Synergistic Molecular Alignment and Dipole Polarization in Stretched Nafion/Poly(vinylidene fluoride) Blend Membranes for High Proton Conduction in PEMFCs.

The nanostructure of Nafion and poly(vinylidene fluoride) (PVDF) blend membranes is successfully aligned through a mechanical uniaxial stretching method. The phase-separated morphology of Nafion molecules distinctly forms hydrophilic proton channels with increased connectivity, resulting in enhanced proton conductivity. Additionally, the crystalline phase of PVDF molecules undergoes a successful transformation from the α- to ß-phase during membrane stretching, demonstrating an alignment of fluorine and hydrogen atoms with a TTTT(trans) structure. The aligned nanostructure of the blend film, combined with the dipole polarization of the ß-phase PVDF, synergistically enhances the proton conduction through the membrane for operating proton-exchange membrane fuel cells (PEMFCs). The controlled structures of the blend membranes are thoroughly investigated using atomic force microscopy and small-angle X-ray scattering. Furthermore, the improved in-plane proton conductivity facilitates increased proton conduction at the interface between the membrane and catalyst layer in the membrane-electrode assembly, ultimately enhancing the power generation of PEMFCs.

A Scalable and Robust Water Management Strategy for PEMFCs: Operando Electrothermal Mapping and Neutron Imaging Study.

Effective water management is crucial for the optimal operation of low-temperature polymer electrolyte membrane fuel cells (PEMFCs). Excessive liquid water production can cause flooding in the gas diffusion electrodes and flow channels, limiting mass transfer and reducing PEMFC performance. To tackle this issue, a nature-inspired chemical engineering (NICE) approach has been adopted that takes cues from the integument structure of desert-dwelling lizards for passive water transport. By incorporating engraved, capillary microchannels into conventional flow fields, PEMFC performance improves significantly, including a 15% increase in maximum power density for a 25 cm2 cell and 13% for a 100 cm2 cell. Electro-thermal maps of the lizard-inspired flow field demonstrate a more uniform spatial distribution of current density and temperature than the conventional design. Neutron radiography provides evidence that capillary microchannels in the lizard-inspired flow field facilitate the efficient transport and removal of generated liquid water, thereby preventing blockages in the reactant channels. These findings present a universally applicable and highly efficient water management strategy for PEMFCs, with the potential for widespread practical implementation for other electrochemical devices.

Water Condensation in the Nanoscale Pores of Pt/C Catalyst Particles and Its Impact on Catalyst Utilization: A Simulation Based on a Reconstructed Structure from Nanoimaging.

In polymer electrolyte membrane fuel cells, carbon-supported platinum (Pt/C) catalyst particles require sufficient water condensation within the nanoscale pores to effectively utilize the interior Pt catalysts. Since experimental visualizations with nanoscale precision of this phenomenon are not yet possible, we utilized a Pt/C catalyst particle reconstructed from segmented nanoimaging of a catalyst powder, which served as the computational domain for lattice density functional theory (LDFT) simulation of water condensation. Paired with experimental water uptake data, LDFT successfully simulated high-resolution water condensation, capturing both thin-film and capillary water condensation phenomena. Using a simple proton movement method within the water network, we reproduced the Pt utilization data from a CO stripping experiment. Our findings highlight that at low relative humidity (RH), Pt utilization is influenced by thin water film formations, mainly dictated by the wettability properties of surfaces within primary pores and the Pt/C catalyst particle's exterior. Conversely, at high RH, Pt utilization is attributed to capillary water condensation in medium-to-large sized pores. This approach contributes a qualitative and quantitative discussion on hypotheses regarding the mechanism of Pt utilization, supporting recent studies (e.g., Girod, R.; Nat. Catal. 2023, 6, (5), 383-391).

Boosting Bulk Oxygen Transport with Accessible Electrode Nanostructure in Low Pt Loading PEMFCs.

