Commercial Proton Exchange Membrane Fuel Cell Research Articles

An Iron-Based Catalyst with Multiple Active Components Synergetically Improved Electrochemical Performance for Oxygen Reduction Reaction

Lack of highly active and stable non-precious metal catalysts (NPMCs) as an alternative to Pt for oxygen reduction reaction (ORR) in the application of zinc-air batteries and proton-exchange membrane fuel cells (PEMFCs) significantly hinders the commercialization of these energy devices. Herein, we synthesize a new type of catalyst composed of nitrogen-coordinated and carbon-embedded metal (Fe-N/Fe3C/Fe/C) by pyrolyzing a precursor at 800 °C under argon atmosphere, and the precursor is obtained by heating a mixture of the tri (dipyrido [3,2-a:2′,3′-c] phenazinyl) phenylene and FeSO4 at 160 °C in a Teflon-lined stainless autoclave. The resultant Fe-N/Fe3C/Fe/C-800 exhibits the highest activity for the ORR with onset and half-wave potentials of 1.00 and 0.82 V in 0.1 M KOH, respectively. Furthermore, it also shows a potential ORR activity in 0.1 M HClO4, which is promising for the application in commercial PEMFCs. Most importantly, Fe-N/Fe3C/Fe/C-800 exhibits a comparable electrochemical performance to Pt/C for the application in zinc-air battery. The specific capacity approaches 700 mAh·g−1, and the maximum power density is also comparable to that of Pt/C at the current density of 200 mA·cm−2. The work opens up a simple strategy to prepare ORR electrocatalyts for zinc-air battery and PEMFCs.

Voltage Reduction Technique for Use With Electrochemical Impedance Spectroscopy in High-Voltage Fuel Cell and Battery Systems

An attractive application of electrochemical impedance spectroscopy (EIS) is for diagnostic of a fuel cell (FC) or a battery system during operation. The use of EIS, however, is mostly limited to low-voltage (LV) FC systems and laboratory environments. Hence, the application of EIS in advanced diagnostics of a high-power system certainly lacks due to the voltage limitation and/or cost of the equipment. In this paper, a precision, low-cost electronic interface is proposed which enables the use of existing LV ac diagnostic tools with a production-size FC or battery stacks without the need for postprocessing of data. The interface, a dc level reducer (DLR), reduces only the dc component of the stack voltage to a safe voltage of <60 without altering the ac diagnostic components. This paper explains in detail the development of the DLR circuitry. The scalability and real-world capability of the interface are demonstrated by developing it for two voltage ratings. A set of circuits rated for 30 V is tested with a nine-cell proton exchange membrane FC (PEMFC) stack, and circuits rated for 200 V are tested on 90- and 110-cell commercial PEMFC stacks. The stack voltage is reduced by 60% on the nine-cell stack, and 60%–90% on the 90- and 110-cell stacks. The accuracy is measured using EIS data for 74 frequency points in the range of 0.1–20 kHz, with and without the DLR. The maximum relative error for point-versus-point comparison of the impedance is measured at 0.8% and 1.4% for 30- and 200-V rated circuits, respectively. These errors are well within the error of the industrial measurement equipment used, proving the fidelity of the ac signal output from the DLR.

Sliding Angle Characterization of Physicochemical and Roughness Changes of GDL Surfaces after Fuel Cell Operation

AbstractThe effect of proton exchange membrane fuel cell (PEMFC) operation on physicochemical properties and roughness of gas diffusion layers (GDL) was evaluated in this work. In addition to static contact angle measurements commonly used for GDLs, sliding angle measurements were also performed on a membrane electrode assembly (MEA) both new and used in service within commercial PEMFC. These latter revealed significant changes after 4,000 h in service that were not detectable with the static counterparts. The main novelty of this study is to correlate the contact and sliding angle measurements and to combine them with various modeling approaches developed for modeled surfaces. After 4,000 h of aging, it was thus shown that the surface of the GDLs became more hydrophilic, contrary to the roughness, which remains unchanged.

