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Solid polymer electrolytes are promising candidates for implementation in next-generation all-solid-state batteries (ASSBs) which could replace conventional batteries used today. However, the materialization of ASSBs on a mass scale is restricted by the low ionic conductivity and high interfacial resistance of solid electrolytes. In this work, succinonitrile (SN) with lithium (trifluoromethylsulphonyl)imide (LiTFSI) and Al-doped Li7La3Zr2O12 (Al-LLZO) nanoparticles were used to improve the ionic conductivity of a polyethylene oxide-based composite electrolyte. The Al-LLZO nanoparticles were synthesized by a facile synthesis process at low temperatures, which contributed to an enhancement in the ionic conductivity. A solid polymer electrolyte with 7.5 wt% of Al-LLZO and 15 wt% of SN achieved a high ionic conductivity of 4.17 × 10-4 Scm-1 at room temperature and a large value of 0.451 for the lithium-ion transport number at 60 °C. By adding 10 wt% SN and 10 wt% of Al-LLZO in the LiFePO4 cathode, the cell could operate at 25 oC with a specific capacity of 130 mAh g-1 and 89% capacity retention after 200 cycles at current density of 20 mA g-1. This study therefore proposes a solution to improve the ionic conductivity of solid polymer electrolytes in all-solid-state batteries.

Sulfur is a prospective material for next-generation batteries with high theoretical capacity, but its drawbacks hinder its commercialization. To overcome the low conductivity of natural sulfur and the shuttle effect of lithium polysulfide, the study proposes a novel sulfur film coated with three-dimensional nitrogen and cobalt-codoped polyhedral carbon wrapped on a multiwalled carbon nanotube sponge (3D-S@NCoCPC sponge) composite as a high-performance cathode material for rechargeable lithium-sulfur batteries. The interconnected conductive carbon network with abundant pores provides more room for the homogeneous distribution of sulfur within the composite and creates a favorable pathway for electrolyte permeability and lithium-ion diffusion. Moreover, the strong interaction between cobalt and lithium polysulfides leads to efficient suppression of the shuttle effect. In addition, the homogeneous distribution of sulfur and cobalt within the composite enhances electronic transfer for the conversion reaction of sulfur. As expected, the cathode with a high sulfur content of 77.5 wt % in the composite achieved a high initial discharge capacity of 1192 mA h g-1 and high Coulombic efficiency of 99.98% after 100 cycles at 100 mA g-1 current density. Stable performance was achieved with 92.9% capacity retention after 200 cycles at 1000 mA/g current density.

Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when H2O and O2 molecules are present at high voltages in polymer electrolyte membrane fuel cells (PEMFCs). In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with H2O and was thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of the F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer's method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. The Pt/F-GNR showed the lowest degradation rate in carbon corrosion and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, the F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.

Seawater electrolysis is a promising technology for the production of hydrogen energy and seawater desalination. To produce hydrogen energy through seawater electrolysis, highly active electrocatalysts for the oxygen evolution reaction (OER) are required. Here, we report the development of a Ni-doped FeOOH anode for high-efficiency anion exchange membrane alkaline seawater electrolysis. The Ni-doped FeOOH anode showed an overpotential of only 301 mV in half-cell tests, reaching a current density of 100 mA cm−2 in 1.0 M KOH + seawater. An anion exchange membrane electrolyzer catalyzed by Ni-doped FeOOH exhibited a current density of 729 mA cm−2 in 1.0 M KOH + seawater with an energy conversion efficiency of 76.35%. Compared to the reported AEM electrolyzer operated in 1.0 M KOH, our AEM electrolyzer catalyzed with Ni-doped FeOOH operated in 1.0 M KOH + seawater exhibited higher performance.

This study proposes a reliable and self-powered hydrogen (H2) gas sensor composed of a chemo-mechanically operating nanostructured film and photovoltaic cell. Specifically, the nanostructured film ...

Uniquely nanostructured CuCo2O4 is presented as an electrocatalyst for oxygen evolution reactions (OER). CuCo2O4 particles in a chestnut-burr-like shape (CCO*, where ∗ = chestnut burr) were hydroth...

The application of electrocatalysts with high activity to a practical water electrolysis cell is a crucial challenge for the production of pure hydrogen and commercialization of the water electrolyzer. Herein, a nanosized Cu0.5Co2.5O4 catalyst synthesized by co-precipitation by adjusting pH is applied to the anion exchange membrane water electrolysis (AEMWE) cell as an anode, which is demonstrated to have higher efficiency and stability than noble metal-based anodes. The composition (Cu/Co) and morphology of Cu0.5Co2.5O4 change as the pH increases and then nanoparticles are formed at pH 11, where oxygen vacancies are formed by the etching of Cu. In the density functional theory study, the electronic structure of Co modified by Cu in the Co3O4 lattice leads to an optimal adsorption strength, resulting in a free energy diagram in which the potential of Cu0.5Co2.5O4 (1.756 V vs. reversible hydrogen electrode, RHE) is more thermodynamically favorable than that of Co3O4 (1.951 V vs. RHE). The Cu0.5Co2.5O4 catalyst has a recorded overpotential of 285 mV at 10 mA cm−2 in 1 M KOH. Furthermore, the AEMWE cell using Cu0.5Co2.5O4 as an anode exhibited a current density of 1.3 A cm−2 at 1.8 V, which is the highest performance among the reported papers and maintains around 80% energy conversion efficiency for 100 hours.

A Cu–Co–P electrocatalyst for hydrogen evolution reaction (HER) was designed with a dendritic and porous foam structure. Fabricated by one-step electrodeposition with binary alloy on a hydrogen bub...

