Outer-sphere Electron Transfer Research Articles

Anti-oxidative reactivity and mechanism of formic hydrazide, acethydrazide and butyrohydrazide towards reduction of single electron oxidant iridium(IV)

Reduction of a well-known single electron oxidant [IrCl6]2– by aliphatic hydrazides, viz. formic hydrazide, acethydrazide and butyrohydrazide, was investigated by use of several techniques including 1H NMR and rapid scan spectroscopies. It was demonstrated that the redox reactions exclusively follow second-order kinetics over a wide pH range; the observed second-order rate constants k' versus pH profiles have been established. When the features revealed by the rapid scan spectra, the reaction stoichiometry and the oxidation products were considered together, a reaction mechanism was proposed involving three parallel rate-determining steps in which [IrCl6]2– reacted with all the three protolytic forms of the hydrazides. Rate constants of the rate-determining steps and the dissociation constants of hydrazides at 25.0 °C and 1.0 M ionic strength were derived from the kinetic data. Activation parameters were determined for the reactions of [IrCl6]2– with the neutral forms of the hydrazides, and an outer-sphere electron transfer mode was implied. The reactivity of each protolytic form of the hydrazides was elucidated and its distribution versus pH was calculated. The reactivity of the protolytic forms was compared with that of the corresponding forms of aryl hydrazides, revealing that both the neutral and enolate forms of aliphatic hydrazides are less reactive than those of the aryl hydrazides towards reduction of [IrCl6]2–. It was concluded that aryl hydrazides are more important than aliphatic ones in the development of new hydrazide-based antioxidants in the future. Additionally, the protolysis equilibria of these aliphatic hydrazides in aqueous solution and their redox properties have been characterized and the dissociation constants in the case of butyrohydrazide are reported for the first time.

Efficient Photosensitization of π-Extended Oligomeric Porphyrin Pigments through TiO2-Mediated Outer-Sphere Electron Transfer in Photochemical CO2 Reduction Systems

Efficient Photosensitization of π-Extended Oligomeric Porphyrin Pigments through TiO₂-Mediated Outer-Sphere Electron Transfer in Photochemical CO₂ Reduction Systems

Outer Sphere Electron Transfer Enabling High-Voltage Aqueous Electrolytes.

Aqueous electrolytes with a low voltage window (1.23 V) and prone side reactions, such as hydrogen evolution reaction and cathode dissolution, compromise the advantages of high safety and low cost of aqueous metal-ion batteries. Herein, introducing catechol (CAT) into the aqueous electrolyte, an outer sphere electron transfer mechanism is initiated to inhibit the water reactivity, achieving an electrochemical window of 3.24 V. In a typical Zn-ion battery, the outer sphere electrons jump from CAT to Zn2+-H2O at a geometrically favorable situation and between the solvation molecules without breaking or forming chemical bonds as that of the inner sphere electron transfers. The excited state π-π stacking further leads to the outer sphere electron transfer occurring at the electrolyte/electrode interface. This high-voltage electrolyte allows achieving an operating voltage two times higher than that of the usual aqueous electrolytes and provides almost the highest energy density and power density for the V2O5-based aqueous Zn-ion full batteries. The Zn//Zn symmetric battery delivers a 4000 h lifespan, and the Zn//V2O5 full battery achieves a ∼380 W h kg-1 energy density and a 92% capacity retention after 3000 cycles at 1 A g-1 and a 2.4 V output voltage. This outer sphere electron transfer strategy paves the way for designing high-voltage aqueous electrolytes.

Mapping the mechanisms of oxidative addition in cross-coupling reactions catalysed by phosphine-ligated Ni(0).

The complexes of first-row transition metals can undergo elementary reactions by multiple pathways due to their propensity to undergo both one- and two-electron redox steps. Classic and recent studies of the oxidative addition of aryl halides to Ni(0)-a common step in widely practised cross-coupling processes-have yielded contradictory conclusions about stepwise, radical versus concerted mechanisms, but such information is crucial to the design of catalysts based on earth-abundant metals. Here we show that the oxidative addition of aryl halides to Ni(0) ligated by monophosphines occurs by both mechanisms and delineate how the branching of radical and non-radical pathways depends on the electronic properties of both the ligand and reactant arene as well as the identity of the halide. The one-electron pathway occurs by outer-sphere electron transfer to form an aryl radical rather than the often-proposed halogen atom transfer.

