Slow Oxidation Research Articles

Experimental and Numerical Investigation of the Low-Frequency Inductive Features in Differential PEMFCs: Ionomer Humidification and Platinum Oxide Effects

The low-frequency inductive features in PEMFC are studied by differential measurements and numerical simulation. Systematic parameter variations are conducted and the discrepancies between the local polarization curve slopes and the capacitive loops of electrochemical impedance spectra (EIS) are evaluated to compute the inductive contributions. These contributions, primarily slow platinum oxide kinetics and ionomer humidification, are disentangled and we show that the latter is more relevant at medium to high currents, leaving mainly kinetics contributions of around 35 mV dec−1 at small currents. We demonstrate that the inductivity reaches over 150 mV dec−1 at high load and that it strongly depends on the current density (j) and on the relative gas humidity (RH), whereas temperature (T) and oxygen partial pressure () play a minor role. A new approach for modeling the combination of the oxygen reduction reaction and platinum oxidation leading to inductive loops is presented and integrated into a 1D through-plane model which we parameterize based on our large dataset. We present a comprehensive parameter study with this model. Its current version contains platinum oxide kinetics and electron, proton as well as oxygen transport and yields a good match with both steady-state and EIS data.

Fast and Durable Alkaline Hydrogen Oxidation Reaction at the Electron-Deficient Ruthenium-Ruthenium Oxide Interface.

The slow hydrogen oxidation reaction (HOR) kinetics under alkaline conditions remain a critical challenge for the practical application of alkaline exchange membrane fuel cells. Herein, Ru/RuO2 in-plane heterostructures are designed with abundant active Ru-RuO2 interface domains as efficient electrocatalysts for the HOR in alkaline media. The experimental and theoretical results demonstrate that interfacial Ru and RuO2 domains at Ru-RuO2 interfaces are the optimal H and OH adsorption sites, respectively, endowing the well-defined Ru(100)/RuO2 (200) interface as the preferential region for fast alkaline hydrogen electrocatalysis. More importantly, the metallic Ru domains become electron deficient due to the strong interaction with RuO2 domains and show substantially improved inoxidizability, which is vital to maintain durable HOR electrocatalytic activity. The optimal Ru/RuO2 heterostructured electrocatalyst exhibits impressive alkaline HOR activity with an exchange current density of 8.86mAcm-2 and decent durability. The exceptional electrocatalytic performance of Ru/RuO2 in-plane heterostructure can be attributed to the robust and multifunctional Ru-RuO2 interfaces endowed by the unique metal-metal oxide domains.

Facile preparation of nickel phosphide for enhancing the photoelectrochemical water splitting performance of BiVO4 photoanodes.

The photoelectrochemical (PEC) water splitting performance of BiVO4 (BVO), a promising photoanode material, is constrained by its extremely short hole diffusion length and slow water oxidation kinetics. Modification of oxygen evolution cocatalysts (OECs) by appropriate methods is a practical solution to enhance the PEC water splitting performance of BVO. In this work, two different nickel phosphides Ni2P and Ni12P5 were prepared by a facile and mild one-step solvothermal method, and used as OECs to modify a BVO photoanode for enhancing the PEC water splitting performance. The BVO/Ni2P and BVO/Ni12P5 photoanodes showed impressive photocurrent densities of 3.3 mA cm-2 and 3.1 mA cm-2, respectively. In addition, the PEC water splitting stability of the BVO/Ni2P photoanode was greatly enhanced compared to that of the bare BVO photoanode. Further characterization and photoelectrochemical analysis revealed that the significant improvement of the BVO photoanode performance was attributed to the effective inhibition of surface charge recombination, facilitation of interfacial charge transfer, and acceleration of water oxidation kinetics after Ni2P and Ni12P5 modification.

Improvements in the stability of biodiesel fuels: recent progress and challenges.

