Search

This article examines the impact of additions or deletions to the ESG index on stock return comovement in the Korean stock market over a 10-year period from 2010 to 2019, using eight ESG indices. Our results show that firms added to the ESG index experience an increased beta, both in the short- and long-term, while deleted stocks from the ESG index show significant decreases in beta. The return comovement following ESG index changes identifies not only the initial ESG index but also the new ESG index launched in 2015. However, comovement to the ESG index inclusion is more pronounced with the initial ESG index. Moreover, we find that comovement largely accounts for the trading behavior of individual investors and is partially related to foreign investors’ trading. Our findings are consistent with previous evidence on comovement with changes in major market index constituents and suggest that ESG index revision by considering non-financial factors also induces stock return comovement. These results can be explained by the investor sentiment-based views.

Current hydrogel strain sensors have met assorted essential requirements of wearing comfort, mechanical toughness, and strain sensitivity. However, an increment in the toughness of a hydrogel usually leads to an increase in elastic moduli that could be unfavorable for wearing comfort. In addition, traits of biofriendly and sustainability require synthesis of the hydrogels from natural polymer-based networks. We propose a novel strategy to fabricate an ionic conductive organohydrogel from natural biological macromolecule "gelatin" and polyacid "tannic acid" to resolve these challenges. Tannic acid modified the structure of the gelatin network in the ionic conductive organohydrogels, that not only led to an increase in toughness accompanying a decrease in elastic moduli but also headed to higher strain sensitivity and tunability. The proposed methodology exhibited tunable tensile modulus from 27 to 13 kPa, tensile strength from 287 to 325 kPa, elongation at fracture from 510 to 620%, toughness from 500 to 550 kJ/m

Ni3FeN and a N-doped carbon shell have improved electrical conductivity with the electronic structure modified through the extra electrons of nitrogen. Ni3FeN@NC in the water splitting reaction provide excellent electrochemical catalytic properties.

We examines whether share pledges by controlling shareholders influence a firm’s cost of debt. We also investigate whether the relationship between share pledges and the cost of debt stems from the managerial risk-taking incentives or pursuing the private benefits of controlling shareholders. We make three major findings. First, we find the cost of debt is higher in firms with share pledges than in firms without share pledges. Furthermore, we identify a positive relationship between the cost of debt and the level of share pledges. Second, we find that there is no increased corporate financial leverage or investment activities in firms with share pledges. Finally, our empirical evidence demonstrates that the positive relationship between share pledges and cost of debt is more pronounced for lower foreign institutional investor stakes or higher controlling shareholders ownership. Overall, the results indicate that share pledges by controlling shareholders negatively affect the cost of debt. However, the effect of share pledges on the cost of debt is differently influenced by a firm’s ownership structure. Our findings suggest that share pledges induce stockholder-bondholder conflict, and the bondholder requires more risk premium due to the decrease of firm value.

The role of a self-assembled monolayer obtained by vacuum deposition of 4-aminopyridine (4-AP), a small organic molecule having amine and pyridine groups, as a metal nucleation inducer and adhesion promoter was verified, and the applicability was evaluated. 4-AP deposited to an extremely thin thickness effectively changed the substrate surface properties, increasing the nucleation density of silver (Ag) more than 3 times and eventually forming a more transparent, low-resistance Ag thin film. The optical transmittance of the Ag thin film, which was less than 60% when 4-AP was not applied, could be increased to about 77% by simply applying 4-AP, and the electrical resistance could be lowered from 37 to 14 Ω/square at the same time. Transmittance could be further improved to higher than 90% by depositing an antireflection layer for use as a transparent Ag electrode. It was also verified that 4-AP not only serves as a nucleation inducer but also contributes to improving interfacial adhesion. The Ag transparent electrode using 4-AP provided the improved performance of the organic light-emitting device due to higher transmittance, lower resistance, and surface roughness. Small organic molecules including functional groups that can be vacuum deposited, such as 4-AP, are expected to be used as surface pretreatment materials for various depositions because they can be easily patterned and can efficiently modify the surface even with extremely thin thickness.