Despite the high potential for reducing carbon emissions and contributing to the future of energy utilization, polymer electrolyte membrane fuel cells (PEMFCs) face challenges such as high costs and sluggish oxygen transport in cathode catalyst layers (CCLs). In this study, the impact of pore size distribution on bulk oxygen transport behavior is explored by introducing nano calcium carbonate of varying particle sizes for pore-forming. Physicochemical characterizations for are employed to examine the electrode structure, while in situ electrochemical measurements are used to scrutinize bulk oxygen transport resistance, effective oxygen diffusivity ( D O 2 eff $D_{{{\mathrm{O}}}_2}^{{\mathrm{eff}}}$ ) and fuel cell performance. Additionally, the CCLs are constructed with aid of Lattice Boltzmann method (LBM) simulations and D O 2 eff $D_{{{\mathrm{O}}}_2}^{{\mathrm{eff}}}$ for CCLs with different pore size distribution are calculated. The findings reveal that D O 2 eff $D_{{{\mathrm{O}}}_2}^{{\mathrm{eff}}}$ initially increases and then decreases as the most probable pore size increases. A "sphere-pipe" model is proposed to describe practical bulk oxygen transport in CCLs, highlighting the significant role of not only the pore size of secondary pores but also the number of primary pores in bulk oxygen transport.

Potential-Dependent Ionomer Rearrangement on the Pt Surface in Polymer Electrolyte Membrane Fuel Cells.

The interface between the catalyst and the ionomer in the catalyst layer of polymer electrolyte membrane fuel cells (PEMFCs) has been a subject of keen interest, but its effect on durability has not been fully understood due to the complexity of the catalyst layer structure. Herein, we utilize a Pt nanoparticle (NP) array electrode fabricated using a block copolymer template as the platform for a focused investigation of the interfacial change between the Nafion thin film and the Pt NP under a constant potential. A set of analyses for the electrodes treated with various potentials reveals that the Nafion thin film becomes densely packed at the intermediate potentials (0.4 and 0.7 V), indicating an increased ionomer-catalyst interaction due to the positive charges formed at the Pt surface at these potentials. Even for a practical PEMFC single cell, we demonstrate that the potential holding at the intermediate potentials increases ionomer adsorption to the Pt surface and the oxygen transport resistance, negatively impacting its power performance. This work provides fresh insight into the mechanism behind the performance fade in PEMFCs caused by potential-dependent ionomer rearrangement.

Redesign of Anode Catalyst for Sustainable Survival of Fuel Cells.

Polymer electrolyte membrane fuel cells (PEMFCs) suffer from severe performance degradation when operating under harsh conditions such as fuel starvation, shut-down/start-up, and open circuit voltage. A fundamental solution to these technical issues requires an integrated approach rather than condition-specific solutions. In this study, an anode catalyst based on Pt nanoparticles encapsulated in a multifunctional carbon layer (MCL), acting as a molecular sieve layer and protective layer is designed. The MCL enabled selective hydrogen oxidation reaction on the surface of the Pt nanoparticles while preventing their dissolution and agglomeration. Thus, the structural deterioration of a membrane electrode assembly can be effectively suppressed under various harsh operating conditions. The results demonstrated that redesigning the anode catalyst structure can serve as a promising strategy to maximize the service life of the current PEMFC system.

Ultrasound-Driven enhancement of Pt/C catalyst stability in oxygen reduction reaction.

Polymer electrolyte membrane fuel cells (PEMFCs) have reached the commercialization phase, representing a promising approach to curbing carbon emissions. However, greater durability of PEMFCs is of paramount importance to ensure their long-term viability and effectiveness, and catalyst development has become a focal point of research. Pt nanoparticles supported on carbon materials (Pt/C) are the primary catalysts used in PEMFCs. Accomplishing both a high dispersion of uniform metal particles on the carbon support and robust adhesion between the metal particles and the carbon support is imperative for superior stability, and will thereby, advance the practical applications of PEMFCs in sustainable energy solutions. Ultrasound-assisted polyol synthesis (UPS) has emerged as a suitable method for synthesizing catalysts with a well-defined metal-support structure, characterized by the high dispersion and uniformity of metal nanoparticles. In this study, we focused on the effect of ultrasound on the synthesis of Pt/C via UPS and the resulting enhanced stability of Pt/C catalysts. Therefore, we compared Pt/C synthesized using a conventional polyol synthesis (Pt/C_P) and Pt/C synthesized via UPS (Pt/C_U) under similar synthesis conditions. The two catalysts had a similar Pt content and the average particle size of the Pt nanoparticles was similar; however, the uniformity and dispersion of Pt nanoparticles in Pt/C_U were better than those of Pt/C_P. Moreover, ex/in-situ analyses performed in a high-temperature environment, in which nanoparticles tend to agglomerate, have revealed that Pt/C_U exhibited a notable improvement in the adhesion of Pt particles to the carbon support compared with that of Pt/C_P. The enhanced adhesion is crucial for maintaining the stability of the catalyst, ultimately contributing to a better durability in practical applications. Ultrasound was applied to the carbon support without the Pt precursor under the same UPS conditions used to synthesize Pt/C_U to identify the reason for the increased adhesion between the Pt particles and the carbon support in Pt/C_U, and we discovered that oxygen functional groups (C-O, C = O, and O-C = O) for anchoring site of Pt particles were generated in the carbon support. Pt/C_U displayed an increase in stability in an electrochemical accelerated stress test (AST) in an acidic electrolyte. The physical and chemical effects of ultrasound on the synthesis of Pt/C via UPS were identified, and we concluded that UPS is suitable for synthesizing carbon supported electrocatalysts with high stability.

