Fuel Cell Cathode Performance Research Articles

Time-Domain Self-Clustering-Based Diagnosis Applied on Open Cathode Fuel Cell

The ability of a diagnosis tool to observe an abnormal state of a system remains a major issue for health monitoring. For that purpose, several diagnosis tools have been proposed in the literature. Most of them are developed for specific system characterization, and the genericity of the approaches is not considered. Indeed, most approaches proposed in the literature are based on an expert offline consideration that makes it hard to apply the strategy to other systems. It is therefore important to develop a diagnostic tool that takes as little as possible expert knowledge to reduce the dependency between the tool and the system. This paper, therefore, focuses on the application of a generic diagnosis tool on an open cathode fuel cell. The goal is to feed the diagnosis algorithm with a voltage measurement and let it proceed to a self-clustering of the signal components. Each cluster’s interpretation remains to be established by the expert point of view that is then involved downstream of the diagnosis tool.

Simulation Approaches and Validation Issues for Open-Cathode Fuel Cell Systems in Manned and Unmanned Aerial Vehicles

Hydrogen is a promising energy carrier in all fields of transportation, including unmanned aerial vehicles (UAVs) and manned vehicles for urban air mobility (UAM). In these applications, one of the biggest challenges is to overcome the limitations of lithium battery technologies, while keeping the advantage of clean energy, at least in terms of direct emissions. For these reasons, there is an ever-increasing interest in the development, simulation, and testing of propulsion systems adopting air-cooled proton exchange membrane fuel cells (PEMFCs). Fuel cells for aerospace must be designed for power-to-weight maximization. For this reason, auxiliary systems are simplified, and the adoption of air-cooling and passive cooling techniques is favored. However, the performance and dynamic behavior of PEMFCs are affected by the operating conditions, which, in applications like UAVs and UAM, are continuously changing due to the variation of speed and altitude during the flight. This investigation analyzes semi-empirical and control-oriented models of fuel cell systems proposed in the scientific literature. The review addresses the whole fuel cell system, inclusive of the balance of the plant, and introduces the transition from dynamic models to digital twins.

Research on the Performance of Self-Made Open-Cathode Fuel Cell Stacks under Different Operating Conditions.

The traditional fuel cell power system requires external ventilation and humidification systems for both the anode and cathode, which not only increases the application cost but also restrict its widespread use. In order to further enhance the applicability and reduce the operating costs of fuel cell power systems, this paper investigates the open-cathode proton exchange membrane fuel cell power system. This approach not only lowers the cost but also reduces the weight of the power system, enabling its potential application in a wider range of vehicles. In this study, two versions of the open-cathode fuel cell stacks were developed and performance and stability tests were conducted under various operating conditions. Additionally, tests were carried out with different materials of carbon paper to find a balance between performance and stability. Through the research presented in this paper, the application scope of fuel cells has been expanded, providing valuable insights for their further development.

A trifunctional N-doped activated carbon–ceria shell, derived from covalent porphyrin polymers for promoting Pt activity in fuel cell cathode performance

Covalent porous porphyrin-derived N-doped hollow carbon-containing ceria as an excellent support for Pt dispersion, improving durability and activity in proton-exchange membrane fuel cell applications.

Hierarchically Porous Carbons Derived from Nonporous Coordination Polymers.

Hierarchically porous carbons (HPCs) with multimodal pore systems exhibit great technological potentials, especially in the fields of heterogeneous catalysis, energy storage, and conversion. Here, we establish a simple and general approach to HPCs by carbonization of nonporous coordination polymers that are produced by mixing metal salts with polytopic ligands in alkaline aqueous solutions at room temperature. The proposed approach is applicable to a wide scope of ligand molecules (18 examples), thus affording the synthesized HPCs with high diversity in porosity, morphology, and composition. In particular, the prepared HPCs exhibit high specific surface areas (up to 2647 m2 g-1) and large pore volumes (up to 2.39 cm3 g-1). The HPCs-supported atomically dispersed Fe-Nx catalysts show much-improved fuel cell cathode performance over the micropore-dominated carbon black-supported catalysts, demonstrating the structural superiority of the HPCs for enhancing the mass transport properties.

