Discharge characteristic of a non-aqueous electrolyte Li/O2 battery

Discharge characteristic of Li/O₂ cells was studied using galvanostatic discharge, polarization, and ac-impedance techniques. Results show that the discharge performance of Li/O₂ cells is determined mainly by the carbon air electrode, instead by the Li anode. A consecutive polarization experiment shows that impedance of the air electrode is progressively increased with polarization cycle number since the surfaces of the air electrode are gradually covered by discharge products, which prevents oxygen from diffusing to the reaction sites of carbon. Based on this observation, we proposed an electrolyte-catalyst “two-phase reaction zone” model for the catalytic reduction of oxygen in carbon air electrode. According to this model, the best case for electrolyte-filling is that the air electrode is completely wetted while still remaining sufficient pores for fast diffusion of gaseous oxygen. It is shown that an electrolyte-flooded cell suffers low specific capacity and poor power performance due to slow diffusion of the dissolved oxygen in liquid electrolyte. Therefore, the status of electrolyte-filling plays an essential role in determining the specific capacity and power capability of a Li/O₂ cell. In addition, we found that at low discharge currents the Li/O₂ cell showed two discharge voltage plateaus. The second voltage plateau is attributed to a continuous discharge of Li₂O₂ into Li₂O, and this discharge shows high polarization due to the electrically isolating property of Li₂O₂.     

Electrocatalytic reduction of O2 and H2O2 by adsorbed cobalt tetramethoxyphenyl porphyrin and its application for fuel cell cathodes

In this paper, the mechanism and kinetics of oxygen and hydrogen peroxide electrochemical reduction that is catalyzed by an adsorbed cobalt tetramethoxyphenyl porphyrin (CoTMPP) on a graphite electrode were investigated using cyclic voltammetry (CV) and the rotating disk electrode (RDE) technique. The temperature and anion effects on O₂ and H₂O₂ electroreduction processes were also studied. The pH dependencies of cobalt redox centers, and oxygen and hydrogen peroxide reductions were measured for the purpose of exploring the reaction mechanism. In neutral solutions, the oxygen reduction reaction was observed to be a two-electron process, producing H₂O₂ in the low potential polarization range. In the high potential polarization range, an overall four-electron reduction of O₂ to H₂O was found to be the dominating process. The kinetic parameters obtained from the RDE experiments indicate that in a neutral solution, the reduction rate at the step from H₂O₂ to H₂O is faster than that seen from O₂ to H₂O₂. Carbon particle-based air cathodes catalyzed by CoTMPP were fabricated for metal-air fuel cell application. The obtained non-noble catalyst content cathodes show considerably improved performance and stability.     

Carbon-coated stainless steel as PEFC bipolar plate material

Stainless steel is quite attractive as bipolar plate material for polymer electrolyte fuel cells (PEFCs). Passive film on stainless steel protects the bulk of it from corrosion. However, passive film is composed of mixed metal oxides and causes a decrease in the interfacial contact resistance (ICR) between the bipolar plate and gas diffusion layer. Low ICR and high corrosion resistance are both required. In order to impart low ICR to stainless steel (SUS304), carbon-coating was prepared by using plasma-assisted chemical vapor deposition. Carbon-coated SUS304 was characterized by Raman spectroscopy and atomic force microscopy. Anodic polarization behavior under PEFC operating conditions (H₂SO₄ solution bubbled with H₂ (anode)/O₂ (cathode) containing 2 ppm HF at 80 °C) was examined. Based on the results of the ICR evaluated before and after anodic polarization, the potential for using carbon-coated SUS304 as bipolar plate material for PEFC was discussed.     

Reversible H2/H2O electrochemical conversion mechanisms on the patterned nickel electrodes

The patterned nickel (Ni) electrode enables to quantify the triple-phase boundary (TPB) length and Ni surface area as well as exclude the interference of bulk gas diffusion. In this study, the patterned Ni electrodes are investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H₂O/H₂. The experimental test shows the patterned Ni electrode keeps stable and intact only at the specific operating condition due to instability of Ni at the H₂O-containing atmosphere. The effects of the temperature, partial pressure of H₂O and H₂ on the electrochemical performance are measured. The electrochemical performance has a positive correlation with the temperature, partial pressure of H₂ and H₂O. Further, the experimental results are compared with the mechanism containing two-step charge-transfer reaction used in the existing literature. An analytical calculation is performed to indicate the rate-limiting steps may be different for SOFC and SOEC modes. In SOFC mode, H₂ electrochemical oxidation could be dominated by both charge transfer reaction at low polarization voltage and by the charge-transfer reaction H(Ni) + O^2?(YSZ) → OH^?(YSZ) + (Ni) + e^? at high polarization voltage, however in SOEC mode, H₂O electrochemical reduction is considered to be dominated by H₂O(YSZ) + (Ni) + e^? → OH^?(YSZ) + H(Ni).     

