Ammonia Gas Flow Research Articles

Position-dependent degradation and damage mechanisms of Inconel 600 in an ammonia gas flow environment at elevated temperatures

With an aim to use ammonia as a direct fuel in gas turbines, an investigation on the degradation of materials used in the turbine components in the ammonia flow environment is important. The present work investigated the surface reaction and degradation of Inconel 600 placed at different positions inside a furnace in the direction of ammonia flow at 400 °C to 600 °C. Severe surface damage and degradation was identified. The effect of specimen position on the extent of degradation and the damage mechanisms were elucidated utilizing XRD, TEM, and Optical Emission Spectroscopy (OES).

Ammonia Decomposition By Microwave Plasma Discharges

The global discourse focuses on future energy vectors, with hydrogen emerging as a robust candidate owing to its established industrial applications. However, a current challenge lies in storing and transporting hydrogen-based fuels. This research focuses on advancing efficient and environmentally friendly techniques for large-scale hydrogen production, leveraging its widespread industrial presence. Ammonia, identified as a promising energy vector, offers advantages in storage and transport over hydrogen. It capitalizes on existing global infrastructures, with approximately 20 million metric tons traded annually, contributing to a total production of 150 million tons annually. If many works focus on producing ammonia by electrical discharges [1], only a few are devoted to ammonia cracking and generally concentrate on catalysis [2]. In this study, we propose an investigation into the decomposition of ammonia by applying microwave (MW) plasma. Utilizing a MW cavity that confines an electromagnetic field excited at 2.45 GHz, we induce electrodeless plasma within a fused silica tube where pure ammonia (NH3) gas flow. At first, the plasma discharge was characterized with Fourier Transform Infrared Spectroscopy (FTIR). This preliminary part of the study exhibited that, for fixed input power (300 W) and fixed working pressure (100 mbar), NH3 decomposition decreased with a flow rate ranging from 0.4 to 2.4 SLM. It also showed that for fixed input power (300 W) and fixed flow rate (2.4 SLM), the NH3 dissociation increased with pressure ranging from 40 to 140 mbar. These experiments exhibited the predominant role of the residence time of ammonia but also reactive species in plasma. To further understand the NH3 cracking mechanisms, we performed optical emission spectroscopy (OES). This technique allowed us to determine the various light-emitting species produced during NH3 dissociation in the discharge and their physical parameters, such as temperatures and relative densities, as a function of different experimental parameters. We study the influence of gas flow rate ranging from 1 to 15 SLM, input power and near-atmospheric pressure on NH3 cracking and hydrogen (H2) recombination mechanisms. Gas chromatography (GC) was employed to measure the dissociation yield of NH3 and assess the efficiency of the H2 production process. In parallel, we synthesize iron (Fe) and nickel (Ni) nanoparticles through a plasma solution process. Both metals are abundant and inexpensive; hence, they are good candidates as catalysts for potential industrial applications. In the experimental setup, a pair of tungsten electrodes, connected by a high-voltage cathode, was submerged in an aqueous solution containing Fe and Ni chlorides. One electrode was the high-voltage cathode, while the other was the grounded anode. Pulsed discharges were generated to produce Fe and Ni compounds. The resulting Fe-Ni nanoparticles (NPs) were characterized by transmission electron microscopy (TEM) to determine their shape, size and composition, which depends on the concentrations of the metal chlorides in the electrolyte solution. Those NPs were then coated on silica tubes inserted in the MW reactor at various positions to establish their influence on the NH3 decomposition and H2 recombination processes. The primary goal of this study is to compare the dissociation of NH3 with and without catalysts, aiming to achieve optimal results for H2 production. This study investigates the impact of experimental parameters on ammonia cracking efficiency within a microwave plasma combined with catalysis. We compare these factors with ruthenium-catalyzed and non-catalyzed thermal processes, recognized as leading methods for ammonia cracking. The goal is to gain insights into the mechanisms of ammonia decomposition in microwave plasmas and evaluate the efficiency of our proposed methodology relative to established thermal processes, contributing to the advancement of sustainable and optimized ammonia cracking practices and decarbonated hydrogen production. Acknowledgements The authors would like to thank the Department of Physics, College of Science, Jazan University, Jazan 45142, Saudi Arabia, for the financial support to M. Awaji and SAKOWIN for the financial support to L. Pentecoste.

