Yiguang Ju

Traditional thermochemical processes typically operate under relatively static conditions, where conventional reactors restrict the time scales over which key reaction parameters (such as temperature) can be varied. Electrification via Joule heating offers a way to overcome this limitation by producing pulsed temperature profiles with millisecond time resolution via programmable electric currents through a lightweight resistive catalyst support. The programmable heating and quenching (PHQ) approach enables access to nontraditional reaction dynamics and may significantly enhance product yield and selectivity with improved energy efficiency. Ammonia (NH 3 ), produced by the Haber-Bosch (HB) process, plays a critical role in fertilizer production and is gaining attention as a potential hydrogen carrier. The conventional HB process requires high temperatures and pressures, limiting energy efficiency and decentralized production. Dong et al. demonstrated NH 3 synthesis from H 2 and N 2 at ambient pressures using a PHQ reactor and an Fe catalyst, with yields higher than under isothermal conditions and stable output (Dong et al. Nature, 605, 470-476 (2022)). Here, we used density-functional-theory-based microkinetic modeling under both steady-state (isothermal) and dynamic (PHQ) conditions to understand the effect of controlled thermal fluctuations on heterogeneous catalysis of NH 3 synthesis on the most stable facet of Fe, namely (110). We demonstrate how PHQ can alter reaction rates and surface species, specifically, we predict fluctuations in concentrations of adsorbed N vs. NH; we also investigate how variations in temperature pulsing, e.g., the maximum temperature allowed and cycle time, influence yield. We find that PHQ enhances NH 3 yield only when the average of the fluctuating temperature deviates from the optimal isothermal temperature (especially when lower). Furthermore, increasing the time between high-temperature pulses could dramatically improve energy efficiency due to the slow temperature decay between pulses.

High Resolution Image Download MS PowerPoint Slide The hydrogen evolution reaction (HER) is an inevitable parasitic process that limits the efficiency and selectivity of electrochemical hydrogenation reactions using water as the hydrogen source. Although introducing oxygen vacancies and heteroatom dopants into transition-metal oxides is widely employed to enhance hydrogenation activity, such modifications often inadvertently promote HER. Here, we demonstrate a counterintuitive suppression of proton intercalation and HER in metalloid phosphorus (P)-doped WO 3 catalysts, with progressively stronger suppression at higher P-doping levels. Electrochemical impedance spectroscopy, Mott–Schottky analysis, and hydrogen bond dissociation free energy (H-BDFE) measurement reveal that, despite enhanced electronic conductivity, improved interfacial charge transfer, and decreased H-BDFE, phosphorus doping significantly increases the adsorption resistance associated with W–H* intermediate formation and reduces H* surface coverage, thereby suppressing HER kinetics. Density functional theory calculations further show that even though the W d-band center was downshifted toward its Fermi level, P-doping broadens the distribution of hydrogen binding strengths across oxygen sites of the WO 3 catalysts, such that many sites bind hydrogen too weakly to support efficient proton intercalation. These insights reveal an alternative HER suppression mechanism whereby heteroatom doping enables local control of proton intercalation and hydrogen adsorption kinetics beyond conventional d-band tuning, proton/electron supply, or charge-transport limitations.

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We demonstrate time-resolved rotational and vibrational temperature measurements to probe plasma non-equilibrium through a simple three-beam hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps CARS) system. A single pump/Stokes pair is employed to generate both the pure-rotational and ro-vibrational Raman coherence. A novel phase-matching scheme, to our knowledge, is employed to spatially overlap the two CARS signals, simplifying the optical design and allowing signal selection by tuning a single spectrometer grating. Measurements were performed near the electrodes in a N 2 DC glow discharge. Both the rotational temperature and the vibrational populations up to v =8 were calculated from the separately measured single-shot pure-rotational and ro-vibrational CARS spectra. Strong rotation–vibration non-equilibrium was observed at both electrodes, with the cathode showing higher vibrational and rotational temperatures. In addition, non-Boltzmann behaviors were observed at both electrodes. This simplified approach enables measurements of rotational and vibrational temperatures with high spatial resolution in non-equilibrium flows.

