Degradation analysis of the core components of metal plate proton exchange membrane fuel cell stack under dynamic load cycles

The durability of metal plate proton exchange membrane fuel cell (PEMFC) stack is still an important factor that hinders its large-scale commercial application. In this paper, we have conducted a 1000 h durability test on a 1 kW metal plate PEMFC stack, and explored the degradation of the core components. After 1000 h of dynamic load cycles, the voltage decay percentage of the stack under the current densities of 1000 mA cm^?2 is 5.67%. By analyzing the scanning electron microscopy (SEM) images, the surfaces of the metal plates are contaminated locally by organic matter precipitated from the membrane electrode assembly (MEA). The SEM images of the catalyst coated membrane (CCM) cross section indicate that the MEA has undergone severe degradation, including the agglomeration of the catalyst layer, and the thinning and perforation of the PEM. These are the main factors that cause the rapid increase in hydrogen crossover flow rate and performance decay of the PEMFC stack.     

1.5 kWe HT-PEFC stack with composite MEA for CHP application

In this work, the performance of a High Temperature (HT) Polymer Electrolyte Fuel Cell (PEFC) stack for co-generation application was investigated. A 3 kW power unit composed of two 1.5 kW modules was designed, manufactured and tested. The module was composed of 40 composite graphite cell with an active area of 150 cm². Composite Membrane Electrode Assemblies (MEAs) based on Nafion/Zirconia membranes were used to explore the behavior of the stack at high temperature (120 °C). Tests were performed in both pure Hydrogen and H₂/CO₂/CO mixture at different humidification grade, simulating the exit gas from a methane fuel processor. The fuel cells stack has generated a maximum power of 2400 W at 105 A with pure hydrogen and fully hydrated gases and 1700 W at 90 A by operating at low humidity grade (95/49 RH% for H₂/Air). In case the stack was fed with reformate simulated stream fully saturated, a maximum power of 2290 W at 105 A was reached: only a power loss of 5% was recorded by using reformate stream instead of pure hydrogen. The humidification grade of Nafion membrane was indicated as the main factor affecting the proton conductivity of Nafion while the addition of the inert compound like YSZ, did not affectthe electrochemical properties of the membrane but, rather has enhanced mechanical resistance at high temperature.     

Influence of ageing on the dynamic behaviour and the electrochemical characteristics of a 500 We PEMFC stack

In this study, a 500 We 19 cells Proton exchange membrane fuel cell (PEMFC) stack was aged for ∼1200 h and submitted to current steps between different operating levels. Using two different multi-channel data acquisition systems (one at 100 kHz and one at 1 Hz). the evolution with ageing of individual cells and full stack's short term (∼10 s) and medium term (∼4 min) dynamic performances was followed. Undershoots and overshoots behaviours were observed for respective current step-up and step-down. It appeared that, in studied operating conditions, the first time constant was related to the charge transfer at electrode/electrolyte interfaces. After the first “plateau”, the voltage evolution was explained by a membrane water content evolution.     

Scale-up of a high temperature polymer electrolyte membrane fuel cell based on polybenzimidazole

A high temperature PEM fuel cell stack with a total active area 150 cm² has been studied. The PEM technology is based on a polybenzimidazole (PBI) membrane. Cast from a PBI polymer synthesised in our lab, the performance of a three-cell stack was analysed in static and dynamic modes. In static mode, operating at high constant oxygen flow rate (QO₂>1105 ml O₂/min) produces a small decrease on the stack performance. High constant oxygen stoichiometry (λO₂>3) does not produce a decrease on the performance of the stack. There are not differences between operating at constant flow rate of oxygen and constant stoichiometry of oxygen in the stack performance. The effect of operating at high temperature with a pressurization system and operating at higher temperatures are beneficial since the performance of the fuel cell is enhanced. A large shut-down stage produces important performance losses due to the loss of catalyst activity and the loss of membrane conductivity. After 150 h of operation at 0.2 A cm⁻², it is observed a very high voltage drop. The phosphoric acid leached from the stack was also evaluated and did not exceed 2% (w/w). This fact suggests that the main degradation mechanism of a fuel cell stack based on polybenzimidazole is not the electrolyte loss. In dynamic test mode, it was observed a rapid response of power and current output even at the lower step-time (10 s). In the static mode at 125 °C and 1 atm, the stack reached a power density peak of 0.29 W cm⁻² (43.5 W) at 1 V.     