Large-area graphene synthesized by a chemical vapor deposition (CVD) method is promising for a flexible, stretchable transparent electrode but suffers from structural defects such as grain boundaries, which causes to degrade its physical properties. Recently, preparation methods of large-scale growth templates for single-crystalline graphene (SCG) were reported, but the macroscopic properties of SCG have not been adequately examined yet. Here, an SCG-based flexible, stretchable graphene transparent electrode is successfully demonstrated, which shows superior optoelectrical, electromechanical, and barrier properties compared to polycrystalline graphene (PCG)-based transparent electrodes. The result exhibits the grain boundary effect of graphene on soft substrates on a macroscopic scale and a great promise toward realizing a tremendous performance improvement of graphene-based flexible transparent electrodes on a large scale.

This paper examines whether insider trade clustering is associated with large stock return variations (i.e. crash or jump risk) in Korea. To investigate private information of insider trade cluster...

The oxygen evolution reaction (OER) at anode requires high overpotential and is still challenging. The metallic core-oxyhydroxide layer structure is an efficient method to lower an overpotential. We synthesized Fe rich FeCo core-Co rich FeCo oxyhydroxide layer with a different particle size of 173 nm, 225 nm, and 387 nm (FeCo 173, 225, 387) through a difference in the reduction rate of Fe/Co precursors using facile modified polyol synthesis. To investigate the effect of conductivity, CoFe2O4 nanoparticles of 80–130 nm were synthesized. Among samples, FeCo 173 showed remarkable catalytic performance of 316 mV at a current density of 10 mA/cm2 in 0.1 M KOH compared to RuO2 (408 mV), FeCo 225 (323 mV), FeCo 387 (334 mV), CoFe2O4 (382 mV). Moreover, FeCo 173 showed good stability for 60,000 s while RuO2 showed a gradual increase in overpotential to maintain 10 mA/cm2 after 15,000 s in chronopotentiometry. The excellent performance was attributed to Fe-rich metallic core, a small amount of Fe doping into CoOOH, and the synergic effect between the active site of Co rich FeCoOOH and conductive Fe rich metallic core. Following this result, it shows that the use of such FeCo electrodes has advantages in the production of hydrogen via electrochemical water oxidation.

With rapid advances in flexible electronics, transparent conductive electrodes (TCEs) have also been significantly developed as alternatives to the conventional indium tin oxide (ITO)-based material systems that exhibit low mechanical flexibility. Nanomaterial-based alternating materials, such as graphene, nanowire, and nanomesh, exhibit remarkable properties for TCE-based applications, such as high electrical conductivity, high optical transparency, and high mechanical stability. However, these nanomaterial-based systems lack scalability, which is a key requirement for practical applications, and exhibit a size-dependent property variation and inhomogeneous surface uniformity that limit reliable properties over a large area. Here, we exploited a conventional ITO-based material platform; however, we incorporated a transparent molecular adhesive, 4-aminopyridine (4-AP), to improve mechanical flexibility. While the presence of 4-AP barely affected optical transmittance and sheet resistance, it improved interfacial adhesion between the substrate and ITO as well as formed a wavy surface, which could improve the mechanical flexibility. Under various mechanical tests, ITO/4-AP/poly(ethylene terephthalate) (PET) exhibited remarkably improved mechanical flexibility as compared with that of ITO/PET. Furthermore, ITO/4-AP/PET was utilized for a flexible Joule heater application having spatial uniformity of heat generation, voltage-dependent temperature control, and mechanical flexibility under repeated bending tests. This molecular adhesive could overcome the current limitations of material systems for flexible electronics.

Demands for electromagnetic interference (EMI) shielding materials with small thickness, lightweight, and flexibility have been increasing to satisfy rapid advances in flexible and wearable electronics. Various EMI shielding materials have been explored and improved to meet these requirements for assist in the miniaturization of electronic devices, but is still a challenging task. In this work, we describe a simple and effective strategy for the fabrication of flexible nanoporous silver (Ag) membranes with unprecedented high effectiveness for EMI shielding. The nanoporous Ag membranes were fabricated by sequential vacuum filtration of a dispersion containing bacterial cellulose and Ag nanoparticles, which were followed by a hot-pressing process. The membrane with nanoporous Ag thickness of 1.2 μm exhibits high EMI shielding effectiveness (SE) of ˜53 dB (99.9%) in 0.5 − 18.0 GHz and an unprecedented high absolute EMI SE of 85,462 dB·cm2 g–1, which could be attributed to the nanoporous structures leading to an increasing of multiple reflections of the electromagnetic waves. In addition, the nanoporous Ag membrane showed highly stable electro-mechanical durability and fast heat dissipation properties, enabling desired EMI shielding performance for the wide range applications.