Ni2Mo3N: crystal structure, thermal properties, and catalytic activity for ammonia decomposition

Abstract Ni2Mo3N was synthesized by ammonolysis of NiMoO4, prepared by a sol-gel-based modified Pechini route. X-ray powder diffraction measurements confirmed that Ni2Mo3N crystallizes in a filled β-Mn type (cubic space group P4132) with a lattice parameter of a = 6.6338 Å. Group theoretical methods were applied to elucidate the relation between the crystal structure of Ni2Mo3N and that of the rock salt type. The high-temperature behavior was investigated in-situ by X-ray diffraction measurements in flowing ammonia gas at temperatures up to 875 °C. Ni2Mo3N exhibits significant catalytical activity for ammonia decomposition, which is critically discussed in comparison to literature.

Discontinuous phase separation, interstitial ordering and recrystallization during nitriding of FeNiCo medium entropy alloy

The sequence of phase transformations triggered as a consequence of inward diffusion of interstitial N during nitriding of FeNiCo medium entropy alloy was investigated. Recrystallized and cold rolled specimens of FeNiCo alloy were nitrided at 580 °C in a flowing ammonia gas atmosphere. Detailed microstructural characterization was carried out using scanning and transmission electron microscopies, X-ray and electron back scattered diffraction and atom probe tomography. Firstly, N supersaturation of about 2 at.% was observed to be established without any nanoscale chemical heterogeneities. Further increase in N-content triggered the occurrence of a discontinuous phase separation reaction, resulting in the formation of alternating Fe+N enriched and Co+Ni enriched phases with a characteristic lamellar morphology and cube-on-cube orientation relationship. The Fe+N enriched lamellae then undergo rapid interstitial N ordering, forming a γ′- Fe4N type nitride phase. The compositional partitioning however is only transient and is followed by a recrystallization of the lamellar microstructure into a compositionally homogeneous γ′-(FeCoNi)4N type matrix. Thermodynamic calculations show that this discontinuous phase separation reaction and subsequent composition homogenization via recrystallization results from isothermally forcing the alloy composition to first enter the metastable miscibility gap in the FeNiCo-N FCC solid solution (at N-supersaturation close to 2 at.%) and then moving out of the miscibility gap at high N contents, beyond 20 at.%. Role of volume misfits, the chemical partitioning and homogenization on the sequential occurrence of different transformations is discussed.

Synthesis and magnetic properties of [formula omitted]-Fe16N2 nanofibers prepared by an electrospinning method

Although the iron-nitride α″-Fe16N2 phase exhibits excellent magnetic properties, its poor thermal and phase stability pose challenges in the fabrication of bulk-type samples. In particular, the low nitriding temperature, below 200 °C, increases possibility of forming the stable nitride phase with higher nitrogen content on the surface due to the slow diffusion rate of nitrogen atoms. To overcome this problem, it is crucial that the α-Fe precursors are small in size, well-dispersed, and that the post-heat treatment is conducted below 200 °C. In this study, we successfully demonstrated the fabrication of α″-Fe16N2 nanofibers through electrospinning process and a two-step heat treatment procedure involving hydrogen reduction at 290 °C for 2 h, followed by nitration at 160 °C for 12 h in an ammonia gas flow rate of 1.5 L/min. Furthermore, these α″-Fe16N2 nanofibers exhibited a saturation magnetization (M2.5T) of 182 emu/g, a residual magnetization (Mr) of 76.1 emu/g, and a coercivity (Hc) of 1.29 kOe.