Recently, copper oxide (CuO)-based visible-light photodetectors have attracted great interest due to their narrow bandgap (1.2 eV), low cost, and ease of fabrication. However, there has been insufficient theoretical analysis and study of CuO-based photodetectors, resulting in inferior performance in terms of responsivity, detectivity, and response speed. This work develops a method to enhance the performance of CuO photodetectors by engineering a grain structure based on a newly-developed theoretical model. In the developed theoretical grain-structure model, the grain size and the connections between grains are considered because they can strongly affect the optoelectronic characteristics of CuO photodetectors. Based upon the proposed model, the engineered CuO device achieves enhanced optoelectronic performance. The engineered device shows high responsivity of 15.3 A/W and detectivity of 1.08 × 1011 Jones, which are 18 and 50 times better than those of the unoptimized device, and also shows fast rising and decaying response speeds of 0.682 s and 1.77 s, respectively. In addition, the proposed method is suitable for the mass-production of performance-enhanced, reliable photodetectors. By using a conventional semiconductor fabrication process, a photodetector-array is demonstrated on a 4-inch wafer. The fabricated devices show uniform, high, and stable optoelectronic performance for a month.

Preparing Pt nanostructure catalysts with better support materials is an efficient catalyst design strategy to develop high performance Pt-based electrocatalysts. Here we report for the first time a method to synthesize highly-dispersed Pt nanoclusters supported on microporous three-dimensional (3D) graphene-like carbon (3D-GLC) for use in the electrochemical oxidation reaction. The Pt nanoclusters loaded on 3D graphene-like carbon (Pt/3D-GLC) are synthesized by Ca2+-exchanged beta zeolite template based carbon synthesis and subsequent Pt impregnation methods. Highly-dispersed Pt nanoclusters (ca. 1.25 ± 0.30 nm) loaded on the 3D-GLC having a large surface area (ca. 2910 m2/g) demonstrate superior electrocatalytic performance for electrochemical glycerol oxidation reaction (GOR) over that of a commercial Pt/C catalyst. We hypothesize in this work that the improved GOR performance of Pt/3D-GLC is related to the increase of Pt active sites by decreasing Pt cluster size and the change in the physicochemical properties of the Pt by interaction between the Pt cluster and 3D-GLC. In addition, first-principle density functional theory (DFT) and ab-initio molecular dynamics (MD) simulations are performed to demonstrate that the finely-dispersed Pt nanoclusters on 3D-GLC support can give rise to excellent GOR activity in accordance with the enhanced adsorption behavior of glycerol on its Pt crystal surfaces.

Pd nanowire-based H2 sensors have attracted significant attention because of their superior sensing performance. However, when exposed to H2 concentrations of more than 2%, Pd experiences volume expansion over 10%, resulting in a significant amount of mechanical stress. Thus, exposure to such high H2 concentrations causes physical destruction of Pd nanowires, such as breaks and peel-offs, leading to severe difficulty in the reliable detection of H2 over a wide concentration range. Here, we proposed a structural approach to resolve this issue by introducing a partially anchored Pd nanowire (PA-PdNW) structure. In this configuration, most of the structure was air-suspended, leaving a small portion anchored to the substrate. Air-suspension enabled PA-PdNW to expand freely, thus relieving the mechanical stress; therefore, the Pd nanowires could withstand numerous exposures to high H2 concentrations. To demonstrate the PA-PdNW structure, we developed a nano-fabrication method based on conventional semiconductor processes and successfully manufactured H2 sensor devices with uniform, perfectly aligned PA-PdNW arrays stably air-suspended with designed gaps from the substrate. The fabricated sensors achieved reliable detection of H2 in the 0.1%–3.9% concentration range with a significant resistance change. In addition, compared with fully anchored Pd nanowire (FA-PdNW) sensors, the PA-PdNW sensors showed superior durability, and the nanowires retained their initial structures even after 300 exposures to high H2 concentrations. Furthermore, it was confirmed that the PA-PdNW sensor can stably operate even in extremely humid environments at 85% relative humidity.

Machine-learning (ML) techniques have drawn an ever-increasing focus as they enable high-throughput screening and multiscale prediction of material properties. Especially, ML force fields (FFs) of quantum mechanical accuracy are expected to play a central role for the purpose. The construction of ML-FFs for polymers is, however, still in its infancy due to the formidable configurational space of its composing atoms. Here, we demonstrate the effective development of ML-FFs using kernel functions and a Gaussian process for an organic polymer, polytetrafluoroethylene (PTFE), with a data set acquired by first-principles calculations and ab initio molecular dynamics (AIMD) simulations. Even though the training data set is sampled only with short PTFE chains, structures of longer chains optimized by our ML-FF show an excellent consistency with density functional theory calculations. Furthermore, when integrated with molecular dynamics simulations, the ML-FF successfully describes various physical properties of a PTFE bundle, such as a density, melting temperature, coefficient of thermal expansion, and Young's modulus.

Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when H2O and O2 molecules are present at high voltages in PEMFC. In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with H2O and thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer’s method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. Pt/F-GNR showed the lowest degradation rate in carbon corrosion, and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.