Multiscale Architectured Membranes, Electrodes, and Transport Layers for Next-Generation Polymer Electrolyte Membrane Fuel Cells.

Over the past few decades, considerable advances have been achieved in polymer electrolyte membrane fuel cells (PEMFCs) based on the development of material technology. Recently, an emerging multiscale architecturing technology covering nanometer, micrometer, and millimeter scales has been regarded as an alternative strategy to overcome the hindrance to achieving high-performance and reliable PEMFCs. This review summarizes the recent progress in the key components of PEMFCs based on a novel architecture strategy. In the first section, diverse architectural methods for patterning the membrane surface with random, single-scale, and multiscale structures as well as their efficacy for improving catalyst utilization, charge transport, and water management are discussed. In the subsequent section, the electrode structures designed with 1D and 3D multiscale structures to enable low Pt usage, improve oxygen transport, and achieve high electrode durability are elucidated. Finally, recent advances in the architectured transport layer for improving mass transportation including pore gradient, perforation, and patterned wettability for gas diffusion layer and 3D structured/engineered flow fields are described.

Ordered intermetallic compounds combining precious metals and transition metals for electrocatalysis.

Ordered intermetallic alloys with significantly improved activity and stability have attracted extensive attention as advanced electrocatalysts for reactions in polymer electrolyte membrane fuel cells (PEMFCs). Here, recent advances in tuning intermetallic Pt- and Pd-based nanocrystals with tunable morphology and structure in PEMFCs to catalyze the cathodic reduction of oxygen and the anodic oxidation of fuels are highlighted. The fabrication/tuning of ordered noble metal-transition metal-bonded intermetallic PtM and PdM (M = Fe, Co) nanocrystals by using high temperature annealing treatments to promote the activity and stability of electrocatalytic reactions are discussed. Furthermore, the further improvement of the efficiency of this unique ordered intermetallic alloys for electrocatalysis are also proposed and discussed. This report aims to demonstrate the potential of the ordered intermetallic strategy of noble and transition metals to facilitate electrocatalysis and facilitate more research efforts in this field.

Ultrasmall, Coating-Free, Pyramidal Platinum Nanoparticles for High Stability Fuel Cell Oxygen Reduction.

Ultrasmall (<5 nm diameter) noble metal nanoparticles with a high fraction of {111} surface domains are of fundamental and practical interest as electrocatalysts, especially in fuel cells; the nanomaterial surface structure dictates its catalytic properties, including kinetics and stability. However, the synthesis of size-controlled, pure Pt-shaped nanocatalysts has remained a formidable chemical challenge. There is an urgent need for an industrially scalable method for their production. Here, a one-step approach is presented for the preparation of single-crystal pyramidal nanocatalysts with a high fraction of {111} surface domains and a diameter below 4 nm. This is achieved by harnessing the shape-directing effect of citrate molecules, together with the strict control of oxidative etching while avoiding polymers, surfactants, and organic solvents. These catalysts exhibit significantly enhanced durability while, providing equivalent current and power densities to highly optimized commercial Pt/C catalysts at the beginning of life (BOL). This is even the case when they are tested in full polymer electrolyte membrane fuel cells (PEMFCs), as opposed to rotating disk experiments that artificially enhance electrode kinetics and minimize degradation. This demonstrates that the {111} surface domains in pyramidal Pt nanoparticles (as opposed to spherical Pt nanoparticles) can improve aggregation/corrosion resistance in realistic fuel cell conditions, leading to a significant improvement in membrane electrode assembly (MEA) stability and lifetime.

