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In this study, a high-entropy approach was employed to design a new single-phase A2B2O7 oxide for thermal insulation applications. Multicomponent high-entropy oxides, containing up to seven different cations, were successfully synthesized in a single defective fluorite structure. We observed that the incorporation of the functional cation, Zn2+, effectively blocked the heat radiation phenomenon by reducing the photon mean free path, and further reduced the high-temperature thermal conductivity owing to the larger free carrier concentration originated from the large number of oxygen vacancies. Although a large concentration of Zn2+ caused a slight reduction in thermal expansion, this study suggests that functional cations can be easily incorporated; thus, expanding the material diversity beyond the typical doping levels to develop new thermal barrier materials.

The development of efficient, low-cost, and stable bifunctional catalysts is necessary for renewable energy storage and conversion, but it remains a challenge. Herein, we first report a novel strat...

Development of efficient and durable electrocatalysts for the oxygen evolution reaction (OER) is essential for sustainable hydrogen production by water splitting. The physicochemical properties of the electrocatalyst can be tailored by defect engineering. Herein, we report the fabrication of [Fe(CN)6]3− coordination sphere vacancies via the rapid coprecipitation in Ni3Ⅱ[FeIII (CN)6]2-x (x ≤ 0.12) electrocatalyst anchored on reduced graphene oxide (v-NiFe PBA@rGO) for OER. The formation of [Fe(CN)6]3− coordination sphere vacancies (VFeCN) via the rapid coprecipitation during the synthesis under the absence of chelating agents enables the regulation of electronic states of Ni active site, leading to the improvement in OER. Reduced graphene oxide (rGO) is employed as a substrate to maximize the concentration of VFeCN and exposed active sites by the uniform formation of nano-sized Ni3Ⅱ[FeIII (CN)6]2-x. The presence of VFeCN and hybridization with rGO effectively suppress Fe leaching behavior. The v-NiFe PBA@rGO shows a low overpotential of 251 mV at 10 mA cm−2 in alkaline condition and the long-term stability for 200 h.

Li dendrite growth and poor Coulombic efficiency still prevent the practical use of Li metal anodes. Here, we report a stable solid electrolyte interphase (SEI) layer consisting of Li3N and LiF by employing lithium nitrate (LiNO3) in carbonate electrolytes for the improved cycle performance with dendrite-free Li deposition for Li metal anodes. We demonstrate that the lower charge transfer activation energy is realized with the Li3N-rich SEI layer and LiF-rich SEI layer in carbonate electrolytes. With the Li3N and LiF composite SEI layer, outstanding improvements are achieved in that the very low charge transfer activation energy of 46.64 KJ mol−1 and stable electrochemical performances with dendrite-free Li deposition. With those benefits, the Li || Cu cell shows stable cyclability with high Coulombic efficiency of ∼ 97% at a current density of 0.5 mA cm−2 with a capacity of 0.5 mAh cm−2 over 200 cycles, and Li can be densely plated with lower porosity of 10.1 % with a plated Li of 2 mAh cm−2. Finally, the outstanding cyclability is demonstrated in full cells consisting of LiNi0.8Co0.1Mn0.1O2 as a cathode and thin Li metal electrode with a thickness of 20 μm in lean electrolytes of 8 μL mAh−1.

The electrocatalytic performance of transition metal sulfide (TMS)–graphene composites has been simply regarded as the results of high conductivity and the large surface/volume ratio. However, unavoidable factors such as degree of oxidation of TMSs have been hardly considered for the origin of this catalytic activity of TMS–graphene composites. To accomplish the reliable application of TMS-based electrocatalytic materials, a clear understanding of the thermodynamic stability of TMS and effects of oxidation on catalytic activity is necessary. In addition, the mechanism of charge transfer at the TMS–graphene interface must be studied in depth to properly design composite materials. Herein, we report a comprehensive study of the physical chemistry at the junction of a Co1–xNixS2–graphene composite, which is a prototype designed to unravel the mechanisms of charge transfer between TMS and graphene. Specifically, the thermodynamic stability and the effects of oxidation of TMSs during the oxygen evolution react...