In this work, we show an effective strategy combining experimental and computational methods to explore and clarify rational design approaches utilizing transition metals for enhanced electrocatalysis of oxygen reactions. We report a bifunctional electrocatalyst synthesized by a chemical deposition of palladium (Pd) nanoparticles on three-dimensionally ordered mesoporous cobalt oxide (Pd@3DOM-Co3O4) demonstrating extreme stability and activity towards electrocatalytic oxygen reduction and evolution reactions (ORR and OER). Pd@3DOM-Co3O4 exhibits a significantly positive-shifted ORR half-wave potential of 0.88 V (vs. RHE) and a higher OER current density of 41.3 mA cm−2 measured at 2.0 V (vs. RHE) relative to non-deposited 3DOM-Co3O4. Moreover, in terms of durability, Pd@3DOM-Co3O4 demonstrates a negligible half-wave potential loss with 99.5% retention during ORR and a high current density retention of 96.4% during OER after 1000 cycles of accelerated degradation testing (ADT). Ab-initio computational simulation of the oxygen reactions reveals that the modification of the electronic structure by combining Pd and Co3O4 lowers the Pd d-band center and enhances the electron abundance at the Fermi level, resulting in improved kinetics and conductivity. Furthermore, it is elucidated that the enhanced electrochemical stability is attributed to an elevated carbon corrosion potential (Ucorr,C) for the Pd@3DOM-Co3O4 surface and an increased dissolution potential (Udiss) of Pd nanoparticles. Meanwhile, synergistic improvements in the bifunctional activity resulting from the combination of Pd and 3DOM-Co3O4 were confirmed by both electrochemical and physical characterization methods, which highlights the practical viability of Pd@3DOM-Co3O4 as an efficient bifunctional catalyst for rechargeable metal-air batteries.

We prepare three-dimensional honeycomb-like Cu0.81Co2.19O4 nanosheet arrays supported by Ni foam via electrochemical codeposition of cobalt and copper hydroxides on Ni foam followed by thermal oxidation. The codeposition with Cu changes the morphology of the cobalt hydroxide deposit to form honeycomb-like nanostructures, significantly decreasing the onset potential for oxygen evolution. The Cu0.81Co2.19O4 anode displays an exceptionally low overpotential of 290 mV at a current density of 10 mA cm–2 in 1 M KOH, and an anion-exchange membrane water electrolysis cell employing the above anode achieves a current density of 100 mA cm–2 at 1.68 V in 0.1 M KOH.

Control of doping levels of nitrogen to carbon support plays a key role to enhance the catalytic activity of the Pt/C catalyst toward oxygen reduction reaction. Mass-production of such materials is still challenging issue for the practical use. Here, we demonstrate a facile approach for fabrication of the nitrogen-doped Pt/C catalysts via direct soft nitriding of the Pt/C catalyst. The commercial 40 wt% Pt/C is first physically mixed with urea and then heat-treated at 300 °C, which allowed a massive production of the 6.6 atom% nitrogen-doped Pt/C catalysts without sacrificing the Pt catalysts. The specific activity increases by 46.9% after the thermal treatment, while the particle size and crystallinity of Pt remain similar to those before the thermal treatment. As a result, the fuel cell test showed a notable increase in the current density by 100% and 18.5% at 0.8 V and 0.5 V, respectively, for the membrane electrode assembly employing urea treated Pt/C catalyst. Hence, the soft nitriding by urea offers great promise as a simple, energy-efficient and eco-friendly way in manufacturing the nitrogen-doped Pt/C catalyst for the polymer electrolyte membrane fuel cell applications.

Hydrogen evolution reaction (HER) using earth abundant catalyst is one of the most promising approaches to replace precious platinum (Pt) and Pt-based catalysts for a green-energy environment. In this work, the HER performance of pristine MoS2 is enhanced by doping of Co and Se atoms, which serve as additional active sites and oxygen defects on HER performance respectively, thereby tuning the electronic structure of pristine MoS2 and further optimizing its hydrogen adsorption energy. The structural and morphological characterizations reveal the presence of the cuboid and raspberry nanostructures with a high order of crystallinity and extended interlayer spacing. The Co- and Se-doped MoS2, display enhanced HER activity than pristine MoS2 with a low onset potential of 181 mV and 166 mV, and a low overpotential of 218 mV and 207 mV at a cathodic current density of 10 mA cm−2. More importantly, the Se-doped MoS2 shows good catalytic stability with a low Tafel slope of 44 mV dec−1 as compared with that of Co-doped MoS2 (50 mV dec−1) and other reported values in the literature. Furthermore, the density functional theory calculations were carried out to get a fundamental understanding of electrocatalytic activity of Co and Se doping onto MoS2. This work can serve as a general methodology to enhance HER activity for the upcoming potential catalysts in the future and may uncover several applications in the field of solar photo-electrochemical (PEC) water-splitting cells and proton exchange membrane (PEM) electrolyzers.

Lithium–sulfur battery possesses high energy density but suffers from severe capacity fading due to the dissolution of lithium polysulfides. Novel design and mechanisms to encapsulate lithium polysulfides are greatly desired by high-performance lithium–sulfur batteries towards practical applications. Herein, we report a strategy of utilizing anthraquinone, a natural abundant organic molecule, to suppress dissolution and diffusion of polysulfides species through redox reactions during cycling. The keto groups of anthraquinone play a critical role in forming strong Lewis acid-based chemical bonding. This mechanism leads to a long cycling stability of sulfur-based electrodes. With a high sulfur content of ~73%, a low capacity decay of 0.019% per cycle for 300 cycles and retention of 81.7% over 500 cycles at 0.5 C rate can be achieved. This finding and understanding paves an alternative avenue for the future design of sulfur–based cathodes toward the practical application of lithium–sulfur batteries., Novel cathode design holds the key to enabling high performance lithium-sulfur batteries. Here the authors utilize anthraquinone to chemically stabilize polysulfides, revealing that the keto groups of anthraquinone play a critical role in forming strong Lewis acid-based chemical bonding.

