Exchange Membrane Fuel Cell Cathode Research Articles

Monosymmetric Fe-N4 sites enabling durable proton exchange membrane fuel cell cathode by chemical vapor modification.

The limited durability of metal-nitrogen-carbon electrocatalysts severely restricts their applicability for the oxygen reduction reaction in proton exchange membrane fuel cells. In this study, we employ the chemical vapor modification method to alter the configuration of active sites from FeN4 to the stable monosymmetric FeN2+N'2, along with enhancing the degree of graphitization in the carbon substrate. This improvement effectively addresses the challenges associated with Fe active center leaching caused by N-group protonation and free radicals attack due to the 2-electron oxygen reduction reaction. The electrocatalyst with neoteric active site exhibited excellent durability. During accelerated aging test, the electrocatalyst exhibited negligible decline in its half-wave potential even after undergoing 200,000 potential cycles. Furthermore, when subjected to operational conditions representative of fuel cell systems, the electrocatalyst displayed remarkable durability, sustaining stable performance for a duration exceeding 248 h. The significant improvement in durability provides highly valuable insights for the practical application of metal-nitrogen-carbon electrocatalysts.

Effect of aging temperature on corrosion resistance of 316L stainless steel in simulated proton exchange membrane fuel cell cathode environment

The effects of aging temperature on the corrosion behavior of 316 L stainless steel in a simulated cathodic environment of a proton exchange membrane fuel cell (PEMFC) were investigated by potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), double-loop electrochemical potential response (DL-EPR). The results show that the corrosion resistance of 316 L is significantly degraded after aging at 750–900 °C for 1 h in the simulated cathodic environment of PEMFC. A strong sensitivity to intergranular corrosion takes place after aging at 850 °C, and chromium rich M23C6 carbides precipitate on grain boundaries. The precipitation of M23C6 leads to discontinuity of the passivation film near the grain boundaries, resulting in Cr-depleted zones at the grain boundaries, increasing intergranular corrosion, and decreasing corrosion resistance. When the aging temperature exceeds 950 °C, grain boundary precipitation of M23C6 does not occur and the corrosion resistance is improved. At an aging temperature of 1050 °C, a dense Cr2O3 film is formed on the surface of the alloy during the polarization test, giving it the best corrosion resistance in the simulated cathodic environment of PEMFC.

Iron and cobalt phthalocyanine embedded electrospun carbon nanofiber-based catalysts for anion exchange membrane fuel cell cathode

The successful implementation of renewable energy transition assumes the introduction and widespread use of zero-emission and sustainable energy conversion devices. Anion-exchange membrane fuel cell (AEMFC) is one of the appliances that meets the prescribed criteria. In this study, Fe(II) phthalocyanine and Co(II) phthalocyanine co-doped polyacrylonitrile-based electrospun carbon nanofibre (CNF) catalysts were prepared via pyrolysis. The influence of carbonisation temperature, acid leaching conditions, presence of ionic liquid (IL) as porogen, and the metal phthalocyanine content were investigated. Physical characterisation revealed the nanofibrous structure, high specific surface area, presence of Co-Nx, Fe-Nx sites, and different N-species with high oxygen reduction reaction (ORR) activity. The catalyst material with the highest ORR performance, D-MN4-CNF-IL-A, showed a half-wave potential of 857 ± 6 mV vs. reversible hydrogen electrode in 0.1 M KOH and the maximum power density value of 231 mW cm−2 when applied as a cathode catalyst in the AEMFC.

Construction of Homogeneous Catalyst Layers at Proton Exchange Membrane Fuel Cell Cathodes

In proton exchange membrane fuel cells (PEMFCs), the performance of the cathode catalyst layer depends on the effective formation and uniform distribution of the three-phase boundary (catalyst, ionomer, and oxygen). However, traditional cathode catalyst layer structures based on heterogeneous catalysis have reduced the catalyst utilization rate and mass transfer efficiency for the oxygen reduction reaction (ORR), which further restricts the development of PEMFCs. Here, we covalently grafted an ORR molecular catalyst, tetrakis(4-methoxyphenyl) porphyrin iron (II), onto the side chain of a Nafion ionomer. This strategy allows the catalytic center of the transition metal macrocycle to be anchored inside the ion flow channel. Mössbauer spectroscopy showed that the kinetics of the electrode reaction were improved owing to the increase in electron density around the Fe center. Additionally, the improvement in catalytic active site utilization and mass (protons, oxygen) transfer effectively promotes the performance output of the fuel cell. This novel catalyst layer structure may provide a new platform for the development of high-performance molecular catalysts for applications in fuel cells and other energy devices.