Electrical characterisation of proton exchange membrane fuel cells stack using grasshopper optimiser

In this study, optimum values of unknown seven parameters of proton exchange membrane fuel cells (PEMFCs) stack are generated for the sake of appropriate modelling. An objective function is adopted to minimise the sum of square errors (SSE) between the experimental data and the corresponding estimated results. A novel application of grasshopper optimisation algorithm (GOA) is engaged to minimise the SSE subjects to set of inequality constraints. Three study cases of typical commercial PEMFCs stacks are demonstrated and verified under various steady-state operating scenarios. Necessary subsequent comparisons to new results by others found in updated state-of-the-art are made. Sensitivity analysis of defined parameters is carried out. It is found that the PEMFC model is susceptible to the deviations of optimised parameters as the errors are substantially disturbed which signifies the value of the GOA-based method. In addition, performance measures to indicate the robustness of the GOA-based methodology are pointed out. At this moment, dynamic model of the stack is addressed and incorporated to demonstrate its dynamic response. Detailed MATLAB/SIMULINK simulation model is implemented to study the PEMFC dynamic performance. The simulated test cases emphasise the viability and effectivity of the GOA-based procedure in steady-state and dynamic simulations.

High Performance Pt-Ni Nanocage Catalyst for the Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells (PEMFCs)

PEMFCs have long been considered to be among the most promising next-generation energy conversion systems for portable devices and transportation vehicles due to their zero or low pollution, high power density and low temperature operation1,2. However, the widespread commercialization of PEMFCs remains challenged by the high cost of cell components and limited cell durability. Therefore, there is a significant need to develop new catalyst materials with high intrinsic oxygen reduction reaction (ORR) activity and stability, as well as a fabrication process that leads to high cell performance and durability with low catalyst loadings. In this work, we investigate the activity and stability of Pt-Ni nanocage oxygen reduction electrocatalysts (Figure 1a) both ex-situ and in-situ in an operating PEMFC. Ex-situ, the catalysts were both physically and electrochemically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and both cyclic and linear sweep voltammetry using a rotating disk electrode (RDE). The nanocages showed 2 and 4 times greater specific and mass activity than Pt/C, respectively, for the ORR with high durability. The catalysts were transitioned from the RDE platform to operating PEMFCs by application onto a Nafion® 212 membrane to form a catalyst-coated membrane (CCM) with a low cost, custom-built air-assisted cylindrical liquid jet spraying system (ACLJS). Several ACLJS parameters were investigated and the optimized parameters were used to produce CCMs that were tested by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), electrochemical impedance spectroscopy (EIS), PEMFC polarization and cyclic voltammetry. The CCM prepared with the Pt-Ni nanocage catalyst showed no obvious Pt and Ni dissolution and redeposition in the membrane even after 30K cycles. The performance and mass activity retention of the Pt-Ni nanocage catalyst was far superior to commercial Pt/C and just short of the US Department of Energy (DOE) 2020 targets3 (Figure 1 b,c), suggesting that Pt-alloy nanocages are very promising candidates for high-performing commercial PEMFCs.

Activity and durability of Pt-Ni nanocage electocatalysts in proton exchange membrane fuel cells

A Ni-rich Pt-Ni alloy was synthesized via a solvothermal method and transformed into platinum-nickel nanocage catalysts (PNCs) by applying a two-phase corrosion process. The catalysts were physically and electrochemically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and both cyclic and linear sweep voltammetry using a rotating disk electrode (RDE). During the RDE testing, the half-wave potential of the PNC was 30mV higher compared to that of a commercial Pt/C catalyst for the oxygen reduction reaction (ORR). The RDE experiments showed that the specific and mass activity of the PNC was 2 and 4 times greater than Pt/C, respectively, at 0.9V. Catalyst-coated membranes (CCMs) were fabricated with the Pt-Ni nanocages using an automated air-assisted cylindrical liquid jet sprayer system. The PNC CCMs were loaded into proton exchange membrane fuel cells (PEMFC) for activity and stability testing. The CCMs showed no obvious Pt and Ni dissolution and redeposition in the membrane even after 30K cycles. The performance and electrochemically active surface area (ECSA) retention of the PNC was far superior to commercial Pt/C, just short of the US Department of Energy (DOE) 2020 targets, suggesting that Pt-alloy nanocages are very promising candidates for high-performing commercial PEMFCs.