Purpose To analyze and draw conclusions from the “Framework for ‘Investment Contract’ Analysis of Digital Assets” (the “Framework”), released by the US Securities and Exchange Commission (the “SEC”) on April 3, 2019, and the SEC’s corresponding no-action letter to TurnKey Jet, Inc. (“TKJ”), which is the SEC’s first no-action letter publicly agreeing with the view that the digital asset described therein is not a security. Design/Methodology/Approach Explains how the Framework assists market participants in analyzing whether a digital asset is a security, by applying the Howey factors for identifying an investment contract. Discusses the SEC’s TKJ Letter, highlighting the factors the SEC emphasized in its analysis of the Framework. Findings While largely reiterating prior guidance, the Framework provides a helpful overview of the SEC’s views on when a digital asset is a security and how to properly analyze the prongs of Howey with respect to digital assets. The Framework also leaves certain important questions unanswered, including, for example, whether digital assets distributed by means of a so-called “Airdrop” are securities under the Framework, and the extent to which the Framework is meant to interact with digital assets that were issued or otherwise operate on platforms that are primarily overseas. Originality/Value Expert guidance from lawyers with broad experience in financial services, securities, investment funds, derivatives, and digital assets regulation and compliance.

We report successfully synthesizing two-dimensional (2D) and nanocrystalline (NC) Fe2Ni2N/rGO nanohybrid sheets (NHSs) via ammonolysis of as-prepared 2D Ni2.25Fe0.75[Fe(CN)6]2/rGO precursors. We co...

Although chemotherapy is mostly performed by direct injection of the chemotherapeutic agents systemically, this approach can cause undesirable side effects in normal tissues and lacks targeting efficiency. In this study, we have developed a micron-sized, bead-type multifunctional anticancer-drug carrier that can be injected in the vicinity of a lesion using a syringe. The multifunctional anticancer-drug carrier bead was fabricated by incorporating functional nanomaterials, such as near-infrared (NIR)-responsive gold nanorod (GNR) and superparamagnetic iron oxide nanoparticles (IONP) that work as a magnetic resonance imaging (MRI) contrast agent, into an alginate hydrogel bead. The carrier bead containing GNR and IONP was spherical, with an average size of 362.2 ± 22.7 µm. These multifunctional anticancer-drug carrier beads could successfully release doxorubicin (Dox) into the external environment upon irradiation with an NIR laser. The laser responsive on-demand release profile demonstrated well-controlled and sustained release of Dox, and the effectiveness of this drug delivery system can be confirmed in vitro by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. Additionally, the control experiments evidenced that the thermal effect of GNR was insignificant and the cytotoxic action of Dox was expressed only after irradiation with the NIR laser. The multifunctional anticancer-drug carrier beads can be precisely monitored with the MRI T2 imaging mode.

본 연구는 최대주주, 주요주주 등과 같은 기업 내부자의 주식담보대출이 주가급락위험에 미치는 영향에 대해 분석한다. 내부자의 주식담보대출은 주주가 개인적으로 행하는 차입의사결정임에도 불구하고 대리인문제를 야기함으로써 기업가치를 하락시키거나 소액주주의 부에 영향을 미칠 가능성이 있다. 본 연구의 주요 분석결과를 요약하면 다음과 같다. 첫째, 주식담보대출과 주가급락의 관련성은 시장별로 상이한 결과를 보인다. 우선, 유가증권시장은 주식담보대출이 주가급락에 일련의 영향을 미치지 않고 있다. 반면, 코스닥시장의 경우에는 내부자의 주식담보대출이 존재하는 기업에서 주가 급락위험이 보다 높게 나타나며, 내부자의 총 주식담보대출비율이나 주식담보대출을 받은 내부자의 인원수가 증가할수록 주가급락위험은 유의미하게 증가한다. 둘째, 코스닥시장에서 내부자들이 주식담보대출을 받은 최초연도에 주가급락위험이 더 높게 나타나며, 주식담보대출비율 변동과 주가 급락위험은 유의적인 양(+) 관련성을 보인다. 셋째, 코스닥시장에서 주식담보대출 기업의 재량적 발생액이 증가할수록 주가급락위험은 보다 높게 나타난다. 종합하면, 내부자가 주식담보대출을 받는 경우에 기업의 주가급락위험은 증가한다. 하지만, 주식담보대출과 주가급락위험의 관련성은 정보비대칭이 높고 재무적 불투명성이 큰 코스닥시장에서 강건한 결과를 보인다. 즉, 코스닥시장에서 행해지는 내부자의 주식담보대출은 소액주주의 부를 저해하는 등 대리인문제를 심화시킬 가능성이 있다. 따라서 주식담보대출과 관련한 제반적인 규정을 견고히 함으로써 주주의 개인적인 차입행태가 기업 및 이해관계자에 미치는 영향을 최소화 할 필요가 있다.