Degradation of Ni-Zr0.9Sc0.1O1.95 anode in H2 + H2O at low temperature: Influence of nickel surface charge

The present paper reports on the data of the Ni-Zr_0.9Sc_0.1O_1.95 anode polarization resistance long-term test (1500 h) at 600 °С in the wet hydrogen and 30% H₂ + 70% H₂O. The results are presented for two type of anodes: initial and impregnated with ceria. The fast degradation of both types of anodes in 30% H₂ + 70% H₂O was observed. After the long-term tests in 30% H₂ + 70% H₂O at 600 °C, heating and exposure at 900 °C in wet hydrogen leads to the restore of anode performance. At the termination of the 1500 h test, the area polarization specific resistance of Ni-Zr_0.9Sc_0.1O_1.95 remained almost unchanged as compared to the initial value, whereas for impregnated anodes the polarization resistance increased three times. The observed phenomena were explained by the OH^? ions adsorption at the positively charged nickel surface. During the long-term tests at 600 °С the electrode microstructure did not change and the significant sintering of highly disperse ceria was not observed.     

Stabilized zirconia-based sensor utilizing SnO2-based sensing electrode with an integrated Cr2O3 catalyst layer for sensitive and selective detection of hydrogen

A highly selective hydrogen (H₂) sensor has been successfully developed by using an yttria-stabilized zirconia (YSZ)-based mixed-potential-type sensor utilizing SnO₂ (+30 wt.% YSZ) sensing electrode (SE) with an intermediate Al₂O₃ barrier layer which was coated with a catalyst layer of Cr₂O₃. The sensor utilizing SnO₂ (+30 wt.% YSZ)-SE was found to be capable of detecting H₂ and propene (C₃H₆) sensitively at 550 °C. In order to enhance the selectivity towards H₂, a selective C₃H₆ oxidation catalyst was employed to minimize unwanted responses caused by interfering gases. Among the examined metal oxides, Cr₂O₃ facilitated the selective oxidation of C₃H₆. However, the addition or lamination of Cr₂O₃ to SnO₂ (+30 wt.% YSZ)-SE was found to diminish the sensing responses to all examined gases. Therefore, an intermediate layer of Al₂O₃ was sandwiched between the SE layer and the catalyst layer to prevent the penetration of Cr₂O₃ particles into the SE layer. The sensor using SnO₂ (+30 wt.% YSZ)-SE coated with a catalyst layer of Cr₂O₃ as well as an intermediate layer of Al₂O₃ exhibited a sensitive response toward H₂, with only minor responses toward other examined gases at 550 °C under humid conditions (21 vol.% O₂ and 1.35 vol.% H₂O in N₂ balance). A linear relationship was observed between sensitivity and H₂ concentration in the range of 20–800 ppm on a logarithmic scale. The results of sensing performance evaluation and polarization curve measurements indicate that the sensing mechanism is based on the mixed-potential model.     

Electrochemical performance and durability of flat-tube solid oxide electrolysis cells for H2O/CO2 co-electrolysis

Co-electrolysis of H₂O and CO₂ by high-temperature solid oxide electrolysis cells (SOECs) is a useful approach for energy storage and carbon dioxide reduction. In this study, we conducted H₂O/CO₂ co-electrolysis using a flat-tube SOEC and studied its electrochemical performance and durability. It was found that the increase of temperature and water fraction in fuel gas promote electrochemical performance. In addition, the co-electrolysis was found to be stable with a constant current density of 300 mA cm^?2 for over 1000 h at 750 °C. The contribution of each electrode process to polarization resistance is elucidated by electrochemical impedance spectroscopy and distribution of relaxation time (DRT) analysis. The fuel electrode was found to degrade more significantly against duration time as compared to the oxygen electrode. Post-mortem analysis of the microstructure revealed the loss and sintering of Ni particles in active cathode functional layer at the inlet of the fuel electrode. Based on these results, the degradation mechanism of H₂O/CO₂ co-electrolysis by the flat-tube SOEC was discussed in details.     

