Temperature-dependent kinetics studies of the reactions of C2H5O2 and n-C3H7O2 radicals with NO

The rate coefficients for the gas-phase reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO have been measured over the temperature range of (201–403) K using chemical ionization mass spectrometric detection of the peroxy radical. The alkyl peroxy radicals were generated by reacting alkyl radicals with O₂, where the alkyl radicals were produced through the pyrolysis of a larger alkyl nitrite. In some cases C₂H₅ radicals were generated through the dissociation of iodoethane in a low-power radio frequency discharge. The discharge source was also tested for the i-C₃H₇O₂ + NO reaction, yielding k_{298 K} = (9.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, in excellent agreement with our previous determination. The temperature dependent rate coefficients were found to be k(T) = (2.6 ± 0.4) × 10⁻¹² exp{(380 ± 70)/T} cm³ molecule⁻¹ s⁻¹ and k(T) = (2.9 ± 0.5) × 10⁻¹² exp{(350 ± 60)/T} cm³ molecule⁻¹ s⁻¹ for the reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO, respectively. The rate coefficients at 298 K derived from these Arrhenius expressions are k = (9.3 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for C₂H₅O₂ radicals and k = (9.4 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for n-C₃H₇O₂ radicals. © 1996 John Wiley & Sons, Inc.     

Sulfone-Modified Covalent Organic Frameworks Enabling Efficient Photocatalytic Hydrogen Peroxide Generation via One-Step Two-Electron O2 Reduction

Photocatalytic oxygen reduction reaction (ORR) offers a promising hydrogen peroxide (H₂O₂) synthetic strategy, especially the one-step two-electron (2e⁻) ORR route holds great potential in achieving highly efficient and selectivity. However, efficient one-step 2e⁻ ORR is rarely harvested and the underlying mechanism for regulating the ORR pathways remains greatly obscure. Here, by loading sulfone units into covalent organic frameworks (FS-COFs), we present an efficient photocatalyst for H₂O₂ generation via one-step 2e⁻ ORR from pure water and air. Under visible light irradiation, FS-COFs exert a superb H₂O₂ yield of 3904.2 μmol h⁻¹ g⁻¹, outperforming most reported metal-free catalysts under similar conditions. Experimental and theoretical investigation reveals that the sulfone units accelerate the separation of photoinduced electron-hole (e⁻-h⁺) pairs, enhance the protonation of COFs, and promote O₂ adsorption in the Yeager-type, which jointly alters the reaction process from two-step 2e⁻ ORR to the one-step one, thereby achieving efficient H₂O₂ generation with high selectivity.     

Nanoarchitectonics in the Ionothermal Synthesis for Nucleation of Crystalline Potassium Poly (heptazine imide) Towards an Enhanced Solar-Driven H2O2 Production

Solar-driven selective oxygen reduction reaction on polymeric carbon nitride framework is one of the most promising approaches toward sustainable H₂O₂ production. Potassium poly(heptazine imide) (PHI), with regular metal sites in the framework and favorable crystalline structure, is highly active for photocatalytic selective 2e oxygen reduction to produce H₂O₂. By introducing NH₄Cl into the eutectic KCl-LiCl salt mixture, the PHI framework exhibits a remarkable performance for photocatalytic production of H₂O₂, for example, a record high H₂O₂ photo-production rate of 29.5 μmol h⁻¹ mg⁻¹. The efficient photocatalytic performance is attributed to the favorable properties of the new PHI framework, such as improved porosity, negatively shifted LUMO position, enhanced exciton dissociation and charges migration properties. A mechanistic investigation by quenching and electron spin resonance technique reveals the critical role of superoxide radicals for the formation singlet oxygen, and the singlet oxygen is one of the critical intermediates towards the formation of the H₂O₂ by proton extraction from the ethanol.     