Fewer fossil fuel deposits, price volatility, and environmental concerns have intensified biofuel-based studies. Saccharification, gasification, and pyrolysis are some of the potential methods of producing carbohydrate-based fuels, while lipid extraction is the preferred method of producing biodiesel and green diesel. Over the years, multiple studies have attempted to identify an ideal catalyst as well as optimize the abovementioned methods to produce higher yields at a lower cost. Therefore, this present study comprehensively examined the factors affecting biodiesel stability. Firstly, isomerization, which is typically used to reduce unsaturated fatty acid content, was found to improve oxidative stability as well as maintain and improve cold flow properties. Meanwhile, polymers, surfactants, or small molecules with low melting points were found to improve the cold flow properties of biodiesel. Meanwhile, transesterification with an enzyme could be used to remove monoacylglycerols from oil feedstock. Furthermore, combining two natural antioxidants could potentially slow lipid oxidation if stainless steel, carbon steel, or aluminum are used as biodiesel storage materials. This present review also recommends combining green diesel and biodiesel to improve stability. Furthermore, green diesel can be co-produced at oil refineries that are more selective and have a limited supply of hydrogen. Lastly, next-generation farming should be examined to avoid competing interests in food and energy as well as to improve agricultural efficiency.

Self-assembled micro-nano flower-like/spherical magnesium hydroxide for heat-energy storage

In response to global energy problems, industrial waste heat storage systems are a useful strategy as important as clean energy. Slow magnesium oxide hydration rate and incomplete hydration are the main obstacles to the application of MgO/Mg(OH)2 to heat storage systems. In this study, porous structures are introduced into pure magnesium oxide materials to increase their specific surface area and enrich their pores, thereby increasing their hydration rate and conversion. The effective exothermic densities of the self-assembled micro-nano flower-like and spherical samples with high specific surface area are 955.6 kJ/kgMg(OH)2 and 1034.8 kJ/kgMg(OH)2, respectively, about 2 to 3 times that of commercially purchased magnesium hydroxide. Their hydration conversion rates are 51.0 % and 57.7 % at 20 min, respectively. They have potential for use in heat storage systems.

Gradient band alignment of N-doped titania nanosheets on TiO2 nanorod arrays for improved solar water oxidation

TiO2 is a typical semiconducting material for photoelectrochemical (PEC) hydrogen generation, but still suffers from poor light capturing capability and slow surface water oxidation kinetics. Herein, a homologous heterojunction has been designed and fabricated based on TiO2 nanorod arrays (NAs) and N-doped titania (Ti0.91O2−xNx) nanosheets (TON NSs). Owing to the narrower band gap, TON broadens light absorption range and enhances absorption intensity. More importantly, the employment of TON for interfacial modulation could accelerate the surface water splitting kinetics due to the gradient band alignment of TON/TiO2. The upshifted valence band could better drive the holes to travel across the surface of photoanode for water oxidation reaction. Consequently, the optimal TON/TiO2 photoanode has achieved a significantly improved photocurrent of 1.62 mA/cm2 at 1.23 V vs RHE, which is 2.45 times of that of TiO2. This work provides an effective strategy for the design and construction of homologous heterojunctions for energy catalytic reactions.

Quantification of plasma produced OH and electron fluxes at the liquid anode and their role in plasma driven solution electrochemistry

Plasma–liquid interactions enable various applications through the generation of a large range of reactive species in solution. In this work, we report on the interaction of a pulsed atmospheric pressure glow-like discharge with a liquid anode. Particularly, the flux of hydroxyl (OH) radicals and electrons in the plasma at the liquid anode are measured by laser induced fluorescence (LIF) spectroscopy and current measurements to investigate the role of OH and electrons in plasma-enabled redox chemistry in solution. The impact of the voltage pulse width, voltage amplitude, liquid temperature and conductivity on the OH density distribution was also investigated. We observed a significant OH density near the liquid surface, which showed a transition from a ring-shaped structure to a more uniform structure with increasing plasma power. This transition coincided with a similar transition in the plasma emission intensity and electron density profile. A Raman laser scattering study indicated that this transition can be attributed to an enhanced N2 mixing at larger plasma-dissipated powers. Besides, a time resolved measurement showed that the OH density segregates radially in the afterglow at velocities exceeding the gas velocity at room temperature due to enhanced gas convection resulting from the plasma-induced gas heating. While the OH flux was of the order of ∼1021 m−2 s−1, approximately two orders of magnitude lower than the electron flux, significant reduction in the solution occurs during the voltage pulse. Nonetheless, a slow oxidation was observed in the afterglow due to the much longer lifetime of OH radicals compared to electrons. The Faradaic efficiency of the liquid redox chemistry was evaluated with H cell measurements and showed a good agreement with a 1D liquid phase model with the measured electron and OH fluxes as the input. This result shows the capability to quantitatively describe the plasma-driven solution electrochemistry for a model redox couple based on OH and electron driven reactions.

