Low Overvoltage Research Articles

Cathodically Deposited Birnessite As the Electrode Material

Various manganese oxides are considered as rather active ORR catalysts and/or supercapacitor materials for operation in alkaline medium. However all these oxides are thermodynamically unstable at high pH and undergo more or less slow transformations to non-stoichiometric oxides containing alkali metal cations M (MxMnO2*nH2O, known also as birnessite mineral). We report a possibility to deposit birnessite thin layers by means of permanganate cathodic reduction. We consider ORR activities and reversible recharging data for birnessite deposited at various potentials with account for XRD information on birnessite cell disordering and microscopic data on the morphology of the deposits.Deposition is complicated by formation of soluble Mn(V) and Mn(VI) species and their disproportionation. However fortunately these by-side reactions appear to be strongly inhibited by forming birnessite solid, and the resulting current efficiencies are high enough. We compare deposition efficiency and adhesion for Pt, Ni, and glassy carbon supports. The best adhesion is found for Ni support.Deposits morphology strongly depends on deposition potential. Thin deposits formed at low overvoltage demonstrate homogeneously distributed pores, and only starting from sub-mkm thickness branched flakes appear, which are typical for natural birnessite morphology. Contrary, at higher overvoltage the deposits start to branch from the very beginning, and consist from thin flakes exclusively. This morphology is unfavorable for electrode behavior because of too high material resistance. Deposition transients allow to monitor the morphology. For flakes formation, oscillatons at deposition transients are observed, which can be associated with layer-by-layer growth.The recharging of all birnessite materials is reversible, but the specific capacity strongly depends on deposition potential and deposit thickness. The best results (ca. 500 mkF/cm2 at scan rates up to 0.1 V/s) are found for thin deposits fabricated at low overvoltage. ORR mass activity is comparable with observed earlier for MnO2, which is believed to undergo slow transformation to birnessite in alkaline solutions. The important advantage of electrodeposited birnessite as compared to the majority of chemically synthesized manganese oxides is a possibility to operate in the absence of conducting binder.

Electrolysis of ammonia in aqueous solution by platinum nanoparticles supported on carbon nanotube film electrode

Electrolysis of ammonia in an aqueous solution can generate hydrogen gas at room temperature. An anode reaction of nitrogen gas desorption on ammonia electrolysis has a much larger overvoltage than that of a cathode reaction, and one of the useful electrode catalysts for the anode reaction is platinum (Pt). In this study, in order to increase the surface area of Pt three-dimensionally, Pt nanoparticles are held on a sponge-like film of carbon nanotubes (CNTs) that has a large surface area of 5000–10000 cm2 per 1 cm2 of the CNT film. The electrodes were adapted to the ammonia electrolysis to increase the current density with a low overvoltage. The Pt nanoparticles were deposited on the CNTs by a polyol method at various temperatures, and the Pt nanoparticles supported on the CNT (Pt-CNT) electrodes were fabricated by vacuum filtration of the Pt-CNT dispersion. The size of the deposited Pt nanoparticles was approximately 2–3 nm. The maximum electrochemical surface area of the Pt nanoparticles was more than 250 cm2 per unit electrode area of 1 cm2. The Pt-CNT film electrode with a large surface area of the Pt catalyst increased the current density of the anode reaction compared with the Pt plate or the Pt-black electrodes. The Pt-CNT decreased both the activation overvoltage corresponding to the high Pt surface area and the concentration overvoltage corresponding to the three-dimensional structure of the CNT films. Moreover, it is clarified that the deactivation of the catalysts by the anode reaction does not occur below −0.2 V (vs Hg|HgO) for the Pt-CNT electrodes.

Enhanced tensile properties and corrosion resistance of stainless steel with copper-coated graphene fillers

Graphene (Gr) can significantly improve the mechanical properties of metal matrix materials. However, the reinforcing effect of Gr on stainless steel (SS) has rarely been investigated due to the difficulty in its uniform dispersion. In this study, 316L stainless steel was reinforced with copper-coated graphene (Gr-Cu/SS) through molecular level mixing, ball milling, and spark plasma sintering (SPS). The tensile strength and yield strength of Gr-Cu/SS have increased by 74.0% and 65.5%, respectively, with 0.2 wt% graphene added. The improvement on the tensile strength and yield strength of Gr-Cu/SS is attributed to the effective load transfer and the increase of relative density due to the addition of graphene. Moreover, the corrosion resistance of Gr-Cu/SS was improved, attributed to the low cathodic overvoltage of copper and the prevention of ionic transfer between stainless steel grains by graphene.

