Proton Exchange Membrane Stack Research Articles

Hydrogen production by water electrolysis technologies: A review

Hydrogen as an energy source has been identified as an optimal pathway for mitigating climate change by combining renewable electricity with water electrolysis systems. Proton exchange membrane (PEM) technology has received a substantial amount of attention because of its ability to efficiently produce high-purity hydrogen while minimising challenges associated with handling and maintenance. Another hydrogen generation technology, alkaline water electrolysis (AWE), has been widely used in commercial hydrogen production applications. Anion exchange membrane (AEM) technology can produce hydrogen at relatively low costs because the noble metal catalysts used in PEM and AWE systems are replaced with conventional low-cost electrocatalysts. Solid oxide electrolyzer cell (SOEC) technology is another electrolysis technology for producing hydrogen at relatively high conversion efficiencies, low cost, and with low associated emissions. However, the operating temperatures of SOECs are high which necessitates long startup times. This review addresses the current state of technologies capable of using impure water in water electrolysis systems. Commercially available water electrolysis systems were extensively discussed and compared. The technical barriers of hydrogen production by PEM and AEM were also investigated. Furthermore, commercial PEM stack electrolyzer performance was evaluated using artificial river water (soft water). An integrated system approach was recommended for meeting the power and pure water demands using reversible seawater by combining renewable electricity, water electrolysis, and fuel cells. AEM performance was considered to be low, requiring further developments to enhance the membrane's lifetime.

Modelling of a Proton-Exchange Membrane Electrolysis Cell with Liquid-Fed Cathode

Conventional proton-exchange membrane (PEM) water electrolysers use much thicker membranes (>175 µm) than their PEM fuel cell counterparts (<25 µm), which reduces hydrogen crossover but also reduces electrolyzer efficiency due to the increased Ohmic resistance1. Reduction of hydrogen crossover is critical in conventional systems to avoid buildup of hydrogen in the anode above the lower explosive limit. Due to the use of liquid water at the anode in conventional systems, the anode cannot be flushed with air or an inert gas to reduce the hydrogen concentration.If the liquid water supply is moved to the cathode, the anode can be easily purged with air, reducing the safety concern related to hydrogen crossover. Proof-of-concept experiments2 have demonstrated the viability of this approach, but many open questions remain regarding the interplay between water transport, water consumption, membrane hydration, and cell performance, as well as understanding what components and properties are most important in improving the efficiency of such a device.In this work, a framework for modelling of PEM electrolysis cells will be outlined, with special attention to wet and dry anode conditions. The model will be used to provide guidance for optimizing system performance while contributing to understanding of local processes inside an electrolysis cell such as water transport, heat generation, reaction distribution, and bubble formation. We study the impact of various design and operational choices, such as membrane thicknesses, PTL structure, air feed humidity, and differential pressure operation, on the rate of water transport from cathode to anode and on overall cell polarization performance. Using these results, we provide design recommendations for PEM electrolysers with liquid-fed cathodes. Finally, progress towards an open-source implementation of this model will be discussed.This work has been performed within the HOPE (Revolutionizing Green Hydrogen Production with Next Generation PEM Water Electrolyser Electrodes) and HYSTACK (Low cost, high efficiency PEM electrolyser stack) projects financially supported by the Research Council of Norway under project numbers 325873 and 321466, respectively. Ayers, K. et al. Perspectives on Low-Temperature Electrolysis and Potential for Renewable Hydrogen at Scale. Annu. Rev. Chem. Biomol. Eng. 10, 219–239 (2019).Barnett, A. O. & Thomassen, M. S. Method for producing hydrogen in a PEM water electrolyser system, PEM water electrolyser cell, stack and system. Patent No.: WO 2019/009732. EP3649276B1. US11408081B2.

