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Electrochemical water splitting involving two-half chemical cell reactions is a promising approach to generate hydrogen and oxygen. Although this method is sustainable, the sluggish kinetics of the oxygen evolution reaction (OER) occurring at the anode due to a high overpotential is an issue to be addressed. Recently, various chemical and structural engineering approaches have been explored to improve the efficiency of the OER by reducing the overpotential. Among them, incorporating noble metals into the electrodes by doping or creating heterojunctions is an appealing approach to develop efficient OER electrocatalysts. Based on this principle, herein, we synthesized a bismuth-oxide (Bi2O3) electrocatalyst incorporated with silver nanoparticles (Ag NPs) by a facile one-step hydrothermal method to take advantage of the high conductivity of Ag NPs and the low band gap along with fast redox reaction of Bi2O3. With the Ag+concentration in the hydrothermal precursor solution, the thickness of hydrothermally formed Bi2O3nanoplates decreases, resulting in the increased electrochemical surface area (ECSA) from 71 to 300 cm2. The optimal electrode, heterojunction-formed Ag–Bi2O3(denoted H-Ag1.00-Bi2O3), exhibits the lowest overpotential of 260 mV for the OER at a current density of 10 mA cm–2with an excellent durability of 77.5% after stability tests for 240 h due to the number of active sites produced by Ag doping (manifesting defects), and heterojunction established between Ag nanoparticles and Bi2O3nanoplates. The approach explored in this work could be further utilized to produce other effective electrocatalysts for accelerating OER performances.

Optoelectronic devices require stable operation to detect repetitive visual information. In this study, endurable arrays based on heterojunction phototransistors composed of indium–gallium–zinc oxide (IGZO) with a low dark current and tin sulfide (SnSx) capable of absorbing visible light are developed for image sensors. The tandem structure of IGZO/SnSx/IGZO (ISI) enables stable operation under repetitive exposure to visible light by improving the transport ability of the photoexcited carriers through mitigated trap sites and their separation into each IGZO layer. Additionally, the structure promotes recombination by confining the holes. Therefore, the optimal ISI phototransistors exhibit a photoresponsivity of 514.50 A/W and a detectivity of 1.31 × 109Jones under red light (635 nm) of 1 mW/mm2and endurable time-dependent photoresponse characteristics, including a slope value of 1.66 × 10–11, without the persistent photoconductivity phenomenon under green light (532 nm) at a frequency of 50 mHz for over 4,000 s. Furthermore, image sensing characteristics of the 6 × 6 arrays based on ISI phototransistors for image sensors are demonstrated by sequentially applying “4” and “2” digit numbers. These technologies contribute to the development of endurable oxide-based optoelectronic devices and provide valuable perspectives on the utility of next-generation image sensors.

Ammonia is a chemical compound in considerable global demand and plays a crucial role as an environmentally friendly energy carrier for hydrogen energy storage. The electrochemical nitrogen reduction reaction (eNRR) using copper sulfide catalysts is being extensively studied as an environmentally sustainable approach to the energy-intensive Haber–Bosch process for ammonia production. In this study, we aimed to prepare CuS hollow spheres modified with Au nanoparticles using an antisolvent crystallization-based method to be used as the catalysts for eNRR. During the addition of Au to the CuS catalysts, the nitrogen adsorption strength and surface area of the CuS catalysts are significantly regulated and expanded, leading to a noticeable enhancement in electrocatalytic performance for eNRR. Specifically, the ammonia production rate of 2.4 μmol cm–2h or jNH3= 0.2 mA cm–2is achieved at a selectivity of 52% in neutral aqueous electrolyte, which is more than a 2-fold increase compared to the unmodified CuS catalyst. The findings of this study can contribute to the development of sustainable and environmentally friendly ammonia production in the future.

A biofuel cell is an electrochemical device using exoelectrogen or biocatalysts to transfer electrons from redox reactions to the electrodes. While wild-type microbes and natural enzymes are often employed as exoelectrogen and biocatalysts, genetically engineered or modified organisms have been developed to enhance exoelectrogen activity. Here, we demonstrated a redox-enzyme integrated microbial fuel cell (REI-MFC) design based on an exoelectrogen-enhancing strategy that reinforces the electrogenic activity of Shewanella oneidensisMR1 by displaying an extra redox enzyme on the cell surface. We constructed the cell-surface display system for Shewanella oneidensisMR-1 by porting the autotransporter of Escherichia coliinto the MR-1 strain. The functionality of the display system was validated by examining the various enzymes displayed on the cell surface of S. oneidensisMR-1. The implementation of the REI-MFC design was accomplished by an engineered MR-1 strain displaying a redox enzyme originating from swine NADH-cytochrome b5 reductase 3 (B5R3). At the polarization test of enhanced exoelectrogen in an operating MFC environment, the current generation (ΔIa, peak: 10.4 ± 1.9 μA) of the MR-1 displaying B5R3 was 4.7-fold higher than that of wild-type MR-1 (2.2 ± 0.3 μA). The maximum charge transfer resistance (Rct) under the optimized electrochemical test conditions was 70% lower than the wild-type MR-1. The cell surface display system for S. oneidensisMR-1 exploited in this study facilitated the exoelectrogen activity in the REI-MFC design.

