Selective recovery of lithium and ammonium from spent lithium-ion batteries using intercalation electrodes.

Recycling lithium-ion batteries has recently become a major concern. Ammonia leaching is commonly employed in such battery recycling methods since it has various advantages such as low toxicity and excellent selectivity toward precious metals. In this study, an electrochemical system with intercalation-type electrodes was used to investigate the selective recovery of lithium and ammonium from ammonia battery leachate. Using an activated carbon electrode as a counter electrode, the selectivity of lithium from the lithium manganese oxide (LMO) electrode and the selectivity of ammonium from the nickel hexacyanoferrate (NiHCF) electrode were examined within the system. The LMO//NiHCF system was next evaluated for lithium and ammonium recovery using a synthetic solution as well as real ammonia battery leachate. When compared to previous ammonium recovery methods, the results revealed good selectivity of lithium and ammonium from each LMO and NiHCF electrode with relatively low energy consumption for ammonium recovery (2.43 Wh g-N-1). The average recovery capacity of lithium was 1.39 mmol g-1 with a purity of up to 96.8% and the recovery capacity of ammonium was 1.09 mmol g-1 with 97.8% purity from the pre-treated leachate. This electrochemical method together with ammonia leaching can be a promising method for selective resource recovery from spent lithium-ion batteries.

Surface Electrochemistry of Carbon Electrodes and Faradaic Reactions in Capacitive Deionization.

Recent advances in electrochemical desalination techniques have paved way for utilization of saline water. In particular, capacitive deionization (CDI) enables removal of salts with high energy efficiency and economic feasibility, while its applicability has been challenged by degradation of carbon electrodes in long-term operations. Herein, we report a thorough investigation on the surface electrochemistry of carbon electrodes and Faradaic reactions that are responsible for stability issues of CDI systems. By using bare and membrane CDI (MCDI) as model systems, we identified various electrochemical reactions of carbon electrodes with water or oxygen, with thermodynamics and kinetics governed by the electrode potential and pH. As a result, a complete overview of the Faradaic reactions taking place in CDI was constructed by tracing the physicochemical changes occurring in CDI and MCDI systems.

Electrochemically Mediated Direct CO2 Capture by a Stackable Bipolar Cell.

The unprecedented increase in atmospheric CO2 concentration calls for effective carbon capture technologies. With distributed sources contributing to about half of the overall emission, CO2 capture from the atmosphere [direct air capture, (DAC)] is more relevant than ever. Herein, an electrochemically mediated DAC system is reported which utilizes affinity of redox-active quinone moieties towards CO2 molecules, and unlike incumbent chemisorption technologies which require temperature or pH swing, relies solely on the electrochemical voltage for CO2 capture and release. The design and operation of a DAC system is demonstrated with stackable bipolar cells using quinone chemistry. Specifically, poly(vinylanthraquinone) (PVAQ) negative electrode undergoes a two-electron reduction reaction and reversibly complexes with CO2 , leading to CO2 sequestration from the feed stream. The subsequent PVAQ oxidation, conversely, results in release of CO2 . The performance of both small- and meso-scale cells for DAC are evaluated with feed CO2 concentrations as low as 400 ppm (0.04 %), and energy consumption is demonstrated as low as 113 kJ per mole of CO2 captured. Notably, the bipolar cell construct is modular and expandable, equally suitable for small and large plants. Moving forward, this work presents a viable and highly customizable electrochemical method for DAC.

Self-supported mesoscopic tin oxide nanofilms for electrocatalytic reduction of carbon dioxide to formate.

Here we report a self-supported SnO2 nanofilm prepared by a robust electrochemical process as an electrocatalyst for the CO2 reduction reaction. The SnO2 film had a large surface area originating from its nano-architecture and manifested high selectivity toward formate (over 60%), which resulted in CO2-to-formate current density up to 33.66 mA cm-2 that is among the state-of-the-art. We unveiled that the high performance of the SnO2 nanofilm is attributable to the presence of a metastable oxide under reductive conditions in addition to the abovementioned advantages.

Understanding the Behaviors of λ-MnO2 in Electrochemical Lithium Recovery: Key Limiting Factors and a Route to the Enhanced Performance.

