This study examines the performance of TiN-coated 304 stainless steel bipolar plates in air-breathing proton exchange membrane fuel cells (PEMFCs). A 1.0 mu m TiN coating was applied to SS304 and compared with graphite bipolar plates. Material characterization included impedance, contact resistance, water contact angle, and corrosion measurements. Long-term tests were conducted at 45 degrees C and 100 % relative humidity for hydrogen. Every 24 h, polarization curves and electrochemical impedance spectroscopy (EIS) were used to assess performance and degradation. A temperature-humidity control chamber and acidic environment were used to simulate fuel cell operating conditions. SEM and EDX spectra were applied to analyze coating degradation. Research results showed that TiN-coated SS304 had lower resistance, higher hydrophobicity, and greater corrosion resistance than uncoated SS304. The initial fuel cell performance was improved by 147 %, with a slower degradation rate due to a reduced ohmic resistance increase rate. After in a 3000-h simulated operation condition, a significant resistance changes were observed, and SEM/EDX spectra analysis revealed coating deterioration and substrate exposure. Overall, TiN coating significantly enhances the performance and durability of SS304 bipolar plates, making it a promising material for PEMFC applications.

Fuel cell technologies are eco-friendly, and thus they are developed to reach the global goal of net-zero carbon emissions. To increase the fuel cell CO tolerance and simplify purification processes of reformate fuel cell systems, the reformate high-temperature proton exchange membrane fuel cell (HTPEMFC) becomes one of the promising solutions. In this research, the effectiveness of air-bleeding on the CO tolerance improvement of HTPEMFCs is studied. The voltage signal-to-noise ratio (SNR) and electrochemical impedance spectroscopy analysis indicate that air-bleeding suppresses the CO poisoning reaction, reduces the poisoning intensity, and improves the stability of the HTPEMFC performance. The air-bleeding concentration for the HTPEMFC between 140-180 degrees C with CO of less than 5% is suggested to be 1-1.5%, because excess air does not enhance its effectiveness. The SNR analysis as well indicates that the working temperature and H-2 concentration affect the CO poisoning intensity more significantly than the air-bleeding concentration.

In this study, different coatings were applied to the bipolar plates (BPs) of proton-exchange membrane fuel cells (PEMFCs). The studied BPs materials include graphite, uncoated Al6061, Al6061 coated with single TiN (0.5 μm) layer, and different composite TiN/Ti layers. Experimental results show that the BP with TiN coating has a higher corrosion potential than those with TiN/Ti coatings, which implies TiN/Ti may have shorter operating life than TiN. The Al6061 with TiN (0.5 μm) has the lowest water contact angle among all the materials. As the Ti proportion on TiN increases, the water contact angle becomes greater, leading to better water removal ability and better fuel cell performance stability. The PEMFC performance with the Al6061 BPs coated with TiN/Ti (0.5μm/0.125 μm) is slightly better than that only coated with TiN. The appropriate thickness of Ti coating improves the PEMFC performance. The BPs made of uncoated Al6061 show the worst performance. After 480-h testing, the cell with uncoated Al6061 BPs has a significant performance degradation due to the increase of the ohmic resistance. The performance degradation rates with TiN/Ti and TiN coated BPs are slightly different, but both coatings significantly improve of the PEMFC life with Al6061 BPs.

An integrated system was developed to produce hydrogen-rich gas with low-level CO via autothermal reforming (ATR) of methanol for the purpose of real-time use in a kW-scale proton exchange membrane fuel cell (PEMFC) system. Methanol was converted into a hydrogen-rich gas through ATR in conjunction with water gas shifting (WGS) and preferential oxidation (PrOX) reactors to reduce the CO concentration. A 29.5% hydrogen-rich gas with a CO concentration of approximately 20 ppm was achieved under the optimal parameter settings (i.e., an H2O/CH3OH ratio = 0.5 and an O-2/CH3OH ratio = 0.55 for the ATR reaction, an H2O/CO ratio = 5.6 for the WGS reaction, and an O-2/CO ratio = 1.08 for the PrOX reaction). Specifically, the reformer system steadily produced low CO, hydrogen-rich gas after 4 h of durability testing. This system was then combined with 40-cell fuel cell stacks with air bleeding and tested for its durability over a period of 6 h. It was verified that the hydrogen-rich gas produced by the reformer system enabled the fuel cell to steadily generate 1040 W of power. Notably, the hydrogen-rich gas (the actual reformate gas) produced herein could generate better performance than the simulated reformate gas reported in the literature. (C) 2021 Elsevier Ltd. All rights reserved.