The suitable materials, metal nitrides, are a promising class of electrocatalyst materials for a highly efficient oxygen evolution reaction (OER) because they exhibit superior intrinsic conductivity and have higher sustainability than oxide-based materials. To our knowledge, for the first time, we report a designable synthesis of three-dimensional (3D) and mesoporous Co3N@amorphous N-doped carbon (AN-C) nanocubes (NCs) with well-controlled open-framework structures via monodispersed Co3[Co(CN)6]2 Prussian blue analogue (PBA) NC precursors using in situ nitridation and calcination processes. Co3N@AN-C NCs (2 h) demonstrate better OER activity with a remarkably low Tafel plot (69.6 mV·dec−1), low overpotential of 280 mV at a current density of 10 mA·cm−2. Additionally, excellent cycling stability in alkaline electrolytes was exhibited without morphological changes and voltage elevations, superior to most reported hierarchical structures of transition-metal nitride particles. The presented strategy for synergy effects of metal-organic frameworks (MOFs)-derived transition-metal nitrides-carbon hybrid nanostructures provides prospects for developing high-performance and advanced electrocatalyst materials.

Herein, we demonstrate that two-dimensional (2D) CdSeS quantum dot monolayers (QDM) can strongly influence efficient charge transport and charge separation, improving the performance of inverted polymer solar cells (iPSCs). Also, for the first time we report the electronic band structure of CdSeS and CdSeS@ZnS QDs and an effective approach to apply the 2D QDM as an effective electron transport layer in iPSCs from work function studies. The iPSCs with the 2D CdSeS QDM showed maximum power conversion efficiencies of 8.83%, which were 26% higher than the reference. Ultraviolet photoelectron spectroscopy and time-correlated single photon counting (TCSPC) measurements were performed to confirm the charge separation and electron transport behavior in the iPSCs with 2D QDMs. The PL decay time of the iPSCs with the CdSeS QDM at 720 nm was ∼60 ps, which is much faster than that of the iPSCs without the 2D QDM. The enhanced photovoltaic performance of the iPSCs with the 2D CdSeS QDM can be attributed to the effective charge separation and electron transport performance due to the high built-in voltage and fast exciton decay time from the 2D QDM.

The development of efficient and stable bifunctional catalysts that outperform noble metal catalysts is a crucial task and an ongoing challenge for sustainable water electrolysis. In this work, large-size-exfoliated MXene sheets render a flat and flexible platform for the decoration of Co(OH)F, CoP and Co7Se8, allowing them to exhibit high electrocatalytic performances; thanks to the maximized surface area and conductivity. CoP/MXene shows enhanced oxygen evolution reaction (OER) activity, with substantially lower overpotential (η = 230 mV) at 10 mA cm−2 compared to those of IrO2 (300 mV). Furthermore, a hybrid bifunctional electrode (CoP/MXene//CoP/MXene) exhibits highly stable and efficient overall water splitting performance (1.56 V@10 mA cm−2) as compared to the benchmark electrode couple IrO2/C//Pt/C (1.62 V@10 mA cm−2) in alkaline solution. Furthermore, we elucidate the oxidation process of the anion components (P and Se) of the hybrid catalysts under OER conditions and verify their significant influence on the activity and stability. Notably, the surface oxidation of CoP/MXene results in a POx-enriched Co–OOH/CoP/MXene hybrid, which enables retention of consistent activity and stability. On the other hand, SeOx deposition on the Co–OOH/Co7Se8/MXene surface significantly deteriorates the activity and stability of the catalyst. These results not only highlight the insight on the correlation between oxidized anion species and the intrinsic activity of hybridized electrocatalysts but also impart the systematic synthetic design of MXene-supported catalysts with high water-splitting efficiency.