Electrochemical performance of nanostructured spinel LiMn2O4 in different aqueous electrolytes

A nanostructured spinel LiMn₂O₄ electrode material was prepared via a room-temperature solid-state grinding reaction route starting with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O) and citric acid (C₆H₈O₇·H₂O) raw materials, followed by calcination of the precursor at 500 °C. The material was characterized by X-ray diffraction (XRD) and transmission electron microscope techniques. The electrochemical performance of the LiMn₂O₄ electrodes in 2 M Li₂SO₄, 1 M LiNO₃, 5 M LiNO₃ and 9 M LiNO₃ aqueous electrolytes was studied using cyclic voltammetry, ac impedance and galvanostatic charge/discharge methods. The LiMn₂O₄ electrode in 5 M LiNO₃ electrolyte exhibited good electrochemical performance in terms of specific capacity, rate dischargeability and charge/discharge cyclability, as evidenced by the charge/discharge results.     

Acetic acid internal reforming in a solid oxide fuel cell-reactor using Cu–CeO2 anodic composites

This work targets to explore the performance of Cu–CeO₂ anodes for the production of hydrogen and power generation during the internal steam reforming of CH₃COOH in SOFC reactors. When the cell operated as an electrochemical membrane reactor, the effect of temperature, reactants' partial pressures and imposed overpotentials on the catalytic activity and selectivity of Cu/CeO₂ electrodes, at both open and closed circuit operations, were investigated. The results show that at open circuit conditions, CH₃COOH is efficiently reformed by H₂O to syngas, where the observed products' distribution is influenced by both the associated CH₃COOH thermal/catalytic decomposition reactions and by the reverse water gas shift reaction. In all cases examined, neither acetone nor carbon is observed at the effluents, with the latter being attributed to the gasification of carbonaceous deposits by H₂O to CO and H₂. At anodic polarization conditions, Cu–CeO₂ exhibits high catalytic activity toward the electro-oxidation of all combustible species. Kinetic experiments show that the reaction mechanism involves the dissociative adsorption and decomposition of both reactants on the catalyst surface, where the subsequent interaction of the resulted fragments leads to the observed final products. In the fuel cell mode, the electrochemical performance of Cu–CeO₂ was investigated by voltage–current density–power density and AC impedance measurements. Ohmic losses are the prevailing source of polarization, mainly attributed to the anodic interfacial resistance, which is significantly influenced by cell temperature and reactants composition. The electrode performance is mainly limited by the diffusion of the charged or neutral species to triple phase boundary while in the case of dry feeding mixtures, the charge transfer processes determine the overall efficiency.     

Kinetics of oxygen reaction in porous La0.6Sr0.4Co0.2Fe0.8O3–δ-Ce0.8Gd0.2O1.9 composite electrodes for solid oxide cells

Kinetics of oxygen reaction in porous La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ (LSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ-Ce_0.8Gd_0.2O_1.9 (LSCF-GDC) electrodes are systematically studied. Normally, there are two pathways of oxygen reaction in porous LSCF: in reaction region with oxygen exchanging at electrode/air interface, and around electrode/electrolyte interface with oxygen exchanging at electrode/electrolyte/air triple-phase boundary (TPB). GDC in porous LSCF-GDC accelerates oxygen transport and oxygen gas diffusion during oxygen reaction. In addition, because the formation of LSCF/GDC interface increases the length of TPB and affects the geometry of reaction region, oxygen reaction in LSCF-GDC tends to proceed in the TPB pathway. The performance and oxygen reactions of LSCF-GDC are evaluated at 650 °C and 850 °C. Oxygen reaction in LSCF-GDC is suppressed by CO₂, but increasing GDC content is able to improve the CO₂ tolerance of electrode. Though the performance reduction by H₂O is unobvious, H₂O can aggravate CO₂ degradation at low temperature.     

