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Boosting Hydrogen Evolution Reaction on Co9S8 in Neutral Media Leveraging Oxophilic CrOx Mosaic Dopant
No full textThe electrochemical production of sustainable hydrogen under neutral conditions is advantageous, as it allows for the use of wastewater or seawater without the need for pH adjustments. However, the low ion concentration in neutral electrolytes typically results in limited adsorption of reactants on the catalyst surfaces, leading to sluggish reaction kinetics. Therefore, enhancing absorption capacity is a key challenge in the development of neutral hydrogen evolution reaction (HER) catalysts. Hetero-structured catalysts may improve surface adsorption through extensive interfacing between phases, enabling active transportation of reaction intermediates. Integrating metal sulfides and oxides, in particular, holds the potential for generating efficient electrocatalysts with improved HER activity and surface adsorption capacity. Herein, the synthesis of CrOx-doped Co9S8/CuCrS2 mosaic hetero-nanostructures is reported as a proficient HER catalyst. Facile Cr-cation migration at the Co9S8/CuCrS2 interface enables the preparation of Cr-oxide sub-nano domains within the sulfide matrix, boosting the HER catalysis in neutral media. The exceptional electrochemical performance is demonstrated in a pH 7.4 phosphate buffer solution, including low overpotential, small Tafel slope, and stability over 60 h. The formulation of catalyst design and synthetic approaches has the potential to pave the way for diverse catalytic applications utilizing metal oxide-doped hetero-nanostructures.
Effects of Framework Structures of Zeolite-Templated Carbons on Their Thermal Structural Transformations
No full textZeolite-templated carbons (ZTCs) are ordered microporous carbons synthesized by replicating the microporous structure of zeolites with carbon. Due to carbon growth within the confined spaces of zeolite micropores, ZTCs are composed of interconnected, buckybowl-like carbon moieties with abundant edge sites terminated by hydrogen (H) atoms. The amount of H-terminated edge sites and the local framework structure of ZTCs depend on their synthesis conditions. In this study, we investigated the effects of the initial framework structures of ZTCs on their thermal structural transformations. Our results demonstrate that ZTC frameworks primarily built with nanoribbon-like carbon moieties containing abundant H-terminated edge sites undergo significant dehydrogenation (removal of H2) and concomitant formation of new C-C bonds upon thermal treatment, leading to increased carbon surface curvature, reduced micropore diameter and volume, and enhanced ultramicroporosity. These structural changes also lead to substantial modifications in macroscopic properties, such as oxidative stability, work function, and ppb-level chloroform adsorption capability in water. The findings highlight the unique potential of synthesizing microporous carbons with tailored structures and physicochemical properties through post-synthesis thermal transformation of ZTCs.
Concurrent electrode-electrolyte interfaces engineering via nano-Si3N4 additive for high-rate, high-voltage lithium metal batteries
No full textElectrolyte engineering is emerging as a key strategy for enhancing the cycle life of lithium metal batteries (LMBs). Fluorinated electrolytes have dramatically extended cycle life; however, intractable challenges in terms of rate capability and fluorine overuse persist. Here, we introduce a lithiophilic, solvent-interactive, and fluorine-free nano-Si3N4 additive that facilitates the fine-tuning of weak Li+ solvation to form inorganic-rich solid-electrolyte interphase (SEI) layers. Additionally, the alloying and conversion reactions between nano-Si3N4 and Li generated a fast Li+-conductive SEI, overcoming the poor rate performance of weakly solvating electrolytes. Simultaneously, nano-Si3N4 interacts with ethylene carbonate (EC), minimizing hydrogen (H)-transfer reactions and scavenging HF, thus increasing the high-voltage tolerance. Consequently, nano-Si3N4 extends the cyclability of the commercial carbonate-based electrolyte in 360 W h kg-1-level Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) pouch-cells, resulting in 74% capacity retention after 100 cycles, whereas failure occurred without it. Our study provides an in-depth understanding of the working mechanisms of suspension electrolytes through comprehensive analysis.