Electrochemical Synergies of Heterostructured Fe2O3-MnO Catalyst for Oxygen Evolution Reaction in Alkaline Water Splitting.

For efficient electrode development in an electrolysis system, Fe2O3, MnO, and heterojunction Fe2O3-MnO materials were synthesized via a simple sol–gel method. These particles were coated on a Ni-foam (NF) electrode, and the resulting material was used as an electrode to be used during an oxygen evolution reaction (OER). A 1000-cycle OER test in a KOH alkaline electrolyte indicated that the heterojunction Fe2O3-MnO/NF electrode exhibited the most stable and highest OER activity: it exhibited a low overvoltage (n) of 370 mV and a small Tafel slope of 66 mV/dec. X-ray photoelectron spectroscopy indicated that the excellent redox performance contributed to the synergy of Mn and Fe, which enhanced the OER performance of the Fe2O3-MnO/NF electrode. Furthermore, the effective redox reaction of Mn and Fe indicated that the structure maintained stability even under 1000 repeated OER cycles.

A High Performance Full SiC Power Module Based On a Novel Stacked DBCs Hybrid Packaging Structure

Abstract This paper proposed a novel stacked DBCs hybrid package structure and designed a low inductive 1200V/120A SiC half-bridge power module based on the package structure. Using the multi-layer structure of DBC+DBC, the main loop parasitic inductance of the power module has been reduced to 1.8nH by optimizing the three-dimensional commutation loop and using the mutual inductance cancellation concept. The module was designed and fabricated, the low inductance characteristics of the module was verified by dual pulse testing and power testing. Dynamic test results show that the module can switch safely with a low overvoltage under zero ohm external drive resistance, and the switching loss is reduced by 57% compared to commercial modules.

Electrochemical insights into layered La2CuO4 perovskite: Active ionic copper for selective CO2 electroreduction at low overpotential

La2CuO4, a layered perovskites oxide was synthesized using solution combustion method at different calcination temperatures. XRD characterization and Rietveld refinement analysis confirms the pure phase of the synthesized material. The effect of calcination causes shrinking in the lattice parameters affirm the change in the oxygen stoichiometry. Four Probe (Van der Pauw’s) and CP-AFM analysis were carried out to understand the influences of calcination temperature on electrical conductivity. Electrochemical investigations on La2CuO4 were performed at various negative potential ranges using cyclic voltammetry (CV) to identify the redox active centre. Thermodynamic calculations are further carried out to validate the electrochemical results in different mediums. Selective electrocatalytic conversion of CO2 to C2-hydrocarbon (C2H4) with FE% of 40.3% which is 10 times higher than CH4 (FE% = 4.1%) emphasized the in-situ formation of Cu2O from the redox active centre present in La2CuO4. Hydrocarbons are generated at a very low overvoltage (−0.4 V RHE) in comparison to literature. XPS analysis indeed confirms the presence of Cu+ species i.e., in-situ generated Cu2O, on La2CuO4 after CV and CO2 electrocatalysis.

Effect of Ionomer Solvents for Pore Size Control of Imidazolium-Base Ionomers in Aemfc

Anion exchange membrane fuel cells (AEMFCs) have a low activation overvoltage due to the fast oxygen reduction reaction (ORR) response to alkaline conditions compared to the acidic condition of proton exchange membrane fuel cells (PEMFCs). The reasons for low activation overvoltage in AEMFCs are diversely studied. Recently, the binder ionomer in the catalyst layer of polymer electrolyte membrane fuel cells has attracted increasing attention because of its critical role in power performance and the durability of the catalyst layer. Ionomer covers the catalyst surfaces, providing anion transport between the catalyst surfaces and the membrane, as well as mechanical connection. Several requirements as a binder are to have high ion conductivity, gas permeability, and electron conductivity. For durability of membrane electrode assembly (MEA), the binder must have high oxidative stability, and mechanical integrity, less excessive swelling is detrimental. Unususally as AEMs and binder materials, functional groups such as quaternary ammonium (QAs), phosphonium, guanidinium, tertiary sulfonium, pyridinium, and imidazolium ionic liquid (IILs) are used as cation groups. Among them, the QAs has higher chemical and thermal stability than phosphonium, guanidinium and tertiary sulfonium ions. However, the QAs groups tend to be degraded by OH- counterion in high pH environments. In this study, we prepared a binder using IILs instead of the commonly used QAs. Imidazolium-based binders are uncomplicated to design the polymer and easy to synthesize. Furthermore, effect of different alcohols in ionomer binder solution on the shale and pore size of catalyst layer is presented here. The aim of this study is to find out the effect of alcohols in binder ionomers for alkaline fuel cell performance. Figure 1

