Slow Oxidation Research Articles

Accelerated Ion‐Electron Transport in Bi‐Heterostructures Constructed Based on Ohmic Contacts for Efficient Bi‐Directional Catalysis of Lithium‐Sulfur Batteries

AbstractAlthough lithium‐sulfur batteries have satisfactory theoretical specific capacity and energy density, they are difficult to further commercialize due to the shuttle effect of soluble polysulfides and slow sulfur oxidation kinetics. Based on this, in this work, the catalyst MXene‐VS4‐SnS2 (MVS), a dual heterostructured catalyst with ohmic contacts, is prepared by a one‐step hydrothermal method and electrostatic self‐adsorption for lithium‐sulfur battery cathode materials. Experimental and theoretical results show that the ohmic contact induces spontaneous charge rearrangement, resulting in the formation of a fast charge transfer pathway at the MVS heterojunction interface, which helps to reduce the energy barrier for polysulfide reduction and Li2S oxidation during the discharge/charge process. In addition, the inherent sulfophilicity of VS4 and SnS2 promotes the conversion of S species, while the pleated MXene nanosheets not only provide a highly conductive network for the active sulfur but also retain a rich internal space to maintain the integrity of the cathode structure during the continuous cycling process. As a result, the MVS cathode exhibits excellent electrochemical performance even under high sulfur loading. The integration of excellent performance with a facile synthesis process provides a promising approach for designing highly efficient electrocatalysts suitable for the energy field.

Synergistic Effect of FeOOH Cocatalyst and Al2O3 Passivation Layer on BiVO4 Photoanode for Enhanced Photoelectrochemical Water Oxidation

BiVO4 is one of the most attractive photoanodes for water oxidation due to its 2.4eV narrow band gap, suitable band edge position, good stability in aqueous solution, low cost and non-toxicity. However, due to some inherent disadvantages such as low carrier mobility, severe charge recombination and slow water oxidation kinetics, the actual BiVO4 photocurrent density is often lower than the theoretical value of 7.5mAcm-2. In this paper, BiVO4 was modified by alkali-treated Al2O3 passivation layer and FeOOH, and the photocurrent density of BiVO4 reached an astonishing 3.8mAcm-2 at 1.23 VRHE, and the ABPE (applied bias photon-to-current efficiency) was close to 1%. The detailed structural characterization and electrochemical test show that Al2O3 prepared by ALD (atomic layer deposition) can play a role in passivation of BiVO4 surface state after alkali treatment, inhibit electron hole recombination on BiVO4 surface, and accelerate hole transfer. As a hole storage layer and catalyst layer, FeOOH promoted the interfacial hole transfer, increased the active sites at the electrode electrolyte interface, and significantly increased the water oxidation activity. This work provides a novel method to enhance the performance of water electrolysis by using ALD to assist passivation of bismuth vanadate photoanode surface states.

Projecting the Long-Term Life of SiC Fibers to Low Stresses: The Competition Effect Between Slow Crack Growth and Oxidation Embrittlement

Projecting the Long-Term Life of SiC Fibers to Low Stresses: The Competition Effect Between Slow Crack Growth and Oxidation Embrittlement

Boosting Photoelectrochemical Water Oxidation Performance of Ti–Fe2O3 Photoanode via NH2–MIL–53(FeCo) as a Cocatalyst