Power quality improvement for 20 MW PEM water electrolysis system

Hydrogen is an important alternative as a clean fuel for industry and power-to-gas energy storage. The water electrolysis process is a promising technology in green hydrogen production where proton exchange membrane (PEM) technology has been keenly interested. Industrial large-scale PEM electrolyzers need a high current power supply. When connected to an alternating current (AC) source, high current power rectifiers are used to convert AC to DC. Currently, the most commonly used topology in large-scale PEM electrolysis systems is the thyristor-based topology due to its technology maturity and low cost. However, this topology presents several drawbacks in terms of power quality and consequently leads to higher stack-specific energy consumption (SEC) and additional losses. In the present research, we demonstrate the potential power quality improvement for a 20 MW PEM water electrolysis system by rectifier topology upgrade. Rather than traditional thyristor-based topology, a 3-phase interleaved buck rectifier topology is proposed. The new topology presents advantages on both AC and DC sides via a validated simulation model, which is built using MATLAB/Simulink and then validated with experimental data from an industrial 20 MW PEM water electrolyzer at Air Liquide's Bécancour plant. Results show a great improvement in terms of power factor, Total Harmonic Distortion (THD), and DC-current ripple reducing the total losses and the SEC of the PEM stack, especially under partial load. Towards a higher power efficiency, the proposed rectifier topology may be considered in the construction of future large-scale PEM systems.

A Cooling design for an end cell in fuel-cell stack using forced air flow in metal foam: Modelling and Experiment

The effect of temperature on an end-cell plate in a proton exchange membrane (PEM) fuel cell stack is presented in this paper. Numerical analysis and experimental work investigated the impact of a heat exchanger filled with metal foam on the end-cell plate used for cooling a PEM stack. One side of the edge plate was subjected to constant heat flux (1.55 W/cm2) while the other side was insulated. A metal foam with a pore density of 40 and having a porosity of 60% was analysed. The model was simulated in ANSYS R3-CFD, and the thermal problem was solved using the local thermal non-equilibrium (LTNE) to investigate the heat transfer between the fluid and solid phases. The thermal solution studied the effect of metal foam heat exchangers at different airflow velocities between 0.2 and 1.5 m/s on end-cell plate’s temperature. The results showed heat transfer enhancement in plate temperature, proving that the use of the LTNE assumption illustrated the difference between the end-cell plate and fluid flow temperatures. The effect of inlet air velocity on the plate temperature was also examined. An experimental model of a commercial PEM stack was constructed out of aluminium. This model was tested at the same conditions as those employed in the numerical solution. The heat generated by a fuel cell was simulated by a surface heater providing the same heat flux as the actual PEM cell. The numerical and experimental results for the end-cell plate for both at flow direction and different inlet velocities were assessed. There was a good agreement between the numerical and experimental results.

Optimal Estimation of Proton Exchange Membrane Fuel Cells Parameter Based on Coyote Optimization Algorithm

In recent years, the penetration of fuel cells in distribution systems is significantly increased worldwide. The fuel cell is considered an electrochemical energy conversion component. It has the ability to convert chemical to electrical energies as well as heat. The proton exchange membrane (PEM) fuel cell uses hydrogen and oxygen as fuel. It is a low-temperature type that uses a noble metal catalyst, such as platinum, at reaction sites. The optimal modeling of PEM fuel cells improves the cell performance in different applications of the smart microgrid. Extracting the optimal parameters of the model can be achieved using an efficient optimization technique. In this line, this paper proposes a novel swarm-based algorithm called coyote optimization algorithm (COA) for finding the optimal parameter of PEM fuel cell as well as PEM stack. The sum of square deviation between measured voltages and the optimal estimated voltages obtained from the COA algorithm is minimized. Two practical PEM fuel cells including 250 W stack and Ned Stack PS6 are modeled to validate the capability of the proposed algorithm under different operating conditions. The effectiveness of the proposed COA is demonstrated through the comparison with four optimizers considering the same conditions. The final estimated results and statistical analysis show a significant accuracy of the proposed method. These results emphasize the ability of COA to estimate the parameters of the PEM fuel cell model more precisely.

Improved butterfly optimization algorithm for CCHP driven by PEMFC

This study presents an optimal design of a combined cooling, heating and power generation system consists of a heat recovery system, a 5 kW proton exchange membrane stack, a small absorption chiller, a humidifier, and a gas compressor based on multi-criteria assessment for apartment simultaneously. The system is analyzed in terms of economics, environment, and thermodynamics. An improved version of butterfly optimization algorithm is employed for optimizing the system performance. The system efficiency is analyzed based on annual cost, exergy and energy efficiencies, and pollutant emission reduction. Final results illustrated that high relative humidity, pressure of inlet gases, and low operating temperature develop GHG emission reduction and system exergy performance. The optimized values of annual GHG reduction and exergy efficiency are 2.67e7 g and 47.1%, respectively, meanwhile, annual cost can be decreased to 3.139e3 $.