Anthraquinone Redox Relay for Dye-Sensitized Photo-electrochemical H2O2 Production

Anthraquinone (AQ) redox mediators are introduced to metal-free organic dye sensitized photo-electrochemical cells (DSPECs) for the generation of H₂O₂. Instead of directly reducing O₂ to produce H₂O₂, visible-light-driven AQ reduction occurs in the DSPEC and the following autooxidation with O₂ allows H₂O₂ accumulation and AQ regeneration. In an aqueous electrolyte, under 1 sun conditions, a water-soluble AQ salt is employed with the highest photocurrent of up to 0.4 mA cm⁻² and near-quantitative faradaic efficiency for producing H₂O₂. In a non-aqueous electrolyte, under 1 sun illumination, an organic-soluble AQ is applied and the photocurrent reaches 1.8 mA cm⁻² with faradaic efficiency up to 95 % for H₂O₂ production. This AQ-relay DSPEC exhibits the highest photocurrent so far in non-aqueous electrolytes for H₂O₂ production and excellent acid stability in aqueous electrolytes, thus providing a practical and efficient strategy for visible-light-driven H₂O₂ production.     

Structure–reactivity relationships for the self‐ reactions of linear secondary alkylperoxy radicals: An experimental investigation

The self‐reactions of the linear pentylperoxy (C₅H₁₁O₂) and decylperoxy (C₁₀H₂₁O₂) radicals have been studied at room temperature. The technique of excimer laser flash photolysis was used to generate pentylperoxy radicals, while conventional flash photolysis was used for decylperoxy radicals. For the former, the recombination rate coefficients were estimated for the primary 1‐pentylperoxy isomer (n‐C₅H₁₁O₂) and for the secondary 2‐ and 3‐pentylperoxy isomers combined (“sec‐C₅H₁₁O₂”) by creating primary and secondary radicals in different ratios of initial concentrations and simulating experimental decay traces using a simplified chemical mechanism. The values obtained at 298 K were: k(n‐C₅H₁₁O₂+n‐C₅H₁₁O₂→Products)=(3.9±0.9)×10⁻¹³ cm³ molecule⁻¹ s⁻¹; k(sec‐C₅H₁₁O₂+sec‐C₅H₁₁O₂→Products)=(3.3±1.2)×10⁻¹⁴ cm³ molecule⁻¹ s⁻¹. Quoted errors are 1σ, whereas the total relative combined uncertainties correspond to an estimated uncertainty factor around 1.65. For decylperoxy radicals, the kinetics of all the types of secondary peroxy isomers reacting with each other were considered equivalent and grouped as sec‐C₁₀H₂₁O₂ (as for sec‐C₅H₁₁O₂). The UV absorption spectrum of these secondary radicals was measured, and the combined self‐reaction rate coefficients then derived as: k(sec‐C₁₀H₂₁O₂+sec‐C₁₀H₂₁O₂)=(9.4±1.3)×10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ at 298 K. Again, quoted errors are 1σ and the total uncertainty factor corresponds to a value around 1.75. The sec‐dodecylperoxy radical was also investigated using the same procedure, but only an estimate of the rate coefficient could be obtained, due to aerosol formation in the reaction cell: k(sec‐C₁₂H₂₅O₂+sec‐C₁₂H₂₅O₂)≡1.4×10⁻¹³ cm³ molecule⁻¹ s⁻¹, with an uncertainty factor of about 2. Despite the fairly high uncertainty factors, a relationship has been identified between the room‐temperature rate coefficient for the self‐reaction and the number of carbon atoms, n, in the linear secondary radical, suggesting: log(k(sec‐RO₂+sec‐RO₂)/cm³ molecule⁻¹ s⁻¹)=−13.0–3.2×exp(−0.64×(n‐2.3)). Concerning primary linear alkylperoxy radicals, no real trend in the self‐reaction rate coefficient can be identified, and an average value of 3.5×10⁻¹³ cm³ molecule⁻¹ s⁻¹ is proposed for all radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 37–46, 1999     

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In situ Generated H2O2 from O2 Electroreduction

Ethylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long-standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H₂O₂, and titanium silicalite-1 catalyst would subsequently oxidize ethylene into ethylene glycol with the in situ generated H₂O₂. This tandem route presents a remarkable activity, i.e., 86 % H₂O₂ conversion with 99 % ethylene glycol selectivity and 51.48 mmol g_ecat⁻¹ h⁻¹ production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H₂O₂ as an oxidant, there exists ⋅OOH intermediate which could omit the step of absorbing and dissociating H₂O₂ over titanium silicalite-1, showing faster reaction kinetics compared to the ex situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in situ generated H₂O₂ in tandem route.     