Mechanistic Basis of Conductivity in Carbon Dioxide-Expanded Electrolytes: A Joint Experimental-Theoretical Study.

Electrolyte conductivity contributes to the efficiency of devices for electrochemical conversion of carbon dioxide (CO2) into useful chemicals, but the effect of the dissolution of CO2 gas on conductivity has received little attention. Here, we report a joint experimental-theoretical study of the properties of acetonitrile-based CO2-expanded electrolytes (CXEs) that contain high concentrations of CO2 (up to 12 M), achieved by CO2 pressurization. Cyclic voltammetry data and paired simulations show that high concentrations of dissolved CO2 do not impede the kinetics of outer-sphere electron transfer but decrease the solution conductivity at higher pressures. In contrast with conventional behaviors, Jones reactor-based measurements of conductivity show a nonmonotonic dependence on CO2 pressure: a plateau region of constant conductivity up to ca. 4 M CO2 and a region showing reduced conductivity at higher [CO2]. Molecular dynamics simulations reveal that while the intrinsic ionic strength decreases as [CO2] increases, there is a concomitant increase in ionic mobility upon CO2 addition that contributes to stable solution conductivities up to 4 M CO2. Taken together, these results shed light on the mechanisms underpinning electrolyte conductivity in the presence of CO2 and reveal that the dissolution of CO2, although nonpolar by nature, can be leveraged to improve mass transport rates, a result of fundamental and practical significance that could impact the design of next-generation systems for CO2 conversion. Additionally, these results show that conditions in which ample CO2 is available at the electrode surface are achievable without sacrificing the conductivity needed to reach high electrocatalytic currents.

A molecular-level mechanistic framework for interfacial proton-coupled electron transfer kinetics.

Electrochemical proton-coupled electron transfer (PCET) reactions can proceed via an outer-sphere electron transfer to solution (OS-PCET) or through an inner-sphere mechanism by interfacial polarization of surface-bound active sites (I-PCET). Although OS-PCET has been extensively studied with molecular insight, the inherent heterogeneity of surfaces impedes molecular-level understanding of I-PCET. Herein we employ graphite-conjugated carboxylic acids (GC-COOH) as molecularly well-defined hosts of I-PCET to isolate the intrinsic kinetics of I-PCET. We measure I-PCET rates across the entire pH range, uncovering a V-shaped pH-dependence that lacks the pH-independent regions characteristic of OS-PCET. Accordingly, we develop a mechanistic model for I-PCET that invokes concerted PCET involving hydronium/water or water/hydroxide donor/acceptor pairs, capturing the entire dataset with only four adjustable parameters. We find that I-PCET is fourfold faster with hydronium/water than water/hydroxide, while both reactions display similarly high charge transfer coefficients, indicating late proton transfer transition states. These studies highlight the key mechanistic distinctions between I-PCET and OS-PCET, providing a framework for understanding and modelling more complex multistep I-PCET reactions critical to energy conversion and catalysis.

Oxidation of Methanesulfinate by Hexachloroiridate(IV) and the Standard Electrode Potential of the Aqueous Methanesulfonyl Radical.

The aqueous reaction of [IrCl6]2- with CH3SO2- is biphasic and yields a 1:1 mixture of [IrCl6]3- and [IrCl5(H2O)]2- and CH3SO2Cl in the initial rapid phase. The next slow phase corresponds to the hydrolysis of CH3SO2Cl to yield CH3SO3- and Cl-. The initial phase shows kinetic inhibition by [IrCl6]3- that can be minimized by the addition of the radical scavenger propiolic acid. A detailed analysis of the kinetics indicates a mechanism with reversible outer-sphere electron transfer from CH3SO2- to [IrCl6]2- as the first step, followed by the irreversible inner-sphere oxidation of CH3SO2• by [IrCl6]2- to yield [IrCl5(H2O)]2- and CH3SO2Cl. Analysis of the inhibition by [IrCl6]3- and the kinetic effects of propiolic acid enable the determination of the equilibrium constant for the first electron-transfer step. This equilibrium constant then yields E° (CH3SO2•/CH3SO2-) = 1.01 V vs NHE at 25 °C. This is the first report of a standard potential for an alkanesulfonyl radical.

Redox reactions of a pyrazine-bridged RuIII(edta) binuclear complex: spectrochemical, spectroelectrochemical and theoretical studies.