Оптическая спектроскопия нанопористых мембран на основе анодного оксида алюминия в газовом потоке аммиака

Оптическая спектроскопия нанопористых мембран на основе анодного оксида алюминия в газовом потоке аммиака

Multiscale modeling of ammonia adsorption on zinc sulfate-doped activated carbon: Sensitivity analysis, parameter identification, and model validation

In this study four models are developed and validated to describe the dynamic adsorption of ammonia on zinc sulfate-doped activated carbon, ranging from simple single-scale to complex multiscale models. They are based on equations for mass balance, thermodynamics, hydrodynamics, and adsorption kinetics. Since the values of the parameters are needed for the implementation of the models, the doped activated carbon is characterized and ammonia isotherms measurements are performed at three different temperatures, i.e., 288, 303, and 313 K. A method based on parameter sensitivity analysis is used to evaluate the estimability of the unknown parameters of the Toth isotherm equation. Experimental breakthrough curves were then measured at various ammonia concentrations and gas flow rates. These curves were used to determine the overall mass transfer and axial dispersion coefficients, as well as the effective and intracrystalline diffusion, involved in the model equations. The models were implemented and solved using Comsol Multiphysics®. The study showed that the adsorption process was limited by the diffusion of ammonia and adsorption on the zinc sulfate crystal. The models were validated using breakthrough curves different from those used for parameter identification. The agreement between model predictions and measurements was evaluated using performance indices and confirmed by a Kolmogorov-Smirnov statistical test.

Fabrication of N-doping activated carbon (NDAC) from saw dust/ZnCl2 for Acid Brown 14 dye removal from water

Abstract Nitrogen-doped activated carbon (NDAC) was prepared from saw dust/zinc chloride (2:1) by heating under the flow of ammonia gas at 600 °C, 700 °C, and 800 °C and tested for Acid Brown 14 (AB14) dye adsorption from aquatic solution. The fabricated N-doping activated carbons (NDACs) were characterized by FTIR, TGA, DTA, BET, BJH, MP, t-plot, SEM, EDX, and XRD. The NDACs fabricated at 600 °C, 700 °C, and 800 °C were tested for their capacity to adsorb AB14 dye from water. The nitrogen mass % content in the prepared activated carbon ranged between 17.99 and 21.43%. The NDAC prepared at 600 °C specific surface area, monolayer volume, and mesoporous mean pore diameter were 281.84 m2/g, 64.753 cm3/g, and 2.352 nm, respectively. The NDAC synthesized at 600 °C with a 21.12% nitrogen content was found to be the best one to remove AB14 dye from water and named as NDAC600. The impact of solution pH, initial concentration, and adsorption dosage on the adsorption of AB14 dye by NDAC600 was tested. The adsorption of AB14 dye by NDAC600 was found to be pH dependent, with the optimal elimination of being obtained at pH value 1.5 with a removal efficiency of 89.03%. The adsorption of AB14 dye is attributed to the electrostatic contact between the NDAC600 positively charged sites and the anionic AB14 dye. The AB14 dye adsorption was perfectly designated by using both pseudo-second-order (PSO) and Temkin adsorption kinetic models. The maximum adsorption capacity (Qm) was 909.09 mg/g; moreover, the adsorption process was monolayer sorption of AB14 dye to NDAC600. NDAC600 had proven itself as an effective, available, and green adsorbent for the adsorption of AB14 dye from water and may be applicable to other hazardous pollutants.

(Digital Presentation) High-Temperature Ammonia Treatment for Carbon Felt Electrodes in All-Vanadium Redox Flow Batteries

Ammonia gas treatments of varying temperature were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without processing, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to improve performance, which has been historically accomplished with thermal treatments ostensibly to promote oxygen functional groups, although this has been the subject of debate as morphological impacts have also been observed. [1-3] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [4-6] Previous research at the University of Tennessee Knoxville suggests edge sites play a role in improving performance. Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. Additional experiments were performed at 900°C by varying length of treatment time, finding four hours to be optimal. [3] New experiments have been done to investigate the kinetic effects of temperature.For these experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at (500°C, 700°C, 900°C, and 1100°C) varying temperatures for four hours. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. This was done to study the mechanism and kinetic effects of ammonia on the carbon felt material as temperature increases during the treatment itself. Samples treated at the highest temperatures exhibited a notable loss of mass, which is observed in the SEM images in Figure 1. This resulted in a significant increase in edge sites and active surface area, along with a substantial increase in cell performance, which was achieved with the ammonia-modified carbon felts described in this work, with over three times the current density at 80% voltage efficiency compared to untreated felt. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment.Electrochimica Acta, 1992. 37(7): p. 1253-1260.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016.Gass, K., High Performance Vanadium Redox Flow Battery Electrodes. [manuscript under submission], 2021.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces.Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries.Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries.Energy Storage Materials, 2020. 25: p. 885-892. Figure 1. SEM images at 30,000X magnification of carbon felt electrodes: a) untreated, b) 4 hours NH3 treated at 500°C, c) 4 hours NH3 treated at 700°C, d) 4 hours NH3 treated at 1100°C. Scale was identical for all micrographs Figure 1