Homeothermic P-Bit Computing Hardware with Stochastic Operations Beyond Limit of Non-Stochastic Materials
No full textProbabilistic computing (p-computing) is a customized approach for solving complex combinatorial optimization problems. However, issues of compatibility with well-established complementary metal-oxide-semiconductor (CMOS) technology, robustness to environmental temperature variations and stochasticity need to be addressed. This study resolves these difficulties using a metal-oxide-semiconductor field-effect transistor (MOSFET) with a floating body as a probabilistic-bit (p-bit) device. Unlike previously reported two-terminal p-bit structures, such as magnetic tunnel junction (MTJ) and memristor-based devices, a MOSFET is commercialized for conventional von Neumann computing. Although MOSFET operation is sensitive to the ambient temperature, a homeothermic characteristic from 20 degrees C up to 110 degrees C is achieved with gate voltage (VG) control, taking advantage of the three-terminal design. The conventional MOSFET operation is stable, reproducible, and, thus, non-stochastic. However, the floating body effect in this specific MOSFET enhances stochasticity, enabling an irregular single transistor latch (STL). Invertible logic operations and a max-cut solver are demonstrated with the proposed p-bits, maintaining desirable performance even at 110 degrees C through VG control. Due to its compatibility with CMOS technology, large-scale cointegration of a p-bit array and supportive CMOS circuits is feasible.
A Single-Duty-Cycled Buck–Boost Converter Achieving Low Output Ripple and Seamless Mode Transition
No full textThis article presents a single-duty-cycled buck-boost (SDC-BB) converter designed to power mobile organic light-emitting diode (OLED) displays featuring a wide dynamic range (WDR). Traditional BB converters often suffer from significant output ripples and voltage spikes, which this work aims to address by employing an inductor-last topology combined with a multilevel switched-capacitor (SC) stage. Previous strategies (both single-and multi-mode) for controlling the SC stage have resulted in either increased output voltage (V-O) ripples or non-smooth transitions between buck and boost modes, leading to V-O fluctuations during mode changes. To overcome these shortcomings, we propose a control technique that seamlessly covers both buck and boost conversions with a single duty cycle ( D ) while maintaining a lower output ripple. In this work, the flying capacitor, employed in the SC stage, is reutilized for driving the power switches, thereby eliminating the bootstrap overhead. In addition, an adaptive ramp generator is incorporated to ensure immunity to time-division multiple access (TDMA) noise for mobile applications. The SDC-BB converter, fabricated using a 180-nm CMOS process, achieved an output ripple of less than 2.1 mV with a peak efficiency of 96.6%, using a 4.7- mu H inductor, a 10- mu F output capacitor, and a 1-MHz switching frequency. Furthermore, it demonstrated output fluctuations within 2.1 mV during transitions between buck and boost modes and verified immunity to TDMA noise with a transient Delta V-O of 5.8 mV under a 0.5-V input voltage change over 20 mu s.
One-Pot Synthesis of a Novel Visible Light-Active Metal-Free Polymer within the Graphitic Carbon Nitride Family with Enhanced Photoelectrochemical Performance
No full textHydrogen fuel is a promising renewable energy source for a sustainable future. To produce green hydrogen gas from ecofriendly energy sources, a photoelectrochemical (PEC) water-splitting reaction can be explored. Metal-free polymer within the graphitic carbon nitride (g-C3N4) family is a feasible photocatalyst due to its low cost and proper light absorption characteristics. Here, we propose a novel visible light-active metal-free polymer fabricated by a one-pot synthesis process. The newly fabricated polymer exhibited a modified structure at the molecular level in cross-polarization-magic angle spinning-nuclear magnetic resonance (CP-MAS NMR) analysis, and the narrowed band gap energy was confirmed from X-ray photoelectron spectroscopy and density functional theory (DFT) simulations. We showed that CN-500 has enhanced photoreactivity for the hydrogen evolution reaction with higher electrical conductivity than g-C3N4. These findings provide a feasible approach to the production of green hydrogen (H2) through a PEC water-splitting reaction with a cost-effective metal-free polymer from a one-pot synthesis procedure.
