A New Integrated GDL with Wavy Channel and Tunneled Rib for High Power Density PEMFC at Low Back Pressure and Wide Humidity.

Proton exchange membrane fuel cells (PEMFCs) have garnered significant attention due to their high efficiency and low emissions. However, PEMFC always suffers mass transfer and water management in performance improvement. Herein, an integrated gas diffusion layer (GDL) with wavy channel and micro-tunneled rib is designed and prepared to achieve faster and gentler mass transfer and excellent water management capability by laser engraving. Outstandingly, the new integrated GDL can use the back pressure of air as low as 0 and 50 kPa to respectively achieve 80% and 90% of fuel cell performance realized under pure oxygen. Such high performance is mainly due to the turbulent flow caused by wavy channel and express removing pathway of liquid water provided by micro-tunneled rib. Moreover, the new integrated GDL also shows wide humidity tolerance from 40% to 100% and a very high specific volume power density of 16,300 W L-1 due to the thin thickness of new integrated GDL. This new integrated GDL is expected to be widely used in PEMFC and other energy conversion devices.

Nanosized Proton Conductor Array with High Specific Surface Area Improves Fuel Cell Performance at Low Pt Loading.

The use of ordered catalyst layers, based on micro-/nanostructured arrays such as the ordered Nafion array, has demonstrated great potential in reducing catalyst loading and improving fuel cell performance. However, the size (diameter) of the basic unit of the most existing ordered Nafion arrays, such as Nafion pillar or cone, is typically limited to micron or submicron sizes. Such small sizes only provide a limited number of proton transfer channels and a small specific area for catalyst loading. In this work, the ordered Nafion array with a pillar diameter of only 40 nm (D40) was successfully prepared through optimization of the Nafion solvent, thermal annealing temperature, and stripping mode from the anode alumina oxide (AAO) template. The density of D40 is 2.7 × 1010 pillars/cm2, providing an abundance of proton transfer channels. Additionally, D40 has a specific area of up to 51.5 cm2/cm2, which offers a large area for catalyst loading. This, in turn, results in the interface between the catalyst layer and gas diffusion layer becoming closer. Consequently, the peak power densities of the fuel cells are 1.47 (array as anode) and 1.29 W/cm2 (array as cathode), which are 3.3 and 2.9 times of that without array, respectively. The catalyst loading is significantly reduced to 17.6 (array as anode) and 61.0 µg/cm2 (array as cathode). Thus, the nanosized Nafion array has been proven to have high fuel cell performance with low Pt catalyst loading. Moreover, this study also provides guidance for the design of a catalyst layer for water electrolysis and electrosynthesis.

Integrated Gas Diffusion Electrode with High Conductivity Obtained by Skin Electroplating for High Specific Power Density Fuel Cell.

Smaller volume/weight and higher output power/energy density are always the goals of electrochemistry energy devices. Here, a simple strategy is proposed to prepare an integrated gas diffusion electrode (GDE) with high conductivity through skin electroplating. The skin electroplating is the combination of magnetron sputtering and spatial confinement electroplating. The electroplated metal obtained by skin electroplating is uniformly, continuously, and tightly attached to the surface of carbon paper like a layer of skin. Uniform and continuous electroplating metal layer endows the integrated electrode excellent conductivity with the square resistance as low as 27 mΩ sq-1 . In application, the self-breathing fuel cell with 1 cm2 active area can harvest ultrahigh volume specific power density (20.9 kW L-1 ). Additionally, the weight of the fuel cell stack (23 W) with the integrated electrode is only 20 g, which is only 7% of the commercial stack with the same power. The mass specific power density reaches 1150 W kg-1 , which is 15 times of the commercial stack. Outstandingly, the stack can charge 4 mobile phones at the same time. More importantly, the skin electroplating provides an effective strategy to improve the specific power density of other energy devices including Zn-air batteries, Li-air batteries, and so on.

Ultralight, Safe, Economical, and Portable Oxygen Generators with Low Energy Consumption Prepared by Air-Breathing Electrochemical Extraction.