Effects of air volume and pre-oxidation on re-ignition characteristics of bituminous coal

Coal spontaneous combustion (CSC) seriously threatens the safety of coal mines. To reduce the spontaneous combustion risk of residual oxidized coal in goaf near coal seam and thick coal seam, it is necessary to study the re-ignition process of coal in depth. The re-ignition process of bituminous coal under different pre-oxidation temperatures and air volume rates was tested by temperature-programmed experiments. The gas index and re-ignition characteristic parameters of low-temperature oxidized coal were analyzed. The results show that CO production, C2H4 concentration, and Graham's fire coefficient (R2, R3) can be used as indicator gases to predict the CSC process. Meanwhile, the oxygen consumption rate and heat release intensity of raw coal and oxidized coal have a good exponential relationship with the coal temperature. In addition, during the slow oxidation stage of bituminous coal, the pre-oxidation process and the increased air volume can increase the oxygen consumption and heat release and reduce the activation energy, which aggravates the risk of spontaneous combustion. The results can enrich the research on the re-ignition characteristics of oxidized coal and can be applied to the management and control of CSC.

Effect of Annealing Time on the Cyclic Characteristics of Ceramic Oxide Thin Film Thermocouples.

Oxide thin film thermocouples (TFTCs) are widely used in high-temperature environment measurements and have the advantages of good stability and high thermoelectric voltage. However, different annealing processes affect the performance of TFTCs. This paper studied the impact of different annealing times on the cyclic characteristics of ceramic oxide thin film thermocouples. ITO/In2O3 TFTCs were prepared on alumina ceramics by a screen printing method, and the samples were annealed at different times. The microstructure of the ITO film was studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results show that when the annealing temperature is fixed, the stability of the thermocouple is worst when it is annealed for 2 h. Extending the annealing time can improve the properties of the film, increase the density, slow down oxidation, and enhance the thermal stability of the thermocouple. The thermal cycle test results show that the sample can reach five temperature rise and fall cycles, more than 50 h, and can meet the needs of stable measurement in high temperature and harsh environments.

Oxides spallation/cracking and oxidation kinetics behaviours of microstructurally different regions of TIG joint in Cr-Mo (T11) boiler steel under cyclic environment

Many times the power industry shutdowns due to unplanned maintenance. In such environments, the spallation/cracking is increased in the protective oxide layer, results an explosion in tube joints which threatens the safety of the power industry. In this investigation, microstructurally different regions of TIG joint in T11 boiler steel were examined by the thermogravimetry method under cyclic conditions. The kinetics of oxides in these regions of TIG joint after some initial cycles was parabolic with increased cracks at cyclic stresses. The higher spallation of oxide scale on the HAZ than the weld metal was because more cracking occurred under the cyclic process. The weld metal showed slow oxidation kinetics in comparison to HAZ.

BiVO4/Rh–Ci/HCO3− hetero-/homogeneous dual co-catalyst-decorated photoanode system for photoelectrochemical water oxidation

Bismuth vanadate is one of the most efficient photoanode materials for solar water-splitting. However, its performance is limited by two main factors: poor charge separation and slow water oxidation kinetics. Herein, Rh–Ci/HCO3− hetero-/homogenous dual co-catalysts were introduced on the BiVO4 surface to improve the water oxidation performance. This Rh–Ci/HCO3− dual co-catalyst system improved the water oxidation activity of BiVO4 by enhancing the charge injection efficiency and stabilizing the photoelectrochemical water oxidation kinetics. BiVO4 decorated with Rh–Ci/HCO3− exhibited a higher photocurrent (2.011 mA∙cm−2) at 1.23 VRHE than bare BiVO4 (1.217 mA∙cm−2).