A key issue with Na-ion batteries is the development of active materials with stable electrochemical reversibility through the understanding of their sodium storage mechanisms. We report a sodium storage mechanism and properties of a new anode material, digenite Cu1.8S, based on its crystallographic study. It is revealed that copper sulfides (CuxS) can have metal-rich formulas (x ≥ 1.6), due to the unique oxidation state of +1 found in group 11 elements. These phases enable the unit cell to consist of all strong Cu–S bonds and no direct S–S bonds, which are vulnerable to external stress/strain that could result in bond cleavage as well as decomposition. Because of its structural rigidness, the Cu1.8S shows an intercalation/deintercalation reaction mechanism even in a low potential window of 0.1–2.2 V versus Na/Na+ without irreversible phase transformation, which most of the metal sulfides experience through a conversion reaction mechanism. It uptakes, on average, 1.4 Na+ ions per unit cell (∼250 mAh g–1) and exhibits ∼100% retention over 1000 cycles at 2C in a tuned voltage range of 0.5–2.2 V through an overall solid solution reaction with negligible phase separation.

We report a polylactic acid (PLA)-polyethylene glycol (PEG) mixture as a thermoplastic binder to prepare shape-machinable ceramic green bodies. During the mixing process, the high viscosity of the PLA binder impedes effective mixing with ceramic powders. To address this issue, PEG was introduced as a plasticizer into ceramic/PLA composites to diminish the overall viscosity of the feedstock, which resulted in effective mixing with ceramic powders. After sintering green bodies composed of PLA-PEG binders and ceramic compounds, the mechanical properties (flexural strength and porosity) of the sintered specimens were investigated and compared with those of sintered specimens made from wax-based green bodies. The sintered specimens made from ceramic/PLA-PEG composites showed comparable mechanical properties and porosities with the sintered specimens made from ceramic/wax composites. In addition, the shape-machinable characteristic of the green bodies made from ceramic/PLA-PEG composites was demonstrated by deforming the entire structure of the green bodies via simple heat treatment.

Alkaline electrolysis is one of the most powerful technologies to produce hydrogen energy, where the electrocatalysts play an important role. The cathode electrocatalysts often suffer from undesirable oxidation due to the oxygen gas crossover through the porous separator during electrolysis. This leads to oxygen reduction reaction (ORR) on the cathode electrocatalysts, resulting in the loss of activity for hydrogen evolution reaction (HER). Here, we report a highly efficient and durable HER and ORR bifunctional electrocatalyst derived from Ni metal-organic frameworks to address the above problem. Decoupled active sites for ORR and HER are induced in a hybrid material, NiFeP@Ni_NC, where an ORR catalytic N-doped nanocarbon layer can protect a HER catalytic Niδ+ from the undesired ORR. Therefore, excellent bifunctional stability is secured for NiFeP@Ni_NC. The strategy to enhance HER stability presented herein can be widely extended to design bifunctional electrocatalysts with improved stability in alkaline electrolysis.

We demonstrate the dual advantages of graded photoabsorbers in mesoporous metal oxide-based hetero interfacial photoanodes in improving photogenerated charge carrier (e−/h+) separation for the solar light-driven water-oxidation process. The pre-deposition of sol–gel-derived, tungsten-doped bismuth vanadate (W:BiVO4) onto a primary BiVO4 water oxidation layer forms graded interfaces, which facilitate charge transfer from the primary photoabsorber to the charge transport layer, thereby superseding the thickness-controlled charge recombination at the BiVO4 water oxidation catalyst. As a result, the WO3/BiVO4 hetero photoanode containing the photoactive W:BiVO4 interfacial layer showed 130% higher photocurrent than that of the interfacial layer-free hetero photoelectrode owing to the enhanced charge separation led water oxidation process.

The practical implementation of the lithium metal anode is hindered by obstacles such as Li dendrite growth, large volume changes, and poor lifespan. Here, copper nitride nanowires (Cu3 N NWs) printed Li by a facile and low-cost roll-press method is reported, to operate in carbonate electrolytes for high-voltage cathode materials. Through one-step roll pressing, Cu3 N NWs can be conformally printed onto the Li metal surface, and form a Li3 N@Cu NWs layer on the Li metal. The Li3 N@Cu NWs layer can assist homogeneous Li-ion flux with the 3D channel structure, as well as the high Li-ion conductivity of the Li3 N. With those beneficial effects, the Li3 N@Cu NWs layer can guide Li to deposit into a dense and planar structure without Li-dendrite growth. Li metal with Li3 N@Cu NWs protection layer exhibits outstanding cycling performances even at a high current density of 5.0 mA cm-2 with low overpotentials in Li symmetric cells. Furthermore, the stable cyclability and improved rate capability can be realized in a full cell using LiCoO2 over 300 cycles. When decoupling the irreversible reactions of the cathode using Li4 Ti5 O12 , stable cycling performance over 1000 cycles can be achieved at a practical current density of ≈2 mA cm-2 .