Efficiency Enhancement of an Open Cathode Fuel Cell Through a Systemic Management

This paper addresses the design of a systemic management to improve the energetic efficiency of an open cathode proton exchange membrane fuel cell (PEMFC) in a hybrid system. Unlike the other similar works, the proposed approach capitalizes on the usage of both thermal management strategy and current control to meet the requested power from the system by the minimum fuel consumption. To do so, firstly, an experimentally based 3D mapping is performed to relate the requested power form the PEMFC to its operating temperature and current. Secondly, the reference temperature which leads to gaining the demanded power by the minimum current level is determined to minimize the hydrogen consumption. Finally, the temperature control is formulated by an optimized fuzzy logic scheme to reach the determined reference temperature by acting on the cooling fan of the PEMFC system, whilst the current is being regulated by its controller. The inputs of the fuzzy controller are the PEMFC current and temperature error and the sole output is the duty factor of the fan. The proposed methodology is tested on an experimental test bench to be better evaluated in a real condition. The obtained results from the proposed systemic management indicate promising enhancement of the system efficiency compared to a commercial controller. The proposed method of this work is extendable and applicable in fuel cell hybrid electric vehicles.

Open-cathode PEMFC heat utilisation to enhance hydrogen supply rate of metal hydride canisters

In this paper, the hydrogen supply to an open-cathode PEM fuel cell (FC) by using metal hydride (MH) storage and thermal coupling between these two components are investigated theoretically. One of the challenges in using MH hydrogen storage canisters is their limited hydrogen supply rate as the hydrogen release from MH is an endothermic reaction. Therefore, in order to meet the required hydrogen supply rate, high amounts of MH should be employed that usually suggests storage of hydrogen to be higher than necessary for the application, adding to the size, weight and cost of the system. On the other hand, the exhaust heat (i.e. that is usually wasted if not utilised for this purpose) from open-cathode FCs is a low-grade heat. However, this heat can be transferred to MH canisters through convection to heat them up and increase their hydrogen release rate. A mathematical model is used to simulate the heat transfer between PEMFC exhaust heat and MH storage. This enables the prediction of the required MH for different FC power levels with and without heat supply to the MH storage. A 2.5-kW open-cathode FC is used to measure the exhaust air temperature at different output powers. It was found that in the absence of heat supply from the FC to the MH canisters, significantly higher number of MH canisters are required to achieve the required rate of hydrogen supply to the FC for sustained operation (specially at high power outputs). However, using the exhaust hot air from the FC to supply heat to the MH storage, can reduce the number of the MH canisters required by around 40% to 70% for power output levels ranging from 500 W to 2000 W.

Multiscale Transient and Steady-State Study of the Influence of Microstructure Degradation and Chromium Oxide Poisoning on Solid Oxide Fuel Cell Cathode Performance

AbstractOxygen reduction in a solid oxide fuel cell cathode involves a nonequilibrium process of coupled mass and heat diffusion and electrochemical and chemical reactions. These phenomena occur at multiple temporal and spatial scales, making the modeling, especially in the transient regime, very difficult. Nonetheless, multiscale models are needed to improve the understanding of oxygen reduction and guide cathode design. Of particular importance for long-term operation are microstructure degradation and chromium oxide poisoning both of which degrade cathode performance. Existing methods are phenomenological or empirical in nature and their application limited to the continuum realm with quantum effects not captured. In contrast, steepest-entropy-ascent quantum thermodynamics can be used to model nonequilibrium processes (even those far-from equilibrium) at all scales. The nonequilibrium relaxation is characterized by entropy generation, which can unify coupled phenomena into one framework to model transient and steady behavior. The results reveal the effects on performance of the different timescales of the varied phenomena involved and their coupling. Results are included here for the effects of chromium oxide concentrations on cathode output as is a parametric study of the effects of interconnect-three-phase-boundary length, oxygen mean free path, and adsorption site effectiveness. A qualitative comparison with experimental results is made.