Effects of potential on corrosion behavior and contact resistance of 446 stainless steel in simulated proton exchange membrane fuel cell cathode environment

Effects of potential on corrosion behavior and contact resistance of 446 stainless steel in simulated proton exchange membrane fuel cell cathode environment

Benchmarking proton exchange membrane fuel cell cathode catalyst at high current density: A comparison between the rotating disk electrode, the gas diffusion electrode and differential cell

The intrinsic activity of oxygen reduction reaction (ORR) electrocatalysts for proton exchange membrane fuel cell (PEMFC) is usually evaluated with the rotating disk electrode (RDE), an easy-to-use technique requiring little amount of electrocatalyst. However, the liquid environment of the RDE implies strong limitation of O2 mass-transport and the intrinsic activity is only accessible on a narrow potential range (from 0.95 to 0.85 V vs. RHE) that is not relevant for the PEMFC operating conditions. This work compares results obtained with the RDE (0.2 cm2), the gas diffusion electrode (GDE, 0.07 cm2) and a small unit PEMFC (DC, 1.8 cm2). Three widely used ORR electrocatalysts are compared: Pt/Vulcan carbon, PtCo/Vulcan carbon and Pt/graphitized carbon, catalytic layers being prepared with a loading of 20 μgPt cm−2 and characterized at 25–30 °C and full hydration. The results show that all setups have their own advantages and drawbacks. Regardless the electrocatalyst nature, the GDE allows to assess the intrinsic activities on a large potential range (from 0.9 to 0.6 V), in agreement with the results obtained in RDE for high potential and with the DC for lower potential. The GDE is therefore promising, enabling easy high current density measurements with little amount of electrocatalyst.

Preparation and properties of conductive Ti4O7 surface coating for Ti bipolar plates of proton exchange membrane fuel cells

Focusing on the special electrical conductivity and corrosion resistance of Ti 4 O 7 , this work proposes for the first time to reduce TiO 2 film grown in situ on Ti substrate in a high-temperature tube furnace by using Ti/TiO 2 mixed powder as reducing agent to obtain Ti 4 O 7 surface coating. By characterization, the surface of the coated sample is identified as a Ti 4 O 7 coating, with a partially unconverted TiO 2 present at the interface between the Ti substrate and the Ti 4 O 7 surface coating. The electrochemical, water contact angle and surface contact resistance tests show that the Ti 4 O 7 surface coating provides superior protection to the Ti bipolar plate in the simulated proton exchange membrane fuel cell cathode environment, and simultaneously improving the electrical conductivity and water contact angle of the sample. • A novel preparation method of Ti 4 O 7 coating is proposed. • Uniform and dense Ti 4 O 7 coating on Ti substrate is obtained in a short time. • Ti 4 O 7 coating maintains excellent corrosion resistance in simulate PEMFC cathode environment . • The Ti 4 O 7 coating exhibits high conductivity and hydrophobicity.

Tracking Nanoparticle Degradation across Fuel Cell Electrodes by Automated Analytical Electron Microscopy.

Nanoparticles are an important class of materials that exhibit special properties arising from their high surface area-to-volume ratio. Scanning transmission electron microscopy (STEM) has played an important role in nanoparticle characterization, owing to its high spatial resolution, which allows direct visualization of composition and morphology with atomic precision. This typically comes at the cost of sample size, potentially limiting the accuracy and relevance of STEM results, as well as the ability to meaningfully track changes in properties that vary spatially. In this work, automated STEM data acquisition and analysis techniques are employed that enable physical and compositional properties of nanoparticles to be obtained at high resolution over length scales on the order of microns. This is demonstrated by studying the localized effects of potential cycling on electrocatalyst degradation across proton exchange membrane fuel cell cathodes. In contrast to conventional, manual STEM measurements, which produce particle size distributions representing hundreds of particles, these high-throughput automated methods capture tens of thousands of particles and enable nanoparticle size, number density, and composition to be measured as a function of position within the cathode. Comparing the properties of pristine and degraded fuel cells provides statistically robust evidence for the inhomogeneous nature of catalyst degradation across electrodes. These results demonstrate how high-throughput automated STEM techniques can be utilized to investigate local phenomena occurring in nanoparticle systems employed in practical devices.