Investigation of the Low Voltage Ride-Through of Inverter Using Virtual Inertia Methods in Microgrid

Inverter based Distributed Energy Resources lack the inertia and damping features of synchronous generators dominated traditional power system. The growing penetration of renewable energy technologies coupled with their inherent intermittency also constitute grid instability challenge due to insignificant inertia and damping. The virtual inertia machine methods for the control of inverter based Distributed Energy Resources present the required inertia support that mimics the dynamic performance of a typical synchronous generator. These control methods provide excellent improvement in the stability of the grid. Several studies and implementations have been carried out on providing virtual inertia support for inverters in steady-state and under balanced grid voltage, however there is a need to investigate the dynamic performances during voltage sags occasioned by faults and other grid transients. Due to the low overvoltage and overcurrent tolerance capabilities of inverters, this investigation is important to observe the inverter transient behavior while ensuring the protection of constituent power electronic switches. Consequently, this work carried out an investigation to assess the two methods of Virtual Inertia Machine in ensuring the inverter sustained grid connection in compliance with grid codes, fault current limitation and fault recovery.

Development of a Novel HVdc Circuit Breaker Combining Liquid Metal Load Commutation Switch and Two-Stage Commutation Circuit

The emerging demand on development of high-voltage direct current (HVdc) networks brings about an increasingly urgent need for a fast and reliable HVdc circuit breaker. This paper proposes a novel topology of HVdc circuit breaker combining a liquid metal load commutation switch and a two-stage commutation circuit, which offers an effective solution for isolating faults while preserving larger current breaking capability and lower overvoltage rate of rise. With the topology optimized in terms of circuit parameters for determining their optimum design values, the handling of short-circuit faults for the proposed circuit breaker in HVdc application is predicted theoretically. Finally, preliminary tests from a developed low-power prototype are presented together with a comparative simulation study provided to verify the performance of the proposed HVdc circuit breaker.

Development of ACLS Electrodes for a Water Electrolysis Cell

An iridium electrocatalyst powder with a platinum-coated porous titanium layer is conventionally used as the anode in polymer electrolyte membrane (PEM) electrolyzers. However, these noble metals are scarce and expensive. To reduce their use, we developed an alternating catalyst layer structure (ACLS) consisting of multiple sputter-deposited iridium sheets and air-gap layers without a platinum coating layer. The ACLS electrocatalyst exhibited lower overvoltage at low iridium loading compared with a powder catalyst, and there was almost no voltage rise during 7,000 h of operation. The ACLS is effective for reducing the amount of noble metals used in PEM electrolyzers.

(Invited) Tuning Matrix Solvation for Adjusting the Formal Potential of Redox-Active Centers

The redox transformation of small molecules such as H2 and CO2 by means of molecular catalysts is of central importance for the conversion of renewable energy. Outer coordination sphere design currently drives the development of such catalysts toward enzyme-like performances. The redox potential of the catalyst is among the key features defining its properties in order to achieve high current densities at low overvoltage. The use of salts from the Hofmeister series in electrolytes provides a new way of adjusting the formal potential of redox systems embedded in polymeric matrices without directly manipulating the chemical structure. Based on viologen moieties serving as model redox active species, we demonstrate that the difference in hydration of chaotropic and kosmotropic anions has an effect on the net solvation of positively charged redox polymers and impact their redox potential. To systematically understand the effect of the counterions on the redox potential shift, electrochemical and spectroscopic analyses of free-diffusing viologens in solution were compared with structure-analog viologen-modified polymer films. Ultimately, the modulation of the solvent induced matrix interactions may be translated as a general lever to control catalyst properties such as electron and proton mobility, substrate binding or product release in analogy to the mode of function of active site of redox enzymes.