Effect of Clamping Compression on the Mechanical Performance of a Carbon Paper Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells.

During all the assembly stages of a polymer electrolyte membrane fuel cell (PEMFC) stack, gas diffusion layers (GDLs) endure clamping loads in the through-plane direction several times. Under such complicated assembly conditions, GDLs have to deform with the changes in structure, surface roughness, pore size, etc. A comprehensive understanding of the compressive performance of GDLs at different clamping phases is crucial to the assembly process improvement of PEMFCs. Two typical clamping compression was designed and performed to get close to the actual assembly conditions of PEMFCs. The results indicate that the initial clamping compression and the magnitude of the maximum clamping load have great impacts on the segmented compressive properties of GDLs. The nonlinear compressive performance of the GDL is mainly attributed to the unique microstructural information. The rough surface morphology contributes to the initial compressive characteristics where the big strain along with the small stress occurs, and the irreversible failures such as carbon fiber breakages and adhesive failures between fibers and binders account for the hysteresis between different compression stages. Importantly, it is found that the clamping compression hardly influences the small pore distribution below 175 µm but affects the large pore distribution over 200 µm.

Acid Dissociation Constants of the Benzimidazole Unit in the Polybenzimidazole Chain: Configuration Effects.

The acid dissociation constant of three benzimidazoles, namely 2,2'-bibenzo[d]imidazole, 2,5'-bibenzo[d]imidazole, and 5,5'-bibenzo[d]imidazole, have been investigated by means of density functional theory calculations in gas phase and in aqueous solution. The theoretical approach was validated by the comparing of predicted and experimentally determined pKa values in imidazole, benzimidazole, and 2-phenylbenzimidazole. From the studied compounds, 2,2'-bibenzo[d]imidazole was found to be the most acidic, which made it a valuable candidate as a material for polymer electrolyte membrane fuel cells.

Boosting Electrocatalytic Activity of Single Atom Catalysts Supported on Nitrogen-Doped Carbon through N Coordination Environment Engineering.

Nonprecious group metal (NPGM)-based single atom catalysts (SACs) hold a great potential in electrocatalysis and dopant engineering has been extensively exploited to boost their catalytic activity, while the coordination environment of dopant, which also significantly affects the electronic structure of SACs, and consequently their electrocatalytic performance, have been largely ignored. Here, by adopting a precursor modulation strategy, the authors successfully synthesize single cobalt atom catalysts embedded in nitrogen-doped carbon, Co-N/C, with similar overall Co and N concentrations but different N types, that is, pyridinic N (NP ), graphitic N (NG ), and pyrrolic N (NPY ). Co-N/C with the Co-N4 moieties coordinated with NG displays far superior activity for oxygen reduction (ORR) and evolution reactions, and superior activity and stability in both zinc-air batteries and proton exchange membrane fuel cells. Density functional theory calculation indicates that coordinated N species in particular NG functions as electron donors to the Co core of Co-N4 active sites, leading to the downshift of d-band center of Co-N4 and weakening the binding energies of the intermediates on Co-N4 sites, thus, significantly promoting catalytic kinetics and thermodynamics for ORR in a full pH range condition.

A Low-Temperature Carbon Encapsulation Strategy for Stable and Poisoning-Tolerant Electrocatalysts.