A corrosion mechanism of NbC/α-C:H films for metallic bipolar plates in proton exchange membrane fuel cell cathode based on percolation model

A series of NbC/α-C:H films were prepared through arc ion plating for the protection of metallic bipolar plates in proton exchange membrane fuel cells (PEMFCs). Phase characterizations show that NbC grains were randomly embedded into the α-C:H matrix and their size and content increased with the decreasing of C2H2 flow rate. Results from the kelvin probe force microscope (KPFM) and conductive atomic force microscope (CAFM) presented a uniform surface potential distribution but significant local conductivity differences. DFT calculations and potentiostatic polarization tests indicated that dissolution of NbC grains were preferred in PEMFC cathode environment due to preferential adsorption of corrosive media. On the basis of theoretical calculations and experimental results, a corrosion mechanism was presented based on percolation model to better understand the corrosion process of NbC/α-C:H films in PEMFC cathode.

Oxygen and Proton Transport in Flooded Graphene Pores with N-Dopants and Defects

Reactant transport is an important consideration in the design of ideal electrode structures. For the oxygen reduction reaction catalyzed by Pt/C in proton exchange membrane fuel cell cathodes, O2 and H+ delivery to Pt surfaces and H2O transport away are required. Some Pt nanoparticles may only be accessible via micropores that are too small for ionomer molecules to enter, possibly requiring flooding for H+ transport. To test if these “buried” Pt particles can play a role in activity through this proposed transport mechanism, we have performed atomic-scale simulations based on reactive force field molecular dynamics with an emphasis on confinement below 20 Å. Diffusion coefficients as a function of the molar concentration and local environment have been evaluated in water domains confined in two-dimensional graphene nanochannels of various channel heights representing a morphological model for micropores in proton exchange fuel cell cathodes. Our study shows that local atomic-scale structures can strongly modify H+, O2, and H2O transport rates in flooded micropores less than 20 Å in size. We find that there is a critical crossover in diffusion behavior around the 20 Å spacing with larger pores having bulk-like diffusion properties and confinement below 20 Å monotonically decreases diffusion rates. As pore size decreases, we observe locally dispersed water regions that ultimately strand reactants from long-distance transport. These findings suggest that flooded micropores may in fact be viable transport pathways for relevant reactants and products if the pore walls on opposite sides remain separated by ≥10 Å separation. Furthermore, the confinement effect is so strong that N-doping and C-vacancy defects in the C pore wall have only a minimal impact on diffusion rates and their effects are counterintuitively more apparent at larger spacings. These findings provide valuable insight regarding cathode performance and the role “stranded” catalyst particles may play in fuel cell cathodes.

Quantification on degradation mechanisms of polymer exchange membrane fuel cell cathode catalyst layers during bus and stationary durability test protocols

Simulating bus and stationary protocols are designed to study the durability and degradation mechanisms of proton exchange membrane fuel cells. A quantitative method combined with characterization techniques, including electrochemical impedance spectroscopy, X-ray fluorescence spectroscopy and X-ray diffraction spectroscopy, is applied to distinguish performance degradation. Experimental results show that, for proton exchange membrane attenuation, chemical attenuation due to high cathode potential with long duration is more severe than mechanism attenuation due to dynamic load. For cathode catalyst layer decay, the principal reason under bus condition is particles growth (∼35%), followed by Pt dissolution (∼34%). In contrast,∼43% ECSA loss results from ionomer/catalyst interface loss under stationary condition. Such information indicates that the bus condition results in particles growth and Pt dissolution while the stationary condition induces ionomer/catalyst interface loss in the cathode catalyst layer. Combining more realistic protocols and quantitative analysis method can reveal the relationship between operating conditions of fuel cell in realistic road and MEA degradation. • Simulating stationary and bus protocols are used to study MEA degradation. • The attenuation mechanisms of MEA under these two protocols is proposed. • Chemical decay by durable high-potential affects severely PEM durability. • Particle growth and Pt dissolution cease CL decay under bus protocol. • Ionomer loss ceases CL degradation under stationary protocol.