Advanced surface engineering of nickel-rich cathode materials greatly enhances their structural/thermal stability. However, their application into lithium-ion full-cells still faces challenges, such as the unstable solid electrolyte interphase (SEI) layer on the anode. Herein, we reveal that the degradation of battery cycle life is caused by the release of divalent nickel ions from the LiNi0.8Co0.1Mn0.1O2 cathode and the formation of nickel metal particles on the graphite anode surface, deteriorating the anode SEI layer and its structural integrity. On the basis of this finding, we demonstrate a stable lithium-ion battery by modifying the cathode surface by creating a nanostructured stabilizer with an epitaxial structure that enhances the morphological robustness. During cycling, the nickel defects in the cathode are significantly suppressed, preventing nickel ion crossover. In particular, the anode SEI layer maintains a uniform and dense structure, leading to outstanding cycling stability in the full-cell with a capacity retention of ∼86% after 400 cycles at 25 °C.

Ni-based electrocatalysts for replacement of precious metal electrocatalyst, the cathode materials of anion exchange membrane water electrolyzer (AEMWE), are seriously unstable and low activity at hydrogen production conditions. This study develops a high-performance, durable non-precious metal electrocatalyst for AEMWE, which show improved activity and durability. First, Ni/C was alloyed with Co and supported on carbon cloth coated with microporous carbon layer to improve the electrocatalytic activity of the hydrogen evolution reaction (HER) electrocatalyst; then, oxide (Ni/Co-O) was locally formed on the synthesized NiCo/C to increase its activity and durability. Specifically, this oxide increased the coverage of OH− ions, formed hydrogen spillover channels, and promoted the HER. Further, its improved electrochemical durability was attributed to the high bond dissociation energy of the metal oxide. The electrocatalyst was also evaluated as the cathode in single-cell (1-cell) and stack cell (5-cell) AEMWE systems to demonstrate that this superior performance would translate to the commercial scale.

Scalable synthesis of active, durable, low-cost, and self-supported electrodes assembled by electrocatalysts towards hydrogen and oxygen generation reactions for water electrolyzers remains a grand challenge. We develop here a facile fabrication of nickel-molybdenum carbide heterostructures embedded in large-area (100 cm2) hierarchically assembled nitrogen-enriched carbon, forming Mott-Schottky array on nickel foam (Ni-Mo2C/NC@NF). The Ni-Mo2C/NC array is directly applied as the bifunctional catalyst with high activity and durability in alkaline electrolyte. Particularly, an extremely low overpotential of 40 mV is needed to generate hydrogen. Density functional theory calculation revealed that the formation of Ni-Mo2C Mott/NC Schottky interfaces enables favorable electronic structures for electrocatalytic water splitting. Besides, 3D hierarchical structure provides exposed active sites, facilitates mass and charge transfer, graphitic shells enhance stability. A symmetric electrolyzer using Ni-Mo2C/NC@NF generates 10 mA cm−2 at 1.59 V and operates steadily for 150 h, which even outperforms the noble metal couple, Pt/C//RuO2 for water electrolysis. The scalability, activity and durability renders Ni-Mo2C/NC@NF potential industrial application. The assembly-carburization strategy could be further applied for preparing Co-Mo2C/NC@NF and Cu-Mo2C/NC@NF.

Converting CO2 into valuable chemicals using electrocatalysis is an attractive approach for sustainable energy storage and artificial carbon cycle. In this study, atomically dispersed Ir species (Ad-Ir) that are supported on three-dimensional (3D) porous carbon networks are proposed as electrocatalysts for highly efficient CO2 conversion. The resulting catalysts can preferentially and rapidly produce CO with a high Faradaic efficiency of 95.6 % and a very high turnover frequency (TOF) value of 33,365 h−1. Furthermore, it shows no obvious decay in both FE for CO and current density over 20 h of continuous operation. Based on detailed experimental studies and density functional theory (DFT) calculations, such outstanding catalytic performance for CO2 conversion to CO production can be attributed to the structural advantages of 3D network of porous carbon and atomically dispersed Ir species on the 3D carbon support.

Air-breathing polymer electrolyte membrane fuel cell (PEMFC) systems without the humidifier and air blower have been developed to overcome the cost and complexity of balance of plants (BOPs). Until now, there has been no specific way to improve the stack's initial performance through the specific activation protocol and maintain the initial performance for a very long time. Herein, we studied a technique for finishing the total activation within 1 h by using a pre-activation process (i.e., soaking the stack in a DI-water reservoir) and applying current at 0.65 V. The pre-activation procedure significantly increased the swelling of the polymer membrane and the Nafion binder in the catalyst layer, reducing the total activation time. Also, we showed that long-term storage using humidified N 2 gas in a closed box did not hinder the electrocatalytic activity of the Pt and the drying of the polymer membrane for 60 days.

A novel self-supported electrode with long cycling life and high mass loading was developed based on carbon-coated Si nanowires grown in situ on highly conductive and flexible carbon fabric substrates through a nickel-catalyzed one-pot atmospheric pressure chemical vapor deposition. The high-quality carbon coated Si nanowires resulted in high reversible specific capacity (∼3500 mA h g–1 at 100 mA g–1), while the three-dimensional electrode’s unique architecture leads to a significantly improved robustness and a high degree of electrode stability. An exceptionally long cyclability with a capacity retention of ∼66% over 500 cycles at 1.0 A g–1 was achieved. The controllable high mass loading enables an electrode with extremely high areal capacity of ∼5.0 mA h cm–2. Such a scalable electrode fabrication technology and the high-performance electrodes hold great promise in future practical applications in high energy density lithium-ion batteries.

This paper first reports a highly reliable self-powered hydrogen (H 2 ) sensor employing a palladium (Pd)-based nano-transducer. The developed sensor is based on the principle of a novel chemomechanical mechanism of the Pd nano-transducer exploiting a solar cell. We theoretically and experimentally demonstrated that the proposed device can achieve highly durable operation for a wide range of H 2 concentrations with remarkable sensitivity (3.1% at 2%-H 2 ) and response time (111 s at 2%-H 2 ) without external power. Significantly, the proposed sensor, which has a novel sensing mechanism, maintains high sensing performance for more than 150 cycles under various H 2 conditions (0.5 to 2%).

