One-dimensional hierarchical nanostructures of NiCo2O4, NiCo2S4 and NiCo2Se4 with superior electrocatalytic activities toward efficient oxygen evolution reaction.

Oxygen evolution reaction (OER), a sluggish multistep process in electrochemical water splitting, is still a challenging issue to achieve with cheap, earth-abundant non-precious and non-polluting materials. In this work, three different electrocatalysts, specifically NiCo2O4, NiCo2 S4, and NiCo2 Se4, synthesized by simple hydrothermal process, show excellent OER activity. This report not only projects OER performances but also demonstrates a modified method for the transformation of NiCo2O4 to NiCo2 S4 and NiCo2 Se4 via sulfidation and selenization reactions. The well crystalline, porous nature of NiCo2O4, NiCo2 S4, and NiCo2Se4 electrocatalysts with one dimensional (1D) structural morphology affords overpotentials of 346 mV, 309 mV and 270 mV at current density of 10 mA cm-2 in 1 M KOH. In particular, NiCo2Se4 exhibits a low overpotential as well as a smaller Tafel slope of 63 mV dec-1, leading to robust stability in alkaline conditions. The abundant active sites, large mass and size of NiCo2Se4 enhances the performance of the OER. This type of selenide-based material with low toxicity is also an advantage for eco-friendly applications.

Nitrogen-doped TiO2(B) nanobelts enabling enhancement of electronic conductivity and efficiency of lithium-ion storage.

To enhance the intrinsic electrical conductivities of TiO2(B) nanobelts, nitrogen(N)-doped TiO2(B) nanobelts (N-TNB) were prepared in this study by a facile and cost-effective hydrothermal method using urea as the nitrogen source with TiO2 (P25) nanoparticles. x-ray photoelectron spectroscopy confirmed that the N-atoms preferentially occupied up to ∼0.516 atom% in the interstitial sites of the N-TNB and the maximum concentration of substituted-N bonds in the N-TNB was ∼0.154 atom%, thereby the total concentration of doped nitrogen elements of ∼0.67 atom% improved the high intrinsic electrical conductivity and ionic diffusivity of the TiO2(B) nanobelts. The as-prepared N-TNB electrode delivered the highest specific capacity of 133.9 mAh g-1 in the first cycle, with an exceptional cyclic capacity retention at an ultrafast current rate of 1000 mA g-1; this is not less than 51% after 500 cycles and represents an excellent rate capability of ∼37 mAh g-1 at an ultra-high rate of 40 C. These values are among the best ever reported on comparison of the delivered highest discharge capacity of N-TNB at 1000 mA g-1 and high-rate capabilities of its Li+ ion storage with the literature data for N-TNB (∼231.5 mAh g-1 at a very low current density of 16.75 mA g-1, ∼0.1 C) of similar materials used in sodium-ion batteries. This implies the potential feasibility of these N-TNB as high-capacity anode materials for next-generation, high-energy-density, electrochemical energy-storage devices.

Nb-doped TiO2 support with enhanced durability as a cathode for polymer electrolyte membrane fuel cells.

Stability is one of the key requirements of electrocatalyst support materials for polymer electrolyte membrane fuel cells. To develop a highly stable Pt catalyst support material, in this work, we have synthesized Nb-doped TiO2 electrocatalyst supports. The amount of Nb dopant is measured using inductively coupled plasma mass spectrometry, while the characteristics of the as-prepared Nb-doped TiO2 supports are analyzed by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy. Durability experiments are conducted by high potential cycling using the as-prepared Pt/TiO2-Nb x materials; half-cell cyclic voltammetry and single-cell performance measurements reveal that Pt/TiO2-Nb4 shows superior durability and corrosion resistance with a degradation rate of only 20% while the performance of commercial Pt/C support decreased 55%.

Fast charging with high capacity for aluminum rechargeable batteries using organic additive in an ionic liquid electrolyte.

Aluminum-ion batteries have many advantages such as the natural abundance of aluminum, high theoretical capacity, and low cost. However, the ionic liquid commonly used as the electrolyte for aluminum-ion batteries has high viscosity, which hinders the migration of charge carriers. In this study, we used various organic solvents as additives for the ionic liquid electrolyte and investigated their effect on the battery performance. The electrolyte containing 45% (v/v) benzene had the best electrochemical properties, which led to a high specific capacity of 90 mA h g-1 at an extremely high current density of 5 A g-1.