Pure oxygen is vital in medical treatment, first aid, and chemical synthesis. Hypoxia can cause severe damage to the organ systems such as respiratory, digestive, and nervous systems and even directly cause death. Notably, the severe Coronavirus disease 2019 (COVID-19) pandemic has exacerbated the shortage of medical oxygen in the world. Hence, a safe, economical, and portable oxygen supply device is urgently needed. Here, we have successfully prepared a device with air-breathing electrochemical extraction of pure oxygen (ABEEPO) with light weight and high energy efficiency. By renovating the structure of the electrolytic cell, the components bipolar plate and end plate are replaced with a plastic membrane, and the component current collector is replaced with a highly conductive graphene composite membrane electrode. Due to the use of the plastic membrane and graphene composite membrane electrode, the weight of the electrolytic cell is reduced from 1319.4 to 1.6 g, and the flexibility of the electrolytic cell is successfully realized. Through optimizing anode catalysts, working area, and operating voltage, a high flow rate per mass (234 mL h-1 g-1) was achieved at a voltage of 1.2 V. The device exhibits high stability in 2 h. The new portable oxygen production device would be effective for hypoxia treatment.

Viscosity-sensitive thiolated gold nanoclusters with diffusion-controlled emission for intracellular viscosity imaging.

A unique diffusion-dependent emission phenomenon of gold nanoclusters was discovered, and can be regulated by the variation in viscosity and temperature. This specific property of gold nanoclusters was further used for viscosity monitoring in live cells, and the results demonstrated that gold nanoclusters are capable of real-time monitoring the abnormal viscosity change inside the cells.

Thiol-ene click reaction-induced fluorescence enhancement by altering the radiative rate for assaying butyrylcholinesterase activity.

Butyrylcholinesterase (BChE) generally acts as an important plasma biomarker for clinical diagnosis due to its major contribution to human plasma cholinesterase levels, but its current fluorometric assay relying on fluorogenic substrates frequently suffers from the lack of sufficiently fast response time and specific recognition of substrates relative to the traditional Ellman's method. In this work, we report a fluorescent molecular probe for assaying BChE activity based on thiol-triggered fluorescence enhancement via thiol-ene click reactions. A low-temperature experiment and theoretical analysis exclude the possibility of weak fluorescence of the probe caused by an intramolecular photoinduced electron transfer process and support the main cause of an ultraslow radiative rate due to the introduction of two acrylyl groups. This probe has sensitive fluorescence responses to thiols via thiol-ene click chemistry, and it can distinguish between glutathione and cysteine or homocysteine in different emission colors. The rapid reaction kinetics of this probe enables it to monitor hydrolysis reactions catalyzed by butyrylcholinesterase (BChE) in a real-time manner. This probe is used to develop the first fluorometric assay of BChE activity based on fluorescence enhancement triggered by thiol-ene click chemistry using butyrylthiocholine as the substrate. The established BChE assay shows excellent sensitivity, and is capable of avoiding the interference from glutathione and acetylcholinesterase (AChE) in a complex matrix. The inhibition test of tacrine on BChE with this assay substantiates its feasibility in screening potential inhibitors of BChE. This work demonstrates a design strategy of fluorescent probes lighted up by thiol-ene click reactions, reveals the main cause of thiol-triggered fluorescence enhancement by altering the radiative rate, and provides the first fluorometric assay of BChE based on rapid thiol-ene click reactions.

Photophysical Tuning of Organic Ionic Crystals from Ultralong Afterglow to Highly Efficient Phosphorescence by Variation of Halides.

Manipulation of photophysical properties of pure organic materials via simple alteration is attractive but extremely challenging because of the lack of valid design strategies for achieving ultralong afterglow or efficient room-temperature phosphorescence. Herein, we report a first photophysical manipulation of organic ionic crystals from ultralong afterglow to highly efficient phosphorescence by variation of halides in the crystals. Crystal structural analysis reveals ultralong organic afterglow of tetraphenylphosphonium chloride is promoted by strong intermolecular electronic coupling in the crystal, and theoretical analysis demonstrates that the tremendous boost of the phosphorescence of tetraphenylphosphonium iodide is caused by the coupling effects of significant heavy atom effect from iodine atoms and a small energy difference between the first singlet and triplet states. This work contributes to regulating long-lived emissive behaviors of pure organic ionic crystals in a controlled way and will promote the development of optical switches controlled by external stimuli.

Ultralong Room-Temperature Phosphorescence from Supramolecular Behavior via Intermolecular Electronic Coupling in Pure Organic Crystals.