High Resolution Image Download MS PowerPoint Slide We report the in situ formation of Ni nitride for plasma-assisted ammonia synthesis. Both the surface nitrogen concentration and the ammonia formation rate exhibit dependence on the N 2:H 2 feed ratio. The maximum surface nitrogen concentration occurs at a N 2:H 2 ratio of 4:1, and the maximum catalytic activity occurs at 2:1. In contrast, the formation of gas phase radicals is less sensitive to feed composition, indicating that Ni nitride is more kinetically relevant to ammonia production than gas-phase radicals. The plasma-induced formation of Ni nitride is therefore proposed to be a critical contributor to the synergistic effects in plasma-assisted catalytic ammonia synthesis. Additionally, Ni nitride alters the surface reaction mechanism of plasma-assisted ammonia synthesis, with the rate-determining-step (RDS) shifting to surface-bound NH 3 formation rather than N 2 activation at temperatures below 373 K. These findings provide mechanistic insight that opens opportunities for optimizing the performance of plasma-assisted catalytic ammonia synthesis.

Vibrationally excited N2 (N2(v)) and H2 (H2(v)) produced in N2/H2 DC glow discharges were characterized by hybrid fs/ps coherent anti-Stokes Raman scattering (CARS). The hybrid CARS system was developed to target both the N2 and H2 ro-vibrational Raman transitions. In addition, the gas temperature was measured from the N2 pure-rotational spectra. The vibrational population distributions of the N2 molecule were calculated based on the vibrational temperatures. Measurements were performed near the anode with different H2/N2 ratios at 75 torr. It is observed that the addition of H2 reduces the N2 vibrational temperature and increases the gas temperature. The gas heating is mainly due to the vibration-translation (V-T) relaxation between N2(v) and H2. Moreover, the N2(v) population stays relatively constant as the H2 concentration increases from 20% to 75%, while the H2(v) population increases. This suggests that vibration-vibration (V-V′) transfer between H2(v) and N2 enhances the generation of N2(v).

Machine learning-based molecular dynamics (ML-MD) has emerged as a powerful tool that bridges the accuracy of quantum mechanical methods with the efficiency of classical molecular dynamics. However, existing ML-MD models often fall short in accurately predicting individual reaction rates due to incomplete sampling of reaction pathways and the absence of a multifidelity framework that combines data of varying precision. In this work, we develop and validate integrated ab initio-trained ML-MD (aML-MD) models for two key radical reactions in hydrogen combustion: H + HO2 → H2 + O2 and O + HO2 → O2 + OH. Using the DeePMD-kit framework, we first construct an aML-MD model trained solely on high-accuracy ab initio data and demonstrate its ability to predict individual reaction rates across distinct pathways via quasi-classical trajectory (QCT) calculations with excellent agreement to PES-based results. We then apply transfer learning to build another aML-MD model that incorporates a large set of moderate-accuracy DFT/PES data and a small subset of ab initio data. This multifidelity approach reduces computational cost by over fivefold while maintaining predictive accuracy within 20% of PES-based benchmarks. Further NEB simulations indicate that transfer learning yields a more accurate reaction barrier, thereby enhancing the model’s fidelity in capturing the underlying reaction dynamics. The results demonstrate the effectiveness of combining multifidelity data and transfer learning to enable general-purpose ML-MD models capable of accurately capturing complex reaction dynamics, with promising applications to larger, multi-reaction chemical systems.

A femtosecond ultraviolet laser absorption diagnostic for simultaneous temperature and NH concentration measurements is developed and demonstrated in an atmospheric ammonia/hydrogen flame produced by a Hencken burner. The diagnostic system provides high-accuracy, calibration-free, single-shot measurement of NH based on the (0, 0) band of the A3Π-X3Σ- electronic transition near 336 nm with an acquisition rate of 156 Hz. Theoretical NH absorbance is simulated using a line-by-line model. NH and temperature profiles along the flame central axis are measured. An estimated NH detection limit of 1.3 ppm was achieved. This diagnostic enables quantitative and time-resolved NH and temperature measurement, providing a new method for probing ammonia reaction kinetics in combustion and chemical synthesis.

Hybrid AC-RF discharges are a promising route for plasma-assisted ammonia synthesis, yet how hybrid waveforms redistribute energy into N2 vibrational modes and reshape discharge morphology remains poorly quantified. Here we study a hybrid AC-RF N2 ferroelectric barrier discharge driven by a 20 kHz AC voltage, with a sub-breakdown 13.56 MHz RF waveform applied between AC bursts and diagnose the plasma using synchronous ICCD imaging and time-resolved hybrid fs/ps N2 vibrational CARS over 13-40 torr. The ICCD images show that the hybrid AC-RF waveform broadens the discharge and distributes emission over a larger volume compared with AC-only operation, whereas RF alone remains strictly sub-breakdown with no visible emission. The N2 vibrational CARS spectra show that, over 13-40 torr, hybrid AC-RF plasmas populate vibrational levels up to v = 2 and yield N2 vibrational temperatures that are systematically higher than in the corresponding AC-only discharges, with the hybrid-induced enhancement in Tvib tending to increase with pressure and reaching up to ~1200 K at 40 torr. These results demonstrate that tailored AC-RF power coupling can efficiently channel energy into N2 vibrational modes, providing a tunable control on internal energy distributions for optimizing plasma-assisted ammonia synthesis and related electrified chemical processes.