Modeling and experimental validation of hybrid proton exchange membrane fuel cell/battery system for power management control

Hybrid proton exchange membrane fuel cell (PEMFC)/battery power system is regarded as one of the most potential alternative power solutions in vehicular application since its low or zero emission and long life comparing to conventional engine and stand-alone battery pack. As the hybridization may reduce the fuel efficiency and battery efficiency because of interconnected power distribution, elaborate power management is prerequisite. This study presents DC/DC power converters including unidirectional boost and bidirectional types by using time delay control (TDC) to implement power management for hybrid power system. The bidirectional DC/DC converter operation mode is automatically switched by power management rules with battery state-of-charge (SOC) constraint. MATLAB/Simulink model of full hybrid power system is constructed to simulate the efficacy of proposed algorithm. Proportional-integral control (PIC) is employed in order to compare the control performance. Experimental validation is also performed with commercial PEMFC Horizon H-100, lithium-ion battery pack, DC/DC unidirectional and bidirectional converter prototype with National Instrument (NI) LabVIEW.

200W PEM Fuel Cell Stack with Online Model-Based Monitoring System

Although various designs have been introduced to improve the performance of a Proton Exchange Membrane Fuel Cell (PEMFC) stack system, fault conditions, such as drying or flooding, may still occur due to the complexity of the process. The development of a system which can detect these fault conditions is a key to operate PEMFC stack system effectively. In this study, a monitoring system for a 200W commercial PEMFC stack system has been developed by constructing models for determining the flooding and drying conditions inside the cell. Since the membrane resistance and pressure drop across the stack are important parameters for determining either drying or flooding conditions taking place inside the fuel cell, the online model-based monitoring system is developed by adopting existing algorithms. A number of instruments are installed to measure relevant data. The data acquisition system and mathematical models have been programmed under LabVIEW TM environment. To indicate the abnormal conditions inside the fuel cell stack, the model prediction is compared with the experimental measured values and the size of the discrepancy will be an indicator.

Advanced Diagnoses on Dead Ended Anode Operations for Proton Exchange Membrane Fuel Cell Stacks

