Open-cathode Polymer Electrolyte Membrane Research Articles

Performance evaluation of cathode channels with different cross-sections for open-cathode polymer electrolyte membrane fuel cell stack

This study proposes six different cross-sectional cathode flow field designs such as square, trapezoid, dome, boot, pentagon, and triangular constructing four cells open cathode polymer electrolyte membrane fuel cell stack with various parameters optimization and suitability for system level development. Parameters, including pressure drop, oxygen concentration, airflow rate, blower power, stack temperature, cooling rates, net power output, and stability are investigated with focus on understanding the trend, interconnected dependencies among the parameters, which collectively influence the overall performance of the cross-section designs. Overall, studies show that, boot cross-section design possessing the optimum pressure drop of 23.9 Pa, shows better performance compared to other cross-section designs due to better oxygen gas distribution, water retention/removal, heat removal/retention, and net power output. Conversely, for galvanostatic analysis done at a higher current value of 35 A, dome and square cross-section designs show highest and stable potential, along with balanced stack temperature.

Experimental Design of High-Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

Open-cathode polymer electrolyte membrane fuel cells (PEMFCs) utilize a unique air-cooled system design to eliminate the humidifiers, air compressor, and liquid cooling loop of conventional, liquid-cooled PEMFC systems, thereby greatly reducing system cost. However, the open-cathode PEMFC performance is restricted by poor humidification, high membrane and charge transfer resistances, and overheating due to inefficient thermal and water management. This work aims to strategically modify the membrane electrode assembly (MEA) design to overcome these issues and achieve high open-cathode PEMFC performance that approaches that of liquid-cooled systems. The use of thinner membrane along with short side chain ionomer is found to elevate the cell performance due to increased water retention at the cathode catalyst layer (CCL) and decreased ohmic losses. Thinner gas diffusion layers with high porosity enable additional cell performance increment by improving oxygen availability at the CCL. An overall current density rise of 88% at 0.6 V and 53% at 0.4 V is achieved by the strategically designed MEA for open-cathode cells. The enhanced power density enabled by the custom MEA can both reduce the stack cost and expand the power range of open-cathode PEMFCs, thus expanding their potential use for low-cost fuel cell system applications.

Integrated Heat Regenerator (IHR) Designs with Hydrogen Preheater and Thermoelectric Generator for Power Enhancement of a 2 kW Fuel Cell Vehicle

The power train efficiency of fuel cell vehicles (FCV) can be enhanced by improving the hydrogen energy utilization. Based on a mini FCV running on a 2 kW open-cathode Polymer Electrolyte Membrane (PEM) fuel cell, a waste heat recovery system design needs to be developed as an approach towards higher energy efficiency. The novelty of the system is on the integration of thermoelectric generator technology with hydrogen preheating process for a combined heat and power output. This manuscript presents the proposed integrated heat regenerator (IHR) designs, analysed using numerical computational modelling. Three IHR designs were proposed where the main design criteria are (i) a minimum of 10oC hydrogen preheating degree, and (ii) non-parasitic active cooling for the Thermoelectric generator (TEG) cells. Three design concepts were studied to identify its design and performance limitations. The numerical results were validated with theoretical modelling analysis for hydrogen exit temperatures and TEG surface temperatures. The analysis on predicted fuel cell power enhancement, TEG power generation and waste heat utilization were performed by relating the temperature profiles of the hydrogen reactant and TEG surfaces to fuel cell reaction models and TEG power relationships. A compact IHR design that produced 7.7 to 8 % total power enhancement and suitable in size for a mini FCV was identified for future development works

Analyzing and Modeling of Water Transport Phenomena in Open-Cathode Polymer Electrolyte Membrane Fuel Cell

Water management is one issue that must be surpassed to ensure high membrane proton conductivity and adequate reactant transport in the membrane-electrode assembly (MEA) simultaneously. A well-designed water management system is based on a comprehensive understanding of water transport in the inner part of the polymer electrolyte membrane (PEM) fuel cell. In this work, the water transport phenomena in the MEA PEM fuel cell are analyzed by using a mathematical model. The transport of diluted species interface is used to model the transport of water in the ionomer phase in the catalytic layer and the membrane domains. The molecular flux of water is defined using Nernst–Planck equations, including migration and Fickian diffusion using parameters obtained experimentally for diffusivity and mobility based on water drag for a fully humidified membrane. The proposed model 1D model includes anode gas channel, cathode gas channel, anode gas diffusion layer (GDL), cathode GDL, anode catalyst layer, cathode catalyst layer, and proton exchange membrane. Water activity, ionomer conductivity, and output voltage are predicted by changing the humidity on the anode side of the fuel cell.