Functional properties and electrochemical performance of Ca-doped Sr2-xCaxFe1.5Mo0.5O6-δ as anode for solid oxide fuel cells

Performance of Ca-doped strontium ferrite-molybdate Sr2-xCaxFe1.5Mo0.5O6-δ (x = 0, 0.05, 0.15, 0.3, 0.5) has been studied under reducing conditions. Thermogravimetry (TG) analysis in 5% H2/Ar and DSC measurements in high-purity argon demonstrated that the compositions are highly stable and there are no phase transitions. The best electrochemical and electrical performances of about 0.12 Ω cm2 and 33 S/cm at 800 °C in wet hydrogen, respectively, were obtained for the Sr1.85Ca0.15Fe1.5Mo0.5O6-δ anode. The EIS spectra were analyzed by means of distribution relaxation times and non-linear least squares methods, which made it possible to determine the behavior of the rate-limiting steps of hydrogen oxidation. Solid oxide fuel cells (SOFC) of planar design with the 1.5 mm LaGaO3-based supporting electrolyte, with the Sr1.85Ca0.15Fe1.5Mo0.5O6-δ symmetrical electrodes and with the Sr2-xCaxFe1.5Mo0.5O6-δ (x = 0.15 and 0.3) anode and the 70 wt% Pr0.9Y0.1BaCo2O6–δ + 30 wt% SDC cathode have been studied. The obtained results demonstrated a low anode overvoltage, which was about 0.12 V at 1 A/cm2 and 800 °C in wet hydrogen. The maximum power density of SOFC with the Sr1.85Ca0.15Fe1.5Mo0.5O6-δ anode and cobaltite cathode was about 0.18 W/cm2 at 800 °С under air/wet hydrogen conditions. The obtained results elucidate that Sr1.85Ca0.15Fe1.5Mo0.5O6-δ is a promising anode for solid oxide fuel cells.

Hierarchical porous FeCo2O4@Ni as a carbon- and binder-free cathode for lithium−oxygen batteries

The electrochemical performance of the lithium−oxygen (Li−O2) batteries largely depends on the material and architecture of the catalytic cathode. In this paper, to avoid the parasitic reactions of carbon and binder with discharge products and reaction intermediates, we proposed an effective design of a free-standing catalytic cathode for Li−O2 batteries. The FeCo2O4@Ni electrode consists of FeCo2O4 nanosheets grown directly on nickel (Ni) foam. The resultant hierarchical macroporous/mesoporous structure provides sufficient space for the insoluble discharge product Li2O2 and catalytically active sites for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Consequently, the carbon- and binder-free self-supporting electrode has demonstrated a high discharge capacity with relatively low charge overvoltage and a better cycle performance than the corresponding carbon-based electrodes.

Polyoxothiometalate-Derivatized Silicon Photocathodes for Sunlight-Driven Hydrogen Evolution Reaction.

Silicon photocathodes coated with drop-casted {Mo3S4}-based polyoxothiometalate assemblies are demonstrated to be effective for sunlight-driven hydrogen evolution reaction (HER) in acid conditions. These photocathodes are catalytically more efficient than that coated with the parent thiomolybdate incorporating an organic ligand, as supported by a higher onset potential and a lower overvoltage at 10 mA cm–2. At pH 7.3, the trend is inversed and the beneficial effect of the polyoxometalate for the HER is not observed. Moreover, the polyoxothiometalate-modified photocathode is found to be also more stable under acid conditions and can be operated at the light-limited catalytic current for more than 40 h. Furthermore, X-ray photoelectron spectroscopy and atomic force microscopy measurements indicate that the cathodic polarization of both photocathodes leads to the release of a large amount of the deposited material into the electrolyte solution concomitantly with the formation of mixed valence species {Mo(IV)3–xMo(III)xO4–nSn}(4–x)+ resulting from the replacement of S2– sulfido ligands in the cluster by oxo O2– groups; these combined effects are shown to be beneficial for the photoelectrocatalysis.

Assessment of Appropriate MMC Topology Considering DC Fault Handling Performance of Fault Protection Devices

The eventual goal of high-voltage direct-voltage (HVDC) systems is to implement HVDC grids. The modular multilevel converter (MMC) has been identified as the best candidate for the realization of an HVDC grid by eliminating the shortcomings of conventional voltage source converter (VSC) technology. The related research has focused on efficient control schemes, new MMC topologies, and operational characteristics of an MMC in a DC grid, but there is little understanding about the fault handling capability of two mainstream MMC topologies, i.e., half bridge (HB) and full bridge (FB) MMCs in combination with an adequate protection device. Contrary to the existing research where the fault location is usually fixed (center of the line), this paper considered a variable fault location on the DC line, so as to compare the fault interruption time and maximum fault current magnitude. From the point of view of fault interruption, AC and DC side transient analyses were performed for both MMC topologies to suggest the appropriate topology. The simulation result confirmed that the fault handling performance of an HB-MMC with a DC circuit breaker is superior due to the smaller fault current magnitude, faster interruption time, lower overvoltage magnitude, and lesser stresses on the insulation of the DC grid.