This manuscript presents spatially resolved measurements of vibrational and rotational excitation in intermediate pressure (20~Torr) N2 plasmas sustained in a radio-frequency (RF) dielectric barrier discharge (DBD) reactor, using a three-beam hybrid femtosecond/picosecond (fs/ps) coherent anti-Stokes Raman scattering (CARS) diagnostic technique. The measurements span RF input powers from 20 to 55~W and include vertical spatial scans across the 4~mm interelectrode gap with a 0.5~mm step size. Notably, we report the experimental observation of vibrational levels up to v = 6 in a pure N2 RF-DBD plasma at 20~Torr. With increasing power, the vibrational temperature rises sharply and then plateaus at higher power inputs, indicating a transition to a regime dominated by enhanced V–T relaxation and dissociation from highly excited vibrational states. Spatially, the vibrational temperature profiles peak near the center of the reactor and decrease toward both electrodes, with a mild asymmetry likely arising from geometric differences between the electrodes and the corresponding sheath dynamics. These results confirm that vibrational excitation in RF-DBD plasmas is structured and non-uniform, despite the discharge’s visually diffuse appearance in optical emission.

Ammonia (NH3) is a carbon-free fuel with strong potential for low-emission combustion systems, but its low reactivity limits practical application. Blending NH3 with oxygenated fuels offers a promising strategy to enhance ignition and oxidation characteristics while influencing NOx formation pathways. In this work, the oxidation of NH3/CH3OCHO(MF)/O2/N2 mixtures is studied in the Princeton supercritical-pressure jet-stirred reactor (SP-JSR) at 100 atm over 350–950 K under fuel-lean and fuel-rich conditions. Quantitative measurements of major species and intermediates are obtained, and a high-pressure kinetic mechanism (HP-Mech) is developed by integrating updated MF oxidation kinetics, NH3 sub-mechanisms, and newly introduced MF/NH3 coupling reactions. The updated mechanism accurately captures NH3 consumption trends and key intermediate profiles, outperforming existing models under ultra-high-pressure conditions. Path-flux analysis shows that MF oxidation is dominated by OH-initiated H-abstraction, while MF/NH3 interactions mainly occur through MF/NO2/NH2 coupling. OH sensitivity analysis at 800 K further confirms the dominant role of CH3OCHO + NO2 in sustaining OH and NOx. Overall, the results provide the first detailed experimental and kinetic study of NH3/MF oxidation at ultra-high pressure and clarify the mechanistic basis for how oxygenated fuels promote or suppress NH3 reactivity, and inform combustion strategies for high-efficiency, low-carbon engine systems.

accuracy, enabling precise concentration- and temperature-resolved modeling of nitrogen diffusion in iron and its nitrides. Arrhenius fitting to the 830-1500 K chemical diffusion coefficients reproduce the experimental activation energy and pre-exponential factor. Extrapolation to 823 K, the temperature at which most of the experiments are performed, yields a coefficient that falls within the experimental uncertainty. The present MLP-MD model will facilitate the mechanistic understanding of iron surface nitridation and quantitative predictions of "unwanted" nitriding of iron-based combustor wall materials induced by ammonia at high temperatures.