Achieving precise and cost-effective etching in the field of silicon three-dimensional (3D) structure fabrication remains a significant challenge. Here, we present the successful fabrication of microscale anisotropic Si structures with an etching anisotropy of 0.73 using Cu-metal-assisted chemical etching (Cu-MACE) and propose a mechanism to elucidate the chemical behavior of Cu within the MACE solution. Our study reveals the formation of cuprous oxide (Cu2O) within Cu thin films in the presence of hydrogen peroxide (H2O2), which plays a key role in Si etching. We propose that the holes generated through the reduction of Cu2O back to Cu are transferred to Si, promoting its etching through a galvanic reaction with Cu2O. This Cu–Cu2O cyclic redox process in the Si–Cu2O galvanic cell under the right conditions enables continuous etching of Si and significantly improves the chemical stability of Cu-MACE. Building on this cyclic process mechanism, we demonstrate the catalytic potential of Cu2O for oxide-assisted chemical etching (OACE) by directly using Cu2O in both thin-film and particle forms, rather than starting from Cu. This study opens possibilities for the precise control of Cu-MACE, extends the existing MACE mechanism, and contributes to our understanding of transition metal oxide behavior in OACE.

Solution-based processing of van der Waals (vdW) one- (1D) and two-dimensional (2D) materials is an effective strategy to obtain high-quality molecular chains or atomic sheets in a large area with scalability. In this work, quasi-1D vdW Ta2Pt3Se8was exfoliated via liquid phase exfoliation (LPE) to produce a stably dispersed Ta2Pt3Se8nanowire solution. In order to screen the optimal exfoliation solvent, nine different solvents were employed with different total surface tensions and polar/dispersive (P/D) component (P/D) ratios. The LPE behavior of Ta2Pt3Se8was elucidated by matching the P/D ratios between Ta2Pt3Se8and the applied solvent, resulting in N-methyl-2-pyrrolidone (NMP) as an optimal solvent owing to the well-matched total surface tension and P/D ratio. Subsequently, Ta2Pt3Se8nanowire thin films are manufactured via vacuum filtration using a Ta2Pt3Se8/NMP dispersion. Then, gas sensing devices are fabricated onto the Ta2Pt3Se8nanowire thin films, and gas sensing property toward NO2is evaluated at various thin-film thicknesses. A 50 nm thick Ta2Pt3Se8thin-film device exhibited a percent response of 25.9% at room temperature and 32.4% at 100 °C, respectively. In addition, the device showed complete recovery within 14.1 min at room temperature and 3.5 min at 100 °C, respectively.

Two-dimensional conductive metal–organic frameworks (2D cMOFs) stand at the forefront of chemiresistive sensing innovations due to their high surface areas, distinctive morphologies, and substantial electronic conductivity. Particularly, 2D cMOFs crafted using 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaiminotriphenylene (HITP) organic ligands have garnered a large amount of attention due to their designable active sites and proper conductive characteristics. Nevertheless, a deeper exploration into their sensing mechanisms is imperative for a comprehensive understanding of the intrinsic chemistry, which is crucial for the intricate design of specialized 2D cMOF chemiresistive sensors. In this study, we fabricate six M-HXTP (M = Co, Ni, and Cu; X = H and I) chemiresistive sensors, focusing on the application of hydrogen sulfide (H2S) detection. Among these, the 2D cMOFs incorporating Cu metal manifested a remarkably enhanced response to H2S. A combination of experimental and computational studies unveils the mechanisms of sulfur oxidation and Cu reduction, wherein distortion of the reduced MX4cluster markedly amplifies the sensing response. Lastly, a real-time and portable wireless H2S sensing module has been demonstrated by using the Cu-HHTP composite material, highlighting the substantial practical significance and potential applicability.

Micrometer-sized single crystal cathodes have garnered significant interest as promising cathode materials for lithium-ion batteries due to their ability to reduce surface area exposure to electrolytes and suppress side reactions, thereby enhancing electrochemical performance. One of the challenging issues with single crystal cathode materials is synthesizing monodisperse and discrete single crystals rather than agglomerated quasi-single crystals. However, conventional solid-state synthesis of most single crystals results in severe agglomeration and cation mixing, as it requires high temperatures to promote particle growth to several micrometers. In this study, a novel morphology-conserving reaction strategy that employs octahedron single crystal intermediates is introduced to synthesize discrete, monodisperse LiNi0.97Co0.02Mn0.01O2octahedron single crystals. This scalable and cost-effective approach involves using rock-salt Ni0.97Co0.02Mn0.01O1+xoctahedrons as single crystal intermediates, which are transformed in unreactive unary lithium salt melts (LiCl and Li2SO4) from spherical Ni0.97Co0.02Mn0.01(OH)2obtained via coprecipitation. These intermediates are then subjected to a stoichiometric amount of Li precursor in a conventional solid-state synthesis to produce layered LiNi0.97Co0.02Mn0.01O2. This process is a morphology-conserving lithiation reaction, leading to the formation of discrete and monodisperse LiNi0.97Co0.02Mn0.01O2octahedron single crystals. The resultant LiNi0.97Co0.02Mn0.01O2single crystals demonstrate superior electrochemical performance, including stable capacity retention over 150 cycles, which surpasses that of typical quasi-single crystals produced through conventional methods. This is attributed to negligible crack formation during cycling, in contrast to significant cracking observed in conventional quasi-single crystals. This implies that single-crystal forms are preferred over agglomerated quasi-single crystal forms for enhancing cycle performance. These findings provide valuable insights into the industrial synthesis of discrete and monodisperse ultrahigh-nickel oxide cathode materials.