Galvano– and Potentio–dynamic studies during ethanol electro-oxidation reaction in acid vs. alkaline media: Energy dissipation and blocking nature of potassium

Despite the net energy yield be the primary goal of ethanol electro-oxidation reaction (EOR), it is never measured in fundamental electrochemical studies. By combining galvanodynamic and potentiodynamic profiles of the steady states of the system, we demonstrate a methodology to estimate the dissipation of chemical energy that allows the inference of the fuel cell power output in relative terms. Apart from the empirical energy dissipation, several kinetic information are unravelled: (a) the kinetics is governed by ethanol adsorption rate for both media and for both external control modes; and (b) either the maximum current sustained by EOR or the steady state currents are, in addition, governed by a global coverage of poisonings species, which includes the contributions from COad and non-reactive OHad. The blocking effect of potassium cations over EOR is clearly verified, reducing the maximum activity up to a factor of 0.19, which is interpreted as an effect of the high coverage of non-reactive OHad. Finally, it is expected a slightly improvement of the power output of a direct ethanol fuel cell operating at steady state in alkaline media due to the lower chemical dissipation at fixed interfacial current value. Nonetheless, the blocking effect of potassium in alkaline media may, depending on the concentration, either induces an oscillatory regime at higher overvoltage (above 0.57 V) along with the preservation of the energy generation at lower overvoltage or completely decrease the energy generation due to a drastic loss of energy used to polarize the EOR.

Low-cost and environment-friendly synthesis of carbon nanorods assembled hierarchical meso-macroporous carbons networks aerogels from natural apples for the electrochemical determination of ascorbic acid and hydrogen peroxide

In this work, the low-cost carbon nanorods assembled hierarchical meso-macroporous carbons networks aerogels (CNs-HMCNAs) was environment-friendly synthesized from a cheap and abundant biomass of apples (Malus pumila Mill) for the first time. The biomass of apples derived CNs-HMCNAs exhibited the unique hierarchical meso-macroporous structure with large specific surface area and high density of edge defective sites. At the CNs-HMCNAs modified GCE (CNs-HMCNAs/GCE), the electron transfer between the glassy carbon electrode (GCE) and the ascorbic acid (AA) (or hydrogen peroxide (H2O2)) was effectively enhanced, and thus induced a low overvoltage for AA electrooxidation (or H2O2 electroreduction). As an electrochemical AA (or H2O2) sensor, the CNs-HMCNAs/GCE exhibited wider linear range, lower detection limit, higher sensitivity and stability than GCE and the carbon nanotubes modified GCE (CNTs/GCE). In particular, the CNs-HMCNAs/GCE showed great potential feasibility in the practical determination of AA (in AA injection, Vitamin C tablet and kiwi juice) or H2O2 (in human urine, milk and beer).

Effect of Carbon Contents on Corrosion and Hydrogen Diffusion Behaviors of Ultra-Strong Steels for Automotive Applications

Recently developed ultra-strong GIGA STEEL exhibites superior mechanical properties, with a high tensile strength of more than 1.5 GPa and good impact toughness. Nevertheless, its application to auto parts has been severely restricted, mainly due to a substantial reduction in the resistance to hydrogen embrittlement (HE) induced by aqueous corrosion. The susceptibility to this HE is closely associated with the carbon content, which leads essentially to the precipitation of iron carbides (Fe2.4C/Fe3C) with a low hydrogen overvoltage. This study focuses mainly on the effect of carbon content on the aqueous corrosion and hydrogen diffusion characteristics of ultra-strong steels. The hydrogen reduction reaction on the steel surface, and its diffusion kinetics in the steel matrix were evaluated using electrochemical polarization and hydrogen permeation tests, respectively. Furthermore, the HE indices of steels with different carbon contents were determined in a weakly acidic solution using the slow strain rate test (SSRT). This study demonstrates clearly that the hydrogen reduction rates were increased and its diffusion kinetics were decreased significantly, with increasing carbon content. Based on the present results, it is concluded that the critical technical issue for the development of ultra-strong automotive steels is the effective control of the carbide fractions in the microstructure. Key words: ultra-strong steel, carbide, corrosion, hydrogen diffusion, hydrogen embrittlement

