A Versatile Strategy for Achieving Fast-Charging Batteries via Interfacial Engineering: Pseudocapacitive Potassium Storage without Nanostructuring.

The rapid transport of alkali ions in electrodes is a long-time dream for fast-charging batteries. Though electrode nanostructuring has increased the rate-capability, its practical use is limited because of the low tap density and severe irreversible reactions. Therefore, development of a strategy to design fast-charging micron-sized electrodes without nanostructuring is of significant importance. Herein, a simple and versatile strategy to accelerate the alkali ion diffusion behavior in micron-sized electrode is reported. It is demonstrated that the diffusion rate of K+ ions is significantly improved at the hetero-interface between orthorhombic Nb2 O5 (001) and monoclinic MoO2 (110) planes. Lattice distortion at the hetero-interface generates an inner space large enough for the facile transport of K+ ions, and electron localization near oxygen-vacant sites further enhances the ion diffusion behavior. As a result, the interfacial-engineered micron-sized anode material achieves an outstanding rate capability in potassium-ion batteries (KIBs), even higher than nanostructured orthorhombic Nb2 O5  which is famous for fast-charging electrodes. This is the first study to develop an intercalation pseudocapacitive micron-sized anode without nanostructuring for fast-charging and high volumetric energy density KIBs. More interestingly, this strategy is not limited to K+ ion, but also applicable to Li+ ion, implying the versatility of interfacial engineering for alkali ion batteries.

Reverse micelle synthesis of colloidal nickel-manganese layered double hydroxide nanosheets and their pseudocapacitive properties.

Colloidal nanosheets of nickel-manganese layered double hydroxides (LDHs) have been synthesized in high yields through a facile reverse micelle method with xylene as an oil phase and oleylamine as a surfactant. Electron microscopy studies of the product revealed the formation of colloidal nanoplatelets with sizes of 50-150 nm, and X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy studies showed that the Ni-Mn LDH nanosheets had a hydrotalcite-like structure with a formula of [Ni3 Mn(OH)8 ](Cl(-) )⋅n H2 O. We found that the presence of both Ni and Mn precursors was required for the growth of Ni-Mn LDH nanosheets. As pseudocapacitors, the Ni-Mn LDH nanosheets exhibited much higher specific capacitance than unitary nickel hydroxides and manganese oxides.

How to Change the Reaction Chemistry on Nonprecious Metal Oxide Nanostructure Materials for Electrocatalytic Oxidation of Biomass-Derived Glycerol to Renewable Chemicals.

Au and Pt are well-known catalysts for electrocatalytic oxidation of biomass-derived glycerol. Although some nonprecious-metal-based materials to replace the costly Au and Pt are used for this reaction, the fundamental question of how the nonprecious catalysts affect the reaction chemistry and mechanism compared to Au and Pt catalysts is still unanswered. In this work, both experimental and computational methods are used to understand how and why the reaction performance and chemistry for the electrocatalytic glycerol oxidation reaction (EGOR) change with electrochemically-synthesized CuCo-oxide, Cu-oxide, and Co-oxide catalysts compared to conventional Au and Pt catalysts. The Au and Pt catalysts generate major glyceric acid and glycolic acid products from the EGOR. Interestingly, the prepared Cu-based oxides produce glycolic acid and formic acid with high selectivity of about 90.0%. This different reaction chemistry is related to the enhanced ability of CC bond cleavage on the Cu-based oxide materials. The density functional theory calculations demonstrate that the formic acids are mainly formed on the Cu-based oxide surfaces rather than in the process of glycolic acid formation in the free energy diagram. This study provides critical scientific insights into developing future nonprecious-based materials for electrochemical biomass conversions.

Perovskite-based electrocatalysts for oxygen evolution reaction in alkaline media: A mini review.