The redox reactions of a pyrazine-bridged binuclear [(edta)RuIIIpzRuIII(edta)]2- (edta4- = ethylenediaminetetraacetate; pz = pyrazine) have been investigated spectrochemically and spectroelectrochemically for the first time. The kinetics of the reduction of [(edta)RuIIIpzRuIII(edta)]2- (RuIII-RuIII) with the ascorbic acid anion (HA-) was studied as a function of ascorbic concentration and temperature at a fixed pH 6.0. The overall reaction of RuIII-RuIII was found to consist of two-steps involving the initial formation of the mixed-valence [(edta)RuIIpzRuIII(edta)]3- (RuII-RuIII) intermediate complex (λmax = 462 nm, εmax = 10 000 M-1 cm-1), which undergoes further reduction by ascorbic acid to produce the [(edta)RuIIpzRuII(edta)]4-(RuII-RuII) ultimate product complex (λmax = 540 nm, εmax = 20 700 M-1 cm-1). Our studies further revealed that the RuII-RuIII and RuII-RuII species are formed in the electrochemical reduction of the RuIII-RuIII complex at 0.0 and -0.4 V (vs. SHE), respectively. Formation of RuII-RuIII and RuII-RuII was further corroborated by magnetic moment measurements and DFT calculations. Kinetic data and activation parameters are interpreted in terms of a mechanism involving rate-determining outer-sphere electron transfer between Ru(III) and the ascorbate monoanion (HA-) at pH 6.0. A detailed reaction mechanism in agreement with the spectral, spectro-electrochemical and kinetic data is presented. The results of the spectral and kinetic studies of the reaction of the RuII-RuII complex with molecular oxygen (O2) reveal the ability of the RuII-RuII species to effect the oxygen reduction reaction (ORR) leading to the formation of H2O2, a partial reduction product of dioxygen (O2).

Rationalizing the regioselectivity of azolation of benzylic C-H bonds under photoredox catalysis

A Density Functional Theory (DFT) study was performed to evaluate the reaction mechanism of the C-N bond formation under an integrated Hydrogen Atom Transfer / Radical Polar Crossover photoredox catalytic cycle. The regioselective activation of a model substrate, including three reactive positions (3º benzylic C-H bond, 2º benzylic C-H bond and primary C-Cl bond) was addressed to distinguish among the radical C-H activation mechanism and the standard SN2 reaction. We demonstrated that activation of tertiary benzylic C-H bond is the most favored and forms exclusively the experimentally observed product. In addition, the whole photoredox catalytic cycle, including the outer sphere electron transfer steps, was characterized computationally.

Tuning the inner- and outer-sphere electron transfer behavior of aqueous {CoW12} polyoxometalate clusters for redox flow batteries exceeding 1.5V

Redox active species as the key component of redox flow batteries (RFBs) directly determine battery performance. Herein, we report a unique redox active specie, {CoW12}, exhibits both outer-sphere electron transfer of the {CoO4} core and inner-sphere electron transfer of the {W12O36} shell in one cluster, which is capable of constructing a symmetric {CoW12}-based RFB with pH-controlled operating voltage output. The DFT calculation discloses the proton-coupled electron transfer process of the {W12O36} shell in thermodynamically and kinetically, explaining the negative shift of the redox potential of {W12O36} shell as the pH increasing from 1 to 4. Interestingly, the redox potential of outer-sphere controlled {CoO4} core is unchanged, which leads to an extension of voltage window from 1.31 to 1.56 V. Consequently, the cycling measurement of the symmetrical battery proves that low capacity decay rate of 0.009 % and high Coulombic efficiency over 99 % can be retained in 400 cycles at pH 4.

Essential Rule Derived from Thermodynamics and Kinetics Studies of Benzopyran Compounds.