Recently, oxygen vacancy engineering represents a new direction for rational design of high-performance catalysts for electrochemical CO2 reduction (CO2RR). In this work, a series of amorphous MnOx catalysts with different concentrations of oxygen vacancies, namely, low (a-MnOx-L), pristine (a-MnOx-P), and high oxygen vacancy (a-MnOx-H), have been prepared by simple plasma treatments. The resultant a-MnOx-H catalyst with a larger amount of oxygen vacancy on the catalyst surface is able to preferentially convert CO2 to CO with a high Faradaic efficiency of 94.8% and a partial current density of 10.4 mA cm−2 even at a relatively lower overpotential of 510 mV. On the basis of detailed experimental results and theoretical density functional theory (DFT) calculations, the enhancement of CO production is attributable to the abundant oxygen vacancies formed in the amorphous MnOx which should favor CO2 adsorption/activation and promote charge transfer with the catalyst for efficient CO2 reduction.

Time-saving stack activation and effective long-term storage are one of most important issues that must be resolved for the commercialization of polymer electrolyte membrane fuel cell (PEMFC). Herein, we developed the cost-effective stack activation method to finish the whole activation within 30 min and the long-term storage method by using humidified N 2 without any significant decrease in cell's performance for 30 days. Specifically, the pre-activation step with the direct injection of DI water into the stack and storage at 65 or 80 °C for 2 h increases the distinctive phase separation between the hydrophobic and hydrophilic regions in Nafion membrane, which significantly reduces the total activation time within 30 min. Additionally, the long-term storage with humidified N 2 has no effect on the Pt oxidation and drying of Nafion membrane for 30 days due to its exergonic reaction in the cell. As a result, the high water content in Nafion membrane and the decrease of Pt oxidation are the critical factors that have a strong influence on the activation and long-term storage for high-performance PEMFC.

We studied the degradation and durability of polymer electrolyte membrane fuel cell (PEMFC) at membrane-electrode-assembly (MEA) level by injection of octamethylcyclotetrasiloxane (D4) as a representative siloxane, which has been found in many industrial and personal products. Specifically, i ) GC/MS analysis demonstrated that the ring-opening polymerization of D4 could result in the formation of various linear and cyclic siloxanes in both electrodes of MEA; ii ) post-test analysis revealed that the transformed siloxanes were transported from the anode to the cathode via free-volumes in the polymer membrane; iii ) RDE measurement and DFT calculation revealed that D4 was not directly responsible for the electrocatalytic activity of Pt; iv ) electrochemical analysis demonstrated that the residual methyl groups of siloxane and various siloxanes did not hinder the proton transport in the polymer membrane; and v ) siloxanes accumulated in the primary and secondary pores with the exception of an external surface of carbon, causing an increase in the oxygen reactant's resistance and resulting in a decrease of the cell performance. In addition, we confirmed that injection of D4 did not affect the carbon corrosion adversely because the siloxane had little influence on water sorption in the catalyst layer.

A convenient enzymatic optical method for uric acid detection was developed based on the fluorescence quenching of ligand-capped CdTe nanoparticles by H2O2 which was generated from the enzymatic reaction of uric acid. The interactions between the CdTe nanoparticles capped with different ligands (glutathione, 3-mercaptopropionic acid, and thioglycerol) and H2O2 were investigated. The fluorescence quenching studies of GSH-capped CdTe nanoparticles demonstrated an excellent sensitivity to H2O2. The effects of uric acid, uricase and H2O2 on the fluorescence intensity of CdTe nanoparticles were also explored. The detection conditions, reaction time, pH value, incubation period and the concentration of uricase and uric acid were optimized. The detection limit of uric acid was found to be 0.10 µM and the linear range was 0.22-6 µM under the optimized experimental conditions. These results typify that CdTe nanoparticles could be used as a fluorescent probe for uric acid detection.

The slow kinetics of the oxygen reduction reaction (ORR) on platinum catalyst is a critical parameter for application in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we study the effects of sulfur on the electrochemical activity and stability of sulfur doped graphene supported platinum nanowires (PtNW/SGs). To investigate the influence of sulfur, a series of sulfur-doped graphene materials with varying sulfur contents ranging from 0.35 to 3.95 at% are applied as platinum nanowire catalyst supports. Based on the physico-chemical characterizations, electrochemical measurements and density functional theory (DFT) calculations, we find that the amount of sulfur significantly affects the electrokinetics of the Pt nanowires. The best ORR kinetics are observed for the platinum nanowires supported on graphene with 1.40 at% sulfur, showing a mass activity of 182 mA/mg Pt and a specific activity of 662 μA/cm 2 Pt at 0.9 V vs. RHE. At this sulfur content, well-defined platinum nanowires with diameters in the range of 4–16 nm are observed that are beneficial for enhancing ORR kinetics.

A chemically etched CuCo-oxide (CE-CCO) electrode prepared by electrodeposition was used for oxygen evolution reaction electrocatalyst. Surface chemical etching of CuCo-oxide (CCO) introduced oxygen vacancies and thus increased electrical conductivity to promote oxygen generation. During practical applicability testing, when CE-CCO was used as the anode of an anion-exchange membrane water electrolyzer, enhanced oxygen evolution performance was observed (current density = 1390 mA/cm2 at 1.8 Vcell), which, among other reactions, was ascribed to the easy removal of O2 from the aerophobic electrode surface. In addition to featuring low mass transfer resistance even at high current density with substantial gas generation, the CE-CCO electrode featured remarkable durability, exhibiting stable performance over 3600 h under the conditions of continuous O2 evolution. Thus, this work shows that the performance of electrodeposited oxide catalysts can be enhanced by introducing oxygen vacancies, while the energy conversion efficiency of the corresponding water electrolysis systems can be increased by lowering mass transfer resistance via efficient gas removal and reactant supply.