Influence of Cathode Catalyst Layer Ionomer on Air-Cooled, Open-Cathode Fuel Cells

Application of a proton exchange membrane fuel cell (PEMFC) in a planar, open-cathode configuration can significantly reduce system weight and complexity compared to a conventional fuel cell stack with closed cathodes. This decrease in device weight makes an array of open-cathode fuel cells a compelling power source for unmanned aerial vehicles because vehicle performance is highly dependent on weight. Forfeiting the ability to precondition incoming air to the cathodes leaves the fuel cells vulnerable to dry-out. Our previous studies on open-cathode fuel cells demonstrate that low porosity gas diffusion media facilitate a lower cell temperature and improve cell hydration but cell performance is still limited by significant ohmic resistance related to dehydration by evaporation at moderate cell temperatures (~40°C). Short-side-chain (SSC) ionomers with high ion exchange capacity have shown promise in closed cathode fuel cells by improving proton conductivity, especially during low RH operation, compared to their long-side-chain counterpart, Nafion. In this work, we study the relationship between cathode catalyst layer ionomer and cell polarization behavior in ambient conditions that have been observed to exacerbate dry-out and flooding in open-cathode fuel cells. Catalyst-coated membranes (CCMs) are prepared in-house with an automated, ultrasonic spray, layer-by-layer deposition method. Catalyst layers are formed with ionomers of variable equivalent weight and pendant side chain length and the catalyst layer proton conductivity is measured as a function of these properties. We use cyclic voltammetry and electrochemical impedance spectroscopy (EIS) to characterize the catalyst layers and performance losses in various ambient conditions.

Influence of Cathode Catalyst Layer Ionomer on Air-Cooled, Open-Cathode Fuel Cells

Reducing considerable ohmic resistances is paramount for improving open-cathode fuel cell voltage and power production. We study the influence of catalyst layer ionomer equivalent weight in open-cathode fuel cells operated in a range of challenging environmental conditions. Reducing catalyst layer ionomer equivalent weight (850EW vs 1100EW) substantially lowers proton transport and ohmic resistances for the MEAs not under active load. However, these implied advantages do not translate to higher cell voltage and power when a load is drawn from the cells. MEAs with catalyst layers bound by 1100EW exhibit significantly lower ohmic resistances during operation at three diverse environmental conditions, pointing to improved cell water management. Cell voltage is insensitive to ionomer equivalent weight at low current densities (<0.15 A/cm2). Increasing the catalyst layer ionomer equivalent weight from 850 to 1100 improves cell voltage and power by 20% at higher current densities, where cell thermal and water management and ohmic losses are more critical. MEAs featuring 1100EW catalyst layer ionomer operate at lower cell temperatures (by up to 2.9°C at 0.4 A/cm2), display lower mass transport resistance ascertained from oxygen gain experiments, and improve cell hydration as determined from electrochemical impedance spectroscopy.

Performance Optimization for Open‐cathode Fuel Cell Systems with Overheating Protection and Air Starvation Prevention

AbstractThe open‐cathode design with simultaneously integrated air supply and coolant flow systems can significantly simplify the structure of proton exchange membrane fuel cell (PEMFC). Typically, the performance of open‐cathode PEMFC system is highly influenced by temperature and oxygen excess ratio which can be regulated by the air flow fan. The axial air flow fan is the only actuator which is responsible for the oxygen supply to the cathode and cooling air at the same time. In this study, oxygen mass flow rate across cathode channels is regarded as the only control variable of the open‐cathode FC system. Air flow is regulated based on a set of optimal oxygen excess ratios in different stack currents for power optimization and overheating protection. However, the air flow rate is determined through a sensor installed to measure the air flow rate in the cathode channels. The control strategy simultaneously focuses on performance optimization with overheating protection and air starvation prevention, whereas the fuel cell operates its full range. The efficacy of the proposed method and control is verified through experiments with a small open‐cathode fuel cell system with a real‐time platform of NI (National Instruments) devices.

Approximate analytical solution to MHM equations for PEM fuel cell cathode performance

We report approximate analytical solutions for the shapes of the overpotential, oxygen concentration and proton current density through the depth of a PEM fuel cell cathode and for the cathode polarization curve. The solution is obtained by applying a homotopy analysis method to the standard macrohomogeneous equations for the electrode performance. For typical cell parameters, the solutions are valid up to the cell current density on the order of ≃ 500mAcm−2.

Addition of conductive particles to improve the performance of activated carbon air-cathodes in microbial fuel cells

Inexpensive carbon black combined with heat-treatment produced the most effective activated carbon catalyst for improving microbial fuel cell cathode performance.