Anion Extraction-Induced Polymorph Control of Transition Metal Dichalcogenides.

Controlled phase conversion in polymorphic transition metal dichalcogenides (TMDs) provides a new synthetic route for realizing tunable nanomaterials. Most conversion methods from the stable 2H to metastable 1T phase are limited to kinetically slow cation insertion into atomically thin layered TMDs for charge transfer from intercalated ions. Here, we report that anion extraction by the selective reaction between carbon monoxide (CO) and chalcogen atoms enables predictive and scalable TMD polymorph control. Sulfur vacancy, induced by anion extraction, is a key factor in molybdenum disulfide (MoS2) polymorph conversion without cation insertion. Thermodynamic MoS2-CO-CO2 ternary phase diagram offers a processing window for efficient sulfur vacancy formation with precisely controlled MoS2 structures from single layer to multilayer. To utilize our efficient phase conversion, we synthesize vertically stacked 1T-MoS2 layers in carbon nanofibers, which exhibit highly efficient hydrogen evolution reaction catalytic activity. Anion extraction induces the polymorph conversion of tungsten disulfide (WS2) from 2H to 1T. This reveals that our method can be utilized as a general polymorph control platform. The versatility of the gas-solid reaction-based polymorphic control will enable the engineering of metastable phases in 2D TMDs for further applications.

In situ durability of various carbon supports against carbon corrosion during fuel starvation in a PEM fuel cell cathode.

In this study, the degradation of different cathode carbon supports is investigated in proton exchange membrane fuel cells (PEMFCs). A platinum catalyst is synthesized using various carbon supports, such as Vulcan XC-72, graphite nanopowder and carbon nanotube, which are evaluated based on the fabrication of membrane electrode assemblies. During the startup and shutdown of PEMFCs, the individual electrode potential can be measured in situ using a dynamic hydrogen electrode. The cathode potential increases instantaneously to 1.4 V in one attempt, when H2/air boundaries are developed on the anode side during the fuel starvation, leading to significant carbon corrosion. The corrosion rates of various carbon supports are calculated from the concentration of gases, such as CO2, CO and SO2, emitted from the cathode outlet, measured directly in situ by Fourier transform infrared gas analysis. The carbon nanotube-supported Pt catalyst shows the best performance against carbon corrosion during fuel starvation, compared to commercial Pt/C catalyst and other types of carbon supports.

Reduction-Triggered Paclitaxel Release Nano-Hybrid System Based on Core-Crosslinked Polymer Dots with a pH-Responsive Shell-Cleavable Colorimetric Biosensor.

Herein, we describe the fabrication and characterization of carbonized disulfide core-crosslinked polymer dots with pH-cleavable colorimetric nanosensors, based on diol dye-conjugated fluorescent polymer dots (L-PD), for reduction-triggered paclitaxel (PTX) release during fluorescence imaging-guided chemotherapy of tumors. L-PD were loaded with PTX (PTX loaded L-PD), via π-π stackings or hydrophobic interactions, for selective theragnosis by enhanced release of PTX after the cleavage of disulfide bonds by high concentration of glutathione (GSH) in a tumor. The nano-hybrid system showed fluorescence quenching behavior with less than 2% of PTX released under physiological conditions. However, in a tumor microenvironment, the fluorescence recovered at an acidic-pH, and PTX (approximately 100% of the drug release) was released efficiently out of the matrix by reduction caused by the GSH level in the tumor cells, which improved the effectiveness of the cancer treatment. Therefore, the colorimetric nanosensor showed promising potential in distinguishing between normal and cancerous tissues depending on the surrounding pH and GSH concentrations so that PTX can be selectively delivered into cancer cells for improved cancer diagnosis and chemotherapy.

Fast-Charging and High Volumetric Capacity Anode Based on Co3 O4 /CuO@TiO2 Composites for Lithium-Ion Batteries.