Proton Exchange Membrane Fuel Cells (PEMFCs) offer the possibility of zero-emission electricity generation. The technology has shown tremendous advances in terms of performance and durability and wide-scale commercialization in a range of applications is imminent. In order to make further improvements to the key performance metrics, it is important that we know as much as possible about the way the fuel cell is working in space and time. Electrochemical impedance spectroscopy (EIS) is a powerful in situ diagnostic technique for monitoring fuel cell performance; however, its use is limited to steady state conditions and typically requires costly hardware. A low-cost multichannel impedance analyzer developed during this project using a commercial data acquisition National Instrument hardware and LabVIEW in house software[1]. This novel diagnostic system is applied to a commercial Intelligent Energy air-cooled open-cathode 5-cell PEMFC stack.Fig. 1. (a) Voltage loss at 0.75A cm-2 in Through flow and Dead ended conditions. (b) Reconstructed Nyquist plots at 0.75A cm-2 in Through flow and Dead ended conditions.This system was used to distinguish the causes of the voltage loss in dead ended anode conditions. A novel reconstructive impedance strategy was developed. The same frequency of interest was measured every 20 seconds in through-flow and dead-ended conditions. The events were repeated, but changing the frequency of interest (1 kHz to 1 Hz) at each repeat. It was found possible to associate Nyquist plots with different stages of the voltage loss over time (Fig 1 a). These results (Fig 1 b) highlight an increase of the resistance in the low frequency region during dead-ended operation, an indication of flooding. Thus the reconstructive impedance technique enables the study of dynamic processes, unsuitable for investigation using steady-state EIS. The influence of the current density on the voltage loss during a purge was also investigated (Fig 2). This result highlights the role of water in causing the voltage drop, since the amount of accumulating water is proportional to the current density. However, off gas analysis, inserting the probe between the hydrogen exhaust and the purge valve, also highlighted that the nitrogen accumulation is also proportional to the current density. This result suggests that the accumulation of nitrogen does not only come from permeation from the air through the membrane, but also from the small quantity contained in the hydrogen (50 ppm at BOC zero grade), with an accumulation rate proportional to the hydrogen consumption rate and to the volume of the anodic compartment.Fig. 2. Evolution of the voltage losses (a) and nitrogen accumulation (b) from 0.4 to 1 A cm-2in dead ended anode.In addition, a 16-segment S++ plate, capable of current, temperature and impedance mapping enabled to move from global to localized in situ measurements. The local and temporal evolution of the ohmic resistance, current density and temperature was studied as the current density was increased in order to provide more information on the process described Fig.2. Also, the heat distribution profile, obtained simultaneously from the S++plate and the thermal imaging camera provided a grid of the temperature distribution inside the stack and at its edges.Reference:[1] Q. Meyer, S. Barass, O. Curnick, T. Reisch, and D. J. L. Brett, “A multichannel frequency response analyser for impedance spectroscopy on power sources,” Journal of Electrochemical Science and Engineering, vol. 3, no. 3, pp. 107–114, 2013.

Dynamic Modelling of Proton Exchange Membrane Fuel Cells for Electric Vehicle Applications

This paper presents a simplified mathematical model for proton exchange membrane fuel cell (PEMFC) systems. The system performance is validated through a comparison with experimental datasheet results of a commercial PEMFC stack. The model is then used to study the transient response of a PEMFC when subjected to different load variations. A PI controller is designed to control the fuel cell output voltage during different transient conditions. The results ensure that the model provides an accurate representation of the dynamic and steady state behaviour of the fuel cell. In addition, the results show the fast response capabilities of the PEMFC for following changes in the load. This model will be useful for the optimal design and real-time control of PEMFC systems especially for electric vehicles applications.

Multirate Fuel Cell Emulation With Spatial Reduced Real-Time Fuel Cell Modeling

This paper presents a multiphysical proton exchange membrane fuel cell (PEMFC) stack model. The stack model is divided into three submodels describing the different physical domains, namely, electrical, fluidic, and thermal. The stacking method has been used to model the fuel cell stack from a single-cell model. The proposed model has been validated against a 1.2-kW commercial PEMFC stack with excellent agreement between simulation and experimentation. Based on the simulation results, a novel model reduction method is proposed. The reduced model is suitable for real-time simulation purpose. Moreover, a real-time-model-based fuel cell emulator is introduced. The emulator has three real-time computation cores with different rates. The three computation cores are interconnected with a digital communication bus. A dc/dc buck converter is designed in order to receive the model-predicted stack power conditions and emulate the real fuel cell stack power output. The experimental test results show that such an emulator is suitable for fuel cell system hardware-in-the-loop applications.

Convergence criteria establishment for 3D simulation of proton exchange membrane fuel cell

A validated 3 dimensional (3D) computational fluid dynamics model of a single cell proton exchange membrane fuel cell (PEMFC) was used for investigating convergence criteria. The simulation study was carried out using the commercial PEMFC simulation module built in to ANSYS FLUENT 12.1 software package and compared with published experimental data. Convergence data up to 19,000 iterations were collected in order to establish expectations for convergence errors and differences in convergence rates for different boundary conditions. Species mass fluxes and current density were used to perform a dual verification of experimentally verifiable simulation predictions. The results of the simulation showed that convergence trends were consistent for different boundary conditions and that the solution trends asymptotically to a final value with species mass flux errors approaching to constant values. The data were used to establish convergence criteria for future 3D PEMFC simulations where residual monitoring alone is insufficient to ensure convergence.