Microporous Layer Design for High Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) are a key sustainable energy source which can cater for energy demands ranging from miniature power requirements to portable, automotive and various stationary power applications. PEMFCs deliver electricity by means of undergoing electrochemical reactions and produce water and heat as by-products. At high current densities, flooding and overheating can cause local hot spots leading to degradation and failure of the membrane electrode assembly (MEA) during long term operations [1]. Hence, hygrothermal management is normally ensured by means of liquid cooling of the bipolar plates. However, this traditional design incurs extra cost of balance-of-plant (BOP) components and enhances the overall size of the system. Using ambient air as oxidant as well as coolant with an ‘open-cathode’ design can drastically reduce the system size and weight, however the performance of such a system is limited by overheating and drying of the MEA.The objective of the present work is to develop a suitable microporous layer (MPL) design for efficient cell performance of an open-cathode PEMFC system operating at hot ambient air conditions. A pre-validated comprehensive, 3D computational fuel cell model [2] is used to study the mass, momentum and heat balance inside the system along with water transport and current distribution in various components of the system. The gas diffusion layer (GDL) comprised of a bi-layer macroporous substrate and MPL structure is one of the key components of the overall system design and plays a significant role in water transport inside the cells [3]. Whereas in conventional liquid-cooled systems, the presence of a hydrophobic MPL can facilitate wicking of liquid water out of the MEA to prevent oversaturation and flooding [4], ‘open-cathode’ fuel cells are more likely to experience drying than flooding and may therefore benefit from alternate MPL designs. As shown in Figure 1, thinner MPLs (30 μm) with higher porosity (60%) are found to result in elevated open-cathode cell performance as a result of optimum water retention and O2 diffusion across the MPL. The increment in performance is found to be broadly visible at higher current densities, where mass transport effects are more dominant. The MPL effective diffusivity which is a function of its porosity along with the MPL thickness are also found to be important for the overall thermal and water balance of the MEA. The optimum RH and temperature levels achieved in the MEA are further found to negate the overheating and drying effects obtained in earlier system designs.AcknowledgmentsThis work was supported by the funding provided by Simon Fraser University and Indian Oil R&D Centre under the SFU-IOCL joint PhD program in clean energy.

A computational analysis on the operational behaviour of open-cathode polymer electrolyte membrane fuel cells

In the present work, a comprehensive, three-dimensional computational fuel cell model is developed, validated, and utilized to study the operational and hygrothermal behaviour of an open-cathode (air cooled) polymer electrolyte membrane fuel cell at various ambient conditions compared to conventional liquid cooled cells and a hypothetical isothermal case. The spatial distributions of relative humidity, temperature, and membrane water content are analysed during operation of the cell and the strong hygrothermal characteristic of the open-cathode fuel cell system is established. The high temperature and relative humidity gradients inside the cell are found to limit the cell performance for open-cathode cells unlike the other operational cases. Moderate self-heating followed by membrane drying is found to be the key factor limiting the net cell performance while in operation at moderate-to-high current densities and high air flow rates. The open-cathode fuel cell is also found to perform better at high temperature and high relative humidity ambient conditions; however, in contrast to liquid cooled cells, the performance is restricted by inefficient thermal and water management.

Development of cathode cooling fins with a multi-hole structure for open-cathode polymer electrolyte membrane fuel cells

The main purpose of this study is to investigate how a newly designed cooling fin affects the performance of open-cathode polymer electrolyte membrane fuel cells (OC-PEMFCs) at high current densities with the aid of experiments and simulation. The novel fin, denoted as the CASE-1 cooling fin, comprises a multi-hole structure (MHS) in the rib region. An OC-PEMFC stack with the CASE-1 cooling fins exhibits a higher performance under higher current densities than that with conventional cooling fins, which are referred to as CASE-2 cooling fins. Owing to several dead zones at the fan duct, sufficient air is not provided to the edges of the OC-PEMFC stack, where the 1st and 20th fuel cells are located; however, the MHS mitigates this decrease in the performance at the edge cells. Results of numerical simulation show that the oxygen mole fraction for CASE-1 cooling fins is higher than that for CASE-2 at the gas diffusion layer/membrane electrode assembly (GDL/MEA) interface indicating uniform oxygen distribution throughout the MEA area. These all results indicate that the CASE-1 cooling fin induces a positive oxygen distribution, resulting in a significant improvement in performance at higher current densities.