This paper presents an investigation of anodic TiO2 nanotube arrays (TNAs), with a Co3 O4 /CuO coating, for lithium-ion batteries (LIBs). The coated TNAs are investigated using various analytical techniques, with the results clearly suggesting that the molar ratio of Co3 O4 /CuO in the TiO2 nanotubes substantially influences its battery performance. In particular, a cobalt/copper molar ratio of 2:1 on the TNAs (Co2 Cu1 @TNAs) features the best LIBs anode performance, exhibiting high reversible capacity and enhanced cycling stability. Noticeably, Co2 Cu1 @TNAs achieve excellent rate capability even after quite a high current density of 20.0 A g-1 (≈25 C, where C corresponds to complete discharge in 1 h) and superior volumetric reversible capacity of ≈3330 mA h-1 cm-3 . This value is approximately seven times higher than those of a graphite-based anode. This outstanding performance is attributed to the synergistic effects of Co2 Cu1 @TNAs: 1) the structural advantage of TNAs, with their large amount of free space to accommodate the large volume expansion during Li+ insertion/extraction and 2) the optimized ratio of Co3 O4 and CuO in the composite for improved capacity. In addition, no binder or conductive agent is used, which is partly responsible for the overall improved volumetric capacity and electrochemical performance.

Hypostatic instability of aluminum anode in acidic ionic liquid for aluminum-ion battery.

Aluminum-ion batteries are considered to be a promising post lithium-ion battery system in energy storage devices because aluminum is earth-abundant, has a high theoretical capacity, and is of low cost. We report on the chemical activities and stabilities of chloroaluminate anions [Al n Cl n+1]- with aluminum metal using a different mole ratio of AlCl3 and 1-ethyl-3-methylimidazolium chloride. The morphological changes in the Al metal surface are investigated as a function of dipping time in electrolyte, revealing that the Al metal surface is locally attacked by chloroaluminate anions followed by the formation of a new Al oxide layer with a specific lattice plane and a craterlike surface around the cracking site. The aluminum-ion battery exhibits outstanding cycle life and capacity even at the high C-rate of 3 A g-1, with a high energy efficiency of 98%, regardless of the differences in the size of chloroaluminate anions.

Electrochemical properties of an aluminum anode in an ionic liquid electrolyte for rechargeable aluminum-ion batteries.

An aluminum metal, both native and with a very thin oxide film, was investigated as an anode for aluminum-ion batteries. Investigations were carried out in an acidic ionic liquid electrolyte, composed of AlCl3 in 1-ethyl-3-methylimidazolium chloride ([EMIm]Cl), with ß-MnO2/C as a cathode. The battery based on Al metal with a very thin oxide film showed high capacity and stable surface corrosion.

Concentration-mediated multicolor fluorescence polymer carbon dots.

Polymer dots (PDs) showing concentration-mediated multicolor fluorescence were first prepared from sulfuric acid-treated dehydration of Pluronic® F-127 in a single step. Pluronic-based PDs (P-PDs) showed high dispersion stability in solvent media and exhibited a fluorescence emission that was widely tunable from red to blue by adjusting both the excitation wavelengths and the P-PD concentration in an aqueous solution. This unique fluorescence behavior of P-PDs might be a result of cross-talk in the fluorophores of the poly(propylene glycol)-rich core inside the P-PD through either energy transfer or charge transfer. Reconstruction of the surface energy traps of the P-PDs mediated through aggregation may lead to a new generation of carbon-based nanomaterials possessing a fluorescence emission and tunable by adjusting the concentration. These structures may be useful in the design of multifunctional carbon nanomaterials with tunable emission properties according to a variety of internal or external stimuli.

N,S-co-doped FeCo Nanoparticles Supported on Porous Carbon Nanofibers as Efficient and Durable Oxygen Reduction Catalysts.