We examined seasonal succession in a phytoplankton and mesozooplankton community in open coastal waters with frequently occurring harmful algal blooms. Chlorophyll a (Chl a) concentration was positively related to the N/P/Si ratio, suggesting that nitrate is a major limiting nutrient for phytoplankton biomass increase. Heterotrophic red Noctiluca, but not toxic dinoflagellate, abundance showed a negative trend with both Chl a and mesozooplankton abundance. The phytoplankton community showed a clear seasonal succession, with an increased abundance of dinoflagellates in the summer community (June–September), which was distinctive from the autumn–winter–spring community (October–May) that was dominated by diatoms. A mesozooplankton community shift followed, with a lag of a couple of months, in the late August to December community that was associated with subtropical copepods. The other community from February to August is associated with marine cladocerans. Although the most dominant mesozooplankton of year was copepod at a rate of over 70%, coexisting gelatinous plankton such as appendicularians and Noctiluca, which may compete with copepods for prey could affect to copepod production in the region.

Centrodinium punctatum is a fusiform dinoflagellate with a global marine distribution. Due to a close phylogenetic relationship of one C. punctatum strain to Alexandrium species, toxin production of this C. punctatum strain was assessed using liquid chromatography coupled to tandem mass spectrometry. The paralytic shellfish toxin (PST) profile of C. punctatum was dominated by six analogs, i.e. STX (30%), GTX-1 (20%) and neoSTX (24%), followed by GTX-2 (9%), GTX-4 (9%) and GTX-3 (8%); deoxy-STX was also putatively identified while no gymnodimines, spirolides or goniodomins were detected. This is the first record of C. punctatum producing saxitoxins. The estimated cellular toxicity was rather elevated, between 91 and 212 pg cell−1 (or 259 and 601 fmol cell−1). When considering the toxicity equivalent factors, results suggest that this species can produce high cellular toxicity compared to other STX-producing dinoflagellates. Morphological details of the sulcal area and the hypotheca of Centrodinium punctatum were re-examined by scanning electron microscopy (SEM); this revealed that in the sulcal area, the left posterior sulcal plate (Ssp) is larger and longer than the left posterior sulcal plate and extended into the hypotheca. Based on the morphological observation, a revised interpretation of the sulcus and hypotheca is proposed.

The recent accelerated ocean acidification and global warming caused by increased atmospheric carbon dioxide may have an impact on the physiology and ecology of marine animals. This study was conducted to determine the egg production rate (EPR) and hatching success (EHS) of Acartia ohtsukai in response to the combined effects of an increase in temperature and a lower pH. Acartia ohtsukai with fresh surface seawater were collected in the northwestern Yeoja Bay of Korea in September 2017. The temperature and pH conditions applied included two different pH levels (representing the present: 7.9 and the future: 7.6) and three temperature values (26 °C, 28 °C, and 30 °C). In the pH 7.9, EPR significantly increased with increased temperature, but in pH 7.6, it significantly decreased as the temperature increased. EHS was lower in pH 7.6 than in pH 7.9. These results suggest that changes in the marine environment due to global warming and ocean acidification may affect Acartia populations and cause overall fluctuations in copepods of the genus Acartia.

The effects of the addition of nutrients (nitrate: N, phosphate: P, and vitamin B1) and trace metals (iron: Fe, Copper: Cu, and selenium: Se) on the growth of Gymnodinium catenatum, which was isolated from Korean coastal waters, were investigated. The Korean isolate of G. catenatum grew under a wide range of concentrations of N and P. Whilst high concentrations of N (&gt, N: P ratio of 23.5) did not stimulate the growth rate, an enhanced growth rate and cell density were observed with the addition of P. The experimental addition of vitamin B1 revealed that G. catenatum is not dependent on vitamin B1 for growth. Moreover, the addition of Fe and Cu resulted in no significant differences in the growth patterns and rates of G. catenatum between the controls and treatments. It is thus possible that growth of the Korean isolate of G. catenatum does not require high concentrations of Fe and Cu. However, the cell densities were enhanced in the stationary phases of treatments upon addition of Se, and the maximum cell densities were higher than those in the culture experiments upon additions of other nutrient and trace metals. Our findings indicate that G. catenatum prefers P and Se for proliferation, rather than other nutritional sources.

Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact–separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact–separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >103 times under hot switching conditions.

This paper reports a novel transfer method to fabricate ultralong, fully aligned nanowires, made of diverse materials on a flexible substrate. For the uniform transfer of nanowires made from a wide range of materials, a facile and robust mechanics-based nano-transfer method has been developed. A selectively dry-removable amorphous carbon nano-sacrificial layer between a vacuum-deposited nanowire and the underlying master mold is newly introduced, and it facilitates the robust and reliable mechanical transfer of dense and aligned nanowires onto a flexible substrate. Using the developed method, we first fabricated ultralong and fully aligned metal/metal-oxide (gold, platinum, and copper-oxide) nanowires on a large-area flexible substrate (2.5 × 2 cm2). We also fabricated a unique nanowire-heater-embedded gas-sensor using the transferred gold and copper-oxide nanowires, respectively. The developed heater-embedded device exhibited a 33-fold enhancement in sensitivity, responding to 10 ppm NO 2 using a 0.6 V heater bias.