Electronic Switching between Hot Electrons and Hot Holes via Schottky Junctions during Chemical Reactions
No full textHot carriers, generated through nonadiabatic energy dissipation during exothermic catalytic reactions, play a pivotal role in enhancing catalytic performance. Upon generation, hot electrons typically reside in the sp-band above the Fermi level, while hot holes are formed in the d-band below the Fermi level, following the energy distribution of the metal's electronic structure. However, it has been technically challenging to simultaneously capture and understand the flow of these two opposite charges during chemical reactions. In this study, we employed Pt/Si Schottky nanodiodes to detect reaction-induced hot carriers. The flux of hot electrons and hot holes was observed to vary depending on whether the Pt catalyst was deposited on n-Si or p-Si, respectively. Indeed, the detection probability of hot holes was lower compared to hot electrons, attributed to the shorter mean free path of hot holes. This demonstrates that for quantitative capture of hot carriers at the metal-semiconductor Schottky junction, the transport process through which the excited carrier passes the metal must also be considered. When a forward bias was applied to the Pt/p-Si nanodiode, a switch from hot hole to hot electron transfer was observed, due to the perturbation of the band structures. Our first prototype platforms, which self-control the transfer of hot carriers during the chemical reaction using Schottky junctions, may offer insights into potential applications of hot carriers in catalytic devices, energy conversion-based devices, or chemical sensors.
ROBOT STATE ESTIMATION SYSTEM AND METHOD
No full text본 발명은 보행 로봇의 몸체에 부착된 카메라를 통한 이미지 데이터를 획득하고, 획득한 이미지 데이터에 기반하여 보행 로봇의 몸체의 속도를 추정하고, 추정된 몸체의 속도에 기반하여 보행 로봇의 발 속도를 추정하고, 추정된 발 속도를 이용하여 보행 로봇의 최종 상태 추정 값을 도출하는 로봇의 상태 추정 장치 및 방법에 관한 것이다
Satellite Network Slice Planning With Handover Trigger and DRL-Based Virtual Network Embedding
No full textFor satellite network slicing, the end-to-end connectivity should be maintained during the service time of slices under the mobility of low Earth orbit satellites. The ground user or station should update the satellite connection at least every 10 min, and the routing paths established through intersatellite links are susceptible to performance degradation as a consequence of fluctuations in relative satellite distances. Therefore, the end-to-end connectivity management of the satellite network slice and its update during the slice service time are crucial issues. In satellite network slice planning (SNSP), the end-to-end connectivity decision is made by solving a virtual network embedding (VNE) problem, and the connectivity is maintained by updating the end-to-end routing path when satellite-ground handover occurs. Hence, an optimal integrated management of VNE and handover is necessary for SNSP. In this article, we propose an efficient SNSP algorithm leveraging a simple and lightweight deep reinforcement learning framework where actions of the learning are to select appropriate embedding methods and optimal pairs of actions and states. Here, a handover trigger (HT) mechanism is developed by introducing an SNSP utility, which is a joint function of end-to-end latency and service available time, so that handover preemptively happens before significant performance degradation. Moreover, dynamic VNE and re-embedding methods are proposed using a deep Q-network (DQN) framework. Extensive simulation results show that the proposed DQN-HT algorithm achieves approximately 36% lower average end-to-end latency compared with benchmarks.
Conformal freeze-in from neutrino portal
No full textWe study a scenario where a dark sector, described by a Conformal Field Theory (CFT), interacts with the Standard Model through the neutrino portal. In this setup, conformal invariance breaks below the electroweak scale, causing the theory to transition into a confined (hadronic) phase. One of the hadronic excitations in this phase can act as dark matter. In the "Conformal Freeze-In" cosmological framework, the dark sector is populated through interactions with the Standard Model at temperatures where it retains approximate conformal symmetry. The dark matter relic density depends on the CFT parameters, such as the dimension of the operator coupled to the Standard Model. We demonstrate that this model can reproduce the DM relic density and meet all observational constraints. The same neutrino portal interaction may also generate masses for the active neutrinos. The dark matter candidate could either be a pseudo-Goldstone boson (PGB) or a composite fermion with the quantum numbers of a sterile neutrino. In the latter case, the model is consistent with the current X-ray constraints, and may be detectable with future X-ray observations.