Probing Anion Exchange Membrane Fuel Cell Cathodes by Varying Electrocatalysts and Electrode Processing

To date, several high-performing anion exchange membrane fuel cells (AEMFCs) have been demonstrated, but most these studies have focused on Pt containing cathodes with high loadings. Here, we explore and compare the performance and perform electrochemical diagnostics on three leading AEMFC cathode electrocatalysts: Pt/C, Ag/C, and Fe–N–C with electrodes that have been processed with either powder or dispersion-based ionomers using perfluorinated anion exchange polymers. Pt/C had the highest performance but also showed a strong dependence on ionomer type, with powder ionomer exhibiting much higher performance. These results were consistent with the observations for Ag/C but did not hold for the Fe–N–C catalyst where almost no change was observed between powder and dispersion-based ionomers. This is the first-time the impact of powder and dispersion ionomer with different classes of cathode electrocatalysts on the fuel cell performance have been compared, and the results have strong implications for the ability to achieve high performance at low loadings and for better understanding catalyst-ionomer interactions within AEMFCs.

Benchmarking Proton Exchange Membrane Fuel Cell Cathode Catalyst at High Current Density: A Comparison between the Rotating Disk Electrode, the Gas Diffusion Electrode and Differential Cell

Benchmarking Proton Exchange Membrane Fuel Cell Cathode Catalyst at High Current Density: A Comparison between the Rotating Disk Electrode, the Gas Diffusion Electrode and Differential Cell

Towards Understanding the Evolution of Electrochemical Properties of Proton Exchange Membrane Fuel Cell Cathode And Performance Decay During Start-Up Phases Using Emulated Mitigation Strategies

Towards Understanding the Evolution of Electrochemical Properties of Proton Exchange Membrane Fuel Cell Cathode And Performance Decay During Start-Up Phases Using Emulated Mitigation Strategies

Modeling Proton Exchange Membrane Fuel Cell Cathode Catalyst Layers with the Lattice Boltzmann Method-Direct Numerical Simulation Framework

Here, a Lattice-Boltzmann-Method-Direct-Numerical-Simulation (LBM-DNS) modelling framework for simulating transport and electrochemical phenomena in a proton exchange membrane fuel cell (PEMFC) electrode is presented. Due to the difficult to probe mesoporous nature of the cathode catalyst layer (CCL) of PEMFCs, researchers have typically used high level approximations that oversimplify the microstructure of the CCL—these are known as macrohomogenous models. However, as the field has progressed, these idealizations have begun to show their flaws, especially in areas of improving catalytic performance with lower Pt-loadings and non-noble metal catalysts. Previously, the microstructure details needed to build an accurate mesoscale model to examine such phenomena have eluded researchers; however, with advances in tomography and focused-ion-beam scanning-electron-microscopy (FIB-SEM), reconstruction of the complex porous media has become possible. Mesoscale modeling in the CCL has been traditionally approached through either the Lattice-Boltzmann-Method (LBM) or electrochemistry coupled Direct-Numerical-Simulation (DNS). These models have been underutilized in the fuel cell community due to their complexity and resource intensiveness; however, with advances in parallel computing, this has become not only a possibility, but a necessity for modeling phenomena such as low platinum loadings and interfacial effects. With these new advances, a synergistic modeling approach can be taken that combines the advantages of each method. This can shed light on transport and degradation phenomena in PEMFCs, particularly for the catalyst layer and carbon corrosion.

Iron and nitrogen doped carbon derived from ferrocene and ZIF-8 as proton exchange membrane fuel cell cathode catalyst