Performance enhancement of air-cooled open cathode polymer electrolyte membrane fuel cell with inserting metal foam in the cathode side

In this study, a novel way to improve performance of the air-cooled open cathode polymer electrolyte membrane fuel cell is introduced. We suggest using a metal foam in the cathode side of the planar unit fuel cell for the solution to conventional problems of the open cathode fuel cell such as excessive water evaporation from the membrane and poor transportation of air. We conduct experiment and the maximum power density of the fuel cell with metal foam increases by 25.1% compared with the conventional fuel cell without metal foam. The open cathode fuel cell with metal foam has smaller ohmic losses and concentration losses. In addition, we prove that the open cathode fuel cell with metal foam prevents excessive water evaporation and membrane drying out phenomena with numerical approach. Finally, we apply the metal foam to the air-cooled open cathode fuel cell stack as well as the planar unit cell.

Data on the thermo-fluid simulation of open-cathode fuel cell stack depending on the location of the oxidizer/cooling supply system.

The content of this paper provides simulation data of the distribution of temperature fields, and oxidizer/cooling agent (air) flows in dependence with location of the oxidizer/cooling supply system in open-cathode polymer electrolyte membrane fuel cell (PEMFC) stack. The finite element method in Solid Works Simulation and Solid Works Flow Simulation software were used for bipolar plate strength calculation and thermo-fluid simulation of PEMFC stack with forced-air convection. The simulations were carried out for two variants of the oxidizer/cooling supply system location - at the entrance to the fuel cell stack (air injection) and at the outlet of the fuel cell stack (air intake).

Improving open-cathode polymer electrolyte membrane fuel cell performance using multi-hole separators

We developed a new separator with a multi-hole structure (MHS) in the rib region for open-cathode polymer electrolyte membrane fuel cell (OC-PEMFC) stack to improve performance. The electrochemical current–voltage performance results clearly demonstrate that the performance of the OC-PEMFC stack using the MHS design was higher than that using the conventional parallel design at high current regions (i.e., over 7 A). The current increased by 11.24% at 12 V (i.e., 0.6 V/cell). The effects of supplying additional oxygen and removing generated water were identified as factors improving the performance. The individual cell voltages demonstrate that the initial value of standard deviation for the OC-PEMFC stack using MHS was somewhat high, but it exhibited better uniformity at higher current regions.

Reticulated porous and parallel channel cathode flow fields in real scale polymer electrolyte membrane fuel cells: A comparative experimental study

This paper focuses on understanding the effect of reticulated porous cathode flow fields in real scale close and open cathode polymer electrolyte membrane fuel cells (PEMFCs) in terms of their thermo-electrical performance. This research contributes to addressing challenges with PEMFCs linked to oxygen supply to the cathode and proper mixing of gasses as well as water removal issues. Parallel channel and porous cathode flow fields in both open and closed cathode PEMFCs of medium scale (active area of 15 × 15 cm2) have been investigated. The porous material consisted of 20 pores per inch with a porosity level of 80%. The cells’ polarisation and impedance characteristics have been analysed. The porous flow field has been found providing better electrical performance in closed cathode PEMFC compared to the open cathode. Improvements in gas diffusion and temperature uniformity were observed with porous flow field; however, water removal has been observed challenging, which need to be addressed before the benefits of using porous flow field are fully realised.

In-situ electrochemically active surface area evaluation of an open-cathode polymer electrolyte membrane fuel cell stack

Abstract The ability to evaluate the electrochemically active surface area (ECSA) of fuel cell electrodes is crucial toward characterising designs and component suites in-situ, particularly when evaluating component durability in endurance testing, since it is a measure of the electrode area available to take part in the fuel cell reactions. Conventional methods to obtain the ECSA using cyclic voltammetry, however, rely on potentiostats that cannot be easily scaled to simultaneously evaluate all cells in a fuel cell stack of practical size, which is desirable in fuel cell development. In-situ diagnostics of an open-cathode fuel cell stack are furthermore challenging because the cells do not each possess an enclosed cathode compartment; instead, the cathodes are rather open to the environment. Here we report on a diagnostic setup that allows the electrochemically active surface area of each cell anode or cathode in an open-cathode fuel cell stack to be evaluated in-situ and simultaneously, with high resolution and reproducibility, using an easily scalable chronopotentiometry methodology and a gas-tight stack enclosure.