Non-volatile memory (NVM) devices based on three-terminal thin-film transistors (TFTs) have gained extensive interest in memory applications due to their high retained characteristics, good scalability, and high charge storage capacity. Herein, we report a low-temperature (&lt, 100 °C) processed top-gate TFT-type NVM device using indium gallium zinc oxide (IGZO) semiconductor with monolayer gold nanoparticles (AuNPs) as a floating gate layer to obtain reliable memory operations. The proposed NVM device exhibits a high memory window (ΔVth) of 13.7 V when it sweeps from −20 V to +20 V back and forth. Additionally, the material characteristics of the monolayer AuNPs (floating gate layer) and IGZO film (semiconductor layer) are confirmed using transmission electronic microscopy (TEM), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) techniques. The memory operations in terms of endurance and retention are obtained, revealing highly stable endurance properties of the device up to 100 P/E cycles by applying pulses (±20 V, duration of 100 ms) and reliable retention time up to 104 s. The proposed NVM device, owing to the properties of large memory window, stable endurance, and high retention time, enables an excellent approach in futuristic non-volatile memory technology.

Developing high-efficiency and low-cost oxygen-evolving electrodes in anion exchange membrane (AEM) water electrolysis technology is one of the major challenges. Herein, it is demonstrated that the surface corrosion of a conventional Ni foam electrode in the presence of Fe3+ and V3+ cations can transform it into an electrode with a high catalytic performance for oxygen evolution reaction (OER). The corroded electrode consists of a ternary NiFeV layered double hydroxide (LDH) nanosheet array supported on the Ni foam surface. This NiFeV LDH electrode achieves an OER current density of 100 mA cm-2 at an overpotential of 272 mV in 1 m KOH, outperforming the IrO2 catalyst by 180 mV. Density functional theory calculations reveal that the unique structure and the presence of vanadium in NiFeV LDH play a key role in achieving improved OER activity. When coupled with a commercial Pt/C cathode catalyst, the resulting AEM water electrolyzer achieves a cell current density as high as 2.1 A cm-2 at a voltage of only 1.8 Vcell in 1 m KOH, which is similar to the performance of the proton exchange membrane water electrolyzer obtained from the IrO2 and Pt/C catalysts pair.

Forecasting of LME (London Metal Exchange) nickel prices remains an interesting topic but lacks consensus. This study aims to fill knowledge gaps by demonstrating the announcement effect of export bans by the Indonesian government. This article focuses on Indonesia because Indonesia produces more than 60% of global nickel ore. We identified the sequence of two episodes in which Indonesian export bans of nickel ore appeared to increase LME nickel prices. The impact of the Indonesian export ban in 2014 is somewhat larger than that of 2019. The shock on the LME nickel market in 2014 was sustained for a while after the ban was implemented. We believe that this is the first export ban that has had unexpected effects within the market.

The motivation of this paper is to identify the effect of treatment charge (TC) on LME (London Metal Exchange) copper prices. It is a fundamental variable as a supply side factor, because it is related to the smelting process and reflects the level of concentrates market tightness. To examine this question carefully, the regression model is applied. This paper finds a statistically significant negative link between TC and LME copper prices. It is found that a 10% increase in TC of copper decreases in copper return by 1.8%. Subsequently, the vector autoregression (VAR) model is introduced to consider the impact of TC to copper prices as a permanent effect. It is found that the negative impact of the TC to copper returns dies out quickly. The statistical estimation in this article will provide a good reference for future study.

We describe a facile chemical transformation method to produce small iron oxyhydroxide (FeOOH) nanoparticles for application in electrochemical oxygen evolution reaction (OER). In this work, iron alkoxide nanosheets were synthesized by heating a mixture of iron nitrate, ethylene glycol (EG), and oleylamine (OAm), which transformed to FeOOH nanoparticles with sizes less than 10 nm upon alkali treatment in aqueous KOH solution. These FeOOH nanoparticles exhibited much enhanced OER activity compared with that of both commercial FeOOH powders and IrO2 catalyst, as well as good stability in high pH conditions.

Silver (Ag) nanowires (NWs) are promising building blocks for flexible transparent electrodes, which are key components in fabricating soft electronic devices such as flexible organic light emitting diodes (OLEDs). Typically, Ag NWs have been synthesized using a polyol method, but it still remains a challenge to produce high-aspect-ratio Ag NWs via a simple and rapid process. In this work, we developed a modified polyol method and newly found that the addition of propylene glycol to ethylene glycol-based polyol synthesis facilitated the growth of Ag NWs, allowing the rapid production of long Ag NWs with high aspect ratios of about 2000 in a high yield (∼90%) within 5 min. Transparent electrodes fabricated with our Ag NWs exhibited performance comparable to that of an indium tin oxide-based electrode. With these Ag NWs, we successfully demonstrated the fabrication of a large-area flexible OLED with dimensions of 30 cm × 15 cm using a roll-to-roll process.