H2-O2 proton exchange membrane fuel cells (PEMFCs), one of the applications of hydrogen energy with specific energy density of 143 MJ/kg, might be a promising alternative to replace the use of fossil energy. The key to accelerate the application of PEMFCs is to design an efficient non-precious metal catalyst to lower the overpotential of the cathode oxygen reduction reaction (ORR). Herein, we developed a novel iron and nitrogen doped carbon (FeNC) catalyst using ferrocene as iron source, ZIF-8 as organic framework as well as the main carbon source. The regular morphology of ZIF-8 and ferrocene can prevent active sites from agglomeration, resulting a homogenous distribution of Fe, N and C. Moreover, the high specific area, porous structure and abundant catalytic Fe and N species gave rise to the ORR performance of the catalyst. As a result, the as-prepared FeNC catalyst showed an onset and half-wave potential of 0.95 V and 0.78 V in 0.1 M HClO4 with 1600 rpm, respectively. The catalysts were also applied in a PEMFC as the cathode catalysts with an open circuit voltage of more than 0.9 V and a maximum power density of 601 mW/cm2. Additionally, the as-prepared FeNC-1:30 catalyst showed a current density of 380 mA/cm2 at 0.7 V, which outperformed other as-prepared catalysts.

Air‐liquid water transport phenomena in a proton exchange membrane fuel cell cathode with a leaf‐like flow field design

Air‐liquid water transport phenomena in a proton exchange membrane fuel cell cathode with a leaf‐like flow field design

Mesoporous iron-nitrogen co-doped carbon material as cathode catalyst for the anion exchange membrane fuel cell

A novel and commercially available electrocatalyst is characterised and used as cathode catalyst in an anion-exchange membrane fuel cell (AEMFC). The catalyst material is prepared using VariPore™ method by Pajarito Powder, LLC, and as dopants iron and nitrogen are used, making it a mesoporous transition metal-nitrogen-carbon type catalyst. The physico-chemical characterisation shows the success of doping as well as almost completely mesoporous structure (average pore size of approximately 7 nm) with high specific surface area. The initial assessment of the oxygen reduction reaction (ORR) activity by the rotating ring-disc electrode method reveals that the material exhibits a very good electrocatalytic performance in alkaline media having a half-wave potential of 0.89 V. The catalyst material is employed as an anion exchange membrane fuel cell cathode and it shows AEMFC performance as good as that of the Pt-based material. The high ORR electrocatalytic activity of this material is due to the synergy of nitrogen-moieties, namely pyrrolic-N, pyridinic-N and graphitic-N, with iron as well as the highly mesoporous nature.

How platinum oxide affects the degradation analysis of PEM fuel cell cathodes

In this work, proton exchange membrane fuel cell cathodes are degraded with accelerated-stress-tests.These PtCo containing cathodes are analyzed at begin-of-life and end-of-test with a dedicated diagnostic procedure. For every individual load point, the oxygen transport resistance and voltage losses due to the formation of platinum oxides were obtained in addition to commonly measured electrochemical surface area, high frequency resistance, as well as cathode ionomer resistance. These data were used to break down the voltage losses into six different contributors. With this break down, performance gains and performance losses were determined at end-of-test. At low current densities, it was found that voltage losses due to degradation are dominated by the loss of specific activity and catalyst surface area - in line with the state-of-the-art knowledge. But by quantifying the losses from platinum oxide formation explicitly, we show that end-of-test an unassigned voltage loss is not only present at highest current densities, but already at low current density. More precisely, the unassigned voltage loss shows a linear increase with decreasing half cell voltage and is independent from the chosen accelerated stress test. As this unassigned loss depends on half cell voltage, it might arise from ionomer adsorption.

Bottom-Up Fabrication of Oxygen Reduction Electrodes with Atomic Layer Deposition for High-Power-Density PEMFCs

As the platinum (Pt) loading in proton exchange membrane fuel cell cathodes is driven down to reduce costs, catalyst utilization becomes increasingly important. Here, we report an atomic layer deposition-facilitated electrode fabrication technique designed to improve the catalyst-ionomer interface. The ionomer solvent environment and carbon support nanoporosity are studied independently, and it is found that the combination of an agglomerated ionomer dispersion and a mesoporous support gives access to a high catalytic activity (mass activity [MA] = 0.31 A/mgPt with pure Pt) that can be maintained at high current densities. We hypothesize that the formulation results in Pt sufficiently withdrawn from the ionomer such that poisoning and transport losses are reduced. When paired with a low-resistance dispersion-cast membrane, a 0.1-mgPt/cm2 cathode can deliver a 0.65-V power density of 1.0 W/cm2 at 150 kPa and 80°C. The assembly also demonstrates impressive durability, losing only 33 mV after 30,000 cycles.