Carbon encapsulation is an effective strategy for enhancing the durability of Pt-based electrocatalysts for the oxygen reduction reaction (ORR). However, high-temperature treatment is not only energy-intensive but also unavoidably leads to possible aggregation. Herein, a low-temperature polymeric carbon encapsulation strategy (≈150 °C) is reported to encase Pt nanoparticles in thin and amorphous carbonaceous layers. Benefiting from the physical confinement effect and enhanced antioxidant property induced by the surface carbon species, significantly improved stabilities can be achieved for polymeric carbon species encapsulated Pt nanoparticles (Pt@C/C). Particularly, a better antipoisoning capability toward CO, SOx , and POx is observed in the case of Pt@C/C. To minimize the thickness of the catalyst layer and reduce the mass transfer resistance, the high mass loading Pt@C/C (40 wt%) is prepared and applied to high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs). At 160 °C, a peak power density of 662 mW cm-2 is achieved with 40% Pt@C/C cathode in H2 -O2 HT-PEMFCs, which is superior to that with 40% Pt/C cathode. The facile strategy provides guidance for the synthesis of highly durable carbon encapsulated noble metal electrocatalysts toward ORR.

Fe-N4 Doped Carbon Nanotube Cathode Catalyst for PEM Fuel Cells.

The earth-abundant iron and nitrogen doped carbon (Fe-N-C) catalyst has great potential to substitute noble metal catalysts for oxygen reduction reaction (ORR) in H2-O2 proton exchange membrane fuel cells (PEMFCs). Herein, we report the preparation of Fe-N4 moiety doped carbon nanotubes (CNTs) by ball milling and two-step pyrolysis with dual metal-organic frameworks (MOFs) as the precursor. This catalyst shows high ORR catalytic performance and stability. Different from traditional inorganic iron sources, the MOF structure can effectively prevent the iron metal from aggregating during pyrolysis. In PEMFC, the catalyst shows high current density (0.39 A/cm2 at 0.7 V) and power density (850 mW/cm2). Such a method brings inspiration for the reasonable design of FeNC catalysts with high catalytic activity for H2-O2 PEMFCs.

A Review on Ionic Liquids-Based Membranes for Middle and High Temperature Polymer Electrolyte Membrane Fuel Cells (PEM FCs).

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than 100 °C with high conductivity and thermal stability. The membranes containing ILs can conduct protons through the PEMs at elevated temperatures (more than 80 °C), unlike the Nafion-based membranes. A wide range of ILs have been identified, including chiral ILs, bio-ILs, basic ILs, energetic ILs, metallic ILs, and neutral ILs, that, from among them, functionalized ionic liquids (FILs) include a lot of ion exchange groups in their structure that improve and accelerate proton conduction through the polymeric membrane. In spite of positive features of using ILs, the leaching of ILs from the membranes during the operation of fuel cell is the main downside of these organic salts, which leads to reducing the performance of the membranes; however, there are some ways to diminish leaching from the membranes. The aim of this review is to provide an overview of these issues by evaluating key studies that have been undertaken in the last years in order to present objective and comprehensive updated information that presents the progress that has been made in this field. Significant information regarding the utilization of ILs in MT-PEMFCs and HT-PEMFCs, ILs structure, properties, and synthesis is given. Moreover, leaching of ILs as a challenging demerit and the possible methods to tackle this problem are approached in this paper. The present review will be of interest to chemists, electrochemists, environmentalists, and any other researchers working on sustainable energy production field.

Nafion-Based Proton-Exchange Membranes Built on Cross-Linked Semi-Interpenetrating Polymer Networks between Poly(acrylic acid) and Poly(vinyl alcohol).

We report semi-interpenetrating polymer network (semi-IPN) membranes prepared easily from a cross-linked network using poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) with interpenetrated Nafion for both proton-exchange membrane fuel cell (PEMFC) and proton-exchange membrane water electrolyzer (PEMWE) applications. Thermal esterification between PAA and PVA induced three-dimensional cross-linking to improve mechanical toughness and reduce hydrogen crossover, while the hydrophilic nature of the PAA-PVA-based cross-linked matrix still enhanced the water uptake (WU) and hence conductivity of the Nafion penetrant. The semi-IPN membrane (NPP-95) composed of Nafion, PAA, and PVA with a ratio of 95:2.5:2.5 showed a hexagonal cylindrical morphology and improved thermal, mechanical, and dimensional stability compared to a recast Nafion membrane (re-Nafion). The membrane was also highly effective at managing water due to its low WU and high conductivity. Furthermore, its hydrogen permeability was 49.6% lower than that of re-Nafion under the actual fuel cell operating conditions (at 100% RH and 80 °C). NPP-95 exhibited significantly improved conductivity and PEMFC performance compared to re-Nafion with a current density of 1561 mA/cm2 at a potential of 0.6 V and a peak power density of 1179 mW/cm2. Furthermore, in the PEMWE performances, NPP-95 displayed about a 1.5-fold higher current density of 4310 mA/cm2 at 2.0 V and much lower ohmic resistance than re-Nafion between 60 and 80 °C.