A Study on Graphene Structure Control Using Ammonia Gas for a Highly Sensitive Pressure Sensor

Graphene has been used in various fields because of its excellent mechanical, optical, electrical, and thermal properties. However, its intrinsic low sensitivity to pressure limits its sensor applications. To overcome this drawback, many researchers have tried to improve the sensitivity by controlling the defects on the graphene, but have yet to report a significant increase in sensitivity compared to the pristine graphene. Herein, we fabricated a graphene-based highly sensitive pressure sensor by flowing ammonia gas during chemical vapor deposition. The ammonia gas assisted the generation of nano-sized defects due to nitrogen doping in the graphene lattice, as well as macro-sized cracks in the graphene layer, due to the corrosion of the Cu surface. We regulated the concentration ratio of ammonia gas and methane gas during the graphene synthesis, which controlled the crack generation. These cracks weakened the in-plane force of the networks in the geometric structure of the graphene, thereby allowing them to deform more easily under external force, and changing the resistance of the sensor dramatically. As a result, the sensitivity of the pressure sensor increased about 10,000 times higher than that of the pristine graphene. These results suggest that controlling defects to improve graphene’s mechanical sensitivity provides a promising route to pressure sensor applications.

Estimated approach development and experimental validation of residual stress-induced warpage under the SiNx PECVD coating process

Depositing silicon nitride (SiNx) coating by utilizing the plasma-enhanced chemical vapor deposition (PECVD) procedure is currently an important approach in the semiconductor industry because SiNx coating has several excellent application functions, such as passivation layer and oxygen/vapor barrier. However, residual stress occurs in the thin film resulted from the coefficient of thermal expansion (CTE) mismatch, lattice mismatch, defects, and impurities during the PECVD process. The SiNx-coated wafer would induce harsh warpage generated by coating film's residual stress. Aforementioned issue might generate the defects in the products, thus resulting in disrupted process and reliability problems. Such warpage is also unfavorable to the high flatness requirement for subsequent fabrication with the continuous scaling of advanced-technology devices. Accordingly, this study presents a novel process-oriented simulation methodology integrated with fluid dynamics-mechanical coupling responses to estimate its induced warpage magnitude affected by the pressure and temperature distributions during PECVD process and the initial intrinsic stress of SiNx coating. Under the consideration of the abovementioned loadings, the resultant stress and warpage after force balance for depositing SiNx coatings are obtained through process-oriented layer-by-layer simulation. On the basis of the simulated results and the data of experimental measurements, an intrinsic stress surface for SiNx is established by the radio frequency power, ammonia, and silane gas flow rate. Accordingly, the warpage magnitude and intrinsic stress of PECVD SiNx thin coating prior to actual processing can be immediately and accurately judged by the simulation methodology and SiNx intrinsic stress surface presented in this investigation.

A composite consisting of intermetallic Ni3Fe and nitrogen-doped carbon for electrocatalytic water oxidation: The effect of increased pyridinic nitrogen dopant

Nitrogen-doped carbon (NC) has been studied as electrocatalysts or electrocatalyst support and the nitrogen content in carbon matrix is mainly dependent on the nitrogen-rich precursors. In this study, we prepare a composite consisting of intermetallic Ni3Fe and NC ([email protected]) via simply heating under ammonia and argon mixed gas atmosphere (Ar/NH3), aiming to further increase the nitrogen content. Compared to [email protected], the NH3-derived electrocatalyst has more N atoms which are in the form of pyridinic N in carbon structure, significantly improving the electron transport efficiency and reaction kinetics, and thereby further boosting the electrocatalytic activity. This work demonstrates that the introduction of ammonia gas flow during calcination is a simple and effective strategy to increase the nitrogen content for engineering NC-based electrocatalysts toward high-performance water splitting.