ZnO-Bi2O3/graphitic carbon nitride photocatalytic system with H2O2-assisted enhanced degradation of Indigo carmine under visible light

Indigo carmine in aqueous solution was effectively degraded using ZnO-Bi₂O₃/Graphitic Carbon Nitride heterojunction structure by visible light/H₂O₂ system. The mechanism of photocatalytic degradation of Indigo carmine shows the responsible species for the degradation of Indigo carmine in the ZnO-Bi₂O₃-xC₃N₄/H₂O₂/visible light system (x = 0, 1, 2, and 3) is the hydroxyl radicals which were generated from the reaction of e⁻ and h⁺ with H₂O₂. Under optimal conditions, ZnO-Bi₂O₃-2C₃N₄/H₂O₂/Vis system degraded more than 93% of Indigo carmine in 180 min. Besides, the kinetic of the photocatalytic process was detailed. These results demonstrate that the ZnO-Bi₂O₃-2C₃N₄/H₂O₂/visible light system may become a promising approach to achieve efficient environmental remediation as an environmentally friendly oxidant.     

Promoting Piezocatalytic H2O2 Production in Pure Water by Loading Metal-Organic Cage-Modified Gold Nanoparticles on Graphitic Carbon Nitride

Piezocatalytic hydrogen peroxide (H₂O₂) production is a green synthesis method, but the rapid complexation of charge carriers in piezocatalysts and the difficulty of adsorbing substrates limit its performance. Here, metal-organic cage-coated gold nanoparticles are anchored on graphitic carbon nitride (MOC-AuNP/g-C₃N₄) via hydrogen bond to serve as the multifunctional sites for efficient H₂O₂ production. Experiments and theoretical calculations prove that MOC-AuNP/g-C₃N₄ simultaneously optimize three key parts of piezocatalytic H₂O₂ production: i) the MOC component enhances substrate (O₂) and product (H₂O₂) adsorption via host–guest interaction and hinders the rapid decomposition of H₂O₂ on MOC-AuNP/g-C₃N₄, ii) the AuNP component affords a strong interfacial electric field that significantly promotes the migration of electrons from g-C₃N₄ for O₂ reduction reaction (ORR), iii) holes are used for H₂O oxidation reaction (WOR) to produce O₂ and H⁺ to further promote ORR. Thus, MOC-AuNP/g-C₃N₄ can be used as an efficient piezocatalyst to generate H₂O₂ at rates up to 120.21 μmol g⁻¹ h⁻¹ in air and pure water without using sacrificial agents. This work proposes a new strategy for efficient piezocatalytic H₂O₂ synthesis by constructing multiple active sites in semiconductor catalysts via hydrogen bonding, by enhancing substrate adsorption, rapid separation of electron-hole pairs and preventing rapid decomposition of H₂O₂.     

Understanding the High-Performance Anode Material of CoC2O4⋅2 H2O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC₂O₄⋅2 H₂O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC₂O₄⋅2 H₂O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC₂O₄⋅2 H₂O. The CoC₂O₄⋅2 H₂O/rGO electrode delivers a specific capacity of 1011.5 mA h g⁻¹ at 0.2 A g⁻¹ after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g⁻¹ at 0.2 A g⁻¹ after 100 cycles for sodium storage. Moreover, the full cell CoC₂O₄⋅2 H₂O/rGO//LiCoO₂ consisting of the CoC₂O₄⋅2 H₂O/rGO anode and LiCoO₂ cathode maintains 138.1 mA h g⁻¹ after 200 cycles at 0.2 A g⁻¹ and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC₂O₄⋅2 H₂O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.     