Compounds with benzopyran as the core structure play an important role in the total synthesis of antioxidants, drugs, and natural products. Herein, the thermodynamic data of benzopyran compounds and their intermediates were measured and calculated by combining thermodynamics with kinetics. The mechanism of reactions between four benzopyran compounds and organic hydride acceptors was proven to be a one-step hydride transfer. The thermodynamic properties of these compounds and their corresponding intermediates were elucidated. The rationality and accuracy of the electrochemical measurement method were proved. Furthermore, the essential rule of unique structures being present between the C-H bond and para-substituent constants on the benzene ring, as shown in previous studies, was investigated. A simultaneous correlation between thermodynamics and kinetics was found for the hydride transfer reaction, in which the reaction site is connected with the substituent through the benzene ring, a double bond, or a N atom. The likely reason for the correlation between thermodynamic and kinetic is that the benzene ring, double bond, or N atom have the role of transferring the electronic effect. This finding can be applied to the calculation of the activation energy of hydride self-exchange reactions, the prediction of kinetic isotope effects, and explorations of selective reduction processes of hydride transfer in such organic hydride compounds.

Theoretical perspectives on the reduction of Pu(IV) and Np(VI) by methylhydrazine in HNO3 solution: Implications for Np/Pu separation

Effective adjustment and control of the oxidation state of plutonium (Pu) and neptunium (Np) is an indispensable component of Np/Pu separation in spent nuclear fuel reprocessing. Some hydrazine derivatives including methylhydrazine (CH3N2H3) effectively achieves the reduction of Np(VI) to Np(V) without reducing Pu(IV). Herein, we explored the reduction mechanisms of Pu(IV) and Np(VI) by CH3N2H3 in HNO3 solution using scalar-relativistic density functional theory. We elucidated the difference in the reduction mechanism between Np(VI) and Pu(IV) ions by CH3N2H3. The energy barrier for the reduction of [NpVIO2(H2O)5]2+ and [NpVIO2(NO3)(H2O)3]+ by CH3N2H3 is largely different due to the coordination of nitrate ion. Moreover, the energy barrier of the reduction of [NpVIO2(H2O)5]2+ is apparently lower than that of [PuIV(NO3)2(H2O)7]2+, which is in line with the experimental observations. The results of Mayer bond order and localized molecular orbitals clarify the structural evolution of the reaction pathways. Analysis of the spin density demonstrates that the first Np(VI) and Pu(IV) reduction belongs to the outer-sphere electron transfer and the second Np(VI) and Pu(IV) reduction is the hydrogen transfer. This study explains theoretically why CH3N2H3 reduces Np(VI) but not Pu(IV), and helps to design promising reductants for the Np/Pu separation in spent nuclear fuel reprocessing.

Kinetics and outer sphere electron transfer of some metallosurfactants by Fe(CN)6 4− in microheterogenous medium: a detailed thermodynamic approach

Abstract We report the rate of electron transfer reaction of complexes, cis-[M(ED)2(DOD)2]3+ (1), cis-[M(DP)2(DOD)2]3+ (2), cis-[M(TRE)(DOD)2]3+ (3), cis-[M(bpy)2(DOD)2]3+ (4) and cis-[M(PA)2(DOD)2]3+ (5) (M:Co, ED: ethylenediamine, TRE: triethylenetetramine, DP: diaminopropane, PA: phenanthroline, C12H25NH2: dodecylamine (DOD) and bpy: bipyridine) and hexacyanoferrate ion in surface active ionic liquids (BMIM)Br were studied at 298–323 K by electronic absorption spectroscopy. Surfactant complexes 4 and 5, which have a higher ETR than complexes 1–3 based on the results obtained, have been explained based on the states of aggregation and hydrophobic transformations between the hydrocarbon portion of the surfactant compounds and (BMIM)Br. As a result, surface-active agent micelles in (BMIM)Br and increase ETR in between the system. The investigation of kinetic statistics outcomes suggest that reduction reaction between surface-active agent Co(III) complexes and hexacyanoferrate occurs via 2nd order and the ET is proposed as outer sphere. The remarkable increase in the rate for the ETR in (BMIM)Br with increase in the concentration of Co(III) complexes from 1–5. This can be attributing due to the fact those reactants with opposite charges and the amphipilicity of the ligand. The OSET of kinetics have been confirmed by the enthalpy and entropy (ΔS # and ΔH #) factors, and the isokinetic plots (ΔS # versus ΔH #) have shown that the reaction’s mechanism does not alter during the (BMIM)Br medium.