Spectral optical properties of ceramic nanoporous membranes based on anodic aluminium oxide coated silver in ammonia vapors

Spectral optical properties of synthesized ceramic nanoporous membranes based on anodic aluminum oxide coated silver in saturated ammonia gas flow have been experimentally investigated. Based on the measured transmission spectra and detected interference part of the spectra in wavelength range from 550 to 900 nm, temporal and spectral dependencies of the effective optical thickness and its changes in non-equilibrium conditions were obtained due to adsorption of ammonia molecules on silver film surface. According to detected and measured interference maximum shifts up to 14 nm in transmission spectra of Al2O3 + Ag membranes in ammonia gas flow, the possibility of constructing a selective interferometric optical sensors with 10-15 min response time is shown. Keywords: porous anodic aluminium oxide, membrane, silver film, light interference, ammonia vapors, effective optical thickness, interference maximum shift.

Спектральные оптические свойства керамических нанопористых мембран на основе анодного оксида алюминия и покрытия из серебра в парах аммиака

Spectral optical properties of synthesized ceramic nanoporous membranes based on anodic aluminum oxide coated silver in saturated ammonia gas flow have been experimentally investigated. Based on the measured transmission spectra and detected interference part of the spectra in wavelength range from 550 to 900 nm, temporal and spectral dependencies of the effective optical thickness and its changes in non-equilibrium conditions were obtained due to adsorption of ammonia molecules on silver film surface. According to detected and measured interference maximum shifts up to 14 nm in transmission spectra of Al2O3 + Ag membranes in ammonia gas flow, the possibility of constructing a selective interferometric optical sensors with 10 − 15 min response time is shown.

Band gap engineered Nb2O5 thin films fabricated from sol-gel processed modified precursors for enhanced photocatalytic activity: A comparative study

Reactions of niobium (V) ethoxide (1) with 2,4-pentanedione derivatives [3-Chloro-2,4-pentanedione, 1,1,1-Trifluoro-2, 4 pentanedione, 3,3-Dimethyl-2,4-pentanedione,] afforded heteroleptic niobium alkoxide complexes [Nb(OEt)4 (CH3COCHClCOCH3)](2), [Nb(OEt)4(CF3COCH2COCH3)] (3) and [Nb(OEt)4(CH3COC(CH3)2COCH3)] (4). Two sets of Nb2O5 sculptured thin films (STFs) were deposited on ITO coated glass substrates by spin casting the gels obtained by sol gel processing of the synthesized complexes (2-4). One set of the films (Na, Nb and Nc) were calcined under ammonia gas flow and the other (a, b and c) under oxygen gas flow respectively at 500°C for 1h. A film (d) was also fabricated from niobium (V) ethoxide and calcined under oxygen gas flow at 500°C for 1h for comparisons with regard to structure, topography, optical and photocatalytic properties of Nb2O5. Crystal structure, topography, optical and photocatalytic properties of the films were determined by X-ray diffraction, atomic force microscopy, ellipsometry and UV-Vis spectroscopy. Significant band gap narrowing i.e. from 3.48 eV (d) to 2.73 eV (Nc) was observed for the films calcined under ammonia gas flux. Investigation of photodegradation of methylene blue (MB) by niobia films under UV irradiation demonstrated enhanced degradation efficiency of methylene blue dye. Copyright © 2018 VBRI Press.

Instantaneous hydrogen production from ammonia by non-thermal arc plasma combining with catalyst

Owing to the storage and transportation problems of hydrogen fuel, exploring new methods of the real-time hydrogen production from ammonia becomes attractive. In this paper, non-thermal arc plasma (NTAP) combining with NiO/Al2O3 catalyst is developed to produce hydrogen from ammonia with high efficiency and large scale. The effects of ammonia gas flow rate and discharge power on the gas temperature, electron density, the hydrogen production rate, and energy efficiency were investigated. Experimental results show that the optical emission spectrum of NTAP working with pure ammonia medium was dominated by the atom spectrum of Hα, Hβ, and molecular spectrum of NH component. Under the optimum experimental condition of plasma discharge, the highest energy efficiency of hydrogen production reached 783.4 L/kW⋅h at NH3 gas flow rate of 30 SLM. When the catalyst was added, and heated by the NTAP simultaneously, the energy efficiency further increased to 1080.0 L/kW⋅h.