Hydrogen preheating through waste heat recovery of an open-cathode PEM fuel cell leading to power output improvement

The electrochemical reaction kinetics in a Polymer Electrolyte Membrane (PEM) fuel cell is highly influenced by the reactants supply pressures and electrode temperatures. For an open cathode PEM fuel cell stack, the power output is constrained due to the use of air simultaneously as reactant and coolant. Optimal stack operation temperatures are not achieved especially at low to medium power outputs. Based on the ideal gas law, higher reactant temperatures would lead to higher pressures and subsequently improve the reaction kinetics. The hydrogen supply temperature and its pressure can be increased by preheating; thus, slightly offsetting the limitation of low operating stack temperatures. The exit air stream offers an internal source of waste heat for the hydrogen preheating purpose. In this study, a PEM open-cathode fuel cell was used to experimentally evaluate the performance of hydrogen preheating based on two waste heat recovery approaches: (1) open-loop and (2) closed loop hydrogen flow. The stack waste heat was channelled into a heat exchanger to preheat the hydrogen line before it is being supplied (open loop) or resupplied (closed loop) into the stack. At a constant 0.3bar hydrogen supply pressure, the preheating increases the hydrogen temperature in the range of 2–13°C which was dependant on the stack power output and cathode air flow rates. The achievable maximum stack power was increased by 8% for the closed loop and 10% for the open loop. Due to the small hydrogen flow rates, the waste heat utilization was only 3–6% from the generated stack heat. The analysis indicates a better potential for open loop hydrogen preheating using fuel cell waste heat for open-cathode stacks.

Performance evaluation of an open-cathode PEM fuel cell stack under ambient conditions: Case study of United Arab Emirates

The open-cathode polymer electrolyte membrane (PEM) fuel cell stack has been a promising candidate as a sustainable energy conversion system for replacing fossil fuel-based energy conversion devices in portable and automotive applications. As the ambient air is directly used to provide both oxidant and cooling, the complex cooling loop can be avoided which reduces the complexity and cost. However, the stack performance is highly affected by ambient conditions, i.e., ambient temperature and humidity. In this study, the effect of monthly ambient air conditions (temperature and humidity) is evaluated with respect to the stack’s power production performance as well as thermal, water and gas management by employing a validated three-dimensional open-cathode PEM fuel cell stack model. The annual climate data from the hot and arid environment of Abu Dhabi, United Arab Emirates (UAE) are used as a case study. The objective is to develop a better fundamental understanding of the interactions of physical phenomena in a fuel cell stack, which can assist in improving the performance and operation of an open-cathode PEM fuel cell-powered vehicle. The results indicate that the stack performance can vary significantly (up to 40%) from winter to summer, especially at high operating currents, with significant changes in the stack temperature and the water content at the membrane. Moreover, the anode humidification results in a significant improvement in the stack performance (up to 40%) in hot and dry conditions. However, a careful balance has to be struck between the humidifier parasitic load and the stack power.

Cell level modeling of the hygrothermal characteristics of open cathode polymer electrolyte membrane fuel cells

Open cathode designs that utilize ambient air for both cooling and oxygen supply are a useful feature for low- to medium-power polymer electrolyte membrane fuel cell (PEMFC) stacks. Elimination of balance-of-plant subsystems greatly reduces the complexity, parasitic power, and cost of the overall system, and therefore increases the appeal of open cathodes. The present research addresses the key challenges of open-cathode PEMFCs related to thermal management and membrane hydration, two highly coupled phenomena. Accurate knowledge of the temperature and relative humidity (RH) distributions in the cell is essential in order to optimize heat removal by suitable strategies. In the present work, a three-dimensional numerical model is developed that can predict the hygrothermal characteristics in a complete open-cathode cell. The model is validated using experimental data obtained with Ballard Power Systems' FCgen®-1020ACS stack under a range of operating conditions. The model is then used to analyze the key flow conditions and properties that control the hygrothermal behavior of open-cathode stacks. Based on the obtained results, flow conditions can affect temperature and RH distributions significantly; in-plane plate thermal conductivity can provide a uniform temperature distribution while adversely reducing the RH; and edge cooling can increase temperature and RH gradients in the cell. Recommendations for hygrothermal design and operation of open cathode stacks are provided.

Electrode structure effects on the performance of open-cathode proton exchange membrane fuel cells: A multiscale modeling approach

In this paper we present a new dynamic multiscale model of an open-cathode Polymer Electrolyte Membrane Fuel Cell (PEMFC). The model describes two-phase water transport, electrochemistry and thermal management within a framework that combines a Computational Fluid Dynamics (CFD) approach with a micro-structurally-resolved model predicting the water filling dynamics of the electrode pores and the impact of these dynamics on the evolution of the electrochemically active surface area (ECSA). The model allows relating for the first time the cathode electrode structure to the cell voltage transient behavior during experimental changes in fuel cell temperature. The effect of evaporation rates, desorption rates and temperature changes on the performance of four different electrode pore size distributions are explored using steady-state and transient numerical simulations. The results are discussed with respect to water management and temperature control.