Optimization of components and assembling in a PEM electrolyzer stack

An optimization study of components and assembling characteristics for a proton exchange membrane (PEM) short stack electrolyzer (3 cells of 100 cm² geometrical area) was carried out. The electrochemical properties were investigated by polarization, impedance spectroscopy and chrono-potentiometric measurements. A decrease of the ohmic contact resistance between the bipolar plates and the electrode backing layer was obtained by using an appropriate thickness for the gas diffusion layers/current collectors as well as by an optimization of stack compression. The amount of H₂ produced was ∼90 l h⁻¹ at 60 A (600 mA cm⁻²) and 75 °C under 300 W of applied electrical power. No significant leakage or gas recombination was observed. The stack electrical efficiency was 75% and 88%, at 60 A and 75 °C, with respect to the low and high heating value of hydrogen, respectively.     

A polymer electrolyte fuel cell life test: 3 years of continuous operation

Implementation of polymer electrolyte fuel cells (PEMFCs) for stationary power applications requires the demonstration of reliable fuel cell stack life. One of the most critical components in the stack and that most likely to ultimately dictate stack life is the membrane electrode assembly (MEA). This publication reports the results of a 26,300 h single cell life test operated with a commercial MEA at conditions relevant to stationary fuel cell applications. In this experiment, the ultimate MEA life was dictated by failure of the membrane. In addition, the performance degradation rate of the cell was determined to be between 4 and 6 μV h⁻¹, at the operating current density of 800 mA cm⁻². AC impedance analysis and DC electrochemical tests (cyclic voltammetry and polarization curves) were performed as diagnostics during and on completion the test, to understand materials changes occurring during the test. Post mortem analyses of the fuel cell components were also performed.     

Addressing LT-PEFC 15 cell stack durability using carbon semi-coated titania nanorods-Pt electrocatalyst

Optimum amount of carbon semi-coated on titania nanorods-Pt (Pt/CCT) electrocatalyst increases the cell performance and long term durability in low-temperature polymer electrolyte fuel cells (LT-PEFC). Semi-coated carbon on titania nanorods support (CCT) is synthesised hydrothermally followed by Pt deposited using polyol method. A thin metal loading of 150 μg cm⁻² with an active area of 50 cm² exhibits a high current of 49 ± 0.5 A at 0.6 V for 100 h without back pressure in H₂:O₂ configuration. In the present study, 5 and 15 cell LT-PEFC stacks and their engineering aspects towards development of indigenous cell fixture and assembly are explored in detail. The 5 cell stack durability at 5 A for 125 h shows a minimal voltage loss of 4 μV h⁻¹. In addition, 15 cell air cooled prototype indigenous fuel cell fixture is fabricated and demonstrated with electrical power of 310 W at 9 V. In a single cell, Pt/CCT retains 85% of initial current at 0.6 V during start-stop cycles (100 h) in H₂:air configuration as compared to Pt/C.     

Evaluation of Ni80Cr20/(La0.75Sr0.25)0.95MnO3 dual layer coating on SUS 430 stainless steel used as metallic interconnect for solid oxide fuel cells

Ni₈₀Cr₂₀/(La_0.75Sr_0.25)_0.95MnO₃ dual-layer coating is deposited on SUS 430 alloy by plasma spray for solid oxide fuel cell (SOFC) interconnect application. The phase structure, area specific resistance (ASR), and morphology of the coating are studied. A two-cell stack is also assembled and tested to evaluate coating performance in an actual SOFC stack. The NiCr/LSM coating adheres well to the SUS 430 alloy after oxidation in air at 800 °C for 2800 h. The ASR and its increasing rate of coated alloy are 25 mΩ cm² and 0.0017 mΩ cm²/h, respectively. In an actual stack test, the maximum output power density of the stack repeating unit increases from 0.32 W cm⁻² to 0.45 W cm⁻² because of the application of NiCr/LSM coating. The degradation rate of the stack repeating unit with no coating is 4.4%/100 h at a current density of 0.36 A cm⁻², whereas the stack repeating unit with NiCr/LSM coating exhibits no degradation. Ni₈₀Cr₂₀/(La_0.75Sr_0.25)_0.95MnO₃ dual-layer coating can remarkably improve the thermal stability and electrical performance of metallic interconnects for SOFCs.     