Cation-induced changes in the inner- and outer-sphere mechanisms of electrocatalytic CO2 reduction

The underlying mechanism of cation effects on CO2RR remains debated. Herein, we study cation effects by simulating both outer-sphere electron transfer (OS-ET) and inner-sphere electron transfer (IS-ET) pathways during CO2RR via constrained density functional theory molecular dynamics (cDFT-MD) and slow-growth DFT-MD (SG-DFT-MD), respectively. Our results show without any cations, only OS-ET is feasible with a barrier of 1.21 eV. In the presence of K+ (Li+), OS-ET shows a very high barrier of 2.93 eV (4.15 eV) thus being prohibited. However, cations promote CO2 activation through IS-ET with the barrier of only 0.61 eV (K+) and 0.91 eV (Li+), generating the key intermediate (adsorbed CO{}_{2}^{delta -}). Without cations, CO2-to-CO{}_{2}^{delta -}(ads) conversion cannot proceed. Our findings reveal cation effects arise from short-range Coulomb interactions with reaction intermediates. These results disclose that cations modulate the inner- and outer-sphere pathways of CO2RR, offering substantial insights on the cation specificity in the initial CO2RR steps.

Unravelling the Effect of Acid-Driven Electron Transfer in High-Valent FeIV =O/MnIV =O Species and Its Implications for Reactivity.

The electron transfer (ET) step is one of the crucial processes in biochemical redox reactions that occur in nature and has been established as a key step in dictating the reactivity of high-valent metal-oxo species. Although metalloenzymes possessing metal-oxo units at their active site are typically associated with outer-sphere electron transfer (OSET) processes, biomimetic models, in contrast, have been found to manifest either an inner-sphere electron transfer (ISET) or OSET mechanism. This distinction is clearly illustrated through the behaviour of [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) complexes, where complex 1 showcases an OSET mechanism, while complex 2 exhibits an ISET mechanism, especially evident in their reactions involving C-H bond activation and oxygen atom transfer reactions in the presence of a Lewis/Bronsted acid. However, the precise reason for this puzzling difference remains elusive. This work unveils the origin of the perplexing inner-sphere vs outer-sphere electron transfer process (ISET vs OSET) in [(N4Py)MnIV (O)]2+ (1) and [(N4Py)FeIV (O)]2+ (2) species in the presence of Bronsted acid. The calculations indicate that when the substrate (toluene) approaches both 1 and 2 that is hydrogen bonded with two HOTf molecules (denoted as 1-HOTf and 2-HOTf, respectively), proton transfer from one of the HOTf molecules to the metal-oxo unit is triggered and a simultaneous electron transfer occurs from toluene to the metal centre. Interestingly, the preference for OSET by 1-HOTf is found to originate from the choice of MnIV =O centre to abstract spin-down (β) electron from toluene to its δ(dxy ) orbital. On the other hand, in 2-HOTf, a spin state inversion from triplet to quintet state takes place during the proton (from HOTf) coupled electron transfer (from toluene) preferring a spin-up (α) electron abstraction to its σ* (dz 2 ) orbital mediated by HOTf giving rise to ISET. In addition, 2-HOTf was calculated to possess a larger reorganisation energy, which facilitates the ISET process via the acid. The absence of spin-inversion and smaller reorganisation energy switch the mechanism to OSET for 1-HOTf. Therefore, for the first time, the significance of spin-state and spin-inversion in the electron transfer process has been identified and demonstrated within the realm of high-valent metal-oxo chemistry. This discovery holds implications for the potential involvement of high-valent Mn-oxo species in performing similar transformative processes within Photosystem II.

Kinetics and mechanism of the oxidation of hydrazine with [RuIII(pic)3] in aqueous solution

The kinetics and mechanism of the oxidation of hydrazine by [RuIII(pic)3] (pic- = picolinate anion) were studied spectrophotometrically as a function of hydrazine concentrations at a constant pH of 5.5. The rate of the reaction was followed by monitoring the appearance of the MLCT band of [RuII(pic)3]- at 466 nm. The reaction rate was found to be first-order for Ru(III)-complex concentration. The observed rate constant (k obs) values increased linearly with increase in the hydrazine concentration. The oxidation reaction was studied at varied temperature (20–40 °C). The ΔH≠ (73 ± 3 kJ mol−1 kJ·mol−1) and the negative ΔS≠ (34 ± 7 J·deg−1mol−1) values are consistent with the proposed outer-sphere electron transfer process operative in the oxidation of hydrazine with [RuIII(pic)3]. A working mechanism involving the formation of an active diazene (HN = NH) intermediate followed by its rapid two-electron oxidation by [RuIII(pic)3] in a kinetically inconsequential step producing N2 as sole product is proposed for an overall four-electron oxidation of hydrazine to dinitrogen.