Hybrid organic-Red-Green-Blue (RGB) color quantum dots were incorporated into consolidated p(polymer)-i(RGB quantum dots)-n(small molecules) junction structures to fabricate a single active layer for a light emitting diode device for white electroluminescence. The semiconductor RGB quantum dots, as an intrinsic material, were electrostatically bonded between functional groups of the p-type polymer organic material core surface and the n-type small molecular organic material shell surface. The ZnCdSe/ZnS and CdSe/ZnS quantum dots distributed uniformly and isotropically surrounding the polymer core which in turn was surrounded by small molecular organic materials. In the present study, we have identified the mechanisms of chemical synthesis and interactions of the p-i-n junction nanocell structure through modeling studies by DFT calculations. We have also investigated optical, structural and electrical properties along with the carrier transport mechanism of the light emitting diodes which have a single active layer of consolidated p-i-n junction nanocells for white electroluminescence.

Pt, a representative electrocatalyst for the oxygen reduction reaction (ORR), has suffered from high cost and poor stability, and thus it is essential to develop alternative electrocatalyst with a high catalytic activity comparable to Pt. Herein, we propose a rationally designed metal-free electrocatalyst with exposed active sites using an N, P, and S ternary-doped and graphene-incorporated porous carbon foam. We developed a novel template-free synthetic approach wherein the electrostatically-mediated complexation of graphene oxide (GO) with 2-aminothiazole (2AT) and branched polyethylenimine (PEI) in the presence of phytic acid (PA) was first induced, followed by a carbonization process to drive the formation of a three-dimensionally interconnected porous carbon foam. The resulting electrocatalyst exhibited a high pore volume and greatly extended specific surface area along with exposed active sites. Benefiting from these properties, the synthesized ternary-doped carbon foam displayed an outstanding electrocatalytic activity for the oxygen reduction ORR through four-electron transfer pathways. We observed that the remarkably improved ORR performance of the synthesized materials manifested an onset and a half-wave potential, mostly close to those of the commercially available ORR electrocatalyst of 20 wt% Pt/C while securing a greater stability in alkaline media.

Transition metal nitrides have received a great deal of attention as highly efficient OER catalysts due to their excellent electrical conductivity, which grants them lower overpotential values than precious metal oxide catalysts (RuO2, IrO2, etc.). Herein, we report the characteristics of Nickel-Iron nitrides, alloy heterogeneous nanostructures (Ni2Fe2N, Ni2Fe2N/Ni3Fe, Ni3Fe/Ni2Fe2N), and amorphous N-doped carbon shells differing only in nitridation temperature. Heterogeneous Nickel-Iron nitrides and alloy with amorphous N-doped carbon shells showed superior OER performance such as a low overpotential value of 251 mV at current density of 10 mA/cm2, Tafel slope of 35.0 mV/dec, and great stability even after 24 h. Additionally, this study accurately identified that the heterogeneous nanostructure and amorphous N-doped carbon shell improve the catalytic properties and durability of the Nickel-Iron nitrides and alloy nanoparticles. The morphological control strategy used to produce the heterogeneous nanostructure and amorphous N-doped carbon shell can be applied to improve electrochemical properties or encapsulation in strong alkaline solution.

Developing high-efficiency and cost-efficient electrodes for hydrogen and oxygen evolution reactions (HER and OER respectively) is a major challenge in water electrolysis technology. We developed a chemical transformation route that can produce both high-performance OER and HER electrodes by corrosion of a Ni foam and subsequent phosphidation process, which generated ternary NiFeCo layered double hydroxide (LDH) and phosphide nanosheets supported on the foam, respectively. Because of their compositions and high electrical conductivities, these ternary LDH and phosphide electrodes exhibited remarkably high activities for OER and HER, respectively, outperforming most of other catalysts reported to date. An alkaline water electrolyzer based on these electrodes achieved a current density of 10 mA/cm2 at an only 1.47 Vcell. In addition, anion exchange membrane water electrolyzer based on these electrodes reached a current density of 500 mA/cm2 at an only 1.75 Vcell.