FeNi-MIL53 bimetallic MOFs as a visible light photocatalyst for water oxidation

Photocatalytic water splitting is an appealing process for solar energy conversions, yet it is often limited by the slow oxidation of water to oxygen half-reaction. Here, a series of Ni (II)-doped Fe-MIL53 to form FeNi(x:1)-MIL53 were synthesized by solvothermal method as water oxidation photocatalysts and their photocatalytic performance was optimized by adjusting the mole ratio of central metal element Fe/Ni. The results showed that the unique bimetallic nanostructure of FeNi(9:1)-MIL53 had been proved to be superior to Fe-MIL53 with a single metal center in photocatalytic water oxidation. The initial quantum yield of FeNi(9:1)-MIL53 reached 47.80 %, and its oxygen evolution rate was 0.587 mmol/(g.s).The high photocatalytic performance of FeNi(9:1)-MIL53 was mainly due to the good synergistic effect and the charge transfer between Fe and Ni ions, which is expected to be an efficient photocatalyst for water oxidation.

Thermal decomposition characterization and kinetic parameters estimation for date palm wastes and their blends using TGA

TGA has been used to evaluate the thermal degradation profiles and kinetic parameters for the pyrolysis of date leaves, date seeds, and leaf stems and their blend at various heating rates (β) in N2. Using Kissinger–Akahira–Sunose (KAS), and Ozawa-Flynn-Wall (OFW), kinetic parameters like activation energy (E) and frequency factor (A) were estimated. The diffusion, reaction order, and power law models were used to estimate the frequency factors based on the (E) values obtained from the OFW and KAS approaches. Thermal degradation profiles showed two major loss processes: volatilization of cellulose, hemicelluloses, and lignin; and slow oxidation of the residual char. The findings demonstrated that as β increased, the TG profiles shifted to higher temperature ranges. The date palm's decomposition was not favourably reflected by the high (ΔGav) values obtained. The high (ΔSav) values obtained using OFW compared to KAS confirm these materials' high reactivity. The average activation energies (Eav) for the different parts of the date palm wastes ranged between 86 and 117 kJ/mole as predicted by the KAS method, while they were between 92 and 120 kJ/mole using the OFW method. The calculated frequency factor (A) values, evaluated by the KAS and the OFW methods, ranged between 0.0 and ∼ 0.8 × 1019min-1. The difference in (Eav) values between the KAS and OFW techniques is no greater than 8 kJ/mole. For the diffusion models of DSW, DL, and Blend, the best frequency distribution profiles are essentially normal, and the blend exhibits high frequency (A) values in a relatively constrained range of (α). That denotes quick and efficient pyrolysis. The pyrolysis index (CPI) significantly increased as β increased, indicating that pyrolysis was profitable at high heating rates. The volatile release index (Ddev) increases significantly with increasing (β) value, showing that volatiles was easier to release at a high heating rate.

Formation of CuO whiskers and facet-controlled oxidation during the oxidation of Au-Cu nanoparticles fabricated by solid-state dewetting

The fabrication of cupric oxide (CuO) nanowires from Cu particles via thermal oxidation provides a simple and scalable method to produce hierarchical structures. A stress-induced growth mechanism is believed to account for the nanowire formation while a slow oxidation rate is favored to sustain the driving force. Here, CuO whiskers are grown from Au-Cu nanoparticles because the formation of Au-Cu phases decreases the Cu diffusion rate and in turn slows down the oxidation rate. The driving force for the whisker growth is attributed to the compressive stress imposed by the CuO shell on the Au-Cu core, which is induced by the significantdifference in their linear thermal expansion coefficients. The contribution of the compressive stress is proved by the calculation. Moreover, preferred oxidation is observed and it is related to the crystalline structures of different facets existing on the surface of Au-Cu nanoparticles. The more compact the plane, the slower the diffusion rate through the plane, resulting in the formation of thinner CuO on the relevant facet. The results open a cost-effect way to fabricate hybrid nanostructures consisting of Cu-based core–shell nanoparticles attached with CuO whiskers and bring new insights into the oxidation behaviors of Cu on different crystal planes.