Recently developed electrochemical lithium recovery systems, whose operation principle mimics that of lithium-ion battery, enable selective recovery of lithium from source waters with a wide range of lithium ions (Li+) concentrations; however, physicochemical behaviors of the key component-Li+-selective electrode-in realistic operation conditions have been poorly understood. Herein, we report an investigation on a λ-MnO2 electrode during the electrochemical lithium recovery process with regards to the Li+ concentration in source water and operation rate of the system. Three distinctive stages of λ-MnO2 originating from different limiting factors for lithium recovery are defined with regard to the rate of Li+ supply from the electrolyte: depleted, transition, and saturated regions. By characterization of λ-MnO2 at different stages using diverse X-ray techniques, the importance of Li+ concentration in the vicinity of the electrode surface is revealed. On the basis of this understanding, increasing the density of the electrode/electrolyte interface is suggested as a realistic and general route to enhance the overall lithium recovery performance and is experimentally corroborated at a wide range of operation environments.

Enhanced Vertical Charge Transport of Homo- and Blended Semiconducting Polymers by Nanoconfinement.

The morphology of conjugated polymers has critical influences on electronic and optical properties of optoelectronic devices. Even though lots of techniques and methods are suggested to control the morphology of polymers, very few studies have been performed inducing high charge transport along out-of-plane direction. In this study, the self-assembly of homo- and blended conjugated polymers which are confined in nanostructures is utilized. The resulting structures lead to high charge mobility along vertical direction for both homo- and blended conjugated polymers. Both semicrystalline and amorphous polymers show highly increased population of face-on crystallite despite intrinsic crystallinity of polymers. They result in more than two orders of magnitude enhanced charge mobility along vertical direction revealed by nanoscale conductive scanning force microscopy and macroscale IV characteristic measurements. Moreover, blends of semicrystalline and amorphous polymers, which are known to show inferior optical and electrical properties due to their structural incompatibility, are formed into harmonious states by this approach. Assembly of blends of semicrystalline and amorphous polymers under nanoconfinement shows charge mobility in out-of-plane direction of 0.73 cm2 V-1 s-1 with wide range of absorption wavelength from 300 to 750 nm demonstrating the synergistic effects of two different polymers.

Alternative Assembly of α-Synuclein Leading to Protein Film Formation and Its Application for Developing Polydiacetylene-Based Sensing Materials.

Understanding the self-assembly process of amyloidogenic protein is valuable not only to find its pathological implication but also to prepare protein-based biomaterials. α-Synuclein (αS), a pathological component of Parkinson's disease, producing one-dimensional (1D) amyloid fibrils, has been employed to generate two-dimensional (2D) protein films by encouraging an alternative self-assembly process. At a high temperature of 50 °C, αS molecules self-assembled into 2D films instead of 1D amyloid fibrils, whereas the fibrils were the major product at 37 °C. Based on circular dichroism and Fourier transform infrared spectroscopy analyses, the film was produced via a structural transition from the initial random to still undefined but mostly the turn or loop structure, which was distinctive from the ß-sheet formation observed with the amyloid fibrils. The αS 2D film was also routinely prepared at the oil-water interface and used as a matrix to produce polydiacetylene-based sensing materials. 10,12-Pentacosadiynoic acids (PCDA) were aligned on the film and photopolymerized to form a π-conjugated molecular assembly yielding a blue color. Its colorimetric transition to red was induced by increasing the temperature. This functionalized protein film increased its height from 40 to 55 nm upon PCDA immobilization and exhibited enhanced physical and chemical stability. In addition, the modified film showed remarkably high electrical conductivity only in the red state. This film, therefore, can be considered as a robust protein-based hybrid biomaterial capable of simultaneously recognizing various external stimuli (heat, pH, and solvents) with changes in color and conductivity, and it is expected to be utilized as a basic material for the development of biocompatible sensors.

Acoustic emission analysis of the compressive deformation of iron foams and their biocompatibility study.

We synthesized Fe foams using water suspensions of micrometric Fe2O3 powder by reducing and sintering the sublimated Fe oxide green body to Fe under 5% H2/Ar gas. The resultant Fe foam showed aligned lamellar macropores replicating the ice dendrites. The compressive behavior and deformation mechanism of the synthesized Fe foam were studied using an acoustic emission (AE) method, with which we detected sudden localized structural changes in the Fe foam material. The evolution of the deformation mechanism was elucidated using the adaptive sequential k-means (ASK) algorithm; specifically, the plastic deformation of the cell struts was followed by localized cell collapse, which eventually led to fracturing of the cell walls. For potential biomedical applications, the corrosion and biocompatibility characteristics of the two synthesized Fe foams with different porosities (50% vs. 44%) were examined and compared. Despite its larger porosity, the superior corrosion behavior of the Fe foam with 50% porosity can be attributed to its larger pore size and smaller microscopic surface area. Based on the cytotoxicity tests for the extracts of the foams, the Fe foam with 44% porosity showed better cytocompatibility than that with 50% porosity.