On the effects of Br−, ClO4−, NO3−anions on the oxygen reduction reaction electrocatalysis at Fe phthalocyanine modified electrodes

Fe phthalocyanine with carbon nanotubes (FePc-CNT) has been used as catalysts for ORR using the following supporting electrolyte: 0.1 M NaOH, 1 M NaOH, 1 M HNO3, 1 M HClO4, and 1 M HBr. The thermodynamic and kinetic information was acquired from cyclic voltammetry in N2 saturated media, and then polarization curves saturating with O2. The rate-determining step is modulated by the formal potential (E0’Fe(III)/(II)) in basic media, coherent with the inner sphere electron transfer mechanism. However, in strong acid electrolytes, the Tafel slope value is ∼ -0.090 V dec−1 at low overpotentials and ∼ -0.120 V dec−1 at high overpotentials indicating that a poisoning process is hampering the ORR, and causing an outer sphere electron transfer mechanism. Impedance spectroscopy and poisoning test (recovery of the activity of the catalyst in NaOH after initial use in acid) support the thesis of ion adsorption/poisoning for the low electrocatalytic activity of FePc based catalysts in acid media.

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices.

Persistent radicals can hold their unpaired electrons even under conditions where they accumulate, leading to the unique characteristics of radical ensembles with open-shell structures and their molecular properties, such as magneticity, radical trapping, catalysis, charge storage, and electrical conductivity. The molecules also display fast, reversible redox reactions, which have attracted particular attention for energy conversion and storage devices. This paper reviews the electrochemical aspects of persistent radicals and the corresponding macromolecules, radical polymers. Radical structures and their redox reactions are introduced, focusing on redox potentials, bistability, and kinetic constants for electrode reactions and electron self-exchange reactions. Unique charge transport and storage properties are also observed with the accumulated form of redox sites in radical polymers. The radical molecules have potential electrochemical applications, including in rechargeable batteries, redox flow cells, photovoltaics, diodes, and transistors, and in catalysts, which are reviewed in the last part of this paper.

FeCo-ZIF derived carbon-encapsulated metal alloy as efficient cathode material for heterogeneous electro-Fenton reaction in 3-electron ORR pathway: Enhanced performance in alkaline condition

Oxygen reduction reaction via 3-electron pathway presents a promising approach for generating reactive oxygen species in heterogeneous electro-Fenton (H-EF) process. This approach overcomes the limitations posed by the slow accumulation of H2O2 via 2- electron ORR and the inefficient activation of H2O2 through Haber-Weiss cycle. In this study, bimetal alloy nanoparticles were encapsulated within carbon layers (FeCo/C) by a general MOF-derived strategy, resulting in an overall electron transfer number of 2.98 during the H-EF process. Under optimal modification conditions, the prepared FeCo/C exhibited exceptional performance in sulfamethoxazole removal. Furthermore, the performance was enhanced under alkaline conditions. The apparent rate constant increased from 0.02 to 0.03 min−1 as the pH value increased from 3 to 11. The mechanism underlying this alkalinity-enhanced activity was attributed to the involvement of a surface-independent outer sphere electron transfer component, which provides valuable insights into the potential application of the H-EF process for treating alkaline wastewater.

Highly efficient electrosynthesis of hydrogen peroxide through the combination of side aeration and vacuum filtration modified graphite felt

The electrocatalytic activity towards two electron oxygen reduction reaction of graphite felt was advanced by incorporating carbon nitride, carbon nanotubes and polytetrafluoroethylene through vacuum filtration, which prevented the cleavage of O-O bond, facilitated the charge transfer, and established more three-phase active sites. To ameliorate the oxygen transfer process, the configuration of side-aeration was proposed, providing forced convection to reduce the thickness of diffusion layer, and increasing the dissolved oxygen. By simplified combination of refining the orientation of gas flow and modified graphite felt, the dual-chamber configuration rendered a qualitative leap in H2O2 generation capacity to 4.44–6.89 mg h−1 cm−2. The alkaline affinity of developed system was discussed in terms of a beneficial outer-sphere electron transfer pathway, the variation on adsorption strength of oxygenated species and working electrode potential range. Finally, Long-term operation stability and successful application in Electro-Fenton indicated great potential of developed system for H2O2 synthesis and environmental remediation.