Surface nitridation induced by ammonia combustion can alter material properties, reducing lifetime and performance of a practical combustor. Although ammonia-induced surface nitriding has been studied at low and moderate temperatures, its behavior at temperatures above 1200 K in flames remains unexplored. This study investigates high-temperature nitriding and the impact of NH radical of nickel rods exposed to NH 3 /H 2 flames above 1500 K. The presence of abundant radicals and complex chemical reactions in NH 3 /H 2 flames, together with flame–wall interactions between reactive gases and metal surfaces, impose great challenges in understanding the underlying nitridation mechanism. In this work, gas-phase characterization was performed using in-situ planar laser-induced fluorescence (PLIF) for NH radical distribution and Rayleigh scattering for temperature, while surface morphology and chemical composition were analyzed by scanning electron microscopy (SEM) and high-resolution X-ray photoelectron spectroscopy (HRXPS). The results show that nickel nitridation can occur within minutes of flame exposure and is strongly dependent on NH concentration at a same flame temperature. In addition, no distinct nitride layer was observed after more than one hour of flame exposure, while pore structures beneath the nickel surface were detected using ion-beam cutting under high vacuum. These observations suggest that high-temperature nitridation under ammonia combustion conditions may proceed through mechanisms that differ from those typically reported at lower temperatures. Novelty and significance statement This study presents the first high-temperature experimental investigation of nickel nitridation under ammonia/hydrogen combustion conditions exceeding 1500 K, moving beyond the moderate-temperature (<1200 K) and non-flame studies that dominate existing literature. By combining operando planar laser-induced fluorescence (PLIF) for NH radicals with ex-situ high-resolution X-ray photoelectron spectroscopy (HRXPS) and scanning electron microscopy (SEM) analysis, the study directly links radical chemistry in the reacting flow to surface phase evolution and microstructural transformation. The findings, characterized by rapid nitride formation, radical-mediated nitrogen incorporation, and lattice instability, highlight that the flame-wall interactions at 1600 K are different from low and moderate temperatures. These insights are essential for predicting material degradation in ammonia-based energy systems and for guiding the design of high-temperature metal components with improved resistance to nitridation and/or oxidation.

Non-equilibrium plasma-assisted ammonia synthesis is investigated through enhanced active species production with ferroelectric discharge. Time-resolved in-situ diagnostics of femtosecond two-photon absorption laser-induced fluorescence, coherent anti-Stokes Raman scattering, and laser absorption spectroscopy, as well as optical emission spectroscopy, were conducted to probe the key intermediate species, such as H and N radicals as well as N2(ν), ions, and NH3 to achieve better understanding of non-equilibrium energy transfer and ammonia formation. The results reveal that ferroelectric discharge improved ammonia yield by four times. Results also show that ferroelectrics not only enhanced ions (N2+) production, radicals (N, H) number density, but also increased the N2 vibrational temperature. Further plasma modeling identified the couplings between elevated radical and ion production and enhanced vibrational excitation reactions, e.g., N + H2(ν)→NH + H, N2(ν)+H → NNH, N2+ + H2 → H + N2H+, and N2H++e→NH + N, facilitated by ferroelectric discharge. These findings provide critical insight into the mechanism of ferroelectric plasma catalysis and highlight their potential in advancing energy-efficient chemical synthesis. This work reports enhancements of radicals, vibrational states, and ammonia output in N2/H2 plasmas by ferroelectric barrier discharge, with evidence from time-resolved laser diagnostics, expanding plasma routes to cleaner chemical production.

Abstract The development of doped organic room‑temperature phosphorescent (RTP) polymers is hampered by the physicochemical incompatibility between hydrophilic hosts such as polyvinyl alcohol (PVA) and conventional hydrophobic phosphors. This mismatch triggers severe phase separation and lowers RTP performance. A molecular engineering strategy that addresses this challenge by introducing intrinsically water‑soluble phosphonium salt emitters is presented. The design combines a bromide counterion that enhances intersystem crossing with a bulky alkyl chain that suppresses aggregation‑induced quenching, while also guaranteeing seamless miscibility with PVA. This approach eliminates phase separation and yields highly efficient, full‑color RTP in doped films, with emissions tunable from 427 to 619 nm. The best performer shows an ultralong lifetime of 2.18 s and a quantum yield of 11.63%. Building on these properties, the versatility of the material in two key applications is demonstrated, namely high‑performance flexible displays and high‑resolution X‑ray imaging with a spatial resolution of 11.51 lp mm −1 .

This study aimed to investigate the bioactivity and structural characteristics of walnut protein hydrolysates prepared by simulated gastrointestinal digestion in vitro (WPH-GI). Moreover, it aimed to identify bioactive peptides in WPH-GI, using LC-MS/MS and database-driven search techniques. The results indicated that WPH-GI exhibited stronger antioxidant activity and inhibitory activities against ACE, α-glucosidase, α-amylase and thrombin than WP. Compared to walnut protein (WP), WPH-GI exhibited maximal enhancements of 33.2% in ABTS · + scavenging ability, 71.2% in hydroxyl radical scavenging ability, 40.2% in ACE inhibitory ability, 30.2% in α-amylase inhibitory activity, 21.1% in α-glucosidase inhibitory activity, and 18.4% in thrombin inhibitory activity. We found that WPH-GI's stronger bioactivities may be due to its loose, flexible molecular structure with numerous exposed hydrophobic groups. Furthermore, WPH-GI contained many bioactive peptides, including 33 peptides with high biological activity identified. In conclusion, consuming walnuts is beneficial for health, largely because of the enhanced biological activity of WP after digestion as a result of molecular structural alterations coupled with the release of active peptides. The results of this study lay a theoretical foundation for the health benefits of WP consumption and promote the high-value utilization of walnut meal. • WPH-GI, the digestive product of WP, exhibited superior bioactivities than WP. • WPH-GI had flexible molecular structure with numerous exposed hydrophobic groups. • WPH-GI was rich in peptides, and 203 peptides were identified. • A total of 33 small peptides are expected to exhibit high biological activity.