Recent Progress in the Design and Synthesis of Nitrides for Mesoscopic and Perovskite Solar Cells.

With growing concerns about global warming and the energy crisis, a variety of photovoltaic devices have attracted worldwide attention as alternative energy sources. Among them, organic-inorganic hybrid photovoltaics, typically mesoscopic and perovskite solar cells, are promising, owing to their potential for low-cost energy production, which mainly comes from unlimited combinations of materials optimized for each step of solar energy conversion. However, the commercialization of organic-inorganic hybrid solar cells is hampered by costly electrocatalysts or hole-transport materials. Currently, state-of-the-art dye- or quantum-dot-sensitized solar cells and perovskite solar cells necessitate noble metals and high-price polymeric materials. In an attempt to resolve this issue, various kinds of metal compounds have been investigated, and nitrides have been actively reported to possess a number of favorable properties for the aforementioned purpose, such as excellent electrical conductivity and superb electrocatalytic performance. Herein, the use of nitrides as cost-effective electrocatalysts or hole-transport materials in organic-inorganic hybrid solar cells is reviewed. Nitrides with a variety of morphologies and scales are discussed, together with the synergistic effect in the case of diverse composites. In addition, prospects and challenges for applying nitride materials are briefly suggested.

Edge-Terminated MoS2 Nanoassembled Electrocatalyst via In Situ Hybridization with 3D Carbon Network.

Transition metal dichalcogenides, especially MoS2 , are considered as promising electrocatalysts for hydrogen evolution reaction (HER). Since the physicochemical properties of MoS2 and electrode morphology are highly sensitive factor for HER performance, designed synthesis is highly pursued. Here, an in situ method to prepare a 3D carbon/MoS2 hybrid catalyst, motivated by the graphene ribbon synthesis process, is reported. By rational design strategies, the hybrid electrocatalysts with cross-connected porous structure are obtained, and they show a high HER activity even comparable to the state-of-the-art MoS2 catalyst without appreciable activity loss in long-term operations. Based on various physicochemical techniques, it is demonstrated that the synthetic procedure can effectively guide the formation of active site and 3D structure with a distinctive feature; increased exposure of active sites by decreased domain size and intrinsically high activity through controlling the number of stacking layers. Moreover, the importance of structural properties of the MoS2 -based catalysts is verified by controlled experiments, validating the effectiveness of the designed synthesis approach.

Highly Efficient Bifacial Dye-Sensitized Solar Cells Employing Polymeric Counter Electrodes.

Dye-sensitized solar cells (DSCs) are promising solar energy conversion devices with aesthetically favorable properties such as being colorful and having transparent features. They are also well-known for high and reliable performance even under ambient lighting, and these advantages distinguish DSCs for applications in window-type building-integrated photovoltaics (BIPVs) that utilize photons from both lamplight and sunlight. Therefore, investigations on bifacial DSCs have been done intensively, but further enhancement in performance under back-illumination is essential for practical window-BIPV applications. In this research, highly efficient bifacial DSCs were prepared by a combination of electropolymerized poly(3,4-ethylenedioxythiphene) (PEDOT) counter electrodes (CEs) and cobalt bipyridine redox ([Co(bpy)3]3+/2+) electrolyte, both of which manifested superior transparency when compared with conventional Pt and iodide counterparts, respectively. Keen electrochemical analyses of PEDOT films verified that superior electrical properties were achievable when the thickness of the film was reduced, while their high electrocatalytic activities were unchanged. The combination of the PEDOT thin film and [Co(bpy)3]3+/2+ electrolyte led to an unprecedented power conversion efficiency among bifacial DSCs under back-illumination, which was also over 85% of that obtained under front-illumination. Furthermore, the advantage of the electropolymerization process, which does not require an elevation of temperature, was demonstrated by flexible bifacial DSC applications.

Electrochemically Synthesized Nanoporous Molybdenum Carbide as a Durable Electrocatalyst for Hydrogen Evolution Reaction.

Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high-performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top-down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion.

Therapeutic efficacy and safety of a 1927-nm fractionated thulium laser on pattern hair loss: an evaluator-blinded, split-scalp study.

Laser- or light-assisted therapies have been used to improve the perifollicular environment by upregulating the expression of growth factors and signaling molecules for hair restoration. The aim of our study was to preclinically and clinically evaluate the therapeutic efficacy and safety of a 1927-nm fractionated thulium laser on pattern hair loss (PHL). An in vivo hairless mouse study and an in vivo human skin environmental scanning electron microscopy (ESEM) study were performed with different power and energy settings. Thereafter, an evaluator-blinded, split-scalp study was conducted to evaluate hair thickness and density in 10 PHL patients treated with 12 sessions of fractionated thulium laser treatment with or without post-laser treatment application of a growth factor-containing (GF) solution. In in vivo hairless mouse skin, inverted cone-shaped zones of thulium laser-induced tissue coagulation (LITC) were noted immediately after treatment in the epidermis and upper to mid-dermis without remarkable ablative tissue injury. The ESEM study revealed round to oval-shaped zones of non-ablative LITC on the surface of the stratum corneum of a human subject immediately after laser irradiation. In PHL patients, 12 sessions of thulium laser monotherapy at 1-week intervals resulted in significantly increased hair density and thickness. Post-laser treatment application of GF solution offered additional therapeutic efficacy by improving hair density and thickness on the split scalp. The use of a fractionated thulium laser with or without post-laser therapy application of GF solution to treat PHL elicited remarkable improvements in hair thickness and hair counts.

Coffee Waste-Derived Hierarchical Porous Carbon as a Highly Active and Durable Electrocatalyst for Electrochemical Energy Applications.

Nitrogen-doped porous carbon materials have been highlighted as promising alternatives to high-cost platinum in various electrochemical energy applications. However, protocols to generate effective pore structure are still challenging, which hampers mass production and utilization of carbon materials. Here, we suggest a facile and effective method for hierarchical porous carbon by a single-step carbonization of coffee waste (CW) with ZnCl2. The CW, which is one of the most earth-abundant organic waste, can be successfully converted to nitrogen-doped porous carbon. It shows outstanding oxygen reduction activity and durability comparable to the state-of-the-art platinum, and the half-wave potential is also comparable to the best metal-free electrocatalysts in alkaline media. Finally, we apply it to counter electrode of dye-sensitized solar cell, whose photovoltaic efficiency surpasses the one made with conventional platinum electrode. We demonstrate the feasibility of our strategies for highly efficient, cheap, and environment-friendly electrocatalyst to replace platinum in various electrochemical energy applications.

Multidimensional Anodized Titanium Foam Photoelectrode for Efficient Utilization of Photons in Mesoscopic Solar Cells.

Mesoscopic solar cells based on nanostructured oxide semiconductors are considered as a promising candidates to replace conventional photovoltaics employing costly materials. However, their overall performances are below the sufficient level required for practical usages. Herein, this study proposes an anodized Ti foam (ATF) with multidimensional and hierarchical architecture as a highly efficient photoelectrode for the generation of a large photocurrent. ATF photoelectrodes prepared by electrochemical anodization of freeze-cast Ti foams have three favorable characteristics: (i) large surface area for enhanced light harvesting, (ii) 1D semiconductor structure for facilitated charge collection, and (iii) 3D highly conductive metallic current collector that enables exclusion of transparent conducting oxide substrate. Based on these advantages, when ATF is utilized in dye-sensitized solar cells, short-circuit photocurrent density up to 22.0 mA cm-2 is achieved in the conventional N719 dye-I3- /I- redox electrolyte system even with an intrinsically inferior quasi-solid electrolyte.

Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting.

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm-2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm-2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance.

High-Density Single-Layer Coating of Gold Nanoparticles onto Multiple Substrates by Using an Intrinsically Disordered Protein of α-Synuclein for Nanoapplications.