Preparation and characterization of a redox-stable Pr0.4Sr0.6Fe0.875Mo0.125O3-δ material as a novel symmetrical electrode for solid oxide cell application

In this work, to simultaneously meet the requirements of good electrochemical performance and redox stability, perovskite oxide Pr_0.4Sr_0.6Fe_0.875Mo_0.125O_3-δ (PSFM) material has been developed as a novel redox-stable electrode for symmetrical cell application. The experimental results obtained by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy show that metallic Fe nanoparticles will exsolve from the parent oxide PSFM through in-situ exsolution method when treating in 97% H₂–3% H₂O atmosphere, and then completely re-incorporate into the parent oxide in air, demonstrating excellent redox stability for PSFM material. In addition, the redox stability in electrochemical performance is also studied by recording the electrochemical impedance spectra and distribution of relaxation times (DRT) analysis. It is demonstrated that a constant electrode polarization resistance (R_p) of ~0.60 Ωcm² is achieved for the symmetrical cell with PSFM electrode in air at 800 °C after activation, and R_p value is significantly increased to 1.59 Ωcm² when exposing the symmetrical cell to 97% H₂–3% H₂O, which is possibly ascribed to the significantly decreased electrical conductivity form 71.0 Scm⁻¹in air to 3.8 Scm⁻¹ in 97% H₂–3% H₂O. Moreover, it is shown that R_p value recorded in air is effectively decreased to ~0.33 Ωcm², and keeps constant during the following 200-h redox stability testing, while R_p value measured in 97% H₂–3% H₂O atmosphere is gradually decreased to 0.82 Ωcm², which can be explained by the enhanced electro-catalytic properties of PSFM electrode induced by the gradually exsolved Fe nanocatalysts from parent PSFM electrode. At the same time, DRT analysis demonstrates that the sub-electrode process including oxygen/hydrogen adsorption, dissociation ionization and surface diffusion to triple phase boundaries occurred at the electrode/electrolyte interfacial is the predominant rate-limiting step, which can be effectively accelerated by surface modification and exsolved Fe nanoparticles. These results indicate that PSFM is a promising symmetrical electrode material for symmetrical cell application because of its good electrochemical performance and excellent long-term redox stability.     

Hydrothermal synthesis of hydrated vanadium oxide nanobelts using poly (ethylene oxide) as a template

With the aim of obtaining nanodevices as batteries, sensors and fuel cells, we prepared V₂O₅ and V₃O₇·H₂O nanobelts by a simple hydrothermal process using poly (ethylene oxide) (PEO) as a template. The yielding percentage of the nanomaterial is less in polymer-free V₂O₅ nanobelts and material size is also big. It is apparent that PEO used V₃O₇·H₂O form a continuous and relatively homogeneous matrix with a clearly 1–5 μm long and 50–150 nm diameter nanobelts morphology. The SEM micrographs suggest that there is no bulk deposition of polymer on the surface of the nano-crystallites. Strong interaction between the vanadyl group and the polymer during the formation process has been identified by the shifts of the vanadyl vibration peaks. The CV curve of the electrode made of the V₃O₇·H₂O nanobelts have higher current densities than the CV curve of the electrode made of V₂O₅ nanobelts.     

Fabrication of graphene/CaIn2O4 composites with enhanced photocatalytic activity from water under visible light irradiation

A series of graphene/CaIn₂O₄ composites were synthesized using a facile solvothermal method to improve the photocatalytic performance of CaIn₂O₄. The reduction of graphene oxide to graphene and the deposition of CaIn₂O₄ nanoparticles on the graphene sheets can be achieved simultaneously during the solvothermal process. The photocatalytic activities of as-prepared graphene/CaIn₂O₄ composites for hydrogen evolution from CH₃OH/H₂O solution were investigated under visible light irradiation. It was found that graphene exhibited an obvious influence on the photocatalytic activity of CaIn₂O₄. The graphene/CaIn₂O₄ composite reached a high H₂ evolution rate of 62.5 μmol h⁻¹ from CH₃OH/H₂O solution when the content of graphene was 1 wt%. Furthermore, the 1 wt% graphene/CaIn₂O₄ composite did not show deactivation for H₂ evolution for longer than 32 h. This work could provide a new insight into the fabrication of visible light driven photocatalysts with efficient and stable performance.     