α–Fe2O3 is a promising photoanode that can be used for solar‐driven photoelectrochemical (PEC) water splitting. However, due to low carrier separation efficiency and slow water oxidation kinetics, the PEC performance of Ti–Fe2O3 is still severely hindered. Here, a novel inorganic–organic hybrid composite photoanode is prepared by depositing NH2–materials of institute Lavoisier (MIL)–53(FeCo) cocatalyst on the surface of Ti–Fe2O3 using solvothermal method. In the results, it is shown that the Ti–Fe2O3/NH2–MIL–53(FeCo) photoanode has a high photocurrent density (3.0 mA cm−2 at 1.23 V vs reversible hydrogen electrode (RHE), which is 5.1 times that of bare Ti–Fe2O3, and the initial potential of water oxidation also undergoes a negative change of about 100 mV. The separation efficiency of Ti–Fe2O3/NH2–MIL–53(FeCo) is significantly enhanced, and the charge injection efficiency increases from 17.6% to 68% at 1.23 V versus RHE. In the further research, it is suggested that the excellent PEC performance of Ti–Fe2O3/NH2–MIL–53(FeCo) may be attributed to an increase in carrier density, prolonged carrier recombination time, and an increase in exposed reactive sites. In this study, a new understanding for the design of Ti–Fe2O3 photoanodes with superior PEC performance based on metal organic framework modification is provided.

Electrothermal Conversion of Methane to Methanol at RoomTemperature with Phosphotungstic Acid.

Traditional methods for the aerobic oxidation of methane to methanol frequently require the use of noble metal catalysts or flammable H2-O2 mixtures. While electrochemical methods enhance safety and may avoid the use of noble metals, these processes suffer from low yields due to limited current density and/or low selectivity. Here, we design an electrothermal process to conduct aerobic oxidation of methane to methanol at room temperature using phosphotungstic acid (PTA) as a redox mediator. When electrochemically reduced, PTA activates methane with O2 to produce methanol selectively. The optimum productivity reaches 29.45 [[EQUATION]] with approximately 20.3% overall electron yield. Under continuous operation, we achieved 19.90 [[EQUATION]] catalytic activity, over 74.3% methanol selectivity, and 10 hours durability. This approach leverages reduced PTA to initiate thermal catalysis in solution phase, addressing slow methane oxidation kinetics and preventing overoxidations on electrode surfaces. The current density towards methanol production increased over 40 times compared with direct electrochemical processes. The in-situ generated hydroxyl radical, from the reaction of reduced PTA and oxygen, plays an important role in the methane conversion. This study demonstrates reduced polyoxotungstate as a viable platform to integrate thermo- and electrochemical methane oxidation at ambient conditions.

Electrothermal Conversion of Methane to Methanol at Room Temperature with Phosphotungstic Acid

Traditional methods for the aerobic oxidation of methane to methanol frequently require the use of noble metal catalysts or flammable H2‐O2 mixtures. While electrochemical methods enhance safety and may avoid the use of noble metals, these processes suffer from low yields due to limited current density and/or low selectivity. Here, we design an electrothermal process to conduct aerobic oxidation of methane to methanol at room temperature using phosphotungstic acid (PTA) as a redox mediator. When electrochemically reduced, PTA activates methane with O2 to produce methanol selectively. The optimum productivity reaches 29.45 [[EQUATION]] with approximately 20.3% overall electron yield. Under continuous operation, we achieved 19.90 [[EQUATION]] catalytic activity, over 74.3% methanol selectivity, and 10 hours durability. This approach leverages reduced PTA to initiate thermal catalysis in solution phase, addressing slow methane oxidation kinetics and preventing overoxidations on electrode surfaces. The current density towards methanol production increased over 40 times compared with direct electrochemical processes. The in‐situ generated hydroxyl radical, from the reaction of reduced PTA and oxygen, plays an important role in the methane conversion. This study demonstrates reduced polyoxotungstate as a viable platform to integrate thermo‐ and electrochemical methane oxidation at ambient conditions.

Influence of Nitride Coatings on Corrosion Resistance and the Biocompatibility of Titanium Alloy Products

