掺硼金刚石膜电极表面产生羟基自由基的原位ESR研究

建立了原位电化学-电子顺磁共振(ESR)方法,系统研究了掺硼金刚石(BDD)膜电极表面在水溶液中的羟基自由基(·OH)产生规律.结果表明,在高于析氧电位时,·OH的生成速率随着阳极电位的升高、电流密度的增加而增大,增加速率逐渐减缓.与此同时,与氢终端的BDD膜电极相比,氧终端的BDD膜电极表面因具有较好的亲水性而具有更高的·OH产生能力.在电化学氧化处理有机废水的过程中,电极表面处于氧终端的状态,有利于·OH产生并保持较高的活性.溶液pH值也在一定程度上影响·OH生成反应,酸性溶液中,BDD膜电极表面的·OH产生能力强于在中性或碱性溶液中.进一步研究发现,BDD膜电极表面还可能生成O3-·0自由基.本研究为深入探索BDD膜电极表面·OH的产生机制提供了研究手段,为阐述BDD膜电极电极在污染物处理中高效性的本质提供了有效的证据.     

多孔Fe3O4修饰的Ni(OH)2纳米片的制备及其析氧性能研究

近年来,基于析氧反应(OER)的电化学能量转换体系(如电化学制氢、金属空气电池、氮气电还原和二氧化碳电还原)日益受到人们的关注.各种过渡金属基(Mn,Ni,Co,Fe,Cu等)纳米材料(硫化物、氢氧化物、氧化物、磷化物和氮化物等)被认为是潜在的、可以代替贵金属的碱性OER催化剂.其中,高活性和低成本的Ni(OH)2基电催化剂被广泛关注.由于面积效应、结构效应、电子效应和协同效应等因素,Ni(OH)2基纳米材料的电化学活性与其形貌和化学成分密切相关.引入纳米尺寸的孔,不仅加快了传质,而且增加了边缘活性原子的数量,因而有利于活性的增强.超薄二维(2D)纳米片因具有独特的结构特征,可以为电催化反应提供充足的反应位点和低配位数的表面活性原子.杂原子的引入可以调节纳米材料的电子结构和几何结构以提高它们的电催化活性.本文提出了一种简单的混合氰胶水解策略,成功合成了Fe掺杂的Ni(OH)2纳米片(Ni(OH)2-Fe H-STs).氰胶前驱体骨架结构有助于形成超薄多孔的2D结构,而且,通过调节前驱体的浓度就可以获得一定镍铁原子比的产物.不同Fe含量的Ni(OH)2纳米片的OER活性测试结果表明,Ni/Fe比为3:1的Ni(OH)2-Fe H-STs-Ni3Fe1在碱性环境中具有最佳的OER活性.由于Ni(OH)2-Fe H-STs-Ni3Fe1的超薄2D结构使大多数金属原子暴露在表面,使原子利用率最大化.同时,超薄表面上高活性的低配位数的中心原子,可以作为催化OER的高活性中心.薄片上的孔隙有效地增加了高活性边缘原子的数量并且能够加速反应物和生成物的传质.XPS测试结果表明,Fe的引入显著改变了Ni的电子结构,提高了Ni(OH)2 H-STs的导电性,从而促进了电化学过程中NiIV活性物种的产生,进而改变其OER本征活性.三维镍泡沫(NF)可以防止负载纳米材料的聚集,提高转移反应物/产物的传质速率.因此,本文将Fe掺杂的Ni(OH)2纳米片直接生长在NF基底(简写为Ni(OH)2-Fe H-STs/NF).结果表明,NF基底的引入进一步提升导电性和增加传质.综上所述,由于具有高比表面积、丰富的活性原子、Fe/Ni原子之间的协同效应以及NF基底的高导电性和三维多孔特性,通过氰胶水解法获得的Ni(OH)2-Fe H-STs/NF在KOH溶液中表现出优异的OER活性,在10 mA cm^–2电流密度下过电位仅为200 mV,Tafel斜率为56 mV dec^?1,并且材料具有良好的稳定性.     