Correlation of optical emission and turbulent length scale in a coaxial jet diffusion flame

This article investigates the correlation between optical emission and turbulent length scale in a coaxial jet diffusion flame. To simulate the H₂O emission from an H₂/O₂ diffusion flame, radiative transfer is calculated on flame data obtained by numerical simulation. H₂O emission characteristics are examined for a one-dimensional opposed-flow diffusion flame. The results indicate that H₂O emission intensity is linearly dependent on flame thickness. The simulation of H₂O emission is then extended to an H₂/O₂ turbulent coaxial jet diffusion flame. Time series data for a turbulent diffusion flame are obtained by Large Eddy Simulation, and radiative transfer calculations are conducted on the LES results to simulate H₂O emission optical images. The length scales of visible structures in the simulated emission images are determined by the procedure proposed by Ivancic and Mayer (2002) [8]. The length scales of emission intensity are compared with the integral length scales of velocity and temperature evaluated from LES flowfield data. The results clearly indicate that the length scale of emission intensity agrees well with the integral length scale of temperature, and is also close to that of the radial velocity component. Finally, the explanation as to why the integral length scale of temperature can be extracted from emission intensity distributions is stated.     

Studying the CO-CO2 characteristics of SOFC anodes by means of patterned Ni anodes

The high potential of solid oxide fuel cells (SOFC) arises due to the high degree of efficiency and fuel flexibility. However, the elementary kinetic steps of the anodic processes taking place at the boundary of electrolyte-anode-gas are still largely unknown. Patterned Ni anodes on Y₂O₃-stabilized ZrO₂ are regarded as a promising method to determine these kinetics.In analogy to our previous study with patterned Ni anodes for the H₂-H₂O system, this study is systematically devoted to the elementary kinetics of the CO electrochemical oxidation in CO-CO₂ gas mixtures. Data analysis is backed by extensive knowledge on patterned anode stability and dynamics gained during previous studies. The electrochemical characterization is performed for a large parameter variation range (pCO₂, pCO and T) by electrochemical impedance spectroscopy.Contrary to the characterization in H₂-H₂O atmosphere no slow relaxation processes were observed and the degradation rate is smaller. Changes in parameter dependency over the investigated parameter range indicate different reaction mechanisms as a function of gas composition. Only slightly higher polarization losses are observed for CO oxidation compared to H₂. The comparison of the results from patterned anodes to high-performance Ni/8YSZ cermet anodes employed in anode supported cells yields good agreement.     

Anodic behavior of 8Y2O3-ZrO2/NiO cermet using an anode-supported electrode

8Y₂O₃-ZrO₂ (8YSZ)/NiO cermet anode-supported symmetric cell is introduced and fabricated using a tape casting process to analyze the anodic behavior of an anode-supported cell. An anode-supported symmetric cell helps us understand the complex anode structure of cermets. The anodic behavior of 8YSZ/NiO is compared to a MIEC electrode of Sm_0.2Ce_0.8O_1.9 (SDC)/NiO. The anodic behavior of a 8YSZ/NiO cermet electrode is investigated and discussed with respect to the hydrogen partial pressure (p(H₂)), water partial pressure (p(H₂O)), area specific resistance (ASR), activation energy (E_a), thermal cycle, and redox process. Based on these studies, an empirical reaction model of 8YSZ/NiO is established, and the related reaction processes are discussed. On impedance spectra diagram, high and medium frequency arcs are associated with the charge transfer process and the H₂O formation reaction, while the low frequency arc corresponds to the dissociative adsorption and the surface diffusion/gas phase diffusion process. Changes in microstructure by redox and thermal cycling have a significant effect on the electrochemical properties and structural stability of a thick anode-supported cermet structure.     

Study of Pt electrode dissolution in H2O2-containing H2SO4 solution using an electrochemical quartz crystal microbalance

Pt electrode dissolution has been investigated using an electrochemical quartz crystal microbalance (EQCM) in H₂O₂-containing 0.5 mol dm⁻³ H₂SO₄. The Pt electrode weight-loss of ca. 0.4 μg cm⁻² is observed during nine potential sweeps between 0.01 and 1.36 V vs. RHE. In contrast, the Pt electrode weight-loss is negligible without H₂O₂ (<0.05 μg cm⁻²). To support the EQCM results, the weight-decrease amounts of a Pt disk electrode and amounts of Pt dissolved in the solutions were measured after similar successive potential cycles. As a result, these results agreed well with the EQCM results. Furthermore, the H₂O₂ concentration dependence of the Pt weight-decrease rate was assessed by successive potential steps. These EQCM data indicated that the increase in H₂O₂ accelerates the Pt dissolution. Based on these results, H₂O₂ is known to be a major factor contributing to the Pt dissolution.     