NOx Reduction Using Pilot-Scale SCR Under Oxyfuel Conditions

This paper presents a comprehensive experimental study of selective catalytic reduction (SCR) of nitrogen oxides formed in the oxyfuel combustion of lignite coal in a 500 kWth pilot-scale bubbling fluidized bed (BFB) boiler using the V2O5 over TiO2 honeycomb catalyst and the ammonia as the reducing agent. The study also compares the performance of the SCR between oxyfuel and air combustion modes. The SCR unit is placed in the tail-end position of the flue gas processing scheme after the cyclone particle separator. Experiments were realized both in air- and oxyfuel combustion regime, evaluating the impact of relevant process conditions on the NOx reduction. The dependence of the NOx reduction efficiency on the catalyst temperature and on the normalized stoichiometric ratio (NSR) of the reducing agent molar flow to the molar flow of NOx were studied. The efficiency of the NOx reduction was evaluated based on the NOx concentration measured simultaneously before and after the SCR unit. In the off-gas, the concentration of unreacted reducing agent (ammonia slip) was measured as well. For evaluation of real NSR, ammonia and flue gas flow rates were measured during each experiment. The catalyst temperature was regulated within the experiments in the range of 260 to 300 °C and the NSR was chosen in the range of 0 to 1.2. From this experimental setup, the correlations of the NOx reduction efficiency related to the different NSR and catalyst temperature were evaluated. The results show the fundamental information about the differences between air and oxyfuel conditions in a real combustion environment. In general, the NOx conversion efficiency was significantly higher during air combustion. In order to get similar results of maximum NOx conversion as reached during air combustion, it was necessary to increase NSR up to 1.8 and more, however at the cost of significantly increased ammonia slip. Although the SCR performance is lower in oxyfuel combustion, it was possible to decrease NOX under 100 ppmv with NSR about 1 and without any significant ammonia slip, which is important prior to further CO2 treatment.

Modifying Carbon Felt Electrodes Using High-Temperature Ammonia Treatment to Improve the Performance of All-Vanadium Redox Flow Batteries

High temperature ammonia treatments were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without intervention, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to make it more effective, which has been historically accomplished with thermal treatments to promote oxygen functional groups. [1] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [2-4] Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. [5]For our experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at 900°C for varying lengths of time. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. A pitting effect was observed in SEM images, preceded by surface blistering at shorter lengths of exposure.Greatly increased active surface area, along with a substantial increase in cell performance, was achieved with the ammonia-modified carbon felts described in this work. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment. Electrochimica Acta, 1992. 37(7): p. 1253-1260.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces. Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries. Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries. Energy Storage Materials, 2020. 25: p. 885-892.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016. Figure 1

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Defect-related photoluminescence of gallium nitride/silicon nanoporous pillar array modulated by ammonia gas flow rate

The structural and physical properties of silicon nanoporous pillar array (Si-NPA) make it an ideal template for preparing Si-based gallium nitride (GaN) optoelectronic devices with promising performances. For satisfying the spectral requirements in different devices, the control of the luminescence is of key importance. Here we report that utilizing Si-NPA as substrates, high-purity metal gallium as gallium source and ammonia gas as nitrogen source, GaN nanostructures were grown on Si-NPA by a chemical vapor deposition method. It was demonstrated that the photoluminescence (PL) properties of GaN/Si-NPA can be tuned effectively by changing the ammonia flow rate used during the growing process. Through analyzing the evolution of the PL spectra of GaN/Si-NPA with ammonia flow rate, the origins of the observed ultraviolet and visible PL were attributed to the near band edge emission and the emissions from Ga vacancy and N interstitial point defects, respectively. Therefore the variation of the PL spectra of GaN/Si-NPA with ammonia flow rate is actually a reflection of the change of the types and concentrations of point defects. The results might provide an efficient path for preparing Si-based GaN with controlled properties.