We first demonstrate a facile and effective strategy to directly deposit a Nafion nanoweb onto a sulfur cathode to address the challenges underlying in Li–S batteries. The Nafion nanoweb not only blocks the diffusion of polysulfides by electrostatic repulsion but also allows fast Li-ion exchange with the sulfur cathode through the selective protection layer. The Nafion nanoweb-sulfur cathode retained an excellent cycle performance over 200 cycles and delivered an improved rate capability, as compared to a sulfur cathode and a Nafion layer-sulfur cathode.

The development of bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has recently attracted significant attention. Transition metal-based electrocatalysts have demonstrated a highly promising catalytic performance in electrochemical HER or OER. Moreover, their electrocatalytic performance can be further improved using a self-supported structure of the electrocatalyst, owing to strong physicochemical contact between the catalyst and current collector. In this context, we propose vanadium-incorporated cobalt phosphide (CoVP) self-supported catalysts on carbon cloth (CoVP@CC) as highly efficient bifunctional electrocatalysts for alkaline HER and OER. In CoVP@CC, V plays a crucial role in modulating the surface electronic structure of the self-supported CoP nanosheets, leading to excellent catalytic activity in both HER and OER. The self-supported CoVP@CC demonstrates a promising overall water-splitting performance, requiring only 1.61 V to afford a current density of 10 mA cm−2.

Metal-based frameworks are developed for lithium metal batteries due to their effective suppression of the lithium dendritic growth. However, the use of appealing metals such as copper (Cu), the best current collector in batteries, are still limited owing to lithiophobicity. Here, we report a facile lithiophilic surface treatment of metal- and metallic compound-based scaffolds via gas nitriding. Due to nitride anion (N3−) from ammonia (NH3) gas that can bond to almost all elements and form lithiophilic binary nitrides, the gas nitriding on a pristine Cu foam and a Cu(OH)2 nanorods grown Cu foam results in a formation of lithiophilic Cu3N film on the surface without a noticeable structural change. After lithium melt infusion, symmetric cells assembled with two types of lithium hosts show stable structural stability and a smooth Li plating/stripping behavior without a dendritic growth of lithium. Particularly, a full cell test demonstrates that lithiated Cu3N nanorods grown Cu foam exhibits enhanced electrochemical performances including capacity, rate capability, and cycle performance compared to a bare Li foil. Our findings demonstrate the gas nitriding is a powerful tool for lithiophilic surface treatment of metals and metallic compounds with various dimensions and sizes from micro to nanoscale.

Transition metal layered double hydroxides (LDHs) have received much attention as high-performance oxygen evolution reaction (OER) catalysts due to their large number of active sites with favorable adsorption/desorption energies for intermittent reactants. However, the relatively sluggish charge transfer kinetics of transition metal LDHs due to their intrinsically low conductivity often hinders their use in practical applications as high-performance water oxidation catalysts. Here, we disclose a novel strategy of metalloid incorporation into transition metal LDHs, allowing us to simultaneously optimize surface electronic configuration and charge transfer between adsorbed reactants and catalyst surface. Importantly, incorporated metalloid can enhance the density of states (DOS) near the Fermi level and alter the nature of the chemical bonds in the catalytically active atoms, resulting in fast reaction kinetics. Thus, metalloid incorporation into transition metal LDHs can substantially improve the overall reaction kinetics and thermodynamics for water oxidation due to a large number of active sites and high conductivity, boosting OER performance of transition metal LDHs. The metalloid-incorporated transition metal LDHs far outperform their counterpart transition metal LDHs and even the noble metal catalyst RuO2.