Preliminary experimental study of the performances for a print circuit board based planar PEMFC stack

This paper presents a novel planar proton exchange membrane fuel cell (PEMFC) stack designed for portable electronic devices, consisting of twenty homemade membrane electrode assemblies (MEAs) arranged on a planar surface and three printed circuit boards (PCBs, including anode, interlayer and cathode PCBs) used to load these MEAs. The current collectors and electrical connectors are manufactured using printed circuit technology. The inlet holes of reaction gases are also machined on PCB substrates. The output performance tests are performed on the MEAs and the assembled planar PEMFC stack. The results show that the power densities of the MEAs and the planar PEMFC stack are 0.6 W/cm² and 0.361 W/cm² at rated voltage under ambient temperature and forced convection air conditions, respectively. The stability tests are also conducted on the planar PEMFC stack, and the results show no significant fluctuations in output current. The feasibility of the application of planar PEMFC stacks in portable electronic devices is preliminarily demonstrated, and the improvement directions for further improving the output performance are proposed accordingly.     

A novel microbial fuel cell stack for continuous production of clean energy

Production of sustainable and clean energy through oxidation of biodegradable materials was carried out in a novel stack of microbial fuel cells (MFCs). Saccharomyces cerevisiae as an active biocatalyst was used for power generation. The novel stack of MFCs consist of four units was fabricated and operated in continuous mode. Pure glucose as substrate was used with concentration of 30 g l⁻¹ along with 200 μmol l⁻¹ of natural red (NR) as a mediator in the anode and 400 μmol l⁻¹ of potassium permanganate as oxidizing agent in the cathode. Polarimetry technique was employed to analyze the single cell as well as stack electrical performance. Performance of the MFCs stack was evaluated with respect to amount of electricity generation. Maximum current and power generation in the stack of MFC were 6447 mA.m⁻² and 2003 mW.m⁻², respectively. Columbic efficiency of 22 percent was achieved at parallel connection. At the end of process, image of the outer surface of graphite electrode was taken by Atomic Force Microscope at magnification of 5000. The high electrical performance of MFCs was attributed to the uniform growth of microorganism on the graphite surface which was confirmed by the obtained images.     

Demonstration of a 20 W class high-temperature polymer electrolyte fuel cell stack with novel fabrication of a membrane electrode assembly

Acid-doped polybenzimidazole (PBI) membrane and polytetrafluoroethylene (PTFE)-based electrodes are used for the membrane electrode assembly (MEA) in high-temperature polymer electrolyte fuel cells (HTPEFCs). To find the optimum PTFE content for the catalyst layer, the PTFE ratio in the electrodes is varied from 25 to 50 wt%. To improve the performance of the electrodes, PBI is added to the catalyst layer. With a weight ratio of PTFE to Pt/C of 45:55 (45 wt% PTFE in the catalyst layer), the fuel cell shows good performance at 150 °C under non-humidified conditions. When 5 wt% PBI is added to the electrodes, performance is further improved (250 mA cm⁻² at 0.6 V). Our 20 W class HTPEFC stack is fabricated with a novel MEA. This MEA consists of 8 layers (1 phosphoric acid-doped PBI membrane, 2 electrodes, 1 sub-gasket, 2 gas-diffusion media, 2 gas-sealing gaskets). The sub-gasket mitigates the destruction of a highly acid-doped PBI membrane and provides long-term durability to the fuel cell stack. The stack operates for 1200 h without noticeable cell degradation.     

Tuning of PEM fuel cell model parameters for prediction of steady state and dynamic performance under various operating conditions

Many models are available with various degrees of complexity to study the behaviour of Proton Exchange Membrane Fuel Cells (PEMFC) under varying operating conditions. To our knowledge no model has been developed from single cells to multiple cells with increased electrode area for PEMFC stacks along with power conditioners, by considering the dynamic characteristics of the fuel cells under the influence of stoichiometry, humidity ratio and their response during their integration with power conditioners. We have developed a model using Matlab to study the transient response of the cell for 30 cm², which has been extended to a multicell stack of 1.2 kW capacity of electrode area 150 cm². The developed model has been validated using PEMFC single cells and stacks, by considering partial pressure of hydrogen, oxygen, and water as three states, anode fuel utilization and all three losses. This model is proposed to evaluate the transient response of all the stacks developed at Centre for Fuel Cell Technology (CFCT) ranging from a few watts to 10 kW that are integrated with various power conditioners depending on the applications.     

Development of self-breathing polymer electrolyte membrane fuel cell stack with cylindrical cells

Self-breathing fuel cells use oxygen directly from the atmosphere and this eliminates the need of air fans and humidifiers, and as such enables applications where a reduction in size and volume of the power systems is important. Herein, we report a novel design and fabrication of a 12 celled cylindrical self-breathing stack made from stainless steel. A cylindrical geometry was implemented to permit higher self-breathing function and means to improve the Membrane Electrode Assembly compaction and thus reduce hydrogen leaks. The stack delivered a maximum voltage of 9.4 V and a maximum power of 1 W cm^?2 while operating under ambient condition (25 °C, 20% relative humidity and with dry hydrogen). The stainless steel bipolar plates provided enough compaction to the stack to minimize ohmic resistance and the hydrogen sealing was done with silicon gaskets which facilitated the stacking of the cells. The developed 12 celled stack delivered a volume power density of 29 W per litre which is 80% higher than previously reported self-breathing polymer electrolyte membrane fuel cells.     

