Solar-Powered AEM Electrolyzer via PGM-Free (Oxy)hydroxide Anode with Solar to Hydrogen Conversion Efficiency of 12.44.

Water electrolyzers powered by renewable energy are emerging as clean and sustainable technology for producing hydrogen without carbon emissions. Specifically, anion exchange membrane (AEM) electrolyzers utilizing non-platinum group metal (non-PGM) catalysts have garnered attention as a cost-effective method for hydrogen production, especially when integrated with solar cells. Nonetheless, the progress of such integrated systems is hindered by inadequate water electrolysis efficiency, primarily caused by poor oxygen evolution reaction (OER) electrodes. To address this issue, a NiFeCo─OOH has developed as an OER electrocatalyst and successfully demonstrated its efficacy in an AEM electrolyzer, which is powered by renewable electricity and integrated with a silicon solar cell.

Self-Powered Water Splitting of Ni3FeN@Fe24N10 Bifunctional Catalyst Improved Catalytic Activity and Durability by Forming Fe24N10 on Catalyst Surface via the Kirkendall Effect.

Highly efficient water splitting electrocatalyst for producing hydrogen as a renewable energy source offers potential to achieve net-zero. However, it has significant challenges in using transition metal electrocatalysts as alternatives to noble metals due to their low efficiency and durability, furthermore, the reliance on electricity generation for electrocatalysts from fossil fuels leads to unavoidable carbon emissions. Here, a highly efficient self-powered water splitting system integrated is designed with triboelectric nanogenerator (TENG) and Ni3FeN@Fe24N10 catalyst with improved catalytic activity and durability. First, the durability of the Ni3FeN catalyst is improved by forming N, P carbon shell using melamine, polyetherimide, and phytic acid. The catalyst activity is improved by generating Fe24N10 in the carbon shell through the Kirkendall effect. The synthesized Ni3FeN@Fe24N10 catalyst exhibited excellent bifunctional catalytic activity (ηOER = 261.8 mV and ηHER = 151.8 mV) and remarkable stability (91.7% in OER and 90.5% in HER) in 1 m KOH. Furthermore, to achieve ecofriendly electricity generation, a rotation-mode TENG that sustainably generate high-performance is realized using butylated melamine formaldehyde. As a result, H2 is successfully generated using the integrated system composed of the designed TENG and catalyst. The finding provides a promising approach for energy generation to achieve net-zero.

Refractive Index Modulation for Metal Electrodeposition-Based Active Smart Window Applications.

One of the remarkable choices for active smart window technology is adopting a metal active layer via reversible metal electrodeposition (RME). As the metal layer efficiently blocks the solar energy gain, even a hundred-nanometer-thick scale, RME-based smart window has great attention. Recent developments are mainly focused on the various cases of electrolyte components and composition meeting technological standards. As metal nanostructures formed through the RME process involve plasmonic phenomena, advanced analysis, including plasmonic optics, which is beyond Beer-Lambert's law, should be considered. However, as there is a lack of debates on the plasmonic optics applied to RME smart window technology, as research is mainly conducted through an exhaustive process. In this paper, in order to provide insight into the RME-based smart window development and alleviate the unclear part of plasmonic optics applied to the field, finite-difference time-domain electromagnetic simulations are conducted. In total, two extremely low-quality (Cr) and high-quality (Mg) plasmonic materials based on a nanoparticle array are considered as a metal medium. In addition, optical effects caused by the metal active layer, electrolyte, and nanoparticle embedment are investigated in detail. Overall simulations suggest that the effective refractive index is a decisive factor in the performance of RME-based smart windows.

Promoted Overall Water Splitting Catalytic Activity and Durability of Ni3Fe Alloy by Designing N-Doped Carbon Encapsulation.

