradaic efficiency and energy efficiency are as high as 72% and 18%, respectively. • 75–87.5% of the cell performance remains when bended by angles from 45° to 135°. • A 4-cell stack is developed with an OCV of 3.8 V and a stacking efficiency of 90.6%. [ABSTRACT FROM AUTHOR]

Highlights • Toluene removal efficiency was greatly improved in the presence of Mn-TiO 2 /CeO 2 catalyst. • Ozone could be completely utilized and removed by compositing Mn-TiO 2 with CeO 2. • CeO 2 improved the generation of hydroxyl radicals (OH) which played a significant role in toluene degradation. Abstract Volatile organic compounds (VOCs) are attracting more and more attention among all the air pollutants. Photocatalytic oxidation under vacuum ultraviolet (VUV) irradiation presents a novel and promising process for VOC degradation while also generating ozone as a byproduct. To improve the degradation efficiency of VOCs and remove the residual ozone Mn-TiO 2 /mesoporous CeO 2 composite catalysts were developed and used as a catalyst in a VUV-PCO system for toluene degradation. Characterizations including SEM, TEM, BET, XRD, XPS, Raman and H 2 -TPR, were conducted to examine the physical and chemical features of the synthetic samples. Results of a toluene degradation test showed that the Mn-TiO 2 /CeO 2 catalyst had superior activity in removing toluene and ozone to Mn-TiO 2 and pure CeO 2. The toluene removal efficiencies of the catalysts with a different molar ratio of Ti/Ce were found to be in the order of Mn-TiO 2 /CeO 2 (1:1) > Mn-TiO 2 /CeO 2 (1:2) > Mn-TiO 2 /CeO 2 (2:1). The mineralization rate increased in the order of Mn-TiO 2 /CeO 2 (1:1) > Mn-TiO 2 /CeO 2 (2:1) ≈ Mn-TiO 2 > Mn-TiO 2 /CeO 2 (1:2) > CeO 2 > VUV photolysis. High ozone removal rates of over 99.9% were obtained for all the doped samples with Mn, resulting in a residual ozone lower than 0.12 ppm. With the use of the scavenger tert-butanol (TBA) and the electron spin resonance (ESR) test, hydroxyl radicals (OH) were found to play a significant role in toluene oxidation in the VUV-PCO process and ozone is also involved in the formation of OH. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface grafted Mn2+ speeds up the photo-generated carrier separation of ultra-small TiO 2 (USTiO 2). • Mn2+ decomposes the surplus ozone effectively through the sustainable valence state shift. • Mn2+ functionalized USTiO 2 loaded on carbon cloth exhibits effective toluene degradation activity and robust stability in a flow reactor. • Porous carbon cloth substrate with appropriate structure provides numerous active sites to allow VUV light penetration for toluene degradation with the low amount of catalyst usage. Vacuum ultraviolet (VUV) light-induced photocatalytic degradation of volatile organic compounds (VOCs) is a promising strategy to solve many air pollution problems. However, the effectiveness of the process depends on the photocatalyst adopted. In this study, ultra-small TiO 2 (USTiO 2) nanoparticles were first synthesized through an acid-assisted solvent method; then, Mn2+ was added to form a Mn2+/USTiO 2 composite, which was then deposited onto a carbon cloth substrate by a facile dropping-drying process. Photo-generated carrier separation of Mn2+/USTiO 2 was enhanced and electron recombination was suppressed ascribed to the Mn2+ grafting. Residual O 3 produced by the VUV light was also thoroughly decomposed via the Mn valence state shift, forming reactive oxygen species to further enhance toluene degradation activity. Under VUV light illumination, the optimized 2.0% Mn2+/USTiO 2 on carbon cloth showed a superior toluene degradation efficiency of 98%, with high mineralization efficiency up to 50%. This hybrid structure exhibited robust stability of over 400 min. [ABSTRACT FROM AUTHOR]

• MnO 2 -rGO composite sample exhibits excellent toluene removal performance in VUV-OZCO process. • With the use of catalysts, more complete reactions occur that by-products with shorter chains can be detected. • Two reaction pathways of toluene degradation are proposed under the action of •O 2 – and OH•. Advanced oxidation processes (AOPs) are regarded as one of the most promising technologies for VOC degradation. In this study, MnO 2 -rGO composite samples were prepared and applied in a system consisting of VUV photolysis and ozone catalytic oxidation for the degradation of toluene. Extensive characterizations, including BET, SEM, TEM, HRTEM, Raman, XRD, FTIR and XPS, were conducted to analyze the features of the composite MnO 2 -rGO samples. Results of toluene removal, mineralization and ozone decomposition showed that the MnO 2 -rGO composite sample with Mn loading of 25 wt% exhibited the best performance in this study due to its superior adsorption activity and moderated MnO 2 loading. The intermediates of the degradation process were analyzed showing more by-products with shorter chains in the presence of the MnO 2 -rGO catalysts compared to VUV photolysis alone, indicating more complete reactions occurred. Generation of hydroxyl radicals (•OH) and superoxide radicals (•O 2 –) were confirmed to contribute in the toluene degradation. Two reaction pathways (i.e. •O 2 – and OH• based) and mechanism of toluene degradation were proposed. [ABSTRACT FROM AUTHOR]