Two-Dimensional Perovskite Oxynitride K2LaTa2O6N with an H+/K+ Exchangeability in Aqueous Solution Forming a Stable Photocatalyst for Visible-Light H2 Evolution

Undoped layered oxynitrides have not been considered as promising H₂-evolution photocatalysts because of the low chemical stability of oxynitrides in aqueous solution. Here, we demonstrate the synthesis of a new layered perovskite oxynitride, K₂LaTa₂O₆N, as an exceptional example of a water-tolerant photocatalyst for H₂ evolution under visible light. The material underwent in-situ H⁺/K⁺ exchange in aqueous solution while keeping its visible-light-absorption capability. Protonated K₂LaTa₂O₆N, modified with an Ir cocatalyst, exhibited excellent catalytic activity toward H₂ evolution in the presence of I⁻ as an electron donor and under visible light; the activity was six times higher than Pt/ZrO₂/TaON, one of the best-performing oxynitride photocatalysts for H₂ evolution. Overall water splitting was also achieved using the Ir-loaded, protonated K₂LaTa₂O₆N in combination with Cs-modified Pt/WO₃ as an O₂ evolution photocatalyst in the presence of an I₃⁻/I⁻ shuttle redox couple.     

Hybridized Polyoxometalate‐Based Metal–Organic Framework with Ketjenblack for the Nonenzymatic Detection of H2O2

The rational design and development of efficient and affordable enzyme‐free electrocatalysts for electrochemical detection are of great significance for the large‐scale applications of sensor materials, and have aroused increasing research interest. Herein, we report that a typical polyoxometalate (POM)‐based metal–organic framework (NENU5) that was hybridized with ketjenblack (KB) was a highly efficient electrochemical catalyst that could be used for the highly sensitive nonenzymatic detection of H₂O₂. The composite catalyst exhibited superb electrochemical detection performance towards H₂O₂, including a broad linear range from 10–50 mm , a low detection limit of 1.03 μm , and a high sensitivity of 33.77 μA mm ⁻¹, as well as excellent selectivity and stability. These excellent electrocatalytic properties should be attributed to the unique redox activity of the POM, the high specific surface area of the metal–organic framework (MOF), the strong conductivity of KB, and the synergistic effects of the multiple components in the composites during the electrolysis of H₂O₂. This work provides a new pathway for the exploration of nonenzymatic electrochemical sensors.     

Thiophene-Containing Covalent Organic Frameworks for Overall Photocatalytic H2O2 Synthesis in Water and Seawater

H₂O₂ is a significant chemical widely utilized in the environmental and industrial fields, with growing global demand. Without sacrificial agents, simultaneous photocatalyzed H₂O₂ synthesis through the oxygen reduction reaction (ORR) and water oxidation reaction (WOR) dual channels from seawater is green and sustainable but still challenging. Herein, two novel thiophene-containing covalent organic frameworks (TD-COF and TT-COF) were first constructed and served as catalysts for H₂O₂ synthesis via indirect 2e⁻ ORR and direct 2e⁻ WOR channels. The photocatalytic H₂O₂ production performance can be regulated by adjusting the N-heterocycle modules (pyridine and triazine) in COFs. Notably, with no sacrificial agents, just using air and water as raw materials, TD-COF exhibited high H₂O₂ production yields of 4060 μmol h⁻¹ g⁻¹ and 3364 μmol h⁻¹ g⁻¹ in deionized water and natural seawater, respectively. Further computational mechanism studies revealed that the thiophene was the primary photoreduction unit for ORR, while the benzene ring (linked to the thiophene by the imine bond) was the central photooxidation unit for WOR. The current work exploits thiophene-containing COFs for overall photocatalytic H₂O₂ synthesis via ORR and WOR dual channels and provides fresh insight into creating innovative catalysts for photocatalyzing H₂O₂ synthesis.     

Efficient removal of tetracycline by H2O2 activated with iron-doped biochar: Performance,mechanism, and degradation pathways

In this study,novel iron-doped biochar（Fe-BC） was produced using a simple method,and it was used as an H₂ O₂ activator for tetracycline（TC） degradation.Generally,iron loading can improve the separation performance and reactivity of biochar（BC）.In the Fe-BC/H₂ O₂ system,92% of the TC was removed within 30 min with the apparent rate constant(k_obs) of 0.155 min^-1,which was 23.85 times that in the case of the BC/H₂ O_2<...     