A Plasma‐Triggered O−S Bond and P−N Junction Near the Surface of a SnS2 Nanosheet Array to Enable Efficient Solar Water Oxidation

A photoelectrochemical (PEC) cell can split water into hydrogen and oxygen with the assistance of solar illumination. However, its application is still limited by excessive bulk carrier recombination and sluggish surface oxygen evolution reaction (OER) kinetics. Taking SnS₂ as an example, a promising layered optoelectronic semiconductor, Ar plasma treatment strategy was used to introduce a SnS/SnS₂ P?N heterojunction and O?S bond near the surface of a SnS₂ nanosheet array, simultaneously increasing the separation efficiency of photogenerated electron–hole pairs in the bulk and lowering the OER overpotential at the surface. The onset potential of the plasma‐treated SnS₂ nanosheet array shifts negatively to 0.16 V, and the photocurrent density at 1.23 V vs. RHE boosts to 2.15 mA cm^?2, which is 7 times that of pristine SnS₂. This work demonstrates a facile plasma treatment strategy to modulate the energy band structure and surface chemical states for improved PEC performance.     

Direct and indirect role of Fe doping in NiOOH monolayer for water oxidation catalysis**

Water oxidation activity of pristine NiOOH is greatly enhanced by doping it with Fe. However, the precise role of Fe is still being debated. Using a first-principles DFT+U approach, we investigate the direct and indirect roles of Fe in enhancing the oxygen evolution reaction (OER) activity of NiOOH monolayers. Considering two Mars-Van-Krevelen mechanisms of OER based on the source of O−O bond formation, we show that a mechanism involving the coupling of lattice oxygen is generally more favorable than water nucleophilic attack on lattice oxygen. On doping with Fe, the overpotential of NiOOH is reduced by 0.33 V, in excellent agreement with experimental findings. Introducing Fe at active sites results in different potential determining steps (PDS) in the two mechanisms. The Ni sites in pristine and Fe-doped NiOOH have the same PDS regardless of the mechanism. The Fe sites not only have the lowest overpotential but also decrease the overpotential for Ni sites.     

Electrocatalytic oxygen evolution from water on a Mn(III-V) dimer model catalyst--a DFT perspective

A complete water oxidation and oxygen evolution reaction (OER) cycle is monitored by means of density functional theory (DFT). A biomimetic model catalyst, comprising a μ-OH bridged Mn(III-V) dimer truncated by acetylacetonate ligand analogs and hydroxides is employed. The reaction cycle is divided into four electrochemical hydrogen abstraction steps followed by a series of chemical steps. The former employ the tyrosine/tyrosyl redox couple acting as electron and proton sink, thus determining the reference potential. Stripping hydrogen from water leads to the formation of two highly unstable Mn(V)=O/Mn(IV)-O˙ moieties, which subsequently combine to form a μ-peroxy O-O bond. O(2) evolution results from subsequent consecutive replacement of the remaining Mn-O bonds by water. A Zener "spintronic" type mechanism for virtually barrierless O(2) evolution is found. The applicability of DFT is discussed and extended to include the rate-limiting steps in the OER. Rather than attempting to compute transition states where KS-DFT is unreliable, an upper bound for the activation barrier of the O-O bond formation step is estimated from the hessians of the relevant intermediates.     

Theoretical study of O--O single bond formation in the oxidation of water by the ruthenium blue dimer

The first key step in the oxidation of water to O(2) by the oxidized species [(bpy)(2)(O)Ru(V)ORu(V)(O)(bpy)(2)](4+) of the Ru blue dimer is studied using density functional theory (DFT) and an explicit solvent treatment. In the model reaction system [L(2)(O)Ru(V)ORu(V)(O)L(2)](4+)·(H(2)O)(4)·W(76), the surrounding water solvent molecules W are described classically while the inner core reaction system is described quantum mechanically using smaller model ligands (L). The reaction path found for the O--O single bond formation involves a proton relay chain: direct participation of two water molecules in two proton transfers to yield the product [L(2)(HOO)Ru(IV)ORu(IV)(OH)L(2)](4+)·(H(2)O)(3)·W(76). The calculated ～3 kcal/mol reaction free energy and ～15 kcal/mol activation free energy barrier at 298 K are consistent with experiment. Structural changes and charge flow along the intrinsic reaction coordinate, the solvent's role in the reaction barrier, and their significance for water oxidation catalysis are examined in detail.     