Electronegative Cl− modified BiVO4 photoanode synergized with nickel hydroxide cocatalyst for high-performance photoelectrochemical water splitting

BiVO4 is a promising photoanode material for converting solar energy into hydrogen fuel, but its practical applicability is primarily constrained by severe surface charge recombination and slow water oxidation processes. Here, the modification of BiVO4 surface by Cl− with appropriate electronegativity greatly promoted the photoelectric water oxidation activity. The Cl-BiVO4 electrode exhibited a photocurrent of 2.55 mA cm−2, at 1.23 V vs RHE. The research shows that the surface anion polarization of BiVO4 is helpful for trapping photogenerated holes and prolonging the electron lifetimes. Then, the cocatalyst Ni(OH)2 is anchored on Cl-BiVO4 by a simple impregnation method, and a high-performance photoanode Ni(OH)2/Cl-BiVO4 is successfully constructed. The photocurrent density of the composite photoanode is 4.33 mA cm−2 (1.23 V vs RHE), which is approximately 3.0 times that of pure BiVO4 (1.44 mA cm−2). Moreover, the initial potential is negatively shifted, and the ABPE, IPCE and charge separation efficiency are also significantly improved. This research presents a simple and effective strategy for producing low-cost, high-performance solar water decomposition catalysts.

Influence of oxygen addition on the oxidation resistance of TiAlN

Here, we explore the effect of O-addition on the oxidation resistance of TiAlN coatings by experimental and theoretical methods. Due to the retarded transformation of anatase to rutile TiO2, Ti0.41Al0.59(O0.08N0.92)1.02 with the raised oxidation onset temperature and slow oxidation process reveals improved oxidation resistance than Ti0.42Al0.58N0.95. Further ab initio calculations attribute the optimization to the preferential adsorption of oxygen to form the protective Al2O3 phase and suppressed formation of metastable a-TiO2 phase in the initial stage of oxidation. However, both experimental and calculated results reveal that further increasing oxygen content to Ti0.41Al0.59(O0.12N0.88)1.06 shows the rapid transformation of TiO2 accompanied with the cracking of the protective Al-oxide rich top-layer, which tremendously deteriorates the oxidation resistance. After oxidation at 800 °C for 30 h, Ti0.42Al0.58N0.95, Ti0.41Al0.59(O0.08N0.92)1.02 and Ti0.41Al0.59(O0.12N0.88)1.06 coatings present oxide layers of ∼953, ∼640 and ∼971 nm, respectively.

Multi-Function of the Ni Interlayer in the Design of a BiVO4-Based Photoanode for Photoelectrochemical Water Splitting.

BiVO4 with an appropriate band structure is considered to be an ideal candidate for photoanodes. However, slow water oxidation kinetics and low charge separation efficiency seriously restrict its application. To address these issues, an NF/N/BVO photoanode with a hierarchical network structure was successfully constructed by direct-current magnetron sputtering of Ni followed by electrochemical deposition of nickel-iron layered double hydroxide (NiFe-LDH) on BiVO4. A photocurrent density of 4.50 mA/cm2 was obtained for NF/N/BVO, which was 2.4 times that for pristine BiVO4. The introduction of the Ni layer contributed to the following growth of NiFe-LDH nanosheets with larger size, which acted as active sites and speeded up water oxidation kinetics. Furthermore, surface photovoltage microscopy revealed that Ni and NiFe-LDH acted as the electron collector and hole reservoir, respectively. The co-existence of the two components constituted a highly efficient surface charge separation structure, which was one of the important issues for the excellent water oxidation activity.