Effect of Water Conductivity on Proton Exchange Membrane (PEM) Catalyst Durability Using Thermal Degradation Resistant Polymer Membranes in Combat Applications

The U.S. Army is taking an increasing interest in fuel cell technology as vehicles require more electrical power to support additional capabilities for different combat roles and adversarial threats. These additional power requirements include silent watch (long term mounted surveillance), advanced radios/jamming devices and exportable power supporting stationary applications and vehicle-to-grid connectivity. Fuel cells are attractive in these roles as they generate a lower thermal and acoustic signature while having the capability of being more efficient than current internal combustion engines. The goal is to have increased energy savings and decreased fuel transport logistic burdens. Despite these advantages, significant work needs to be completed before fuel cell technology can be integrated into combat vehicles. In addition to the thermal-cycling and stack sealing issues leading to stack power degradation, the U.S. Army has unique challenges engineering fuel cells into vehicles. One challenge is that air flow for prime mover heat rejection for combat vehicles is significantly restricted (due to many components competing for the same space and the use of ballistic grills) compared to civilian automobiles. This can increase the internal temperature inside the stack to 140°C when operating in hot environments. One commercial market approach the U.S. Army is analyzing to address increased stack internal temperature is the incorporation of silicon (as quartz or silica) into the polymer membrane, which literature studies have shown can reduce polymer thermal degradation. Even though polymer thermal degradation has been shown to be reduced when silicon is incorporated, it is likely not completely eliminated, and the elevated temperatures the U.S. Army expects to experience could easily degrade membranes, even with the added silicon, and produce side products which are rejected into the exhaust water generated by fuel cells. This is a concern since many polymer materials, such as Perfluorosulfonic Acid and other novel proprietary membranes, incorporate acid side chains into the polymer chemistry to enhance their material properties for increased fuel cell power and durability. These acid side chains, or smaller compounds which contain these side chains, have the potential to be removed under thermal degradation. The removed compounds would contaminate the water produced by the stack, making it weakly acidic and electrically conductive. Studies have shown that strong acids in contact with PEM catalysts, with current cycling remove platinum electrocatalyst materials through dissolution and lower the overall stack power. Since there is the potential for PEM stack catalyst degradation and overall loss of vehicle capabilities due to elevated operating temperatures, this effect of weakly acidic and electrically conductive water was investigated in this study. Quartz containing Polybenzimidazole polymer membranes were sputter-coated with a platinum layer 6nm thick, on a single side of each sample, to simulate the boundary layer between the nano-particle electrocatalysts coated on carbon supports and polymer membrane in fuel cells. These 6nm thick sputter-coatings were applied to polymer membrane samples as thin strips (0.635cm in length and 0.238cm in width) to direct the applied electrical current, which simulated fuel cell operating current passing through the electrocatalysts generated by electrochemical reactions inside the fuel cell. Water, combined with various amounts of acetic acid, was placed in contact with the platinum coated membrane samples while electrical current cycles, between 50 and 400, were applied through sample coatings. Each cycle used a square wave profile which consisted of current being applied for 5s and then removed for 5s. Figure 1 shows Energy Dispersive Spectroscopy (EDS) scans (1a,b) and optical microscopy images (1c,d) of platinum coating levels before and after electrical currents (1a) 0.7mA and (1b,c,d) 30mA were applied through sample coatings. EDS results show that both 0.7mA and 30mA currents were sufficient to remove platinum when in contact with water containing 5 vol% acetic acid. Results showed a 38% loss of platinum when 400 cycles of 0.7mA electrical current was applied and platinum degradation was even more sever, only requiring optical microscopy images to observe the platinum loss, when using a 30mA current and a minimum of 50 cycles. Removal of platinum from membranes was also a fast process that was completed in ~8 minutes for 50 cycles and ~66 minutes for 400 cycles. Overall sample parameter testing indicated water electrical conductivity was the primary driving force for catalyst degradation. Figure 1

Optimization Design of Bipolar Plate Flow Field in PEM Stack

A new design of bipolar plate flow field in proton exchange membrane (PEM) stack was presented to develop a high-performance transfer efficiency of the two-phase flow. Two different flow fields were studied by using numerical simulations and the performance of the flow fields was presented. the hydrodynamic properties include pressure gap between inlet and outlet, the Reynold’s number of the two types were compared based on the Navier–Stokes equations. Computer aided optimization software was implemented in the design of experiments of the preferable flow field. The design of experiments (DOE) for the favorable concept was carried out to study the hydrodynamic properties when changing the design parameters of the bipolar plate.