Phase Inversion-Induced Porous Polybenzimidazole Fuel Cell Membranes: An Efficient Architecture for High-Temperature Water-Free Proton Transport.

To cope with the demand for cleaner alternative energy, polymer electrolyte membrane fuel cells (PEMFCs) have received significant research attention owing to their high-power density, high fuel efficiency, and low polluting by-product. However, the water requirement of these cells has necessitated research on systems that do not require water and/or use other mediums with higher boiling points. In this work, a highly porous meta-polybenzimidazole (m-PBI) membrane was fabricated through the non-solvent induced phase inversion technique and thermal cross-linking for high-temperature PEMFC (HT-PEMFC) applications. Standard non-thermally treated porous membranes are susceptible to phosphoric acid (PA) even at low concentrations and are unsuitable as polymer electrolyte membranes (PEMs). With the porous structure of m-PBI membranes, higher PA uptake and minimal swelling, which is controlled via cross-linking, was achieved. In addition, the membranes exhibited partial asymmetrical morphology and are directly applicable to fuel cell systems without any further modifications. Membranes with insufficient cross-linking resulted in an unstable performance in HT-PEMFC environments. By optimizing thermal treatment, a high-performance membrane with limited swelling and improved proton conductivity was achieved. Finally, the m-PBI membrane exhibited enhanced acid retention, proton conductivity, and fuel cell performance.

New Perspectives on Fuel Cell Technology: A Brief Review.

Energy storage and conversion is a very important link between the steps of energy production and energy consumption. Traditional fossil fuels are a natural and unsustainable energy storage medium with limited reserves and notorious pollution problems, therefore demanding a better choice to store and utilize the green and renewable energies in the future. Energy and environmental problems require a clean and efficient way of using the fuels. Fuel cell functions to efficiently convert oxidant and chemical energy accumulated in the fuel directly into DC electric, with the by-products of heat and water. Fuel cells, which are known as effective electrochemical converters, and electricity generation technology has gained attention due to the need for clean energy, the limitation of fossil fuel resources and the capability of a fuel cell to generate electricity without involving any moving mechanical part. The fuel cell technologies that received high interest for commercialization are polymer electrolyte membrane fuel cells (PEMFCs), solid oxide fuel cells (SOFCs), and direct methanol fuel cells (DMFCs). The optimum efficiency for the fuel cell is not bound by the principle of Carnot cycle compared to other traditional power machines that are generally based on thermal cycles such as gas turbines, steam turbines and internal combustion engines. However, the fuel cell applications have been restrained by the high cost needed to commercialize them. Researchers currently focus on the discovery of different materials and manufacturing methods to enhance fuel cell performance and simplify components of fuel cells. Fuel cell systems' designs are utilized to reduce the costs of the membrane and improve cell efficiency, durability and reliability, allowing them to compete with the traditional combustion engine. In this review, we primarily analyze recent developments in fuel cells technologies and up-to-date modeling for PEMFCs, SOFCs and DMFCs.

On the Influence of Oxygen on the Degradation of Fe-N-C Catalysts.

Fe-N-C catalysts containing atomic FeNx sites are promising candidates as precious-metal-free catalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The durability of Fe-N-C catalysts in fuel cells has been extensively studied using accelerated stress tests (AST). Herein we reveal stronger degradation of the Fe-N-C structure and four-times higher ORR activity loss when performing load cycling AST in O2 - vs. Ar-saturated pH 1 electrolyte. Raman spectroscopy results show carbon corrosion after AST in O2 , even when cycling at low potentials, while no corrosion occurred after any load cycling AST in Ar. The load-cycling AST in O2 leads to loss of a significant fraction of FeNx sites, as shown by energy dispersive X-ray spectroscopy analyses, and to the formation of Fe oxides. The results support that the unexpected carbon corrosion occurring at such low potential in the presence of O2 is due to reactive oxygen species produced between H2 O2 and Fe sites via Fenton reactions.