The bioadhesion of bacteria to the surface of samples with Ti–TiN, Zr–ZrN, Zr–(Zr, Nb)N, and Zr–(Zr, Hf)N coatings was studied via incubation with gram-positive strains of Staphylococcus aureus. The samples were kept at 25 °C for 30 days in a 3% NaCl solution. The deposition of coatings slows, whereas oxidation processes intensify. The oxygen content on the TiN and (Zr, Nb)N coating surfaces was higher than that of the Ti sample without a coating. Samples with ZrN and, especially, (Zr, Hf)N coatings resist oxidation better. Regarding bioactivity toward S. aureus, the highest density of biological forms was observed on the surfaces of TiN and (Zr, Hf)N coatings. The lowest density was on the surfaces of uncoated, ZrN-coated, and (Zr, Nb)N-coated samples. On Ti–TiN, Zr–ZrN, and Zr–(Zr, Nb)N coatings, the formation of surface biostructures of a filamentary type was observed. In the uncoated sample, the biostructures have an island character, and in the sample with a Zr–(Zr, Hf)N coating, the formation of extensive areas of biostructures was observed. Between the biostructures and coating, a layer 5 to 15 nm thick was observed, presumably associated with bacterial adhesion. The presence of biostructures on the coating surface can activate or slow oxidation processes.

Colorimetric Oxygen Sensing by Analyzing Chromaticity Points for Polymer Cobalt Schiff Base in CIELAB

AbstractPolymer membranes of a copolymer ligand (L) coordinated to tetra‐coordinated N,N'‐ethylene bis(salicylideneiminato) cobalt(II) at the fifth coordinating site of the center cobalt(II), Co(II)S‐L, are prepared to measure colorimetrically the color changes in response to rapid reversible oxygen binding simultaneously with slow oxidation under moist conditions to yield Co(III)S‐L. The chromaticity point observed in CIELAB is the endpoint of the vector sum of the unit vectors for Co(II)S‐L, O2‐Co(II)S‐L, and Co(III)S‐L, scaled by their respective abundance ratios: (1 − m)(1 − n), m(1 − n), and n, where m is the ratio of O2‐Co(II)S‐L to the sum of Co(II)S‐L and O2‐Co(II)S‐L and n is the ratio of Co(III)S‐L to the total of the three cobalt complexes. The observed limited area in CIELAB as a stoichiometric Euclidean space is supported by the following two different reaction processes of the polymer membranes: an oxygen‐binding reaction under several different partial pressures of oxygen supplied to the membranes in a short period, during which oxidation of the cobalt(II) complexes is negligible, and an oxidation reaction over a long period at a constant partial pressure of oxygen. The chromaticity points in both processes progress linearly in three different two‐dimensional coordinates: a*b*, a*L*, and b*L*.

Enhancing hydrogen oxidation by Modulating Ru species on Ni3N@Mo2C through a Support-Induced Strategy

The use of hydrogen as an intermediator to convert and store electrochemical energy has been a subject of significant interest and focus. Unfortunately, the slow alkaline hydrogen oxidation reaction (HOR) is a barrier to further development of hydrogen–oxygen fuel cells. Ruthenium (Ru) has recently been investigated as a possible replacement for platinum (Pt) catalyst in the HOR because of the similar hydrogen binding energy (HBE) to Pt. Herein, Ru species was loaded on Ni3N@Mo2C support, which was used as an electrocatalyst for HOR. The catalyst presents an exchange current density and kinetic current densities of 3.05 and 4.76 mA cmdisk−2 that are 2 and 1.4 times greater than that of commercial Pt/C, respectively. The findings indicate that the Ni3N@Mo2C support reduces the hydrogen binding energy on Ru sites. This improves the Volmer step for HOR and increases the catalytic activity. This study thus provides some guidance in the designing of HOR catalysts for efficient hydrogen energy conversion.

Enhancing the photoelectrochemical performance of TiO2 photoanode by employing carbon nanoparticles as electron reservoirs and photothermal materials.

Photoelectrochemical (PEC) water splitting is regarded as a potential technique for converting solar energy. However, the fast charge recombination and slow water oxidation kinetics significantly have hindered its practical application. It is found that an elevation in operation temperature can activate the charge transport in the photoanodes. Here, a strategy was performed that carbon nanoparticles were employed to TiO2 nanorods, acting as electron reservoirs as well as photothermal materials. More specifically, a record photocurrent density of 1.62mAcm-2 at 1.23V vs. RHE has been achieved, accompanied by a high charge separation efficiency of 96% and a long-term durability for 8h. The detailed experimental results reveal that under NIR light irradiation, the synergistic effect between electron storage and temperature rise leads to accelerated charge transport in the bulk and water oxidation kinetics on the surface. This research offers a new perspective on how to boost the PEC performance of photoelectrodes.