Finding high-performance, low-cost, efficient catalysts for oxygen reduction reactions (ORR) is essential for sustainable energy conversion systems. Herein, highly efficient and durable iron (Fe) and cobalt (Co)-supported nitrogen (N) and sulfur (S) co-doped three-dimensional carbon nanofibers (FeCo-N, S@CNFs) were synthesized via electrospinning followed by carbonization. The as-prepared FeCo-N,S@CNFs served as efficient ORR catalysts in alkaline 0.1 m KOH solutions that were N2 and O2 -saturated. The experimental results revealed that FeCo-N,S@CNFs were highly active ORR catalysts with defect-rich active pyridinic N and pyrrolic N and metal bonds to N and S atom sites, which enhanced the ORR activity. FeCo-N,S@CNFs exhibited a high onset potential (Eonset =0.89 V) and half-wave potential (E1/2 =0.85 V), similar to the electrocatalytic activity of commercial Pt/C. Additionally, the durability of the as-prepared FeCo-N,S@CNFs catalysts was maintained for 14 h with long-term stability and high tolerance to methanol stability, accounting for their excellent catalytic ability. Furthermore, Co-N@CNFs, Fe-N@CNFs, and varying Fe and Co ratios were compared with those of FeCo-N,S@CNFs. Synergistic interactions between metals and heteroatoms were believed to play a significant role in enhancing the ORR activity. Owing to their excellent catalytic reduction ability, the as-prepared FeCo-N,S@CNFs can be widely used in battery-based systems and replace commercial Pt/C in fuel cell applications.

Electrochemical and fluorescent dual-mode sensor of acetylcholinesterase activity and inhibition based on MnO2@PD-coated surface.

We developed an electrochemical and fluorescent dual-mode sensor for assessing acetylcholinesterase (AChE) activity and inhibition by taking advantage of the high redox sensitivity of surface-coated mesoporous MnO2@polymer dot (MnO2@PD) towards AChE. The following phenomena constitute the basis of the detection mechanism: fluorescence resonance energy transfer (FRET) effect between MnO2 and PD; catalytic hydrolysis of acetylthiocholine (ATCh) to thiocholine (TCh) by AChE expressed by PC-12 cells, inducing fluorescence restoration and change in the conductivity of the system due to MnO2 decomposition; the presence of the inhibitor neostigmine preventing the conversion of ATCh to TCh. The surface-coated biosensor presents both fluorescence-based and electrochemical approaches for effectively monitoring AChE activity and inhibition. The fluorescence approach is based on the fluorescent "on/off" property of the system caused by MnO2 breakdown after interaction with TCh and the subsequent release of PDs. The conductivity of the coated electrode decreased dramatically as AChE concentration increased, resulting in electrochemical sensing of AChE activity and inhibition screening. Real-time wireless sensing can be conducted using a smartphone to monitor the resistance change, investigating the potential use of MnO2@PD nanocomposites in biological studies, and offering a real-time redox-fluorescent test for AChE activity monitoring and inhibitor screening.

Ultrahigh Energy Density and Long-Life Cyclic Stability of Surface-Treated Aluminum-Ion Supercapacitors.

In this study, aluminum-graphene supercapacitors (denoted as aluminum-ion supercapacitors; ASCs), consisting of a battery-type aluminum anode, a capacitor-type graphene cathode, and ionic liquid 1-ethyl-3-methylimidazolium chloride (EMImCl) and aluminum chloride (AlCl3) electrolyte, were prepared. This study primarily aimed to investigate the enhanced electrochemical performance of ASCs arising from changes in the surface oxide layer and morphology via electrochemical surface treatments, including electropolishing and electrodeposition of aluminum anodes. The ASC devices based on an electrodeposited anode at a current density of 3 A g-1 exhibited a high specific capacity of 211 F g-1 compared to that of the electropolished anode (∼186 F g-1); these were 20 and 5.7%, respectively, higher than that of the pristine aluminum anode. In particular, the electrodeposited ASC delivered an energy density of 151 W h kg-1 at a power density of 3,390 W kg-1. Furthermore, a maximum power density of 11,104 W kg-1 was achieved at an energy density of 124.3 W h kg-1. These values are among the best as compared to those of previously reported aluminum-based supercapacitors, suggesting the potential feasibility of these ASCs with outstanding energy and power densities for next-generation energy storage devices.

Hollow Porous N and Co Dual-Doped Silicon@Carbon Nanocube Derived by ZnCo-Bimetallic Metal-Organic Framework toward Advanced Lithium-Ion Battery Anodes.