The oxygen reduction reaction, ORR, performances of graphene-supported palladium (Pd) and palladium alloys (Pd3X: X = Ag, Co and Fe) catalysts with highly dispersed catalyst particles are investigated in acidic and alkaline conditions using a rotating disk electrode, RDE. Graphene nanosheet, GNS, supported Pd based catalysts are fabricated without surfactant through the impregnation of Pd and 2nd metal precursors on GNS, leading to small and uniformly dispersed nanoparticles, even when high metal loading of up to 60 wt.% are deposited on supports. The ab-initio density functional theory, DFT, calculations, which are based on the d-band center theory, have been applied to correlate with the results of the ORR performances obtained by half-cell tests. Additionally, the cohesive energy, Ecoh, and dissolution potential, Um, for the Pd nanoparticles have been calculated to understand thermodynamic stability. To elucidate the d-band center shift, the Pd 3d5/2 core-level binding energies for Pd/GNS, Pd3Ag/GNS, Pd3Fe/GNS and Pd3Co/GNS have been investigated by X-ray photoelectron spectroscopy, XPS. The GNS-supported Pd, or Pd-based alloy-nanoparticle catalyst shows good ORR activity under acidic and alkaline conditions, suggesting it may offer potential replacement for Pt for use in cathode electrodes of anion-exchange membrane fuel cell, AEMFC, and acid based polymer electrolyte fuel cell, PEMFC.

Herein, non-precious cobalt doped lanthanum manganese perovskite oxide nanoparticles are used as a growth substrate for nitrogen-doped carbon nanotubes to form efficient and durable hybrid bi-functional catalyst (LMCO/NCNT). LMCO/NCNT demonstrates significantly enhanced onset and half-wave oxygen reduction reaction (ORR) potentials (−0.11 and −0.24 V vs. SCE, respectively), and oxygen evolution reaction (OER) current density (27 mA cm−2 at 0.9 V vs. SCE). Likewise, practical rechargeable zinc–air battery testing using atmospheric air reveals superior discharge voltages obtained with LMCO/NCNT, particularly at current densities higher than 30 mA cm−2, and significantly lower charge voltages at all current densities tested, compared to state-of-art commercial platinum on carbon catalyst. In addition, very stable charge and discharge voltages of 2.2 and 1.0 V, respectively, are obtained over 60 cycles. The excellent performance and durability of the hybrid catalyst are attributed to very uniformly distributed LMCO nanoparticles on the surface of NCNT resulting in enhanced surface area and material utilization. Keywords: Hybrid, Bi-functional, Oxygen reduction reaction, Oxygen evolution reaction, Rechargeable, Zinc–air battery

Perovskite oxides (ABO3) have recently attracted attention since tailoring their chemical compositions has resulted in remarkable activity toward oxygen evolution reaction (OER) which governs rechargeability of recently spotlighted metal–air batteries and regenerative fuel cells. For further development of highly OER active perovskite oxides, however, the exact mechanism the OER must be well understood. Herein, we introduce investigation of the OER mechanism of perovskite oxides by ab initio analysis based on well-defined model systems of LaMnO3 (LMO), LaCoO3 (LCO), and La0.5Sr0.5CoO3 (LSCO). In addition, we have systematically conducted electrochemical experiments from which we have observed an increasing trend in the OER activity in the order of LSCO > LCO > LMO based on the cyclic voltammetry (CV) results obtained in the alkaline medium. To validate the experimental results, free-energy diagrams have been constructed for oxygen intermediates on the surface of the defined models to find the limiting ste...

Replacement of expensive platinum-based catalysts at the cathode of fuel cells by low-cost alternatives represents an important milestone to achieve significant system cost reductions. In this work, single crystal cobalt disulfide (CoS2) octahedral nanoparticles supported on graphene/carbon nanotube composites were prepared as oxygen reduction reaction (ORR) catalysts in acidic electrolyte. During the simplistic, one-pot solvothermal synthesis, the nanostructured carbon supports were also simultaneously doped with nitrogen and sulfur. Time dependent studies elucidated the growth process of the {111} facet encased octahedra that could only be prepared when carbon support materials were incorporated into the reaction mixture. Through computational simulations, the shape directed growth process was found to be driven thermodynamically towards surface energy minimization. Control experiments and spectroscopy characterization were also used to investigate the occurrence and nature of nitrogen and sulfur doping into the graphitic structure of the graphene/carbon nanotube composite support. The impact of carbon support on ORR activity was clear, with the graphene/carbon nanotube composite supported CoS2 octahedra (CoS2-CG) outperforming CoS2 supported on just graphene or carbon nanotubes. Additionally, CoS2-CG provided an on-set potential (0.78 V vs. RHE) and half-wave potential (0.66 V vs. RHE) that was 60 mV and 150 mV higher than the CoS2 particle agglomerates formed when no carbon support was included during catalyst preparation. This improved activity can be attributed to the beneficial properties of the nitrogen and sulfur doped graphene/carbon nanotube composite support, and also may arise due to the more favourable oxygen adsorption on the (111) surface of the octahedral particles predicted by theoretical calculations. By combining the synergistic properties of the graphene/carbon nanotube composite and unique shape controlled single crystal CoS2 nanoparticles, CoS2-CG is presented as an emerging catalyst for the ORR in fuel cells.

Cu@N-C with the Cu particles encapsulated in N-doped carbon shells, which was activated by CO2 treatment, is an excellent electrocatalyst for the oxygen reduction reaction (ORR) with a high activity and durability.