A synthetic method for lanthanum hydroxychloride suitable for industrialization and its thermal decomposition properties.

A reactive crystallization method for the synthesis of lanthanum hydroxychloride (La(OH)2Cl) was developed to provide a new low-carbon route for the purification of rare earth elements in hydrometallurgy. The synthetic method reported herein represents a unique low-temperature route, short preparation time and inexpensive materials compared with previous methods, thus making it promising for industrial applications. The key factors controlling the product's phase were determined using single factor tests involving temperature, concentration of NH4Cl in the base solution and the molar ratio of NH4OH/La3+ added per minute into the base solution. Otherwise, the outcome is lanthanum hydroxide (La(OH)3). Subsequently, the synthesized products were characterized by employing X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). Finally, the thermal decomposition behavior of La(OH)2Cl was assessed using thermogravimetry (TG) and differential scanning calorimetry (DSC). Lanthanum oxychloride (LaClO) was obtained at about 360 °C. The thermal transformation from LaClO to La2O3 started at 400 °C and was a slow oxidation process. Pure La2O3 could be obtained when the temperature increased to 1500 °C.

Role of volatile secondary char on the combustion behavior of cellulose-based hydrochars

Hydrothermal carbonization (HTC) can transform a wide range of biomass into renewable biofuels. Hydrochar, the solid fuel resulting from HTC, has a similar energy density to low-rank coals. Despite an extensive body of literature detailing the thermogravimetric analysis (TGA) of hydrochar under slow pyrolysis and oxidation, there remains a limited understanding of hydrochar's behavior in realistic combustion settings. In this work, we integrate combustion experiments and TGA to understand the combustion characteristics of a model hydrochar fuel. Cellulose-based hydrochars produced at different temperatures along with solvent-extracted chars are tested in a Hencken burner across varying temperatures and oxygen concentrations in the oxidizer gas. Simultaneous CH* chemiluminescence, particle image velocimetry, and two-color pyrometry are used to measure ignition delay time and identify homogeneous/heterogeneous ignition mechanisms and combustion phases. Incorporating TGA with combustion results shows that the ignition mode and combustion processes are strong functions of surrounding gas temperature and oxygen mole fraction. The level of carbonization of the hydrochar dictates the ignition delay time and combustion modes. Further, the presence of a tar-like secondary char on the as-carbonized hydrochars leads to more rapid ignition due to high volatility.

Pd-Ru pair on Pt surface for promoting hydrogen oxidation and evolution in alkaline media

Hydrogen oxidation reaction in alkaline media is critical for alkaline fuel cells and electrochemical ammonia compressors. The slow hydrogen oxidation reaction in alkaline electrolytes requires large amounts of scarce and expensive platinum catalysts. While transition metal decoration can enhance Pt catalysts’ activity, it often reduces the electrochemical active surface area, limiting the improvement in Pt mass activity. Here, we enhance Pt catalysts’ activity without losing surface-active sites by using a Pd-Ru pair. Utilizing a mildly catalytic thermal pyrolysis approach, Pd-Ru pairs are decorated on Pt, confirmed by extended X-ray absorption fine structure and high-angle annular dark-field scanning transmission electron microscopy. Density functional theory and ab-initio molecular dynamics simulations indicate preferred Pd and Ru dopant adsorption. The Pd-Ru decorated Pt catalyst exhibits a mass-based exchange current density of 1557 ± 85 A g−1metal for hydrogen oxidation reaction, demonstrating superior performance in an ammonia compressor.