Control and energy efficiency of PEM water electrolyzers in renewable energy systems

The practical dynamic properties and operational limitations of a commercial differential pressure 1 Nm3h−1 proton exchange membrane (PEM) water electrolyzer are studied from the viewpoint of renewable power production. Measured values from a 5 kWp solar photovoltaic (PV) power plant and PEM electrolyzer are analyzed to study factors affecting the control of PEM water electrolyzers operating as a part of renewable power production systems. Specific energy consumption of the PEM stack as a function of stack hydrogen outlet pressure is estimated based on measured values from two different measurement systems. Electrical energy consumption of the stack does not show any notable increase as the hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. However, the stack specific energy consumption increases by a maximum of 0.2 kWh/Nm3 when hydrogen outlet pressure is increased from 2.0 MPa to 4.0 MPa. The increase in specific energy consumption at high differential pressure operation is due to a decrease in Faraday efficiency. Selection and control of the hydrogen outlet pressure can minimize the specific energy consumption and maximize the real hydrogen production in dynamic PEM water electrolyzer operation.

Development of Megawatt Scale Proton Exchange Membrane Electrolysis for Energy Storage Applications

As the percentage of the traditional electrical grid power supplied by renewable sources such as wind and solar energy grows, energy storage solutions are required in order to maintain stable grid performance. These solutions have to provide both generation capacity for periods of low renewable generation or peak demand, and storage capacity for peak periods such as high wind periods and mid-day with low cloud cover. In addition, with increased renewable penetration, ancillary services such as frequency regulation to maintain grid stability increase in importance. Specific areas of the world such as Germany and California are already requiring energy storage as part of new renewable installations based on these issues. A recent study (Navigant Research) projects the value of energy storage for wind and solar integration worldwide to exceed $30 Billion by 2023. Hydrogen from electrolysis is a promising technology for all of the above applications, and also provides potential linkages between other infrastructures such as transportation and manufacturing to provide flexibility in the overall solution. Hydrogen has the capability to store massive amounts of energy in a relatively small volume, with no carbon footprint when generated from electrolysis of water. Electrolysis can also provide ancillary services (e.g., load shifting and frequency regulation) to the grid, resulting in multiple value streams. The hydrogen produced can be injected into the natural gas pipeline, in the production of high value chemicals such as ammonia, in upgrading of biogas, or used as a transportation fuel.Europe in particular has been committed to these pathways and making heavy investment in both materials research and system design and development as well as technology demonstration. In Germany, hydrogen is looked upon as a key part of the energy storage solution under “Energiewende,” their national sustainable energy transition plan. Hydrogen provides a unique link between the electric and gas grid infrastructures (often referred to as “Power-to-Gas”). Germany is also considered the global leader in biogas energy generation, with 18,244 GWh of generation in 2012 forecasted to grow to 28,265 GWh by 2025.Commercial electrolysis currently consists of alkaline liquid electrolysis, based on concentrated potassium hydroxide as the electrolyte and circulating fluid, or proton exchange membrane (PEM) electrolysis, based on a solid electrolyte and deionized water as the circulating fluid. PEM electrolysis is attractive for hydrogen generation applications because of the lack of corrosive electrolytes, small footprint, and ability to generate at high hydrogen pressure, requiring only water and an energy source. The major market challenge for PEM competing directly with alkaline technology has been product scale. However, that obstacle is decreasing as PEM-based products have increased in output. Several companies have already announced development plans for commercial megawatt (MW)-scale PEM electrolysis units in the 2014-2015 timeframe and there have been recent announcements of large scale renewable energy storage projects based on electrolysis.This presentation will provide an update on Proton OnSite’s MW product development effort, including a new large format PEM stack that achieves 40% cost reduction over the current design (Figure 1). These reductions were achieved through research in bipolar plates and the membrane electrode assembly, and additional improvements are possible based on Proton’s ongoing projects. Endurance and variable load testing will be presented as well as discussion of Proton’s current plans for introduction of the MW-scale product for the renewable energy storage market. Discussion of electrolysis performance with simulated loads and frequency variation will also be discussed (Figure 2).