气相中HRnCCH和X(X=H_2O,NH_3)反应机理的理论研究

在CCSD(T)//MP2/aug-cc-pVTZ-pp理论水平上,研究了HRnCCH与大气中H2O及NH3分子反应的机理,反应主要包括HRnCCH与HRnOH及HRnNH2之间的转化、H2O和NH3在HRnCCH中的碳碳三键上的加成反应以及HRnCCH与双分子水反应等.结果表明,HRnCCH与H2O反应生成HCCH和HRnOH及HRnCCH与NH3反应生成HCCH和HRnNH2的能垒分别为54.1和75.2 kJ/mol,而生成HRnCHC(OH)H,HRnC(OH)CH2,HRnCHC(NH2)H和HRnC(NH2)CH2的活化能分别为219.6,220.5,174.4和182.4kJ/mol,此结果表明HRnCCH反应性较弱且是稳态存在的.此外,在HRnCCH与H2O反应中加入单个水分子,仍然生成HRnCHC(OH)H,但反应活化能却降低了96.4 kJ/mol,说明水分子对该反应有明显的催化作用.     

Red Bean Pod Derived Heterostructure Carbon Decorated with Hollow Mixed Transition Metals as a Bifunctional Catalyst in Zn-Air Batteries

Design and synthesis of low-cost and efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zn-air batteries are essential and challenging. We report a facile method to synthesize heterostructure carbon consisting of graphitic and amorphous carbon derived from the agricultural waste of red bean pods. The heterostructure carbon possesses a large surface area of 625.5 m² g⁻¹, showing ORR onset potential of 0.89 V vs. RHE and OER overpotential of 470 mV at 5 mA cm⁻². Introducing hollow FeCo nanoparticles and nitrogen dopant improves the bifunctional catalytic activity of the carbon, delivering ORR onset potential of 0.93 V vs. RHE and OER overpotential of 360 mV. Electron energy-loss spectroscopy (EELS) O K-edge map suggests the presence of localized oxygen on the FeCo nanoparticles, suggesting the oxidation of the nanoparticles. Zn-air battery with these carbon-based catalysts exhibits a peak power density as high as 116.2 mW cm⁻² and stable cycling performance over 210 discharge/charge cycles. This work contributes to the advancement of bifunctional oxygen electrocatalysts while converting agricultural waste into value-added material.     

One-step synthesis of Fe-Ni hydroxide nanosheets derived from bimetallic foam for efficient electrocatalytic oxygen evolution and overall water splitting

For the first time, the Fe-Ni LDH nanosheets were prepared through simple one-step hydrothermal treatment of Fe-Ni bimetallic foam both as the substrate and Fe/Ni sources. The ratio of Ni/Fe elements played the important role in realizing the optimal catalytic activities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). An alkaline water electrolyzer was constructed with the Fe-Ni hydroxide nanosheets/Fe-Ni alloy foam-60% Fe as anode and Ni(OH)₂/Fe-Ni alloy foam-25% Fe as cathode, which displays superior electrolytic performance (affording 10 mA/cm² at 1.62 V) and lasting durability.     

Slab model studies of water adsorption and decomposition on clean and X- (X = C, N and O) contaminated Pd(111) surfaces

To explore the effect of surface contaminants on water chemistry at metallic surfaces, adsorption and decomposition of water monomers on clean and X/Pd(111)(X = C, N and O) surfaces are investigated based on density functional theory calculations. It is revealed that H(2)O binds to Pd(111) surface primarily through the mixing of its 1b(1) with the Pd 4d(z(2)) state. A charge accumulation between the oxygen atom of water and the bound Pd atom is calculated, which is found to be relevant to the H(2)O-Pd interaction. Water adsorption results in a reduction of surface work function and the polarization of the X 2p states. The O-H bond scission of H(2)O on the clean Pd(111) is an energy unfavorable process. In the case of X-assisted O-H bond breaking on X/Pd(111) surfaces, however, the reaction barrier tends to be lower than that on the clean surface and decreases from C/Pd(111) to O/Pd(111). In particular, water decomposition is found to become feasible on O/Pd(111), in agreement with the experimental observations. The calculated barrier is demonstrated to be correlated linearly with the density of X 2p states at the Fermi level. A thorough energy analysis demonstrates that the following geometrical and electronic factors favor the barrier reduction on X/Pd(111) with respect to water decomposition on clean Pd(111): (i) the less deformed structure of water in TS; (ii) the decreased bonding competition between the fragments OH and H. The remarkable decrease of the barrier on O/Pd(111) is revealed to be due to the largest stabilization of the split H atom and the least deformation of water in the TS.     