Functional graffiti of nanoparticles onto target surface is an important issue in the development of nanodevices. A general strategy has been introduced here to decorate chemically diverse substrates with gold nanoparticles (AuNPs) in the form of a close-packed single layer by using an omni-adhesive protein of α-synuclein (αS) as conjugated with the particles. Since the adsorption was highly sensitive to pH, the amino acid sequence of αS exposed from the conjugates and its conformationally disordered state capable of exhibiting structural plasticity are considered to be responsible for the single-layer coating over diverse surfaces. Merited by the simple solution-based adsorption procedure, the particles have been imprinted to various geometric shapes in 2-D and physically inaccessible surfaces of 3-D objects. The αS-encapsulated AuNPs to form a high-density single-layer coat has been employed in the development of nonvolatile memory, fule-cell, solar-cell, and cell-culture platform, where the outlying αS has played versatile roles such as a dielectric layer for charge retention, a sacrificial layer to expose AuNPs for chemical catalysis, a reaction center for silicification, and biointerface for cell attachment, respectively. Multiple utilizations of the αS-based hybrid NPs, therefore, could offer great versatility to fabricate a variety of NP-integrated advanced materials which would serve as an indispensable component for widespread applications of high-performance nanodevices.

Electrochemical synthesis of nanoporous tungsten carbide and its application as electrocatalysts for photoelectrochemical cells.

Photoelectrochemical (PEC) cells are promising tools for renewable and sustainable solar energy conversion. Currently, their inadequate performance and high cost of the noble metals used in the electrocatalytic counter electrode have postponed the practical use of PEC cells. In this study, we report the electrochemical synthesis of nanoporous tungsten carbide and its application as a reduction catalyst in PEC cells, namely, dye-sensitized solar cells (DSCs) and PEC water splitting cells, for the first time. The method employed in this study involves the anodization of tungsten foil followed by post heat treatment in a CO atmosphere to produce highly crystalline tungsten carbide film with an interconnected nanostructure. This exhibited high catalytic activity for the reduction of cobalt bipyridine species, which represent state-of-the-art redox couples for DSCs. The performance of tungsten carbide even surpassed that of Pt, and a substantial increase (∼25%) in energy conversion efficiency was achieved when Pt was substituted by tungsten carbide film as the counter electrode. In addition, tungsten carbide displayed decent activity as a catalyst for the hydrogen evolution reaction, suggesting the high feasibility for its utilization as a cathode material for PEC water splitting cells, which was also verified in a two-electrode water photoelectrolyzer.

Wrinkled silica/titania nanoparticles with tunable interwrinkle distances for efficient utilization of photons in dye-sensitized solar cells.

Efficient light harvesting is essential for the realization of high energy conversion efficiency in dye-sensitized solar cells (DSCs). State-of-the-art mesoporous TiO2 photoanodes fall short for collection of long-wavelength visible light photons, and thus there have been efforts on introduction of scattering nanoparticles. Herein, we report the synthesis of wrinkled silica/titania nanoparticles with tunable interwrinkle distances as scattering materials for enhanced light harvesting in DSCs. These particles with more than 20 times larger specific surface area (>400 m(2)/g) compared to the spherical scattering particles (<20 m(2)/g) of the similar sizes gave rise to the dye-loading amounts, causing significant improvements in photocurrent density and efficiency. Moreover, dependence of spectral scattering properties of wrinkled particles on interwrinkle distances, which was originated from difference in overall refractive indices, was observed.

Inhibition of pyrite oxidation by surface coating: a long-term field study.

Pyrite and other iron sulfides are readily oxidized by dissolved oxygen in aqueous phase, producing acidity and Fe(2+), which causes significant environmental problems. Applications of surface coating agents (Na2SiO3 and KH2PO4) were conducted at Boeun (Chungbuk, South Korea) outcrop site, and their efficiencies to inhibit the oxidation of sulfide minerals were monitored for a long-term period (449 days). The rock sample showed positive Net Acid Production Potential (NAPP = 20.23) and low Net Acid Generation pH (NAGpH = 2.42) values, suggesting that the rock sample was categorized in the potential acid-forming group. For the monitored time period (449 days), field study results showed that the application of Na2SiO3 effectively inhibited the pyrite oxidation as compared to KH2PO4. Na2SiO3 as a surface coating agent maintained pH 5-6 and reduced oxidation of pyrite surface up to 99.95 and 97.70 % indicated by Fe(2+) and SO4 (2-) release, respectively. The scanning electron microscope and energy-dispersive X-ray spectrometer analysis indicated that the morphology of rock surface was completely changed attributable to formation of iron silicate coating. The experimental results suggested that the treatment with Na2SiO3 was highly effective and it might be applicable on field for inhibition of iron sulfide oxidation.