In recent years, pediatric brain tumors have emerged as one of the most common malignant tumors among children. The site of tumor growth and the selected treatment modalities can potentially have a profound and significant impact on the reproductive function of pediatric patients, which is intimately associated with the physical and psychological health of children during their developmental process. Current research studies have demonstrated that pediatric patients diagnosed with germ cell tumors, craniopharyngiomas, and medulloblastomas commonly present with reproductive dysfunction. Regrettably, in clinical practice, neurosurgeons frequently fail to allocate sufficient attention to this particular aspect. It is of critical and urgent necessity to explore and elucidate the alterations in reproductive function among pediatric patients with brain tumors, and subsequently institute essential protective measures. This article is dedicated to comprehensively reviewing the latest research advancements regarding the relationship between pediatric brain tumors and reproductive function, thereby providing a valuable reference for safeguarding the reproductive function of pediatric patients afflicted with brain tumors.

Electrocatalytic nitrogen reduction (eNRR) offers a green pathway for the production of NH 3 from N 2 and H 2 O under ambient conditions. Transition metal oxynitrides (TMO x N y ) are among the most promising catalysts but face challenges in achieving a high yield and faradaic efficiency (FE). This work develops a hybrid WO x N y /WO 3 catalyst with a unique heterogeneous interfacial complexion (HIC) structure. This design enables in situ generation and delivery of highly active hydrogen atoms (H*) in acidic electrolytes, promoting nitrogen hydrogenation and the formation of nitrogen vacancies (Nv) on the WO x N y surface. This significantly enhances the selectivity of eNRR for NH 3 synthesis while suppressing the hydrogen evolution reaction (HER). A simple two-step fabrication process─microwave hydrothermal growth followed by plasma-assisted surface nitridation─was developed to fabricate the designed catalyst electrode, achieving an NH 3 yield of 3.2 × 10 –10 mol·cm –2 ·s –1 with 40.1% FE, outperforming most TMN/TMO x N y electrocatalysts. Multiple control experiments confirm that the eNRR follows an HIC-enhanced Mars–van Krevelen (MvK) mechanism.

ABSTRACT This paper is devoted to pseudo almost periodic solutions for the distribution‐dependent SDEs, where the coefficients of the distribution‐dependent SDEs rely on the state of the unknown process and its probability distribution. By the Banach fixed point theorem and ergodic perturbation theory, one establishes some theorems of (pseudo) almost periodic solutions in distribution for the distribution‐dependent SDEs. Further, one discusses the Hyers‐Ulam stability of pseudo almost periodic solutions and provides an example to illustrate the results.

Plasma Assisted Combustion and Chemical Processing provides an introduction to the opportunities of plasma-assisted combustion and chemical processing for green energy conversion using renewable electricity. Covering the fundamentals of combustion and plasma physics and chemistry,&nbsp;it details the mechanisms and technologies of plasma-enhanced combustion, chemical process, materials manufacturing and recycling, and pollutant control. Addressing future challenges and opportunities of plasma-assisted combustion and electrified green manufacturing, this book covers the state-of-art methods of modeling and diagnostic tools to optimize the process design. This book offers graduate students and researchers a comprehensive review of the fundamentals and research frontier in this emergent field.

Plasma dynamics and chemistry have a broad range of timescales from picoseconds to milliseconds. In addition, it involves nonequilibrium energy transfer between electrons, ions, electronically and vibrationally excited states, radicals, intermediate species, and reactants and products as well as surface charges and chemistry. To understand plasma physics and chemistry, it is essential to conduct time and space resolved, quantitative detection of nonequilibrium temperature distributions, electron energy and number density, electric field, and species concentrations. There are enormous publications and review articles on this subject. The focus of this chapter is to be placed on the most recent progress in gas phase plasma properties and chemistry, especially on optical emission spectroscopy, laser absorption spectroscopy, Faraday rotational spectroscopy, Raman and Thompson scattering, femtosecond and picosecond (fs/ps) coherent anti-Stokes Raman scattering (CARS) spectroscopy, and electric field-induced second harmonic generation methods.