Combining an electrochemically stable material onto the surface of a catalyst can improve the durability of a transition metal catalyst, and enable the catalyst to operate stably at high current density. Herein, the contribution of the N-doped carbon shell (NCS) to the electrochemical properties is evaluated by comparing the characteristics of the Ni3Fe@NCS catalyst with the N-doped carbon shell, and the Ni3Fe catalyst. The synthesized Ni3Fe@NCS catalyst has a distinct overpotential difference from the Ni3Fe catalyst (ηOER = 468.8 mV, ηHER = 462.2 mV) at (200 and -200) mA cm-2 in 1 m KOH. In stability test at (10 and -10) mA cm-2, the Ni3Fe@NCS catalyst showed a stability of (95.47 and 99.6)%, while the Ni3Fe catalyst showed a stability of (72.4 and 95.9)%, respectively. In addition, the in situ X-ray Absorption Near Edge Spectroscopy (XANES) results show that redox reaction appeared in the Ni3Fe catalyst by applying voltages of (1.7 and -0.48) V. The decomposition of nickel and iron due to the redox reaction is detected as a high ppm concentration in the Ni3Fe catalyst through Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis. This work presents the strategy and design of a next-generation electrochemical catalyst to improve the electrocatalytic properties and stability.

Exceptional Thermochemical Stability of Graphene on N-Polar GaN for Remote Epitaxy.

In this study, we investigate the thermochemical stability of graphene on the GaN substrate for metal-organic chemical vapor deposition (MOCVD)-based remote epitaxy. Despite excellent physical properties of GaN, making it a compelling choice for high-performance electronic and light-emitting device applications, the challenge of thermochemical decomposition of graphene on a GaN substrate at high temperatures has obstructed the achievement of remote homoepitaxy via MOCVD. Our research uncovers an unexpected stability of graphene on N-polar GaN, thereby enabling the MOCVD-based remote homoepitaxy of N-polar GaN. Our comparative analysis of N- and Ga-polar GaN substrates reveals markedly different outcomes: while a graphene/N-polar GaN substrate produces releasable microcrystals (µCs), a graphene/Ga-polar GaN substrate yields nonreleasable thin films. We attribute this discrepancy to the polarity-dependent thermochemical stability of graphene on the GaN substrate and its subsequent reaction with hydrogen. Evidence obtained from Raman spectroscopy, electron microscopic analyses, and overlayer delamination points to a pronounced thermochemical stability of graphene on N-polar GaN during MOCVD-based remote homoepitaxy. Molecular dynamics simulations, corroborated by experimental data, further substantiate that the thermochemical stability of graphene is reliant on the polarity of GaN, due to different reactions with hydrogen at high temperatures. Based on the N-polar remote homoepitaxy of µCs, the practical application of our findings was demonstrated in fabrication of flexible light-emitting diodes composed of p-n junction µCs with InGaN heterostructures.

Fabrication of phosphor in glass using waste glass for automotive lighting application.

With advancement of technology, requirements for light-emitting devices are increasing. Various types of packaging technologies have been suggested to improve the performance of light-emitting diode (LED). Among them, phosphor in glass (PiG) is attracting attention due to its manufactural facility and easily tunable characteristics. As PiG draws increasing attention, research on glass materials is also being actively conducted. However, studies about glass in the field of phosphor are mainly conducted on fabrication. Only a few studies about recycling have been reported. Thus, the objective of this study was to recycle waste glass discarded in other fields due to breakage and failure and use it to fabricate phosphor in glass. Cylindrical waste glass was pulverized into powder with an average size of 12 µm, mixed with a phosphor and sintered to be reborn as a phosphor in glass to broaden the recycling route for waste glass.

Fabrication of LuAG:Ce3+ Ceramic Phosphors Prepared with Nanophosphors Synthesized by a Sol-Gel-Combustion Method.

The aim of this study was to investigate properties of ceramic phosphors fabricated using nano Lu3Al5O12:Ce3+ phosphors produced with a sol-gel-combustion method. These nano Lu3Al5O12:Ce3+ phosphors had a size of about 200 nm, leading to high density when fabricated as a ceramic phosphor. We manufactured ceramic phosphors through vacuum sintering. Alumina powder was added to improve properties. We mounted the manufactured ceramic phosphor in a high-power laser beam projector and drove it to determine its optical performance. Ceramic phosphor manufactured according to our route will have a significant impact on the laser-driven lighting industry.

Preparation of high-quality YAG:Ce3+ ceramic phosphor by high-frequency induction heated press sintering methods.