An improved H2/O2 mechanism based on recent shock tube/laser absorption measurements

An updated H₂/O₂ reaction mechanism is presented that incorporates recent reaction rate determinations in shock tubes from our laboratory. These experiments used UV and IR laser absorption to monitor species time-histories and have resulted in improved high-temperature rate constants for the following reactions: H+O₂=OH+OH₂O₂(+M)=2OH(+M)OH+H₂O₂=HO₂+H₂OO₂+H₂O=OH+HO₂ The updated mechanism also takes advantage of the results of other recent rate coefficient studies, and incorporates the most current thermochemical data for OH and HO₂. The mechanism is tested (and its performance compared to that of other H₂/O₂ mechanisms) against recently reported OH and H₂O concentration time-histories in various H₂/O₂ systems, such as H₂ oxidation, H₂O₂ decomposition, and shock-heated H₂O/O₂ mixtures. In addition, the mechanism is validated against a wide range of standard H₂/O₂ kinetic targets, including ignition delay times, flow reactor species time-histories, laminar flame speeds, and burner-stabilized flame structures. This validation indicates that the updated mechanism should perform reliably over a range of reactant concentrations, stoichiometries, pressures, and temperatures from 950 to greater than 3000 K.     

Mesoporous CexMn1−xO2 composites as novel alternative carriers of supported Co3O4 catalysts for CO preferential oxidation in H2 stream

The mesoporous Co₃O₄ supported catalysts on Ce–M–O (M = Mn, Zr, Sn, Fe and Ti) composites were prepared by surfactant-assisted co-precipitation with subsequent incipient wetness impregnation (SACP–IWI) method. The catalysts were employed to eliminate trace CO from H₂-rich gases through CO preferential oxidation (CO PROX) reaction. Effects of M type in Ce–M–O support, atomic ratio of Ce/(Ce + Mn), Co₃O₄ loading and the presence of H₂O and CO₂ in feed were investigated. Among the studied Ce–M–O composites, the Ce–Mn–O is a superior carrier to the others for supported Co₃O₄ catalysts in CO PROX reaction. Co₃O₄/Ce_0.9Mn_0.1O₂ with 25 wt.% loading exhibits excellent catalytic properties and the 100% CO conversion can be achieved at 125–200 °C. Even with 10 vol.% H₂O and 10 vol.% CO₂ in feed, the complete CO transformation can still be maintained at a wide temperature range of 190–225 °C. Characterization techniques containing N₂ adsorption/desorption, X-ray diffraction (XRD), H₂ temperature-programmed reduction (H₂-TPR) and scanning electron microscopy (SEM) were employed to reveal the relationship between the nature and catalytic performance of the developed catalysts. Results show that the specific surface area doesn’t obviously affect the catalytic performance of the supported cobalt catalysts, but the right M type in carrier with appropriate amount effectively improves the Co₃O₄ dispersibility and the redox behavior of the catalysts. The large reducible Co³⁺ amount and the high tolerance to reduction atmosphere resulted from the interfacial interaction between Co₃O₄ and Ce–Mn support may significantly contribute to the high catalytic performance for CO PROX reaction, even in the simulated syngas.     

Effect of H2O2 on Nafion properties and conductivity at fuel cell conditions

During PEM fuel cell operation, formation of H₂O₂ and material corrosion occurs, generating trace amounts of metal cations (i.e., Fe²⁺, Pt²⁺) and subsequently initiating the deterioration of cell components and, in particular, PFSA membranes (e.g., Nafion). However, most previous studies of this have been performed using conditions not relevant to fuel cell environments, and very few investigations have studied the effect of Nafion decomposition on conductivity, one of the most crucial factors governing PEMFC performance. In this study, a quantitative examination of properties and conductivities of degraded Nafion membranes at conditions relevant to fuel cell environments (30-100%RH and 80 °C) was performed. Nafion membranes were pre-ion-exchanged with small amounts of Fe²⁺ ions prior to H₂O₂ exposure. The degradation degree (defined as loss of ion-exchange capacity, weight, and fluoride content), water uptake, and conductivity of H₂O₂-exposed membranes were found to strongly depend on Fe content and H₂O₂ treatment time. SEM cross-sections showed that the degradation initially took place in the center of the membrane, while FTIR analysis revealed that Nafion degradation preferentially proceeds at the sulfonic end group and at the ether linkage located in the pendant side chain and that the H-bond of water is weakened after prolonged H₂O₂ exposure.