Al-air batteries are generally fabricated by rigid and heavyweight materials such as metal or plastic, meanwhile a bulky electrolyte solution either in static or circulation is requisite to ensure their steady operation. Therefore, they are less suitable for powering flexible and portable devices with lower power demand, such as wearable electronics, point-of-care test assays, RFID tags, etc. This work develops a flexible and lightweight Al-air battery with much less electrolyte storage, which is totally fabricated on a cellulose paper. The Al foil anode is embedded inside the paper substrate during paper-making process, while the air-breathing cathode is deposited onto the paper surface using an oxygen reduction ink. Despite its simple structure and low cost, this flexible Al-air battery can deliver a satisfactory power density of 19 mW cm−2 with alkaline electrolyte, and its operation lifespan is as long as 58 h with only 25 mg Al when saline electrolyte is employed. The corresponding Al specific capacity is as high as 2338 mA h g−1. In addition, this battery exhibits an excellent flexibility when facing different bending angles from 60 to 180° and multiple bending times greater than 1000. Furthermore, a flexible current or voltage output can be easily obtained by scaling up or stacking the present flexible Al-air battery, respectively, and the corresponding stacking efficiency is as high as 94%. In the future, non-metal oxygen catalyst will be employed to improve its environmental friendliness, and hot-pressing will be adopted to further increase its robustness to external deformation. • A flexible Al-air battery is developed for powering flexible and portable devices. • Al anode is embedded inside the paper, while ink cathode is deposited on the paper. • Peak power density of 19 mW cm−2 and specific capacity of 2338 mA h g−1 is obtained. • Battery performance is very stable even it is bended to 180° and by 1000 times. • Battery scaling-up and stacking is very convenient and highly-efficient (94%). [ABSTRACT FROM AUTHOR]

Since its first appearance in 2002, microfluidic fuel cell has received great attention in the past two decades, which is mainly targeted at its use in portable electronics. This micro fuel cell technology utilizes microfluidic flows as electrolyte instead of conventional polymer membranes. To date, various fuels have been utilized in it, such as vanadium species, hydrogen, hydrocarbons, hydrogen peroxide, borohydride and nitrogenous materials, each of which has its specific merits and demerits. To optimize its power output and fuel utilization, innovative cell structures and advanced catalysts have been continuously developed for different fuels, with remarkable improvements achieved. The power output can be elevated from several mW cm−2 to several W cm−2 at room temperature, while the fuel utilization per single pass can reach 100% by using 3D flow-through electrodes. Also, investigations in recent years have shown that microfluidic fuel cell stacking increases the working voltage. In addition to cells with plastic channel, novel cell designs based on cellulose paper and fabric materials have also been proposed; apart from being lightweight, they are also free from pumping. These innovative cell designs represent a promising route for achieving real applications in areas such as medical diagnostic, wearable healthcare and smart logistics. As for the conventional plastic cells, they are currently less competitive against batteries and other fuel cells because of the extra pumping requirement, which should be resolved in future by developing passive pumps instead. Alternatively, they can be applied in specific circumstances where the extra pumping loss is tolerable. • Microfluidic fuel cells with different types of fuels are summarized and compared. • Various flow configurations and electrode structures are reviewed in detail. • Stacking efficiency is compared among different microfluidic fuel cell stacks. • Paper-based and fabric-based microfluidic fuel cells without pumping are introduced. • An outlook on their future development and application is provided. [ABSTRACT FROM AUTHOR]

A printable Al-air battery is successfully developed for the first time by printing the Al ink and the oxygen reduction ink onto a cellulose paper. Currently, the printable Al-air battery can provide an open-circuit voltage of 1 V, a peak power density of 6.6 mW cm−2 and a maximum current density of 40 mA cm−2 when using salt water as the electrolyte. With 6 mg Al, the battery can discharge at 1 mA cm−2 for almost 6 h, leading to a high specific capacity of 951 mA h g−1. It is found that a moderate concentration of the polymer binder and a high concentration of the carbon support are of great importance to the ink functionality, while the hot-press treatment can dramatically improve the electrode performance and robustness. Finally, screen-printed battery prototypes with a specific electrode pattern are demonstrated for powering a small electric fan and a light-emitting diode. The present printable Al-air battery is a novel type of primary power source with low fabrication cost, high energy density and great environmental friendliness, which is especially suitable for powering various disposable printed electronics in the future. Image 1 • An all screen-printed Al-air battery is proposed for powering printed electronics. • The Al ink is composed of Al microsphere, carbon nanotube and cellulose binder. • Peak power density of 6.6 mW cm−2 and current density of 40 mA cm−2 can be obtained. • The battery discharge specific capacity is as high as 951 mA h g−1. • Hot-pressing is found to significantly improve the printed anode integrity. [ABSTRACT FROM AUTHOR]