Operational and safety analyses of a commercial PEMFC system

A commercial, transportable proton-exchange-membrane fuel-cell (PEMFC) system rated at 7 kW nominal power was the subject of an operational (reliability, availability, and maintainability) and process-safety analysis. The scope of the analysis included the system start-up to engine-run mode, the maintenance tasks, as well as the continuous power-production mode, carried out with a hazard and operability (HAZOP) study and a failure-scenarios' development. The failure and process-safety risks were categorized and the probabilities were assessed with a fault-tree analysis (FTA) using equipment-failure-rate data from the literature, if available. The results led to similar conclusions to those previously reported in similar studies, and the most important equipment/devices with respect to reliability and safety aspects were identified. While the most important uncertainty in the complete analysis comes from the generic equipment failure-rate data used, about three failures in the first year of operation are estimated together with an availability of about 98% (a point value figures, confidence interval analysis was also made). The process-safety analysis revealed four potential accident scenarios involving hydrogen releases, fires and explosions. Finally, detailed suggestions and recommendations for changes/improvements with respect to the reliability/availability, maintainability and safety aspects of the system analysed are presented.

Mechanism of Catalyst Degradation in Proton Exchange Membrane Fuel Cells

A mechanism of catalyst particle growth in proton exchange membrane fuel cells (PEMFCs) by Ostwald ripening is presented. Particle growth occurs as a coupled process involving platinum ion transport through aqueous liquid and/or ionomer, and electron transport through a carbon support. The dominating factor in degradation of a catalyst supported on carbon is the presence of platinum ions in solution (in liquid and/or in ionomer). Experiments were conducted on commercial PEMFC electrodes in three liquids, solution, dilute acid solution, and deionized water. Pt particle size grew from to after in solution. By contrast, no detectable growth occurred in dilute acid or in deionized water. This demonstrates that the higher the Pt ion concentration, the faster the kinetics. The role of electronic conduction through support was verified by conducting experiments in solution on Pt supported on an electronically insulating material, namely alumina. While significant growth occurred in Pt supported on carbon, no detectable growth occurred in Pt supported on alumina. This observation is in complete accord with the model, and demonstrates the role of electronic transport on degradation. That is, when supported on alumina, lack of an electronically conducting path suppresses degradation even with present in solution.

Low Cost Electrodes for Proton Exchange Membrane Fuel Cells: Performance in Single Cells and Ballard Stacks

For widespread exploitation of proton exchange membrane fuel cells (PEMFCs) the cost of the stack must be reduced, and the performance per unit volume increased. Significant cost reduction has been achieved by the development of a high‐volume, low cost, electrode manufacturing process and from reductions in the electrode precious metal catalyst loadings. The performance of membrane electrode assemblies (MEAs) employing printed cathodes (⩽0.6 mg Pt/cm2) and anodes (⩽0.25 mg Pt/cm2, 0.12 mg Ru/cm2) in Ballard Mark V single‐cell and advanced‐stack hardware are at least comparable to current stack MEAs comprising high loading unsupported platinum black electrodes containing 4.0 mg Pt/cm2. Optimum cell performance has provided high power densities of 0.42 W/cm2 at 0.7 V. Furthermore, under motive and utility test conditions, the low‐cost electrodes show minimal loss in performance after over 3000 h of stack operation and, in short and full sized stacks, the cell‐to‐cell reproducibility is excellent, highlighting the high consistency of product available from the electrode manufacturing process. Incorporation of the low cost electrodes in commercial PEMFC stacks is anticipated in the near future.