An Open-Cathode Fuel Cell for Atmospheric Flight

We detail the relationships between operating environment and performance of a thin and lightweight open-cathode fuel cell based on flexible circuits that may be advantageous for unmanned air vehicle (UAV) propulsion. The open-cathode fuel cell performance is studied in a broad range of realistic atmospheric flight conditions by mounting it in a wind tunnel within an environmental chamber. The relationships between the operating environment and performance are quantitated in terms of polarization behavior and the underlying loss mechanisms are discussed qualitatively in the context of electrochemical impedance spectroscopy (EIS), DC resistance and infrared temperature measurements. The wind tunnel experiments demonstrate that open cathode operation is possible over wide ranges of ambient temperature (5–55°C), relative humidity (22–90% RH), air speed (0–15.4 m s−1) and altitude (240–3240 m). Forced airflow is shown to improve mass transport, waste heat rejection, and water management, broadening the effective operating envelope of this open-cathode fuel cell over others that rely on free convection. Sacrificing air preconditioning renders open-cathode fuel cell performance sensitive to the conditions of the surrounding environment. The lightweight open-cathode fuel cell in this study has high specific power, exceeding 1.3 kW/kgcell in favorable ambient conditions of 5°C, 50% RH at sea level.

Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles. The flow of ambient air over vehicle-mounted cells can improve oxygen, waste heat, and water transport between the catalyst layer and bulk air. We previously studied the effect of environmental conditions on cell polarization and found that ambient temperature, relative humidity, altitude and air speed all influence cell temperature, which affects water balance and oxygen transport to the catalyst layer. In this work, we relate gas diffusion media (GDM) properties to cell polarization behavior in a broad range of anticipated flight conditions. We study the effect of gas diffusion layer thickness and porosity on cell polarization and discuss its influence on cell temperature, oxygen transport and water management. Similarly, we investigate the polytetrafluoroethylene (PTFE) content in the GDM and the influence of hydrophobicity on cell water management and performance in a broad range of anticipated flight conditions. We use cyclic voltammetry and AC impedance spectroscopy to characterize performance losses associated with GDM properties to guide GDM selection.

Gas Diffusion Media for Open-Cathode Fuel Cells in Atmospheric Flight

Operating a proton exchange membrane fuel cell (PEMFC) in a planar, open cathode configuration can enable significant reductions in overall device weight and system complexity compared to a conventional fuel cell stack. This decrease in device weight makes an array of open-cathode, planar fuel cells a compelling candidate power source for unmanned aerial vehicles (UAVs) that can utilize the flow of ambient air over the vehicle-mounted cells to improve oxygen transport, waste heat rejection, and ultimately, water transport in the open-cathode. The effectiveness of each of these processes is largely influenced by the thickness and porosity of the cathode gas diffusion layer (GDL). We relate these cathode GDL properties to open-cathode fuel cell polarization behavior in a broad range of atmospheric conditions in active air flow and in passive, air-breathing mode to study the effect of gas diffusion layer thickness and porosity on cell performance through polarization and AC impedance measurements. Reducing cathode GDL porosity leads to a decrease in cell temperature and ohmic resistance, which improves water retention. Reducing cathode GDL thickness facilitates O2 and H2O transport, increasing oxygen availability to the electrocatalyst at the expense of improved water retention. After observing open-cathode fuel cell performance in a broad range of environmental conditions including ambient temperature, relative humidity, altitude, and in active and stagnant air flows, we find that application of a thicker cathode GDL (315 μm) with lower porosity (75%) yields the highest open-cathode fuel cell voltages and power generation; the open-cathode fuel cell achieves a maximum power-to-weight ratio of 1.44 kW kg-1.

In-plane gas permeability and thought-plane resistivity of the gas diffusion layer influenced by homogenization technique and its effect on the proton exchange membrane fuel cell cathode performance

In this study, in-plane gas permeability and through-plane resistivity of gas diffusion layer (GDL) made by different microporous layers (MPLs) were characterized by a new combined measurement setup under different compression ratios. Applied MPL ink-homogenizing techniques were pulse sonication, continuous sonication, bath ultrasonic and mechanical stirring. Results showed that 20% GDL compression produced optimized in-plane gas permeability and through plane resistivity, which is suitable for application in proton exchange membrane fuel cell (PEMFC). However, bath ultrasonic technique is more desirable technique for MPL ink homogenization in term of obtained gas permeability and total resistivity values; 0.45 (×10−12 m2) and 2.63 (mΩ cm2) respectively.Morphological investigation was also presented a uniformly distributed MPL microstructure without large cracks for the MPL which was prepared by bath ultrasonic technique (MPL-C).The Obtained results in H2/air PEMFC under various cathode relative humidity (RHC), 33–100%, revealed that the performance of the MEA made by MPL-C is 20% higher than others; 504 mWcm−2 versus 385 mWcm−2at 33% RHC. More analysis by electrochemical impedance spectroscopy demonstrated that MPL ink preparation by bath ultrasonic techniques resulted a lower ohmic and charge transfer resistance in PEMFC at least in small scale MEA.