Silicon (Si) has been recognized as a promising alternative to graphite anode materials for advanced lithium-ion batteries (LIBs) owing to its superior theoretical capacity and low discharge voltage. However, Si-based anodes undergo structural pulverization during cycling due to the large volume expansion (ca. 300-400%) and continuous formation of an unstable solid electrolyte interphase (SEI), resulting in fast capacity fading. To address this challenge, a series of different amounts of silicon nanoparticles (Si NPs)-encapsulated hollow porous N-doped/Co-incorporated carbon nanocubes (denoted as p-CoNC@SiX, where X = 50, 80, and 100) as anode materials for LIBs are reported in this paper. These hollow nanocubic materials were derived by facile annealing of different contents of Si NPs-encapsulated Zn/Co-bimetallic zeolitic imidazolate frameworks (ZIF@Si) as self-sacrificial templates. Owing to the advantages of well-defined hollow framework clusters and highly conductive hollow carbon frameworks, the hollow porous p-CoNC@SiX significantly improved the electronic conductivity and Li+ diffusion coefficient by an order of magnitude higher than that of Si NPs. The as-prepared p-CoNC@Si80 with 80 wt % Si NPs delivered a continuously increasing specific capacity of 1008 mAh g-1 at 500 mA g-1 over 500 cycles, excellent reversible capacity (∼1361 mAh g-1 at 0.1 A g-1), and superior rate capability (∼603 mAh g-1 at 3 A g-1) along with an unprecedented long-life cyclic stability of ∼1218 mAh g-1 at 1 A g-1 over 1000 cycles caused by low volume expansion (9.92%) and suppressed SEI side reactions. These findings provide new insights into the development of highly reversible Si-based anode materials for advanced LIBs.

Robust Co alloy design for Co interconnects using a self-forming barrier layer.

With recent rapid increases in Cu resistivity, RC delay has become an important issue again. Co, which has a low electron mean free path, is being studied as beyond Cu metal and is expected to minimize this increase in resistivity. However, extrinsic time-dependent dielectric breakdown has been reported for Co interconnects. Therefore, it is necessary to apply a diffusion barrier, such as the Ta/TaN system, to increase interconnect lifetimes. In addition, an ultrathin diffusion barrier should be formed to occupy as little area as possible. This study provides a thermodynamic design for a self-forming barrier that provides reliability with Co interconnects. Since Cr, Mn, Sn, and Zn dopants exhibited surface diffusion or interfacial stable phases, the model constituted an effective alloy design. In the Co-Cr alloy, Cr diffused into the dielectric interface and reacted with oxygen to provide a self-forming diffusion barrier comprising Cr2O3. In a breakdown voltage test, the Co-Cr alloy showed a breakdown voltage more than 200% higher than that of pure Co. The 1.2 nm ultrathin Cr2O3 self-forming barrier will replace the current bilayer barrier system and contribute greatly to lowering the RC delay. It will realize high-performance Co interconnects with robust reliability in the future.

High-Defect-Density Graphite for Superior-Performance Aluminum-Ion Batteries with Ultra-Fast Charging and Stable Long Life.

Rechargeable aluminum-ion batteries (AIBs) are a new generation of low-cost and large-scale electrical energy storage systems. However, AIBs suffer from a lack of reliable cathode materials with insufficient intercalation sites, poor ion-conducting channels, and poor diffusion dynamics of large chloroaluminate anions (AlCl4- and Al2Cl7-). To address these issues, surface-modified graphitic carbon materials [i.e., acid-treated expanded graphite (AEG) and base-etched graphite (BEG)] are developed as novel cathode materials for ultra-fast chargeable AIBs. AEG has more turbostratically ordered structure covered with abundant micro- to nano-sized pores on the surface structure and expanded interlayer distance (d002 = 0.3371 nm) realized by surface treatment of pristine graphite with acidic media, which can be accelerated the diffusion dynamics and efficient AlCl4- ions (de)-intercalation kinetics. The AIB system employing AEG exhibits a specific capacity of 88.6 mAh g-1 (4 A g-1) and ~ 80 mAh g-1 at an ultra-high current rate of 10 A g-1 (~ 99.1% over 10,000 cycles). BEG treated with KOH solution possesses the turbostratically disordered structure with high density of defective sites and largely expanded d-spacing (d002 = 0.3384 nm) for attracting and uptaking more AlCl4- ions with relatively shorter penetration depth. Impressively, the AIB system based on the BEG cathode delivers a high specific capacity of 110 mAh g-1 (4 A g-1) and ~ 91 mAh g-1 (~ 99.9% over 10,000 cycles at 10 A g-1). Moreover, the BEG cell has high energy and power densities of 247 Wh kg-1 and 44.5 kW kg-1. This performance is one of the best among the AIB graphitic carbon materials reported for chloroaluminate anions storage performance. This finding provides great significance for the further development of rechargeable AIBs with high energy, high power density, and exceptionally long life.