Integrated Lipidomic and Metabolomics Analysis Revealing the Effects of Frozen Storage Duration on Pork Lipids.

Frozen storage is an important strategy to maintain meat quality for long-term storage and transportation. Lipid oxidation is one of the predominant causes of the deterioration of meat quality during frozen storage. Untargeted lipidomic and targeted metabolomics were employed to comprehensively evaluate the effect of frozen duration on pork lipid profiles and lipid oxidative products including free fatty acids and fatty aldehydes. A total of 688 lipids, 40 fatty acids and 14 aldehydes were successfully screened in a pork sample. We found that ether-linked glycerophospholipids, the predominant type of lipids, gradually decreased during frozen storage. Of these ether-linked glycerophospholipids, ether-linked phosphatidylethanolamine and phosphatidylcholine containing more than one unsaturated bond were greatly influenced by frozen storage, resulting in an increase in free polyunsaturated fatty acids and fatty aldehydes. Among these lipid oxidative products, decanal, cis-11,14-eicosenoic acid and cis-5,8,11,14,17-dicosapentaenoic acid can be considered as potential indicators to calculate the freezing time of unknown frozen pork samples. Moreover, over the three-month frozen storage, the first month was a rapid oxidation stage while the other two months were a slow oxidation stage.

Evaluation of the factors affecting arsenic distribution using geospatial analysis techniques in Dongting Plain, China

Due to high toxicity, arsenic is regarded as a major global environmental pollutant. The present study is investigated the potential factors influencing to elevate concentration of arsenic in groundwater, surface water, and soil of the Dongting basin. The arsenic contamination potential prediction map and categories were developed using various GIS techniques such as Ordinary Kriging and the Quantile method. Then the “Raster calculator” tool was applied to verify the impact of the factors on arsenic. Eighty-four single-factor, bi-factor, and multi-factor models were established to investigate effective combinations among factors of each phase. Additionally, statistical tests were computed to evaluate arsenic between classes and factors. The arsenic value varies in groundwater from 0.0001 to 0.1582 mg/l, while in surface water between 0.0001–0.0287 mg/l and soil sediments range from 1.8–45.69 mg/kg. JunShan and GongAn groundwater resources have been identified as posing a high risk to human health. The single factors showed the best match frequency of arsenic with a population density of 66.86% in water and land use depicted match frequency of arsenic 73.19% in soil. The statistical calculations with percentage frequency factors also depicted positive trends. The correlation of the factors with arsenic in soil and water showed slow oxidation and reduction in the groundwater system. Treated portable water could be the best option to reduce the health risk of the local community.

A Study on the Influence of Air Humidity on the Characteristic Parameters and Thermal Effect of Coal Spontaneous Combustion

ABSTRACT Air humidity has a significant effect on the characteristic parameters and heat changes of the coal spontaneous combustion process. In this study, a self-built precision humidity-generating device with adjustable humidity was used to investigate the effect of different humidity conditions on the spontaneous combustion process of coal. The release of indicator gases was determined by a humidity-generating unit in conjunction with a temperature-programmed device for coal oxidation, and the effect of air humidity on coal spontaneous combustion was studied from a macroscopic perspective. A quantitative study of the effect of air humidity on the heat released during the spontaneous combustion of coal was carried out by obtaining data for exothermic heat release intensity by conducting thermal analysis. Meanwhile, the numerical simulation method was used to study the influence of air humidity on the heat released during the coal spontaneous combustion process. The experimental results indicated that the introduction of moist air could significantly increase the oxygen consumption rate of the coal samples and promote the production of CO and CO2. In the slow oxidation stage, the air humidity has a greater effect on the heat release than that in the accelerated and fast oxidation stages. The simulated results of heat release in the slow oxidation phase are consistent with the experimental data, verifying that the moisture in the air can increase the amount of heat release and promote the coal-oxygen reaction. When the moisture in the air first came into contact with the coal, it released a large amount of adsorption heat in a short time, which increased the coal temperature.