This study investigates the characteristics of a ceramic phosphor (CP) for the converter of a high-power laser diode-based automobile headlamp synthesized by high-frequency induction heated press (HFP) sintering. The CP prepared by an HFP method exhibits remarkable optical properties that are comparable to spark plasma sintering. The effects of post-treatment process for controlling residual pores, as well as sintering temperature, sintering pressure and heating rate for optimization of the HFP sintering method, were studied. The HFP sintering process can be widely used in ceramics and lighting fields because it is designed relatively low cost compared to other techniques and exhibits excellent productivity.

Chemically controlled megasonic cleaning of patterned structures using solutions with dissolved gas and surfactant.

Acoustic cavitation is used for megasonic cleaning in the semiconductor industry, especially of wafers with fragile pattern structures. Control of transient cavitation is necessary to achieve high particle removal efficiency (PRE) and low pattern damage (PD). In this study, the cleaning performance of solutions with different concentrations of dissolved gas (H2) and anionic surfactant (sodium dodecyl sulfate, SDS) in DIW (DI water) on silicon (Si) wafers was evaluated in terms of PRE and PD. When only DIW was used, PRE was low and PD was high. An increase in dissolved H2 gas concentration in DIW increased PRE; however, PD also increased accordingly. Thus, we investigated the megasonic cleaning performance of DIW and H2-DIW solutions with various concentrations of the anionic surfactant, SDS. At 20 ppm SDS in DIW, PRE reached a maximum value and then decreased with increasing concentration of SDS. PRE decreased slightly with increasing concentrations of SDS surfactant when dissolved in H2-DIW. Furthermore, PD decreased significantly with increasing concentrations of SDS surfactant in both DIW and H2-DIW cases. A high-speed camera setup was introduced to analyze bubble dynamics under a 0.96 MHz ultrasonic field. Coalescence, agglomeration, and the population of multi-bubbles affected the PRE and PD of silicon wafers differently in the presence of SDS surfactant. We developed a hypothesis to explain the change in bubble characteristics under different chemical environmental conditions.

Facet-selective morphology-controlled remote epitaxy of ZnO microcrystals via wet chemical synthesis.

We report on morphology-controlled remote epitaxy via hydrothermal growth of ZnO micro- and nanostructure crystals on graphene-coated GaN substrate. The morphology control is achieved to grow diverse morphologies of ZnO from nanowire to microdisk by changing additives of wet chemical solution at a fixed nutrient concentration. Although the growth of ZnO is carried out on poly-domain graphene-coated GaN substrate, the direction of hexagonal sidewall facet of ZnO is homogeneous over the whole ZnO-grown area on graphene/GaN because of strong remote epitaxial relation between ZnO and GaN across graphene. Atomic-resolution transmission electron microscopy corroborates the remote epitaxial relation. The non-covalent interface is applied to mechanically lift off the overlayer of ZnO crystals via a thermal release tape. The mechanism of facet-selective morphology control of ZnO is discussed in terms of electrostatic interaction between nutrient solution and facet surface passivated with functional groups derived from the chemical additives.

Remote heteroepitaxy of GaN microrod heterostructures for deformable light-emitting diodes and wafer recycle.

There have been rapidly increasing demands for flexible lighting apparatus, and micrometer-scale light-emitting diodes (LEDs) are regarded as one of the promising lighting sources for deformable device applications. Herein, we demonstrate a method of creating a deformable LED, based on remote heteroepitaxy of GaN microrod (MR) p-n junction arrays on c-Al2O3 wafer across graphene. The use of graphene allows the transfer of MR LED arrays onto a copper plate, and spatially separate MR arrays offer ideal device geometry suitable for deformable LED in various shapes without serious device performance degradation. Moreover, remote heteroepitaxy also allows the wafer to be reused, allowing reproducible production of MR LEDs using a single substrate without noticeable device degradation. The remote heteroepitaxial relation is determined by high-resolution scanning transmission electron microscopy, and the density functional theory simulations clarify how the remote heteroepitaxy is made possible through graphene.

Flexible Graphite/PPG Hybrid Composite-Based Resistive Sensor for Sensing Organic Compounds.