Electrochemical oxidation of boron-doped nickel-iron layered double hydroxide for facile charge transfer in oxygen evolution electrocatalysts.

The oxygen evolution reaction (OER) is the key reaction in water splitting systems, but compared with the hydrogen evolution reaction (HER), the OER exhibits slow reaction kinetics. In this work, boron doping into nickel-iron layered double hydroxide (NiFe LDH) was evaluated for the enhancement of OER electrocatalytic activity. To fabricate boron-doped NiFe LDH (B:NiFe LDH), gaseous boronization, a gas-solid reaction between boron gas and NiFe LDH, was conducted at a relatively low temperature. Subsequently, catalyst activation was performed through electrochemical oxidation for maximization of boron doping and improved OER performance. As a result, it was possible to obtain a remarkably reduced overpotential of 229 mV at 10 mA cm-2 compared to that of pristine NiFe LDH (315 mV) due to the effect of facile charge-transfer resistance by boron doping and improved active sites by electrochemical oxidation.

Thermodynamically driven self-formation of Ag nanoparticles in Zn-embedded carbon nanofibers for efficient electrochemical CO2 reduction.

The electrochemical CO2 reduction reaction (CO2RR), which converts CO2 into value-added feedstocks and renewable fuels, has been increasingly studied as a next-generation energy and environmental solution. Here, we report that single-atom metal sites distributed around active materials can enhance the CO2RR performance by controlling the Lewis acidity-based local CO2 concentration. By utilizing the oxidation Gibbs free energy difference between silver (Ag), zinc (Zn), and carbon (C), we can produce Ag nanoparticle-embedded carbon nanofibers (CNFs) where Zn is atomically dispersed by a one-pot, self-forming thermal calcination process. The CO2RR performance of AgZn-CNF was investigated by a flow cell with a gas diffusion electrode (GDE). Compared to Ag-CNFs without Zn species (53% at -0.85 V vs. RHE), the faradaic efficiency (FE) of carbon monoxide (CO) was approximately 20% higher in AgZn-CNF (75% at -0.82 V vs. RHE) with 1 M KOH electrolyte.

Diselenide-Bridged Carbon-Dot-Mediated Self-Healing, Conductive, and Adhesive Wireless Hydrogel Sensors for Label-Free Breast Cancer Detection.

Recently, a great deal of research has focused on the study of self-healing hydrogels possessing electronic conductivity due to their wide applicability for use in biosensors, bioelectronics, and energy storage. The low solubility, poor biocompatibility, and lack of effective stimuli-responsive properties of their sp2 carbon-rich hybrid organic polymers, however, have proven challenging for their use in electroconductive self-healing hydrogel fabrication. In this study, we developed stimuli-responsive electrochemical wireless hydrogel biosensors using ureidopyriminone-conjugated gelatin (Gel-UPy) hydrogels that incorporate diselenide-containing carbon dots (dsCD) for cancer detection. The cleavage of diselenide groups of the dsCD within the hydrogels by glutathione (GSH) or reactive oxygen species (ROS) initiates the formation of hydrogen bonds that affect the self-healing ability, conductivity, and adhesiveness of the Gel-UPy/dsCD hydrogels. The Gel-UPy/dsCD hydrogels demonstrate more rapid healing under tumor conditions (MDA-MB-231) compared to that observed under physiological conditions (MDCK). Additionally, the cleavage of diselenide bonds affects the electrochemical signals due to the degradation of dsCD. The hydrogels also exhibit excellent adhesiveness and in vivo cancer detection ability after exposure to a high concentration of GSH or ROS, and this is comparable to results observed in a low concentration environment. Based on the combined self-healing, conductivity, and adhesiveness properties of the Gel-UPy/dsCD, this hydrogel exhibits promise for use in biomedical applications, particularly those that involve cancer detection, due to its selectivity and sensitivity under tumor conditions.