Future energy conversion that will replace fossil energy can be expected from oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) among high-performance bi-functional electrocatalysts. Herein, a hybrid material, CoFe@N-C/MNGF containing an N-doped carbon shell on the surface of CoFe alloy nanoparticles and three-dimensional (3D) mesoporous N-doped graphene foam with exposed active sites as an electron transfer substrate has been successfully synthesized to replace noble-metal catalysts. The electrocatalytic performance of CoFe@N-C/MNGF demonstrates better OER activity in 0.1 M KOH alkaline electrolyte with a remarkably low overpotential of 330 mV and low Tafel plot 130.6 mV⋅dec-1 at a current density of 10 mA⋅cm−2. And CoFe@N-C/MNGF has considerable ORR performance in terms of catalyst activity, electron transfer number and stability, which suggests its usefulness as a suitable replacement for ORR catalysts based on noble-metal used for cathode electrode of alkaline fuel cells. In particular, it showed a potential of 0.87 V in 0.1 M KOH alkaline electrolyte and low Tafel plot 71.7 mV⋅dec-1 at 5 mA⋅cm−2 and the number of electrons (n) transferred was estimated to be 2.1–3.61 at 0.15 to 0.35 V. Based on these results, this study provides new insights into a cost-efficient non-noble metal bi-functional electrocatalyst.

Developing high-performance and low-cost oxygen-evolving electrodes is one of major challenges in electrochemical water splitting technology. We demonstrated that the aqueous-phase corrosion of a conventional Ni foam in the presence of exotic Fe3+ cations can directly transform it into an electrode with high catalytic activity and stability for oxygen evolution reaction (OER). The surface of the corroded electrode consisted of densely packed, small Ni0.75Fe2.25O4 nanoparticles with sizes less than 5 nm. This electrode required an overpotential of only 192 mV to reach an OER current density of 10 mA/cm2 in 1 M KOH, outperforming the state-of-the-art IrO2 catalyst by 73 mV. Density functional theory calculations revealed that the unique surface structure and iron composition of Ni0.75Fe2.25O4 nanoparticles play a key role in achieving an improved OER activity. When coupled with a Pt/C hydrogen-evolving catalyst, the resulting anion-exchange membrane (AEM) water electrolyzer achieved an overall water-splitting current density as high as 2.0 A/cm2 at a cell voltage of 1.9 V in 1 M KOH, which was 1.7 times that obtained from the IrO2 and Pt/C catalyst pair and also much greater than reported values from other AEM water electrolyzers. By revisiting and exploiting a traditional corrosion process, our work opens a simple, cost-effective, and scalable route to a high-performance OER electrode for efficient AEM water electrolysis.

A patchable triboelectric nanogenerator (TENG) is highly promising for self-powered human-motion detection, but it may undergo repeated stretching/releasing cycles during daily activities of a human, which may lead to mechanical fracture of each component and degradation in electrical output performance of the TENG device. Here, we report a fully stretchable and durable triboelectric nanogenerator (TENG) with gold (Au) nanosheets (NSs) embedded into both PDMS matrix and micropyramid-patterned PDMS. It was found that a new design of the Au NS electrodes dramatically improves the mechanical flexibility and stretchability, enabling to achieve the outstanding output stability of the Au NS electrode-based TENG (Au NS-TENG) during 10,000 cycles of repeated pushing and stretching tests. Our fully stretchable and durable Au NS-TENGs were successfully applied to the hand joints that can be used in the self-powered human-motion detection processes for wearable applications.

The introduction of inorganic nanoparticles into carbon nanotube (CNT) papers can provide a versatile route to the fabrication of CNT papers with diverse functionalities, but it may lead to a reduction in their mechanical properties. Here, we describe a simple and effective strategy for the fabrication of mechanically robust magnetic CNT papers for electromagnetic interference (EMI) shielding and magnetomechanical actuation applications. The magnetic CNT papers were produced by vacuum filtration of an aqueous suspension of CNTs, CoFe2O4 nanoparticles, and poly(vinyl alcohol) (PVA). PVA plays a critical role in enhancing the mechanical strength of CNT papers. The magnetic CNT papers containing 73 wt % of CoFe2O4 nanoparticles exhibited high mechanical properties with Young’s modulus of 3.2 GPa and tensile strength of 30.0 MPa. This magnetic CNT paper was successfully demonstrated as EMI shielding paper with shielding effectiveness of ∼30 dB (99.9%) in 0.5–1.0 GHz, and also as a magnetomechanical actuator i...