The properties of the fuel electrode of solid oxide cells under simulated seawater electrolysis

In this study, electrolysis of seawater in flat-tube nickel-yttria-stabilized zirconia (Ni-YSZ) electrode-supported solid oxide electrolysis cells (SOECs) were modeled and the effects of variations in electrical conductivity and microstructure of Ni-YSZ electrode support were investigated. When the current density was greater than 700 mA·cm⁻², the conductivity of the electrode support decreased slightly with an increase in current density at 800 °C in hydrogen reduction environment; the conductivity of the electrode support decreased with an increase in the current density when the current density was greater than 400 mA·cm⁻² at 800 °C in the seawater electrolysis environment. During long-term durability experiment of seawater electrolysis, the degradation rates in area specific resistance (ASR) were 0.096 mΩ·cm²/100 h and 0.207 mΩ·cm²/100 h with a current density of 300 mA·cm⁻² (i.e., ≤400 mA·cm⁻²) and 1000 mA·cm⁻² (i.e., ≥400 mA·cm⁻²), respectively. Besides, the various ions commonly present in seawater did not contaminate the Ni-YSZ support during the long-term durability test. The degradation mechanism of seawater electrolysis in flat-tube SOECs is discussed and clarified.     

Stack performance of phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite high temperature proton exchange membrane fuel cells

In this paper, a series of short stacks with 2-cell, 6-cell and 10-cell employing phosphotungstic acid functionalized mesoporous silica (HPW-meso-silica) nanocomposite proton exchange membranes (PEMs) have been successfully fabricated, assembled and tested from room temperature to 200 °C. The effective surface area of the membrane was 20 cm² and fabricated by a modified hot-pressing method. With the 2-cell stack, the open circuit voltage was 1.94 V and it was 5.01 V for the 6-cell stack, indicating a low gas permeability of the HPW-meso-silica membranes. With the 10-cell stack, a maximum power density of 74.4 W (equivalent to 372.1 mW cm⁻²) occurs at 150 °C in H₂/O₂, and the stack produces a near-constant power output of 31.6 W in H₂/air at 150 °C without external humidification for 50 h. The short stack also displays good performance and stability during startup and shutdown cycling testing for 8 days at 150 °C in H₂/air. Although the stack test period may be too short to extract definitive conclusions, the results are very promising, demonstrating the feasibility of the new inorganic HPW-meso-silica nanocomposites as PEMs for fuel cell stacks operating at elevated temperatures in the absence of external humidification.     

Experimental investigation on the voltage uniformity for a PEMFC stack with different dynamic loading strategies

The operating life of the proton exchange membrane fuel cell stack is mainly decided by performances of its weakest single cell because of the “Buckets effect”, thus high voltage uniformity during a dynamic loading process is key to the stack durability. In this work, a 3-kW stack is examined experimentally on its voltage uniformity (voltage coefficient variation (Cv)) under conditions of loading from open-circuit state (0 A) to nominal current (165 A) and stack temperatures of 30 °C, 45 °C and 65 °C. Different dynamic loading strategies, namely constant loading rate strategy, decreasing loading rate strategy, and increasing loading rate (square/cube increasing loading rate) strategy, are examined and compared. Results display that during the loading process, (a) the voltage uniformity rises abruptly and goes down quickly when the loading current is small (e.g. from 0 A to 22 A), (b) the voltage uniformity under a small loading current is better than that under the open-circuit state, and (c) voltage uniformity decreases as the loading current increases from a small value to the nominal current. Comparisons of different current loading strategies show that as the stack temperature rises from 30 °C to 65 °C, the stack Cv value under the open-circuit state increases from 1.12 to 1.84 and decreases from 3.85 to 2.45 in the nominal current state. The maximum Cv for the decreasing loading rate strategy decreases from 16.25 to 9.49 and that of the constant loading rate strategy also decreases from 5.85 to 4.96. Cv values of the square current increasing loading rate strategy keep below 3.85 under conditions of the three stack temperatures and display a slight fluctuation during the whole current loading process, which indicates that the strategy can effectively make the stack being of an excellent voltage uniformity during the instantaneous response process.     