Herein, holey, thin, conductive nickel substituted cobalt molybdenum boride (Ni-CMB) nanosheets have been designed to obtain superior electrochemical HER performance with small overpotential of 69 mV at 10 mA cm-2 current density and lower Tafel slope of 76.3 mV dec-1 in alkaline medium. Incorporation of Ni leads to improved conductivity and favorable hydrogen adsorption on Mo sites, which collectively yield efficient electrocatalytic H2 production from Ni-CMB catalyst. The ultrathin nature (thickness = 5.0 nm) of the designed material expectedly helps to attain high exposure of active sites and facile charge transportation through the nanosheets. Additionally, the decorated mesopores (average size = 3.86 nm) on nanosheets have benefitted towards faster electrolyte diffusion, easy gas escape from catalyst surface to support high electrocatalytic performance. Finally, well-maintained morphology of the sample and evolution of HER active sites in the material have guaranteed long-term, sustainable hydrogen production even at high current densities, which clearly demonstrate its superiority over an expensive electrolyzer (Pt-C) in alkaline water.

H0.43Ti0.93Nb1.07O5 engineered with large d-spacing of ~8.3 Å and two-dimensional ionic channels enables easy Na+ ion uptake., Key issues for Na-ion batteries are the development of promising electrode materials with favorable sites for Na+ ion intercalation/deintercalation and an understanding of the reaction mechanisms due to its high activation energy and poor electrochemical reversibility. We first report a layered H0.43Ti0.93Nb1.07O5 as a new anode material. This anode material is engineered to have dominant (200) and (020) planes with both a sufficiently large d-spacing of ~8.3 Å and two-dimensional ionic channels for easy Na+ ion uptake, which leads to a small volume expansion of ~0.6 Å along the c direction upon Na insertion (discharging) and the lowest energy barrier of 0.19 eV in the [020] plane among titanium oxide–based materials ever reported. The material intercalates and deintercalates reversibly 1.7 Na ions (~200 mAh g−1) without a capacity fading in a potential window of 0.01 to 3.0 V versus Na/Na+. Na insertion/deinsertion takes place through a solid-solution reaction without a phase separation, which prevents coherent strain or stress in the microstructure during cycling and ensures promising sodium storage properties. These findings demonstrate a great potential of H0.43Ti0.93Nb1.07O5 as the anode, and our strategy can be applied to other layered metal oxides for promising sodium storage properties.

Here we report the fabrication of a novel three-dimensional conjugated porous polymer (CPP–P1) developed by a palladium-catalysed Sonogashira poly-condensation reaction. The solid polymer was thoroughly characterized by 13C cross-polarization solid-state NMR and X-ray photoelectron spectroscopy (XPS). The pristine nitrogen-containing CPP was explored as an electrocatalyst for the oxygen reduction reaction (ORR) in alkaline media 0.1 M KOH. We observed that in the case of pristine polymer CPP-P1 oxygen reduction occurs through four electron transfer pathway with excellent stability and good tolerance to methanol. The detailed molecular-level structure for oxygen reduction and mode of oxygen binding site to the polymer was explained by density functional theory (DFT) calculation.

In spite of the promising future of the Sodium (Na)-ion batteries (NIBs), it still suffers with low specific capacity and stability mostly owing to the slow kinetics associated with Na ion. In this regard, transition metal sulfides (TMSs) are considered to be one of the best anode materials that can efficiently store Na ions not only owing to their graphite-like layered structure but also through conversion reactions facilitated by their multi-oxidation states. However, the poor cyclic stability of these TMSs attributed to the low electronic conductivity of the TMSs hinders the practical use. Therefore, understanding on an optimized mass loading (or physical dimensions) and configuration of such active electrode material are essential to improve the kinetics associated with Na-ion and electron pathway. To study this, plasma-enhanced atomic layer deposition (PEALD) is employed to grow WS2 using tungsten hexacarbonyl [W(CO)6] and H2S plasma as a precursor and reactant, respectively. The thin films of WS2 deposited directly on stainless steel coin with varying ALD cycles (200–600) are then tested as anode in NIBs without any binder or conducting carbon. Two-stage growth mode is observed with increasing number of ALD cycles which leads to WS2 nano-flakes formation on top of a two-dimensional film of the same. Reversible conversion and intercalation reactions from the cyclic voltammetry measurements are evident for the electrochemical stability of these pristine-WS2 films. While the highest areal capacity of ∼58.8 μAh/cm2 at a current density of 50 μA/cm2, after 50 charge-discharge cycles, is achieved with 400 ALD cycles, the highest capacity retention (∼72.5%) is observed for the film deposited with minimum (200) ALD cycles under same conditions. However, the capacity as well as its retention degrades drastically when the number of ALD cycles is further increased beyond 400. In this study, we address a critical issue associated with WS2 as an anode material for NIBs which should be similarly true for other TMSs as well.