Arc erosion characteristics of cables with heatproof insulations in AC series circuits at low pressure

Abstract The droplet diameter, dripping frequency, and arc bead appearances vary significantly with pressure. This study investigated the arc erosion characteristics of copper-core cable with mica insulation (HC0) and aluminum-core cable with PI insulation (HA0) at different pressures. During arcing of HC0, the diameters of dripping droplets decrease as pressure decreases, but the dripping frequency exhibits an increasing trend. The primary arc beads (PABs) of HA0 at atmospheric pressure are mainly globular arc beads. HA0 PABs at 60 kPa are mostly coral arc beads, which is attributed to the slow oxidation rate and easier outflow of liquid aluminum through cracks at low pressure. HA0 PABs have the characteristics of coral arc beads and gradual necking, which broadens the previous theory in accident investigations that coral arc beads and gradual necking are considered as physical evidences of fire globules and short-circuit melted marks. Besides, the influence of pressure on arc duration of HC0 and HA0 is revealed. This study could provide support for fire accident investigation and arc accident prevention.

Ageing characterization and origin traceability of archaeological amber artefacts via FTIR spectroscopy and pyrolysis-gas chromatography/mass spectrometry

The archaeological amber artefacts from various periods in China provide valuable insights into ancient international trade and cultural interactions. This study investigated several archaeological amber artefacts (Arc 1–6) from the collection of the Hunan Museum, originating from different historical periods. The examination of the ageing characteristics of the cross-section and weathered surface was carried out using scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) spectroscopy and Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) to analyse the functional groups and chemical compositions. FTIR spectroscopy proved limited information in determining the origin due to natural ageing causing alterations in peak shape/position or signal noise. Py-GC/MS analysis identified the amber artefacts as succinite and revealed that a set of compounds can serve as markers for identifying the origin. The pyrogram patterns classified the samples into two groups based on the marker content. Py-GC/MS results indicated that hydrolysis is an inevitable degradation process during the burial of succinite. Additionally, amber went slow oxidation in low-oxygen environments, leading to cyclization and the formation of polycyclic structures. This research highlights the ageing characteristics of amber artefacts and demonstrates that Py-GC/MS is an effective way in determining the provenance of significantly degraded samples, providing clues to ancient trade routes and cultural exchanges via the Silk Road.

(Invited) Understanding Photo-Driven Water Oxidation Mechanisms

Water oxidation is an important reaction that produces electrons and protons, which are important for downstream reactions such as hydrogen production and carbon dioxide reduction. Presently, the slow water oxidation is a key limiting factor for the development of hydrogen production and/or carbon dioxide reduction into practical solar energy storage technologies. An important reason for the slow progress in solve water oxidation problems is the lack of knowledge on the detailed mechanisms by which water is oxidized. As a multi-step process, the reaction involves at least 4 protons and 4 holes (when the desired product is oxygen gas). Intuitively, the coordination of charges and protons plays a critical role, but the details remain unknown. In this talk, we report our recent progress in understanding how water oxidation is influenced by surface hole behaviors. Using an Ir-based catalyst that features atomically defined structures, we were able to systematically vary a number of parameters, including the hole concentration, the density of active sites, as well as the properties of the supporting substrate that determines hole accumulation. It was found that matching the concentrations of surface holes and active site densities is critical. It was also revealed that the support substrate could have a profound influence on the reaction kinetics, even though they do not directly participate in the reactions. This knowledge is expected to propel the development of catalysts for improved water oxidation under photochemical conditions.

Recrystallization reduces surface oxygen vacancies to unlock hole transfer channel for hematite photoelectrochemistry

Hematite is a promising photoanode in photoelectrochemical water splitting system, but the slow water oxidation kinetics at the photoanode/electrolyte interface seriously limits the photoelectrochemical properties. Improving the surface state of hematite is an effective method to improve the transport and separation of carriers. Herein, we propose a strategy to recrystallize the hematite, which can effectively reduce the oxygen vacancies on the surface of hematite, increase active sites and improve the oxidation activity of water. The experimental results show that the charge recombination rate of the recrystallized Fe2O3 photoanode is reduced, and the carrier transport efficiency is improved. The photocurrent density at 1.23 V is four times higher than that of the original hematite, and the initial potential shifts negatively by about 20 mV, which is attributed to the upward bending of hematite energy band and the reduction of surface defects after treatment. This research provides a feasible strategy for designing efficient α-Fe2O3 photoanode.