Water electrolysis is one of the attractive technologies for producing clean and sustainable hydrogen fuels with high purity. Among the various kinds of water electrolysis systems, anion exchange membrane water electrolysis has received much attention by combining the advantages of alkaline water electrolysis and proton exchange membrane water electrolysis. However, the sluggish kinetics of the oxygen evolution reaction, which is based on multiple and complex reaction mechanisms, is regarded as a major obstacle for the development of high-efficiency water electrolysis. Therefore, the development of high-performance oxygen evolution reaction electrocatalysts is a prerequisite for the commercialization and wide application of water electrolysis systems. This mini review highlights the current progress of representative oxygen evolution reaction electrocatalysts that are based on a perovskite structure in alkaline media. We first summarize the research status of various kinds of perovskite-based oxygen evolution reaction electrocatalysts, reaction mechanisms and activity descriptors. Finally, the challenges facing the development of perovskite-based oxygen evolution reaction electrocatalysts and a perspective on their future are discussed.

Synthesis of Sodium Cobalt Fluoride/Reduced Graphene Oxide (NaCoF3/rGO) Nanocomposites and Investigation of Their Electrochemical Properties as Cathodes for Li-Ion Batteries.

In this study, sodium cobalt fluoride (NaCoF3)/reduced graphene oxide (NCF/rGO) nanocomposites were fabricated through a simple one-pot solvothermal process and their electrochemical performance as cathodes for Li-ion batteries (LIBs) was investigated. The NCF nanoclusters (NCs) on the composites (300-500 nm in size) were formed by the assembly of primary nanoparticles (~20 nm), which were then incorporated on the surface of rGO. This morphology provided NCF NCs with a large surface area for efficient ion diffusion and also allowed for close contact with the conductive matrix to promote rapid electron transfer. As a cathode for LIBs, the NCF/rGO electrode achieved a high reversible capacity of 465 mAh·g-1 at 20 mA·g-1 via the conversion reaction, and this enhancement represented more than five times the reversible capacity of the bare NCF electrode. Additionally, the NCF/rGO electrode exhibited both better specific capacity and cyclability within the current density testing range (from 20 to 200 mA·g-1), compared with those of the bare NCF electrode.

Unveiling the enhanced electrocatalytic activity at electrochemically synthesized Pt-WOx hybrid nanostructure interfaces.

Here we report a simple synthesis strategy for Pt-WOx hybrid nanostructures using a metal-dissolution-based electrodeposition technique. The hybrid nanostructures demonstrate an excellent catalytic hydrogen evolution reaction performance with an approximately 17 times higher Pt mass activity and a 7.4 times higher turnover frequency than those of commercial Pt catalysts. The enhanced electrocatalytic performance is related to the creation of Pt-WOx interfacial sites.

Improved pseudocapacitive charge storage in highly ordered mesoporous TiO2/carbon nanocomposites as high-performance Li-ion hybrid supercapacitor anodes.

A Li-ion hybrid supercapacitor (Li-HSCs), an integrated system of a Li-ion battery and a supercapacitor, is an important energy-storage device because of its outstanding energy and power as well as long-term cycle life. In this work, we propose an attractive material (a mesoporous anatase titanium dioxide/carbon hybrid material, m-TiO2-C) as a rapid and stable Li+ storage anode material for Li-HSCs. m-TiO2-C exhibits high specific capacity (∼198 mA h g-1 at 0.05 A g-1) and promising rate performance (∼90 mA h g-1 at 5 A g-1) with stable cyclability, resulting from the well-designed porous structure with nanocrystalline anatase TiO2 and conductive carbon. Thereby, it is demonstrated that a Li-HSC system using a m-TiO2-C anode provides high energy and power (∼63 W h kg-1, and ∼4044 W kg-1).

Binder-Free Hybrid Titanium-Niobium Oxide/Carbon Nanofiber Mats for Lithium-Ion Battery Electrodes.