Hollow Nanotube Ru/Cu2+1O Supported on Copper Foam as a Bifunctional Catalyst for Overall Water Splitting

Hydrogen energy is considered as one of the ideal clean energies for solving the energy shortage and environmental issues, and developing highly efficient electrocatalysts for overall water splitting to produce hydrogen is still a huge challenge. Herein, for the first time, Ru-doped Cu₂₊₁O vertically arranged nanotube arrays in situ grown on Cu foam (Ru/Cu₂₊₁O NT/CuF) are reported and further investigated for their catalytic properties for overall water splitting. The Ru/Cu₂₊₁O NT/CuF presents ultrahigh catalytic activities for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, and it exhibits a small overpotential of 32 mV at 10 mA cm⁻² in the HER, and only needs 210 mV overpotential to achieve a current density of 10 mA cm⁻² in the OER. Importantly, the alkaline electrolyzer using Ru/Cu₂₊₁O NT/CuF as a bifunctional electrocatalyst only needs 1.53 V voltage to deliver a current density of 10 mA cm⁻², which is much lower than the benchmark of IrO₂(+)/Pt(−) counterpart (1.64 V at 10 mA cm⁻²). The excellent performance of the Ru/Cu₂₊₁O NT/CuF catalyst is attributed to its high conductive substrate and special Ru-doped nanotube structure, which provides a high electrochemical active surface area and 3D gas diffusion channel.     

Photosystem II Inspired NiFe-Based Electrocatalysts for Efficient Water Oxidation via Second Coordination Sphere Effect

The mismatched fast-electron-slow-proton process in the electrocatalytic oxygen evolution reaction (OER) severely restricts the catalytic efficiency. To overcome these issues, accelerating the proton transfer and elucidating the kinetic mechanism are highly sought after. Herein, inspired by photosystem II, we develop a family of OER electrocatalysts with FeO₆/NiO₆ units and carboxylate anions (TA²⁻) in the first and second coordination sphere, respectively. Benefiting from the synergistic effect of the metal units and TA²⁻, the optimized catalyst delivers superior activity with a low overpotential of 270 mV at 200 mA cm⁻² and excellent cycling stability over 300 h. A proton-transfer-promotion mechanism is proposed by in situ Raman, catalytic tests, and theoretical calculations. The TA²⁻ (proton acceptor) can mediate proton transfer pathways by preferentially accepting protons, which optimizes the O−H adsorption/activation process and reduces the kinetic barrier for O−O bond formation.     

In-situ surface self-reconstruction in ternary transition metal dichalcogenide nanorod arrays enables efficient electrocatalytic oxygen evolution

Water splitting has received more and more attention because of its huge potential to generate clean and renewable energy.The highly active and durable oxygen evolution reaction(OER)catalysts play a decisive factor in achieving efficient water splitting.The identification of authentic active origin under the service conditions can prompt a more reasonable design of catalysts together with well-confined micro-/nano-structures to boost the efficiency of water splitting.Herein,Fe,Co,and Ni ternary transition metal dichalcogenide(FCND)nanorod arrays on Ni foam are purposely designed as an active and stable low-cost OER pre-catalyst for the electrolysis of water in alkaline media.The optimized FCND catalyst demonstrated a lower overpotential than the binary and unary counterparts,and a 27-fold rise in kinetic current density at the overpotential of 300 m V compared to the nickel dichalcogenide counterpart.Raman spectra and other structural characterizations at different potentials reveal that the in-situ surface self-reconstruction from FCND to ternary transition metal oxyhydroxides(FCNOH)on catalyst surfaces initiated at about 1.5 V,which is identified as the origin of OER activity.The surface selfreconstruction towards FCNOH also enables excellent stability,without fading upon the test for 50 h.     