Our objective in this study was to investigate a sensor for volatile organic compounds based on a graphite (G)/polypropylene glycol (PPG) hybrid composite (HC) for sensing hybrid elements. The G/PPG HC sensor films for organic-matter detection were successfully fabricated on polyethylene terephthalate (PET) film with a simple blade-coating method. The sensing paste based on G/PPG (1:2) HC showed good dispersibility and stability. In addition, G/PPG HC sensor films with organic compounds showed different thickness changes as a function of the G/PPG ratio because of the swelling effect of the polymer. The observed differences in resistance of the G/PPG HC films corresponded to those of common organic compounds, suggesting that the disconnection of graphite caused by the swollen PPG matrix caused explosive resistance change. Moreover, we evaluated the sensitivity of typical hydrocarbon materials, such as benzene and toluene, in the sensor film as well as petroleum materials without moisture-induced malfunctions. This study could provoke knowledge about superior sensing with cost-effective and easily scalable materials using polymer/graphite composite-based sensors to improve the sensitivity, selectivity, and stability of chemical sensor applications.

Luminescent down-shifting CsPbBr3 perovskite nanocrystals for flexible Cu(In,Ga)Se2 solar cells.

To overcome the parasitic absorption of ultraviolet (UV) light in the transparent conductive oxide (TCO) layer of flexible Cu(In,Ga)Se2 (CIGS) thin film solar cells, a CsPbBr3 perovskite nanocrystal based luminescent down-shifting (LDS) layer was integrated on CIGS solar cells fabricated on a stainless steel foil. The CsPbBr3 perovskite nanocrystal absorbs solar irradiation at wavelengths shorter than 520 nm and emits photons at a wavelength of 532 nm. These down-shifted photons pass the TCO layer without parasitic absorption and are absorbed in the CIGS absorber layer where they generate photocurrent. By minimizing the parasitic absorption in the TCO layer, the external quantum efficiency (EQE) of the CIGS solar cell with the CsPbBr3 perovskite nanocrystal layer is highly improved in the UV wavelength range between 300 and 390 nm. Additionally, in the wavelength range between 500 and 1100 nm, the EQE is improved since the surface reflectance of the CIGS device with the CsPbBr3 perovskite LDS layer was reduced. This is because the CsPbBr3 perovskite nanocrystal layer, which has an effective refractive index of 1.82 at a wavelength of 800 nm, reduces the large refractive index mismatch between air (nair = 1.00) and the TCO layer (nZnO = 1.96 at a wavelength of 800 nm). Both the short circuit current density and power conversion efficiency of the flexible CIGS solar cell integrated with the CsPbBr3 perovskite are improved by 4.5% compared with the conventional CIGS solar cell without the CsPbBr3 perovskite LDS layer.

Synthesis and Characterization of Co-Mn (O)OH Nanosheets Assembled Structure Covered of Reduced Graphene Oxide Hybrid Structures by Hydrothermal Method.

In this study, we prepared cobalt-manganese (oxy) hydroxide nanosheets assembled structure covered of reduced graphene oxide hybrid structure (Co-Mn (O)OH NAS@rGO HS) via reduction and hydroxylation of Mn1.5Co1.5[Co(CN)6]2@graphene oxide (GO). Obtained precursors were optimized at 15 mg GO, and these are hybrid structures in which nanocubes 200-400 nm in size were fully covered by multi-layered GO. The functional group (-COOH, -OH, C-O-C) of GO was removed through reduction by L-ascorbic acid. We obtained MnCOOH, Co(OH)2, and Co-Mn LDH synthesized by hydroxylation of Mn1.5Co1.5[Co(CN)6]2@GO via ion exchange between the CN group and OH-. The hybrid nanostructure between transition-metal oxide/hydroxide and reduced graphene oxide could be used in various fields, including lithium ion batteries, supercapacitors, and electrocatalyst for water splitting.

Millerite Core-Nitrogen-Doped Carbon Hollow Shell Structure for Electrochemical Energy Storage.