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2O2 Production

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn−N₂O₂ moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N₂O₂−S). Systematic analyses demonstrate that the synergetic effects between the N₂O₂ species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O₂ reduction to H₂O₂. Remarkably, the Zn−N₂O₂ moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H₂O₂ generation. Consequently, the Zn−N₂O₂−S SAC exhibits impressive electrochemical H₂O₂ production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm⁻² in the flow cell, it shows a high H₂O₂ production rate of 6.924 mol g_cat⁻¹ h⁻¹ with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.     

Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals,the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

The rate constant for the reaction of CH₃OCH₂ radicals with O₂ (reaction (1)) and the self reaction of CH₃OCH₂ radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k₁ was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# → CH₂OCH₂O₂H^# → 2HCHO + OH (k_prod) CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# + M → CH₃OCH₂O₂ + M (k_RO2) k = k_RO2 + k_prod, where k_RO2 is the rate constant for peroxy radical production and k_prod is the rate constant for formaldehyde production. The k₁ values obtained at 296K together with the available literature values for k₁ determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: k_RO2,0 = (9.4 ± 4.2) × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k_RO2,∞ = (1.14 ± 0.04) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_prod,0 = (6.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, where k_RO2,0 and k_RO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH₃OCH₂O₂ radicals and k_prod,0 represents the bimolecular rate constant for the reaction of CH₃OCH₂ radicals with O₂ to yield formaldehyde in the limit of low pressure. k_RO2,∞ = (1.07 ± 0.08) × 10⁻¹¹ exp(−(46 ± 27)/T) cm³ molecule⁻¹ s⁻¹ was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k₅ = (4.1 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and at 18 bar total pressure over the temperature range 296–523K, k₅ = (4.7 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. As a part of this study the decay rate of CH₃OCH₂ radicals was used to study the thermal decomposition of CH₃OCH₂ radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH₃OCH₂ radicals were consistent with the literature value of k₂ = 1.6 × 10¹³exp(−12800/T)s⁻¹. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.     

Atomically Dispersed Iron Regulating Electronic Structure of Iron Atom Clusters for Electrocatalytic H2O2 Production and Biomass Upgrading

The integration of highly active single atoms (SAs) and atom clusters (ACs) into an electrocatalyst is critically important for high-efficiency two-electron oxygen reduction reaction (2e⁻ ORR) to hydrogen peroxide (H₂O₂). Here we report a tandem impregnation-pyrolysis-etching strategy to fabricate the oxygen-coordinated Fe SAs and ACs anchored on bacterial cellulose-derived carbon (BCC) (FeSAs/ACs-BCC). As the electrocatalyst, FeSAs/ACs-BCC exhibits superior electrocatalytic activity and selectivity toward 2e⁻ ORR, affording an onset potential of 0.78 V (vs. RHE) and a high H₂O₂ selectivity of 96.5 % in 0.1 M KOH. In a flow cell reactor, the FeSAs/ACs-BCC also achieves high-efficiency H₂O₂ production with a yield rate of 12.51±0.18 mol g_cat⁻¹ h⁻¹ and a faradaic efficiency of 89.4 %±1.3 % at 150 mA cm⁻². Additionally, the feasibility of coupling the produced H₂O₂ and electro-Fenton process for the valorization of ethylene glycol was explored in detail. The theoretical calculations uncover that the oxygen-coordinated Fe SAs effectively regulate the electronic structure of Fe ACs which are the 2e⁻ ORR active sites, resulting in the optimal binding strength of *OOH intermediate for high-efficiency H₂O₂ production.     