Design and optimization of a proton exchange membrane fuel cell CHP system for residential use

This work deals with the analysis of a micro-cogeneration system for residential use based on a 1kWe proton exchange membrane (PEM) fuel cell. A detailed system analysis of the fuel cell stack operating at an average temperature of 62°C and the surrounding balance-of-plant (BoP) are taken into account. The gas processing section and the heat recovery system were also designed and optimized in term of heat recovery. Low-grade waste heat, mainly recovered from the PEM stack and the burner exhaust, has been found suitable for feeding a low-temperature thermal user such a radiant floor heating system (operating at ∼35–45°C). According to this configuration, the heat-exchanger network has been optimized following the pinch analysis methodology, and the floor heating system has been sized accordingly.The micro-cogeneration system has been modelled in term of mass and energy balances while efficiency maps were obtained for a varying fuel utilization and current density of the stack. The maximum electrical efficiency achieved is around 36% (AC, LHV), with a stack current of 30A and a Fuel Utilization (FU) of 80%. The global efficiency (that includes also heat recovery toward the thermal utility) is above 75% for same stack operating conditions.From the floor heating system sizing, the considered micro-CHP PEM system is able to supply around 22.4% of the heat demand by a 50m2 medium-low efficiency building (class E – EU classification) during the winter season. Nevertheless, taking into account a high efficiency building (class A++ – EU classification), the heat released by the PEM plant can supply the overall required thermal load without requiring an auxiliary boiler.

An electrochemical study of a PEM stack for water electrolysis

The electrochemical properties of a proton exchange membrane (PEM) stack electrolyzer (9 cells of 100 cm2 geometrical area) were investigated at different temperatures. An amount of H2 of ∼270 l h−1 was produced at 60 A (600 mA cm−2) and 70 °C under 876 W of applied electrical power. The corresponding specific energy consumed in the process was 3.24 Wh·l−1H2. The Faradic and electrical efficiencies were determined. Overall stack efficiencies of 73% and 85%, at 60 A and 70 °C, with respect to the low and high heating value of hydrogen, respectively, were obtained. These results confirmed the successful scale-up of a previous lab-scale device.

Hydrogen and proton exchange membrane fuel cells for clean road transportation

In this paper the main issues related to the working of hydrogen fuel cells and their utilization in the transportation field are presented and discussed, starting from the experimental analysis of dynamic performance of a laboratory fuel cell system based on a 20 kWe H 2/air proton exchange membrane stack. The experiments were carried out on successive load steps characterized by low reactant relative pressures (15–50 kPa) and stack temperature of 310–350 K. The effect of air flow rate, hydrogen purge and membrane humidification strategy on stack output voltage was evaluated evidencing the role of different sub-systems in stack management (for reactant feeding, stack cooling, membrane humidification) and their effect on efficiency losses of the overall system. The results presented in this paper provide experimental indications about potentialities of hydrogen fuel cell systems as clean electric energy generators for automotive applications.

Dynamic Simulation of a Stationary Proton Exchange Membrane Fuel Cell System

A dynamic model of a stationary proton exchange membrane (PEM) fuel cell system has been developed in MATLAB-SIMULINK®. The system model accounts for the fuel processing system, PEM stack with coolant, humidifier with anode tail-gas oxidizer, and an enthalpy wheel for cathode air. Four reactors are modeled for the fuel processing system: (1) an autothermal reformation (ATR) reactor, (2) a high temperature shift (HTS) reactor, (3) a low temperature shift (LTS) reactor, and (4) a preferential oxidation reactor. Chemical kinetics for ATR that describe steam reformation of methane and partial oxidation of methane were simultaneously solved to accurately predict the reaction dynamics. The chemical equilibrium of CO with H2O was assumed at HTS and LTS reactor exits to calculate CO conversion corresponding to the temperature of each reactor. A quasi-one-dimensional PEM unit cell was modeled with five control volumes for solving the dynamic species and mass conservation equations and seven control volumes to solve the dynamic energy balance. The quasi-one-dimensional cell model is able to capture the details of membrane electrode assembly behavior, such as water transport, which is critical to accurately determine polarization losses. The dynamic conservation equations, primary heat transfer equations and equations of state are solved in each bulk component, and each component is linked together to represent the complete system. The model predictions well matched the observed experimental dynamic voltage, stack coolant outlet temperature, and catalytic partial oxidation (CPO) temperature responses to perturbations. The dynamic response characteristics of the current system are representative of a typical stationary PEM fuel cell system. The dynamic model is used to develop and test a proportional-integral (PI) fuel flow controller that determines the fuel flow rate to maintain the uniform system efficiency. The dynamic model is shown to be a useful tool for investigating the effects of inlet conditions, load, and fuel flow perturbations and for the development of control strategies for enhancing system performance.