Metal-Oxide-Supported Ir-Decorated Electrocatalysts for Polymer Electrolyte Membrane Water Electrolysis

Introduction Since polymer electrolyte membrane water electrolysis (PEMWE) is similar in cell structure to polymer electrolyte fuel cells (PEFC), technologies used for PEFCs can be applied to PEMWEs. However, Pt electrocatalysts supported on carbon black (Pt/C) typically used for PEFCs cannot be applied under a high potential up to 2.0V [1]. Here, we apply SnO2 and titanium as alternative support materials. SnO2 may be promising as an anode electrocatalyst support material since it has relatively high electronic conductivity and stability against a high potential, among various metal oxides [2 ,3 ]. The top surface of metallic titanium is naturally oxidized to form stable titanium oxide, so that titanium supports may exhibit high durability under the strongly-acidic PEMWE condition [4]. In this study, we prepare the iridium-decorated SnO2/VGCF electrocatalysts (IrO2/Nb-SnO2/VGCF). Furthermore, by making such Ti sheet acting as the gas diffusion layer (GDL) and current collector, we prepare a GDL-integrated PEMWE electrode consisting of Ir electrocatalyst and Ti-based catalyst support (Ir/Ti). Experimental Sn0.98Nb0.02O2/VGCF was prepared via an ammonia co-precipitation method. IrO2 nanoparticles were decorated on Sn0.98Nb0.02O2/VGCF by evaporating the aqueous solution mixture containing Sn0.98Nb0.02O2/VGCF and H2IrCl6.nH2O while stirring, followed by heat treatment at 440°C in air. The Ti sheet was etched with 1M NaOH solution at 60°C for 1 hour, followed by heat treatment at 400°C in 5%H2-N2 for 30 minutes. Ir nanoparticles were decorated on the NaOH-etched Ti sheet by the arc plasma deposition (APD). The microstructure of the IrO2/Nb-SnO2/VGCF and the Ir/Ti sheet was observed by SEM, STEM, and TEM. Electrochemical measurements were made for the half cell and the single cell. Results and discussion We prepared IrO2/Sn(Nb)/VGCF with IrO2 loading of 23.6wt.%. Figure 1 shows the micrograph of the IrO2/Nb-SnO2/VGCF electrocatalyst. The micrograph indicates that Ir (or IrO2) nanoparticles have particle size of 1 to 3nm in diameter. I-V characteristics and durability of the MEA made with the IrO2/Sn(Nb)O2/VGCF electrocatalyst were evaluated. The MEA exhibited low activation overvoltage, but still with high IR loss and poor durability Figure 2 shows the STEM image of the Ir/Ti sheet after 2000 pulses of the APD with the Ir loading of 0.086mg/cm2, showing Ir particles of 1 to 2 nm on the etched Ti-based material. I-V characteristics of the MEA made with the Ir/Ti with the oxidized Ti surfaces were evaluated. The Ir/Ti MEA exhibited higher performance than that of the IrO2/Sn(Nb)O2/VGCF electrocatalyst despite very low Ir loading, indicating that the Ir/Ti MEA could be of interest for PEMWE applications.

3D Ag/NiO-Fe2O3/Ag nanomembranes as carbon-free cathode materials for Li-O2 batteries

The Li-O2 battery is considered as an appealing candidate for future energy supplies due to its exceptionally high energy density. A key issue of prevailing aprotic Li-O2 batteries is exploring carbon-free electrode materials to avoid the irreversible side reactions produced by carbonaceous electrode. Here, three-dimensional (3D) curved Ag/NiO-Fe2O3/Ag hybrid nanomembranes induced by a facile thermal treatment method are fabricated, for the first time, as carbon-free cathode materials in Li-O2 batteries. A competing scheme between the intrinsic strain built in the oxide nanomembranes and the external driving force provided by the metal nanoparticles is introduced to tune the morphology of the 3D tubular architectures. The tubular structure of the nanomembranes provides continuous tunnels for the diffusion of O2 and electrolyte as well as the accommodation of discharge products without clogging. More importantly, the side reactions are effectively mitigated by such carbon-free nanomembrane materials. Therefore, enabled by such 3D hybrid nanomembranes with particularly interesting morphology and structure, the Li-O2 batteries exhibit enhanced electrochemical performance with low overvoltages, high capacity retention and greatly prolonged cycle life.