Ultralong room-temperature phosphorescence (RTP) of organic materials is extremely attractive for its tremendous potential use. However, the design of organic materials with ultralong and efficient RTP is very challenging due to the lack of general design principles. A new design principle for organic materials with ultralong room-temperature phosphorescence based on π-π-dominated supramolecular aggregates in crystal is proposed, and strong intermolecular electronic coupling with specific molecular alignment is identified to be responsible for supramolecular behavior in persistent emission. Small substituents in molecular structure favor the formation of supramolecular aggregates in the crystal, thus facilitating the generation of ultralong RTP under ambient conditions. Our results also reveal that the introduction of heavy atoms into supramolecular aggregates as a general rule can be used to achieve efficient persistent phosphorescence.

Reversible Switching between Phosphorescence and Fluorescence in a Unimolecular System Controlled by External Stimuli.

Manipulation of the emission properties of pure organic molecules through external stimuli is attractive but challenging. Herein, a dual-emissive hexathiobenzene-based molecule is reported with significant aggregation-induced phosphorescence characteristics, and demonstrates reversible switching among blue, green, and yellow phosphorescence by controlling molecular aggregation state or protonation state. Variation of solvent or pH value manipulates the interconversion between fluorescence and phosphorescence, while the change in protonation state in organic solvent switches two short-lived emissions in a controllable manner. Such a controlled manipulation is achieved by the rational design of combining a twisted structure and the proper arrangement of energy gaps among different excited states. This work provides a new design principle for organic molecules with efficient room-temperature phosphorescence and tunable singlet-triplet emissive properties, and contributes to the design and development of smart materials and intelligent optoelectronic devices.

Redox-Controlled Fluorescent Nanoswitch Based on Reversible Disulfide and Its Application in Butyrylcholinesterase Activity Assay.

Butyrylcholinesterase (BChE) mainly contributing to plasma cholinesterase activity is an important indicator for routinely diagnosing liver function and organophosphorus poisoning in clinical diagnosis, but its current assays are scarce and frequently suffer from some significant interference and instability. Herein, we report a redox-controlled fluorescence nanoswtich based on reversible disulfide bonds, and further develop a fluorometric assay of BChE via thiol-triggered disaggregation-induced emission. Thiol-functionalized carbon quantum dots (thiol-CQDs) with intense fluorescence is found to be responsive to hydrogen peroxide, and their redox reaction transforms thiol-CQDs to nonfluorescent thiol-CQD assembly. The thiols inverse this process by a thiol-exchange reaction to turn on the fluorescence. The fluorescence can be reversibly switched by the formation and breaking of disulfide bonds caused by external redox stimuli. The specific thiol-triggered disaggregation-induced emission enables us to assay BChE activity in a fluorescence turn-on and real-time way using butyrylthiocholine iodide as the substrate. As-established BChE assay achieves sufficient sensitivity for practical determination in human serum, and is capable of avoiding the interference from micromolar glutathione and discriminatively quantifying BChE from its sister enzyme acetylcholinesterase. The first design of reversible redox-controlled nanosiwtch based on disulfide expands the application of disulfide chemistry in sensing and clinical diagnostics, and this novel BChE assay enriches the detection methods for cholinesterase activity.

Hydrophobicity-guided self-assembled particles of silver nanoclusters with aggregation-induced emission and their use in sensing and bioimaging.

Distinctive aggregation-induced emission (AIE) phenomenon of thiolate-protected silver nanoclusters (AgNCs) has been revealed; these AgNCs have shown great potential for exploitation and utilization, but their applications as a bright luminogen in the chemosensing and bioimaging areas are greatly limited by their ultralow brightness in an aqueous solution. Herein, we report facile fabrication of hydrophobicity-guided self-assembled particles of silver nanoclusters with aggregation-induced emission. A hydrophobic ligand, thiosalicylic acid, was adopted to prepare AgNCs via a one-step way, and thiosalicylic acid-capped AgNCs showed significant AIE behavior. This AIE property of AgNCs enables them to selectively respond to multiple external stimuli such as solvent polarity, pH and environmental temperature. The hydrophobic nature of thiosalicylic acid as capping ligands of AgNCs drives a self-assembly process of AgNCs in an aqueous solution that results in the formation of self-assembled particles of AgNCs with bright luminescence. Sensitive detection of mercuric ion based on the highly luminescent AgNC AIE particles was achieved in terms of a strong quenching effect of mercuric ion. Cellular viability and luminescence imaging performance of the AgNC AIE particles on living cells were also evaluated for the first time. This study demonstrates the fabrication of AIE particles of silver nanoclusters with bright luminescence guided by hydrophobic interaction and reveals excellent bioimaging performance of AIE particles in living cells.