Bifunctional g-C3N4 nanospheres/CdZnS QDs S-scheme photocatalyst with boosted H2 evolution and furfural synthesis mechanism

Photocatalytic H2 evolution coupled with organic oxidation could replace the slow four-electron water oxidation and utilize charge carriers to obtain high-valued chemicals. Herein, inorganic CdZnS quantum dots (QDs) are skillfully deposited on g-C3N4 nanospheres to construct an inorganic-polymeric S-scheme heterostructure. The C3N4-CdZnS photocatalyst presents enhanced light absorption, abundant active sites, and intimate interface contact. The optimized composite exhibits an enhanced H2 evolution rate of 582.3 μmol/g/h and a furfuryl alcohol (FAL) conversion of 84.2 %. Femtosecond transient absorption (fs-TA) spectroscopy, in-situ irradiation X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and theoretical calculation (DFT) verify the S-scheme mechanism, which promotes charge separation and strengthens carrier redox ability. In-situ infrared spectra reveal that FAL is first activated to ·C5H5O2 radical by holes in CdZnS and further oxidized to furfural (FF) with dehydrogenation of its hydroxyl group. This work supplies new insight into designing efficient photocatalysts for H2 generation and organic synthesis.

Selective atomic sieving across metal/oxide interface for super-oxidation resistance

Surface passivation, a desirable natural consequence during initial oxidation of alloys, is the foundation for functioning of corrosion and oxidation resistant alloys ranging from industrial stainless steel to kitchen utensils. This initial oxidation has been long perceived to vary with crystal facet, however, the underlying mechanism remains elusive. Here, using in situ environmental transmission electron microscopy, we gain atomic details on crystal facet dependent initial oxidation behavior in a model Ni-5Cr alloy. We find the (001) surface shows higher initial oxidation resistance as compared to the (111) surface. We reveal the crystal facet dependent oxidation is related to an interfacial atomic sieving effect, wherein the oxide/metal interface selectively promotes diffusion of certain atomic species. Density functional theory calculations rationalize the oxygen diffusion across Ni(111)/NiO(111) interface, as contrasted with Ni(001)/NiO(111), is enhanced. We unveil that crystal facet with initial fast oxidation rate could conversely switch to a slow steady state oxidation.

Photothermal catalysis enhances cellulose oxidation kinetics to promote the hydrogen evolution in alkaline solution over Pt/ZnIn2S4

The slow oxidation kinetics of cellulose severely limits photocatalytic cellulose reforming for hydrogen production. Herein, ZIS photocatalysts with different morphologies were prepared and Pt nanoparticles were deposited on their surfaces. The cellulose oxidation kinetics were enhanced through the strategy of photothermal catalysis and pH optimization, which led to efficient hydrogen generation. The ultrathin nanosheet structure endows 1 % Pt/ZIS-300 with a stronger photogenerated carrier separation ability than 1 % Pt/ZIS-0 (nanoflower) and facilitates ·OH generation. Heat can induce the production of ·OH from 1 % Pt/ZIS-300 and enhance the adsorption of 1 % Pt/ZIS-300 to cellulose by changing the surface potential of 1 % Pt/ZIS-300, which promotes the oxidation kinetics of cellulose. As a result, the hydrogen yield of 1 % Pt/ZIS-300 under photothermal catalytic condition (80 ℃) reached 1218 μmol/gcat after 4 h of reaction. Appropriate NaOH concentration contributes to cellulose solubilization and ·OH production, but too high OH− concentration causes a negative shift of the potential on the 1 % Pt/ZIS-300 and cellulose surface, which hinders the mass transfer process and reduces the oxidation kinetics of cellulose.