Lightweight current collector based on printed-circuit-board technology and its structural effects on the passive air-breathing direct methanol fuel cell

To realize lightweight design of the fuel cell system is a critical issue before it is put into practical use. The printed-circuit-board (PCB) technology can be potentially used for production of current collectors or flow distributors. This study develops prototypes of a single passive air-breathing direct methanol fuel cell (DMFC) and also an 8-cell mono-polar DMFC stack based on PCB current collectors. The effects of diverse structural and operational factors on the cell performance are explored. Results show that the methanol concentration of 6 M promotes a higher cell performance with a peak power density of 18.3 mW cm⁻². The combination of current collectors using a relatively higher anode open ratio and inversely a lower cathode open ratio helps enhance the cell performance. Dynamic tests are also conducted to reveal transient behaviors and its dependence on the operating conditions. To validate the real working status of the DMFC stack, it is coupled with an LED lightening system. The performance of this hybrid system is also reported in this study.     

Novel 3-D urchin-like Ni– Co–W porous nanostructure as efficient bifunctional superhydrophilic electrocatalyst for both hydrogen and oxygen evolution reactions

Fabrication of an electrocatalyst with remarkable electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is important for the production of hydrogen energy. In this study, Ni–Co–W alloy urchin-like nanostructures were fabricated by binder-free and cost-effective electrochemical deposition method at different applied current densities and HER and OER electrocatalytic activity was studied. The results of this study showed that the microstructure and morphology are strongly influenced by the electrochemical deposition parameters and the best electrocatalytic properties are obtained at the electrode created at the 20 mA.cm⁻²applied current density. The optimum electrode requires −66 mV and 264 mV, respectively, for OER and HER reactions for delivering the 10 mA cm⁻² current density. The optimum electrode also showed negligible potential change after 10 h electrolysis at 100 mA cm⁻², which means remarkable electrocatalytic stability. In addition, when this electrode used as a for full water splitting, it required only 1.58 V to create a current density of 10 mA cm⁻². Such excellent electrocatalytic activity and stability can be related to the high electrochemical active surface area, being binder-free, high intrinsic electrocatalytic activity and hydrophilicity. This study introduces a simple and cost-effective method for fabricating of effective electrodes with high electrocatalytic activity.     

Development of a novel portable-size PEMFC short stack with electrodeposited Pt hydrogen diffusion anodes

This paper presents, for the first time, a five-cell polymer electrolyte membrane fuel cell (PEMFC) short stack with electrodeposited hydrogen diffusion anodes. The anodes were manufactured by means of galvanostatic pulse electrodeposition and the cathodes by air-brushing. Nafion^® 212 was employed as a solid polymer electrolyte membrane in all cases. The short stack, whose cells had an active geometric area of 14 cm², was assembled and tested under different operating conditions. A peak power of about 11 W was obtained at 50 °C and atmospheric pressure using hydrogen and air feed, whereas a smaller value of 8.6 W was obtained from a five-cell short PEMFC stack with conventional hydrogen diffusion anodes under the same operating conditions. The better performance of the cells described in this paper has been assigned to the higher utilization of the platinum in the electrodeposited anodes compared to the conventional ones.     

Cu2S@NiFe layered double hydroxides nanosheets hollow nanorod arrays self-supported oxygen evolution reaction electrode for efficient anion exchange membrane water electrolyzer

Herein, we prepared highly active self-supported Cu₂S@NiFe layered double hydroxides nanosheets (LDHs) oxygen evolution reaction (OER) electrode (Cu₂S@NiFe LDHs/Cu foam) with three-dimensional (3D) multilayer hollow nanorod arrays structure, which is composed of the outer layer (two-dimensional (2D) NiFe LDHs) and the inner layer (one-dimensional (1D) Cu₂S hollow nanorod arrays). The unique structure of NiFe LDHs and Cu₂S hollow nanorod composites can expose more active sites, and simultaneously promote electrolyte penetration and gas release during the water electrolysis process. Thus, the Cu₂S@NiFe LDHs/Cu foam electrode exhibits a significant OER performance, with the overpotentials of 230 and 286 mV at 50 and 100 mA cm⁻², respectively. Anion exchange membrane water electrolyzer (AEMWE) with the prepared electrode can attain a voltage of 1.56 V at the current density of 0.50 A cm⁻², showing a good performance that is comparable to the-state-of-the-art AEMWE in 1 M KOH. In addition, the AEMWE can be run for 300 h at the current density of 0.50 A cm⁻². The high performance and good stability of AEMWE are attributed to the special structure of the OER electrode, which can prevent the agglomeration of nanosheets and thus expose more active sites at the edge of the nanosheets.