Development of a fast empirical design model for PEM stacks

A simple and fast empirical design model for a 5 kW proton exchange membrane (PEM) stack is presented in this paper. The performance analysis of the PEM stack operating on a membrane humidifying method is made through a series of experiments, including current–voltage–power characteristics, uniformity of cell unit voltages, gas pressure impact and air flux impact. Based on the above analysis, an empirical predicted model for the PEM stack has been developed by the combination of mechanistic and empirical modeling approaches to characterize and predict the voltage–current characteristics without examining in depth all physical/chemical phenomena. The good agreement between the predicted and experimental results covering a range of optimal operating conditions shows that the proposed model provides an accurate representation of the behavior for the PEM stack.

Development of a PEM stack and performance analysis including the effects of water content in the membrane and cooling method

For the use of proton exchange membrane (PEM) fuel cell systems to become widespread, the components required to build one should be minimized. Because a PEM fuel cell has a limited operating temperature range, it requires some kind of cooling method. In this study, different cooling methods were investigated experimentally. A PEM fuel cell stack with an active area of 100cm2 and 8 cells in series was developed and used in this research. When 50% relative humidity inlet gases were supplied (at 15A of current discharge and 70°C), cell temperatures at the center increased from around 60°C to 85°C, and cell voltage dropped from 4.8V to 3.2V because of membrane drying (insufficient cooling). When fully hydrated inlet gases (100% relative humidity) were supplied to the PEM stack at the same test conditions, the cell temperature remained around 65°C, and stack voltage remained around 5.7V at 15A of current discharge. Fully hydrated inlet gases play a positive role both for water transport (when the proton moves from the anode to the cathode) and to maintain the fuel cell stack temperature to prevent stack drying.

Experimental analysis and management issues of a hydrogen fuel cell system for stationary and mobile application

A laboratory fuel cell system based on a 20 kW H2/air proton exchange membrane stack was designed, realized and characterized with the aim to elucidate specific concerns to be considered for both hydrogen stationary power systems and automotive applications. The overall system characterization permitted the effect of the main operative variables (temperature, pressure and stoichiometric ratio) on stack power and efficiency to be evaluated. Reactant feeding, humidification and cooling problems are discussed, evidencing in particular the roles of air compressor, fuel purge, stack temperature and humidification strategy in system management. The characterization results are analyzed in terms of H2 consumption and available power, evidencing the energy losses of the individual fuel cell system components. In particular, the data obtained on key components (stack, reactants, heat and water management devices) are used for a critical discussion about their specifications and operation characteristics as demanded by both stationary and mobile applications.

A Dynamic PEM Fuel Cell Model

This paper proposes a relatively simple, physically motivated, dynamic electrical terminal model of a proton exchange membrane (PEM) fuel cell. The dynamic model is obtained by extending a static current voltage description to include temperature dependence, and by dynamically modeling the temperature of the membrane. Model performance is validated using experimental data collected from a 500-W commercial PEM stack.

Reliability of Plug Power GenSys™ fuel cell systems

The pace at which fuel cell systems are widely adopted by the marketplace will be determined primarily by two factors: (1) the rate at which system cost decreases and (2) the rate at which system reliability increases. This paper describes the field reliability and its improvement through a combination of software and hardware changes of Plug Power's GenSys™ fleet of 5 kWe (plus up to 9 kW of thermal energy) proton exchange membrane (PEM) fuel cell systems. Plug Power has shipped more than 300 of these systems to more than 50 customer locations in more than 10 countries. This fleet is of sufficient size, and has been operating for a sufficient length of time, to develop statistically significant observations of system reliability. Nondimensionalized probability plots of PEM stack lifetime in field units are presented, and a series of system-level changes are described that have increased PEM stack life by about a factor of 4. Nondimensionalized, system-level reliability statistics are also presented for the installed fleet. Pareto charts describing the top causes for system failures in the field are shown, and the general methodologies for improving system-level reliability are discussed.

A dynamic model for a stand-alone PEM fuel cell power plant for residential applications

A dynamic electrochemical simulation model of a grid independent proton exchange membrane (PEM) fuel cell power plant is presented. The model includes the methanol reformer, the PEM stack, and the power conditioning unit. The model is then used to predict the output voltage and study the transient response of a PEM power plant when subjected to rapid changes in a residential load connected to it. The results show the fast response capabilities of the PEM power plant in following changes in the load.