基于四硫富瓦烯的无金属共价有机框架材料用于高效电催化析氧反应

共价有机框架(COFs)在电催化析氧反应(OER)中的应用得到了广泛的关注。然而,大多数无金属共价有机框架(COFs)的导电性较差,不利于OER反应。四硫富瓦烯(TTF)是一种良好的电子供体,具有快速的电子转移能力,将TTF整合到共价有机框架骨架中将有助于电子的转移。在此,我们报道了一种基于四硫富瓦烯的二维无金属共价有机框架材料,JUC-630。与不含四硫富瓦烯的同类材料(Etta-Td COF)相比,JUC-630具有较低的过电位(400 mV)和塔菲尔斜率(104 mV∙dec⁻¹)。本研究提出了合理设计功能基元的策略,这有助于大大提高COF材料的OER催化活性。     

Theoretical Studies on Models for the Oxo-Transfer Reaction of Dioxomolybdenum Enzymes

Patterned after synthetic model systems for dioxomolybdenum enzymes, our theoretical model system produces an energy profile and structures for the various species and oxidation states in the catalytic cycle. A key step in this cycle is the oxo-transfer reaction. Here, our substrate, PMe(3), approaches [Mo(VI)O(2)](2+) at an O-Mo-O-P dihedral angle of 90 degrees, i.e. perpendicular to the MoO(2) plane, crosses over a barrier of 14 kcal/mol, and rotates to an O-Mo-O-P dihedral angle of 0 degrees to form an intermediate, [Mo(IV)O(OPMe(3))](2+), which is 69 kcal/mol more stable than the reactants. The direction of the substrate's attack leaves the two d electrons of this Mo(IV) system in an orbital which is delta with respect to the remaining spectator Mo-O bond, a configuration which allows this O to form a formal triple Mo-O bond. The displacement of the product, OPR(3), by water, H(2)O, proceeds via an associative mechanism with a barrier of only 19 kcal/mol. In our model, [Mo(IV)O(OH(2))](2+) then reacts with [Mo(VI)O(2)](2+) to form [Mo(V)O(OH)](2+), a process which is exothermic by 14 kcal/mol. The addition of O(2) then oxidizes [Mo(V)O(OH)](2+) to [Mo(VI)O(2)](2+) to complete our model catalytic cycle.     

Interface‐Engineered Ni(OH)2/β‐like FeOOH Electrocatalysts for Highly Efficient and Stable Oxygen Evolution Reaction

Iron‐based (oxy)hydroxides are especially attractive electrocatalysts for the oxygen evolution reaction (OER) owing to their earth abundance, low cost, and nontoxicity. However, poor OER kinetics on the surface restricts the performance of the FeOOH electrocatalyst. Herein, a highly efficient and stable Ni(OH)₂/β‐like FeOOH electrocatalyst is obtained by facile electroactivation treatment. The activated Ni(OH)₂/β‐like FeOOH sample indicates an overpotential of 300 mV at 10 mA cm⁻² for the OER, and no clear current decay after 50 h of testing; this is comparable to the most efficient nickel‐ and cobalt‐based electrocatalysts on planar substrates. Furthermore, studies suggest that β‐like FeOOH plays a key role in remarkably enhancing the performance during the electroactivation process owing to its metastable tunnel structure with a lower barrier for interface diffusion of Ni²⁺ ions between the bilayer electrocatalyst. This study develops a new strategy to explore efficient and low‐cost electrocatalysts and deepens understanding of bilayer electrocatalysts for the OER.     

NiFe_2O_4/NiO纳米复合材料的制备及电催化水氧化性能

以镍铁水滑石为单一前驱体,通过高温焙烧制备了NiFe_2O_4/NiO纳米复合材料,对该纳米复合材料在碱性介质中电催化水的氧化性能进行了研究.结果表明,相比于化学共沉淀法制备的单独NiFe_2O_4、NiO及其物理混合物NiFe_2O_4+NiO,NiFe_2O_4/NiO纳米复合材料具有更高的电催化水氧化活性和更好的循环稳定性.电流密度为10 m A/cm2时过电位仅为364 m V.     