Free-standing, binder-free, titanium-niobium oxide/carbon hybrid nanofibers are prepared for Li-ion battery applications. A one-pot synthesis offers a significant reduction of processing steps and avoids the use of environmentally unfriendly binder materials, making the approach highly sustainable. Tetragonal Nb2 O5 /C and monoclinic Ti2 Nb10 O29 /C hybrid nanofibers synthesized at 1000 °C displayed the highest electrochemical performance, with capacity values of 243 and 267 mAh g-1 , respectively, normalized to the electrode mass. At 5 A g-1 , the Nb2 O5 /C and Ti2 Nb10 O29 /C hybrid fibers maintained 78 % and 53 % of the initial capacity, respectively. The higher rate performance and stability of tetragonal Nb2 O5 compared to that of monoclinic Ti2 Nb10 O29 is related to the low energy barriers for Li+ transport in its crystal structure, with no phase transformation. The improved rate performance resulted from the excellent charge propagation in the continuous nanofiber network.

A mini review of designed mesoporous materials for energy-storage applications: from electric double-layer capacitors to hybrid supercapacitors.

In recent years, porous materials have attracted significant attention in various research fields because of their structural merits. In particular, well-designed mesoporous structures with two- or three-dimensionally interconnected pores have been recognized as electrode materials of particular interest for achieving high-performance electrochemical capacitors (ECs). In this mini review, recent progress in the design of mesoporous electrode materials for ECs, from electric double-layer capacitors (EDLCs) and pseudocapacitors (PCs) to hybrid supercapacitors (HSCs), and research challenges for the development of new mesoporous electrode materials has been discussed.

Ammonium Fluoride Mediated Synthesis of Anhydrous Metal Fluoride-Mesoporous Carbon Nanocomposites for High-Performance Lithium Ion Battery Cathodes.

Metal fluorides (MFx) are one of the most attractive cathode candidates for Li ion batteries (LIBs) due to their high conversion potentials with large capacities. However, only a limited number of synthetic methods, generally involving highly toxic or inaccessible reagents, currently exist, which has made it difficult to produce well-designed nanostructures suitable for cathodes; consequently, harnessing their potential cathodic properties has been a challenge. Herein, we report a new bottom-up synthetic method utilizing ammonium fluoride (NH4F) for the preparation of anhydrous MFx (CuF2, FeF3, and CoF2)/mesoporous carbon (MSU-F-C) nanocomposites, whereby a series of metal precursor nanoparticles preconfined in mesoporous carbon were readily converted to anhydrous MFx through simple heat treatment with NH4F under solventless conditions. We demonstrate the versatility, lower toxicity, and efficiency of this synthetic method and, using XRD analysis, propose a mechanism for the reaction. All MFx/MSU-F-C prepared in this study exhibited superior electrochemical performances, through conversion reactions, as the cathode for LIBs. In particular, FeF3/MSU-F-C maintained a capacity of 650 mAh g-1FeF3 across 50 cycles, which is ∼90% of its initial capacity. We expect that this facile synthesis method will trigger further research into the development of various nanostructured MFx for use in energy storage and other applications.

Development of a noncontact heart rate monitoring system for sedentary behavior based on an accelerometer attached to a chair.

Although people spend a third of their day engaged in sedentary activities, research on heart activity during sitting is almost nonexistent because of the discomfort experienced when electrocardiogram (ECG) measurement electrodes are attached to the body. Accordingly, in this study, a system was developed to monitor heart rate (HR) in a noncontact and unconstrained way while subjects were seated, by attaching an accelerometer on the backrest of a chair. Acceleration signals were obtained three times from 20 healthy adults, a detection algorithm was applied, and HR detection performance was evaluated by comparing the R-peak values from the ECG. The system had excellent performance results, with a sensitivity of 96.10% and a positive predictive value of 96.43%. In addition, the HR calculated by the new system developed in this study was compared with HR calculated using ECG. The new system exhibited excellent performance; its results were strongly correlated with that of ECG (r = 0.97, p [Formula: see text] 0.0001; average difference of -0.08  ±  4.60 [mean ± 1.96∙standard deviation] in Bland-Altman analysis). Accordingly, the method presented in this study is expected to be applicable for evaluating diverse autonomic nervous system components in a noncontact and unconstrained way using an accelerometer to monitor the HR of sedentary workers or adolescents.

Mesoporous Ge/GeO2/Carbon Lithium-Ion Battery Anodes with High Capacity and High Reversibility.