Nickel sulfides have drawn much attention with the benefits of a high redox activity, high electrical conductivity, low cost, and fabrication ease; however, these metal sulfides are susceptible to mechanical degradation regarding their cycling performance. Conversely, hollow carbon shells exhibit a substantial electrochemical steadiness in energy storage applications. Here, the design and development of a novel millerite core-nitrogen-doped carbon hollow shell (NiS-NC HS) structure for electrochemical energy storage is presented. The nitrogen-doped carbon hollow shell (NC HS) protects against the degradation and the millerite-core aggregation, giving rise to an excellent rate capability and stability during the electrochemical charging-discharging processes, in addition to improving the NiS-NC HS conductivity. The NiS-NC HS/18h supercapacitor electrode displays an outstanding specific capacitance of 1170.72 F g-1 (at 0.5 A g-1 ) and maintains 90.71% (at 6 A g-1 ) of its initial capacitance after 4000 charge-discharge cycles, owing to the unique core-shell structure. An asymmetric-supercapacitor device using NiS-NC HS and activated-carbon electrodes exhibits a high power and energy density with a remarkable cycling stability, maintaining 89.2% of its initial capacitance after 5000 cycles.

Innovatively Continuous Mass Production Couette-taylor Flow: Pure Inorganic Green-Emitting Cs4PbBr6 Perovskite Microcrystal for display technology.

We report for the first time the mass production of Cs4PbBr6 perovskite microcrystal with a Couette-Taylor flow reactor in order to enhance the efficiency of the synthesis reaction. We obtained a pure Cs4PbBr6 perovskite solid within 3 hrs that then realized a high photoluminescence quantum yield (PLQY) of 46%. Furthermore, the Cs4PbBr6 perovskite microcrystal is applied with red emitting K2SiF6 phosphor on a blue-emitting InGaN chip, achieving a high-performance luminescence characteristics of 9.79 lm/W, external quantum efficiency (EQE) of 2.9%, and correlated color temperature (CCT) of 2976 K; therefore, this perovskite is expected to be a promising candidate material for applications in optoelectronic devices.

Synergistically Active NiCo2 S4 Nanoparticles Coupled with Holey Defect Graphene Hydrogel for High-Performance Solid-State Supercapacitors.

Nickel cobalt sulfide nanoparticles embedded in holey defect graphene hydrogel (HGH) that exhibit highly porous structures and uniform nickel cobalt sulfide nanoparticle sizes are successfully prepared by a facile solvothermal-hydrothermal method. As an electrode material for supercapacitors, the as-prepared NiCo2 S4 @HGH shows ultra-high specific capacitances of 1000 F g-1 and 800 F g-1 at 0.5 and 6 A g-1 , respectively, owing to the outstanding electrical conductivity of HGH and high specific capacitance of NiCo2 S4 . After 2100 charge/discharge cycles at a current density of 6 A g-1 , 96.6 % of the specific capacitance was retained, signifying the superb durability of NiCo2 S4 @HGH. Moreover, remarkable specific capacitance (312.6 F g-1 ) and capacity retention (87 % after 5000 cycles) at 6 A g-1 were displayed by the symmetric solid-state supercapacitor fabricated by using NiCo2 S4 @HGH electrodes. These auspicious supercapacitor performances demonstrate that the as-developed solvothermal-hydrothermal approach can be widely used to prepare graphene-coupled binary metal sulfides for high-performance supercapacitor applications.

Efficient removal of arsenic by strategically designed and layer-by-layer assembled PS@+rGO@GO@Fe3O4 composites.

The PS@+rGO@GO@Fe3O4 (PG-Fe3O4) hybrid composites for Arsenic removal were successfully fabricated and well dispersed using layer-by-layer assembly and a hydrothermal method. The PG-Fe3O4 hybrid composites were composed of uniformly coated Fe3O4 nanoparticles on graphene oxide layers with water flow space between 3D structures providing many contact area and adsorption sites for Arsenic adsorption. The PG-Fe3O4 hybrid composite has large surface adsorption sites and exhibits high adsorption capacities of 104 mg/g for As (III) and 68 mg/g for As (V) at 25 °C and pH 7 comparison with pure Fe3O4 and P-Fe3O4 samples.

Long-term stable stacked CsPbBr3 quantum dot films for highly efficient white light generation in LEDs.

We report highly efficient ethyl cellulose with CsPbBr3 perovskite QD films for white light generation in LED application. Ethyl cellulose with CsPbBr3 quantum dots is applied with Sr2Si5N8 : Eu2+ red phosphor on an InGaN blue chip, achieving a highly efficient luminous efficacy of 67.93 lm W-1 under 20 mA current.