Excited-state proton transfer in 7-hydroxy-4-methylcoumarin along a hydrogen-bonded water wire

TDDFT, RI-CC2, and CIS calculations have been performed for the nondissociative excited-state proton transfer (ESPT) in the S1 state of 7-hydroxy-4-methylcoumarin (7H4MC) along a H-bonded water wire of three water molecules bridging the proton donor (OH) and the proton acceptor (C[double bond]O) groups (7H4MC.(H2O)3). The observed structural reorganization in the water-wire cluster is interpreted as a proton-transfer (PT) reaction along the H2O solvent wire. The shift of electron density within the organic chromophore 7H4MC due to the optical excitation appears to be the driving force for ESPT. All the methods used show that the reaction path occurs in the 1pipi* state, and no crossing with a Rydberg-type 1pisigma* state is found. TDDFT and RI-CC2 calculations predict an exoergic reaction of the excited-state enol-to-keto transformation. The S1 potential energy curve reveals well-defined Cs minima of enol- and keto-clusters, separated by a single barrier with a height of 17-20 kcal/mol. After surmounting this barrier, spontaneous PT along the water wire is observed, leading without any further barrier to the keto structure. The TDDFT and RI-CC2 methods appear to be reliable approaches to describe the energy surfaces of ESPT. The CIS method predicts an endoergic ESPT reaction and an energy barrier, which is too high.     

DFT计算研究碱性条件下γ-FeOOH(010)上氧析出反应机理

一个高效经济的氧析出反应(OER)催化剂是大范围应用太阳能转化能源的关键.在众多有潜力的OER催化剂中,金属氢氧化物,尤其是FeOOH表现出很高的OER活性.我们采用DFT+U研究了γ-FeOOH(010)表面上OER反应机理;得到了OH– 和空穴对的化学势,并将OH–阴离子包含在反应机理中,以此来说明碱性条件下阳极的OER过程.随后分析了催化剂中OH-,O-和Fe-终止的表面上OER反应路径.含有OH-,O-终止的表面上,O2分子是通过OH与表面氧物种(–OH*和–O*)反应,或二个表面氧物种相结合而形成的.在Fe-终止的表面上,O2只能通过首先在Fe位上吸附OH而形成.不同形式表面上O2析出的化学势决定步骤取决于每个路径中基元步骤自由能的变化.结果表明,O2的形成需要重建表面Fe位,因此,有利于部分暴露Fe位的条件也将促进O2的形成.     

Insights into electrocatalysis

When standard reversible potentials for bulk solution reactions, U(0), are known, the reversible potentials when the reactant and product are adsorbed on an electrocatalyst surface, U(surf)(rev), are given in terms of these potentials and the adsorption Gibbs energy bond strengths: U(surf)(rev) = U0 + D(ads)G (Ox)/F-Δ(ads)G (R)/F (i). When the Δ(ads)G (Ox) and Δ(ads)G (Red) values are known at potential U, this equation is exact. When the overpotential for a multi-electron transfer reaction is minimal, each electron transfer takes place at the standard reversible potential for the overall reaction. In the case of O(2) reduction to water via the intermediate step OOH(aq) → O(aq) + OH(aq), or via O(2)(g) → 2O(aq), the respective endergonic O-O dissociation Gibbs energies are shown to be 2.52 eV and 4.76 eV. When the oxygen product and water reactant adsorb weakly, as on platinum, the adsorption Gibbs energies, Δ(ads)G, for O, OH, and OOH intermediates can be uniquely predicted using these data. All of the above depend exclusively on experimentally determined data. Reversible potentials have been calculated for oxygen reduction steps on the platinum electrocatalyst surface using Interface 1.0, a comprehensive computational code for the potential dependence of the electrochemical interface. Using these results as benchmarks, is found to be accurate to around 0.1 V when the Δ(ads)G are values calculated for the potentials of zero charge, instead of 1.229 V, which is a significant simplification. The variation in Δ(ads)G values between the calculated potentials of zero charge and 1.229 V are found to be 0.2 eV V(-1) or less. Prior work, using internal adsorption energies calculated at the potential of zero charge in place of Gibbs energies in was found to be accurate to within about 0.2 V. On platinum Δ(ads)G of the reaction OOH(ads) → O(ads) + OH(ads) is calculated at the potential of zero charge for the reactant and product to be about 1.2 eV exergonic under Langmuir conditions, and this Gibbs energy loss reduces the 1.229 V four-electron reversible potential on the platinum surface to an effective reversible potential of about 0.93 V for this mechanism on platinum. The effective reversible potential is a consequence of efficiency loss, not kinetics. Based on these values, the onset potential for four-electron oxygen reduction will be less than or equal to the effective reversible potential and on pure Pt(111) it appears to be equal to it.