Oxidation of manganese(II) by ozone and reduction of manganese(III) by hydrogen peroxide in acidic solution

Manganese(II) is oxidized by ozone in acid solution, k=(1.5±0.2)×10³ M⁻¹ s⁻¹ in HClO₄ and k=(1.8±0.2)×10³M⁻¹ s⁻¹ in H₂SO₄. The plausible mechanism is an oxygen atom transfer from O₃ to Mn²⁺ producing the manganyl ion MnO²⁺, which subsequently reacts rapidly with Mn²⁺ to form Mn(III). No free OH radicals are involved in the mechanism. The spectrum of Mn(III) was obtained in the wave length range 200–310 nm. The activation energy for the initial reaction is 39.5 kJ/mol. Manganese(III) is reduced by hydrogen peroxide to Mn(II) with k(Mn(III)+H₂O₂)=2.8×10³M⁻¹ s⁻¹ at pH 0–2. The mechanism of the reaction involving formation of the manganese(II)-superoxide complex and reaction of H₂O₂ with Mn(IV) species formed due to reversible disproportionation of Mn(III), is suggested. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 207–214, 1998.     

Superoxide Anion Disproportionation Induced by Li+ and H+: Pathways to 1O2 Release in Li−O2 Batteries

We explore the disproportionation reaction of superoxide anions in the presence of H⁺ and Li⁺ cations with high quality multiconfigurational ab-initio methods. This reaction is of paramount importance in Li−O₂ battery chemistry as it represents the source of a major degrading impurity, singlet molecular oxygen. For the first time, the thermodynamic and kinetic data of the reaction are drawn from an accurate theoretical model where the electronic structure of the reactant and products is treated at the necessary level of theory. Overall, the H⁺ catalyzed O₂⁻+O₂⁻ disproportionation follows a very efficient thermodynamic and kinetic reaction path leading to neutral ³O₂, ¹O₂ and peroxide anions. On the contrary, we have found that the Li⁺ catalysis promotes only the release of ³O₂ whereas the ¹O₂ formation is energetically unfeasible at room temperature.     

Photo-Driven Quasi-Topological Transformation Exposing Highly Active Nitrogen Cation Sites for Enhanced Photocatalytic H2O2 Production

Herein, the exposure of highly-active nitrogen cation sites has been accomplished by photo-driven quasi-topological transformation of a 1,10-phenanthroline-5,6-dione-based covalent organic framework (COF), which contributes to hydrogen peroxide (H₂O₂) synthesis during the 2-electron O₂ photoreduction. The exposed nitrogen cation sites with photo-enhanced Lewis acidity not only act as the electron-transfer motor to adjust the inherent charge distribution, powering continuous and stable charge separation, and broadening visible-light adsorption, but also providing a large number of active sites for O₂ adsorption. The optimal catalyst shows a high H₂O₂ production rate of 11965 μmol g⁻¹ h⁻¹ under visible light irradiation and a remarkable apparent quantum yield of 12.9 % at 400 nm, better than most of the previously reported COF photocatalysts. This work provides new insights for designing photo-switchable nitrogen cation sites as catalytic centers toward efficient solar to chemical energy conversion.     

Spectrokinetic study of SF5 and SF5O2 radicals and the reaction of SF5O2 with NO

UV spectra of SF₅ and SF₅O₂ radicals in the gas phase at 295 K have been quantified using a pulse radiolysis UV absorption technique. The absorption spectrum of SF₅ was quantified from 220 to 240 nm. The absorption cross section at 220 nm was (5.5 ± 1.7) × 10⁻¹⁹ cm². When SF₅ was produced in the presence of O₂ an equilibrium between SF₅, O₂, and SF₅O₂ was established. The rate constant for the reaction of SF₅ radicals with O₂ was (8 ± 2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The decomposition rate constant for SF₅O₂ was (1.0 ± 0.5) × 10⁵ s⁻¹, giving an equilibrium constant of K_eq = [SF₅O₂]/[SF₅][O₂] = (8.0 ± 4.5) × 10⁻¹⁸ cm³ molecule⁻¹. The SF₅ O₂ bond strength is (13.7 ± 2.0) kcal mol⁻¹. The SF₅O₂ spectrum was broad with no fine structure and similar to the UV spectra of alkyl peroxy radicals. The absorption cross section at 230 nm was found to (3.7 ± 0.9) × 10⁻¹⁸ cm². The rate constant of the reaction of SF₅O₂ with NO was measured to (1.1 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ by monitoring the kinetics of NO₂ formation at 400 nm. The rate constant for the reaction of F atoms with SF₄ was measured by two relative methods to be (1.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1994 John Wiley & Sons, Inc.