In this study, we report self-assembled nitrogen-doped fullerenes (N-fullerene) as non-precious catalysts, which are active for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and thus applicable for energy conversion and storage devices such as fuel cells and metal–air battery systems. We screen the best N-fullerene catalyst at the nitrogen doping level of 10 at%, not at the previously known doping level of 5 or 20 at% for graphene. We identify that the compressive surface strain induced by doped nitrogen plays a key role in the fine-tuning of catalytic activity.

Despite many efforts to create nanogratings to exploit exceptionally enhanced nano-sized effects, realizing sub-10 nm nanogratings on a large area still remains a great challenge. Herein, we demonstrate fabrication of an inch-scale sub-10 nm nanogratings with simple and reliable features, by employing a repetitive wet-chemical oxidation and etching technique. We found that a few atomic layers of the silicon surface are naturally oxidized in a nitric acid (HNO3) solution, which enables the surface of the silicon to be etched with 1.0 nm resolution by selectively removing the oxide layers. By combining this high-precision etching technique with silicon nanogratings previously prepared by conventional methods, we successfully demonstrated a sub-10 nm silicon nanogratings on an inch-scale wafer.

The present work introduces spinel oxide nanocrystals self-assembled into mesoporous spheres that are bifunctionally active towards catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). The electrochemical evaluation reveals that (Ni,Co)3 O4 demonstrates a significantly positive-shifted ORR onset and half-wave potentials [-0.127 and -0.292 V vs. saturated calomel electrode (SCE), respectively], whereas Co3 O4 results in a negative-shifted OER potential (0.65 V vs. SCE) measured at 10 mA cm-2 . Based on the DFT analysis, the potential at which all oxygen intermediate reactions proceed spontaneously is the highest for (Ni,Co)3 O4 (U=0.66 eV) during ORR, whereas it is the lowest for Co3 O4 (U=2.09 eV) during OER. The high ORR activity of (Ni,Co)3 O4 is attributed to the enhanced electrical conductivity of the spinel lattice, and the high OER activity of Co3 O4 is attributed to relatively weak adsorption energy promoting rapid release of evolved oxygen.

A unique array structure of highly aligned and suspended palladium nanowires was demonstrated for application in self-heating type hydrogen gas sensors. Unlike conventional devices which employ randomly distributed bottom-up grown nanowires, in this study a top-down method which enables controllable and uniform device fabrication was used to produce the highly aligned nanowire array. Moreover, by suspending the array, heat loss through the substrate was eliminated, leading to a more efficient self-heating and rapid gas sensing response. As a result, with only a few milliwatts of power, the self-heated gas sensing device exhibited a considerably faster response time upon exposure to hydrogen gas than the device operating at room temperature.

The current generation is not only facing the shortage of fossil fuels in the near future, but also is responsible for preserving the environment for future generations. As a result, the development of clean energy systems is becoming an urgent focus for the research community. Metal air batteries have attracted much attention due to their extremely high energy density, and the rechargeability which is directly governed by the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we present a new class of hybrid bi-functional catalyst consisting of porous nanorod perovskite La0.5Sr0.5Co0.8Fe0.2O3 (LSCF-PR) combined with nitrogen-doped reduced graphene oxide (NRGO) active towards both ORR and OER. The novel morphology of LSCF-PR is prepared by an electrospinning method, and incorporated into NRGO sheets. Electron microscopy reveals interesting composite morphology in which LSCF-PR is embedded between the sheets of NRGO, forming an efficient LSCF-PR/NRGO composite morphology for the electrochemical oxygen reactions. Electrochemical testing of the LSCF-PR/NRGO composite in alkaline medium results in excellent ORR and OER catalytic activities, verifying the effective combination for bi-functionality. LSCF-PR/NRGO presents not only a comparable or superior performance to state-of-the-art Pt/C catalyst for ORR or OER, respectively, but also better durability. These results highlight the applicability of LSCF-PR/NRGO composite having unique and efficient morphology as a promising bi-functional catalyst for metal air battery applications.

Nano-scale Pt particles are often reported to be more electrochemically active and stable in a fuel cell if properly displaced on support materials; however, the factors that affect their activity and stability are not well understood. We applied first-principles calculations and experimental measurements to well-defined model systems of N-doped graphene supports (N-GNS) to reveal the fundamental mechanisms that control the catalytic properties and structural integrity of nano-scale Pt particles. DFT calculations predict thermodynamic and electrochemical interactions between N-GNS and Pt nanoparticles in the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Moreover, the dissolution potentials of the Pt nanoparticles supported on GNS and N-GNS catalysts are calculated under acidic conditions. Our results provide insight into the design of new support materials for enhanced catalytic efficiency and long-term stability.

A novel procedure for the optosensing of clenbuterol and melamine was developed using molecularly imprinted polymer-capped CdTe quantum dots (MIP-CdTe QDs). The MIP-CdTe QDs were synthesized by a radical polymerization process among CdTe QDs, a template, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS). The sizes of the MIP-CdTe particles were controlled by the speed of polymerization, concentration of the template, concentration of the quantum dots, and the ratio of template, monomer and cross-linker. Excellent selectivity and high sensitivity of MIP-CdTe QDs toward clenbuterol/melamine molecules were observed based on the fluorescence quenching of QDs. Experimental results showed that the optimum molar ratios of template, monomer, and cross-linker were 1:8:20 and 1:4:20 for analyzing clenbuterol and melamine, respectively. Under optimum conditions, these MIP-CdTe QDs showed a limit of detection of 0.4 μM (120 ng/mL) for clenbuterol and 0.6 μM (75 ng/mL) for melamine. The feasibility of the developed method in real samples was successfully evaluated through the analysis of clenbuterol and melamine in milk and liver samples with satisfactory recoveries of 92-97%. The MIP-CdTe QDs could be easily regenerated for subsequent sample analysis with water.