We report mesoporous composite materials (m-GeO2, m-GeO2/C, and m-Ge-GeO2/C) with large pore size which are synthesized by a simple block copolymer directed self-assembly. m-Ge/GeO2/C shows greatly enhanced Coulombic efficiency, high reversible capacity (1631 mA h g(-1)), and stable cycle life compared with the other mesoporous and bulk GeO2 electrodes. m-Ge/GeO2/C exhibits one of the highest areal capacities (1.65 mA h cm(-2)) among previously reported Ge- and GeO2-based anodes. The superior electrochemical performance in m-Ge/GeO2/C arises from the highly improved kinetics of conversion reaction due to the synergistic effects of the mesoporous structures and the conductive carbon and metallic Ge.

Facile Synthesis of Nb2O5@Carbon Core-Shell Nanocrystals with Controlled Crystalline Structure for High-Power Anodes in Hybrid Supercapacitors.

Hybrid supercapacitors (battery-supercapacitor hybrid devices, HSCs) deliver high energy within seconds (excellent rate capability) with stable cyclability. One of the key limitations in developing high-performance HSCs is imbalance in power capability between the sluggish Faradaic lithium-intercalation anode and rapid non-Faradaic capacitive cathode. To solve this problem, we synthesize Nb2O5@carbon core-shell nanocyrstals (Nb2O5@C NCs) as high-power anode materials with controlled crystalline phases (orthorhombic (T) and pseudohexagonal (TT)) via a facile one-pot synthesis method based on a water-in-oil microemulsion system. The synthesis of ideal T-Nb2O5 for fast Li(+) diffusion is simply achieved by controlling the microemulsion parameter (e.g., pH control). The T-Nb2O5@C NCs shows a reversible specific capacity of ∼180 mA h g(-1) at 0.05 A g(-1) (1.1-3.0 V vs Li/Li(+)) with rapid rate capability compared to that of TT-Nb2O5@C and carbon shell-free Nb2O5 NCs, mainly due to synergistic effects of (i) the structural merit of T-Nb2O5 and (ii) the conductive carbon shell for high electron mobility. The highest energy (∼63 W h kg(-1)) and power (16 528 W kg(-1) achieved at ∼5 W h kg(-1)) densities within the voltage range of 1.0-3.5 V of the HSC using T-Nb2O5@C anode and MSP-20 cathode are remarkable.

A combinatorial chemistry method for fast screening of perovskite-based NO oxidation catalyst.

A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (α) and NO (ß), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations.

Advanced hybrid supercapacitor based on a mesoporous niobium pentoxide/carbon as high-performance anode.

Recently, hybrid supercapacitors (HSCs), which combine the use of battery and supercapacitor, have been extensively studied in order to satisfy increasing demands for large energy density and high power capability in energy-storage devices. For this purpose, the requirement for anode materials that provide enhanced charge storage sites (high capacity) and accommodate fast charge transport (high rate capability) has increased. Herein, therefore, a preparation of nanocomposite as anode material is presented and an advanced HSC using it is thoroughly analyzed. The HSC comprises a mesoporous Nb2O5/carbon (m-Nb2O5-C) nanocomposite anode synthesized by a simple one-pot method using a block copolymer assisted self-assembly and commercial activated carbon (MSP-20) cathode under organic electrolyte. The m-Nb2O5-C anode provides high specific capacity with outstanding rate performance and cyclability, mainly stemming from its enhanced pseudocapacitive behavior through introduction of a carbon-coated mesostructure within a voltage range from 3.0 to 1.1 V (vs Li/Li(+)). The HSC using the m-Nb2O5-C anode and MSP-20 cathode exhibits excellent energy and power densities (74 W h kg(-1) and 18,510 W kg(-1)), with advanced cycle life (capacity retention: ∼90% at 1000 mA g(-1) after 1000 cycles) within potential range from 1.0 to 3.5 V. In particular, we note that the highest power density (18,510 W kg(-1)) of HSC is achieved at 15 W h kg(-1), which is the highest level among similar HSC systems previously reported. With further study, the HSCs developed in this work could be a next-generation energy-storage device, bridging the performance gap between conventional batteries and supercapacitors.