La0.6Sr0.4CoO3−δ –Ce0.8Gd0.2O2−δ nanocomposites prepared by a sol–gel process for intermediate temperature solid oxide fuel cell cathode applications

La0.6Sr0.4CoO3−δ (LSC)–Ce0.8Gd0.2O2−δ (GDC) nanocomposite materials were prepared by a modified sol–gel method to improve solid oxide fuel cell cathode performance in intermediate temperature. Metal acetates precursors and citric acid combined with ethylene glycol as complex agents were used in the sol–gel process. Nano foam-like GDC powders were introduced into the sol–gel process to get the nanocomposites with the GDC content in the range of 10–50 wt%. In addition, pure LSC nano powders were also synthesized for comparison. The crystalline phases, morphologies, and elemental distributions of the pure LSC and LSC–GDC composite powders were characterized, and their electrode performances were investigated with electrochemical impedance spectroscopy. The results showed the GDC particles were largely covered by LSC, and the optimal GDC content was 30 wt% for the LSC–GDC electrode performance in this study.

Exergy Efficiency Profile of A 1kW Open Cathode Fuel Cell with Pressure and Temperature Variations

A proposed electric vehicle using proton exchange membrane (PEM) as clean energy have been attracting due to their high efficiency, high energy density and zero emissions. Standard exergy analysis of a mini urban vehicle powered by a 1kW Proton Exchange Membrane (PEM) fuel cell engine system has been presented in this manuscript. A sensitivity analysis has been studied in order to evaluate the effect of variable operating temperatures and pressures on the physical exergy and efficiency of a 1kW PEM fuel cell engine. The calculation of the physical and chemical exergies, mass flow rate and exergy efficiency are performed at temperature ratio (T/T0) and pressure ratio (P/P0) ranging from 1 to 1.15 and 1 to 4, respectively. The findings of the exergy analysis reveal that the overall efficiency of the fuel cell system was observed to be 61.3%. The result of the parametric study show that an increase in operating temperature and pressure results in an increase in exergy efficiency of the system.

Precursor solution additives improve desiccated La0.6Sr0.4Co0.8Fe0.2O3–x infiltrated solid oxide fuel cell cathode performance

Here, the addition of the surfactant Triton X-100 or the chelating agent citric acid to Solid Oxide Fuel Cell (SOFC) La0.6Sr0.4Co0.8Fe0.2O3–x (LSCF) precursor nitrate solutions is shown via scanning electron microscopy (SEM) and X-ray diffraction (XRD) to reduce average infiltrate nano-particle size and improve infiltrate phase purity. In addition, the desiccation of LSCF precursor solutions containing the aforementioned organic solution additives further reduces the average LSCF infiltrate nano-particle size and improves the low-temperature infiltrate phase purity. In particular, CaCl2-desiccation reduces the average size of Triton X-100 derived (TXD) LSCF particles fired at 700 °C from 48 to 22 nm, and reduces the average size of citric acid derived LSCF particles fired at 700 °C from 50 to 41 nm. Modeling and electrochemical impedance spectroscopy (EIS) tests indicate that particle size reductions alone are responsible for desiccation-induced cathode performance improvements such as CaCl2-desiccated TXD La0.6Sr0.4Co0.8Fe0.2O3-x – Ce0.9Gd0.1O1.95 (LSCF-GDC) cathodes reaching a polarization resistance of 0.17 Ωcm2 at 540 °C, compared to 600 °C for undesiccated TXD LSCF-GDC cathodes. This excellent low-temperature performance, combined with a low open-circuit 540 °C degradation rate, suggests that the desiccation of organic-additive-containing infiltrate precursor solutions may be useful for the development of durable, high-power, low-temperature SOFCs.