A new method of fabricating translucent alumina brackets using powder injection molding (PIM) is reported. Alumina powder was mixed with MgO, La 2 O 3 , and Y 2 O 3 to control grain size and porosity. The powders were mixed with a binder consisting of a mixture of paraffin wax and polyethylene in a 1:1 ratio to make feedstock for injection molding. The total amount of binder was limited to 14 wt% to minimize shrinkage and cracking after sintering. After injection molding, debinding was performed using the wicking method and samples were sintered in a vacuum at 1700 °C to achieve high density. Ultimately, translucent corundum was fabricated. The sintering additives resulted in a decrease in porosity and an improvement in translucency by promoting grain growth during pressure-less sintering. After sintering, Vickers hardness, bending strength, density, and transmittance of the fabricated parts were measured to show that those values were comparable to those of the commercially available dental brackets. Therefore, the translucent alumina block was successfully fabricated using PIM method to be potentially used as a dental bracket.

The development of electrochemical devices for renewable energy depends to a large extent on fundamental improvements in catalysts for oxygen evolution reactions (OERs). OER activity of transition metal sulfides (TMSs) can be improved by compositing with highly conductive supports possessing a high surface-to-volume ratio, such as reduced graphene oxide (rGO). Herein we report on the relationship between synthetic conditions and the OER catalytic properties of TMSs and rGO (TMS–rGO) hybrids. Starting materials, reaction temperature and reaction time were controlled to synergistically boost the OER catalytic activity of TMS–rGO hybrids. Our results showed that (i) compared with sulfides, hydroxides are favourable as starting materials to produce the desired TMS–rGO hybrid nanostructure and (ii) high reaction temperatures and longer reaction times can increase physico-chemical interaction between TMSs and rGO supports, resulting in highly efficient OER catalytic activity.

Lithium sulfur (Li-S) batteries have drawn much attention as next-generation batteries because of their high theoretical capacity (1672 mAh g−1), environmental friendliness and low cost. However, several critical issues, which are mainly associated with the polysulfide shuttling effect, result in their poor electrochemical performance. Carbon-modified separators have been introduced to attempt to address these systemic challenges. However, this approach focused only on the suppression of dissolved polysulfides on the cathodic side without considering the further entrapment of polysulfides on the anodic side. In this study, we first designed a multifunctional trilayer membrane comprising a carbon layer and a boron nitride (BN) layer to facilitate the electrochemical performance of Li-S batteries and protect the Li anode from unexpected side reactions. When a BN-carbon separator was employed, the sulfur cathode delivered stable capacity retention over 250 cycles and an excellent specific capacity (702 mAh g−1) at a high current density (4 C). The BN-carbon separator also facilitated the uniform plating/striping of Li and, thus, suppressed the severe growth of dendritic Li on the electrode; this led to the stable operation of the Li anode with a high Coulombic efficiency and improved cycling performance. A membrane that enhances the performance of high-capacity lithium–sulfur batteries has been developed by a team in Korea and the USA. Adding sulfur to lithium-ion batteries is predicted to improve their storage capacity, but in practice the number of times a battery can be charged and discharged is limited by the formation of compounds called polysulfides, which corrode the lithium anode. Now, Ungyu Paik from Hanyang University and co-workers have shown that using a three-layer membrane made of carbon, a polymer and boron nitride can limit this problem. Unlike previous carbon-modified separators, the trilayer membrane both suppresses dissolution of polysulfides on the cathode side and protects the anode from unwanted side reactions. The separator enabled the sulfur cathode to maintain a stable capacity over 250 cycles. The BN-carbon separator was first demonstrated as a multifunctional trilayer membrane to facilitate the better electrochemical performances of Li-S batteries and protect a Li anode from unexpected side reactions. Unlike the previous approach to block the polysulfides only within the cathodic side, the concept of placing a BN interlayer on anodic side showed promising results in achieving high electrochemical performances of Li-S batteries and stable operations of lithium metal at a high current density.