The high temperature proton exchange membrane (HT-PEM) fuel cell using metal bipolar plates (BPs) can solve some challenges of traditional PEM fuel cells, including low CO tolerance and high BP cost. To improve its operating life, understanding the deterioration phenomena of the HT-PEM fuel cells using bare metal BPs is necessary. This work studies this fundamental subject and verifies the reasons for the cell deterioration. The experimental results indicate that the cell power with bare SS304 BPs decreases by about 53.5%, and the total cell resistance increases by about 92.5% after a continuous 384-h operation. The increase in the electrical resistance of the BPs due to formation of a passivation film on the SS304 surface is the major reason for the deterioration phenomena. Moreover, the cathodic BP after a continuous operation has a larger rugged surface area and a wider O and P elements distribution than the anodic BP, because of more produced water and more phosphoric acid leaks on the cathode side during operation, which causes more serious oxidation and corrosion problems. A stricter anti-corrosion criterion for the cathodic metal BP may be needed for this type of fuel cell.

In the present study, the performance of a planar membrane humidifier for proton exchange membrane fuel cell is evaluated experimentally for different channel structures. For this purpose, three performance indices including water flux, water recovery ratio (WRR), and pressure loss are employed. The measured results disclose that the humidifier using counter flow approach and the channel with width of 1 mm and depth of 1.5 mm has the best overall humidification performance in this work. Increasing the channel depth increases the water flux and therefore increases the WRR of the humidifier. Moreover, the pressure loss decreases with increasing the channel depth because the friction factor at an identical flow rate decreases with increasing the hydraulic diameter of the flow channel. Increasing the channel width expands the contact area with the membrane, leading to an improvement of heat and water vapor transfer. Thus, a higher WRR and pressure loss can be obtained at elevated channel widths. Both depth and width of the channel must be taken into precise consideration in order to minimizing the pressure loss and maximizing the heat and mass transfer. (C) 2020 Elsevier Ltd. All rights reserved.

The present study aims to examine the effect of nitrogen and carbon monoxide concentrations as well as the working temperature and the stoichiometry number on the performance of a self-made five-cell high-temperature Proton-exchange membrane fuel cell stack (PEMFC). The concentration of hydrogen in a reformed gas can be varied, and it may contain poisonous substances such as carbon monoxide. Hence, the composition of the fuel gas could affect the performance of the PEMFC. The polarization curve and the electrochemical impedance spectrogram are utilized to examine the behaviors of PEMFC. The cell temperature of 160 degrees C is found as an optimal working temperature in this study for high-temperature PEMFC. Measured results show that the stoichiometry of the anode gas has a minimal effect on the PEMFC performance. A high percentage of nitrogen makes hydrogen dilute and leads to poor cell performance. When carbon dioxide exceeds 3%, the pt-catalyst was covered with the CO and the cell performance significantly decreased. Finally, a raise of the PEMFC temperature boosted the catalyst energy and improved the detachment of the carbon monoxide and eventually enhanced carbon monoxide tolerance. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Air-breathing is known as a way to reduce the weight, volume, and the cost of PEMFCs. In this study, the thermal management of the high-powered air-breathing PEMFC stacks by applying different cathode flow channel configurations is carried out to improve the stack performance. In order to verify the thermal management results, numerical simulation is also performed. The research results show that a combination of the 50% and 58.3% opening ratios in the air-breathing stack reduces the stack temperature and enhances the temperature distribution uniformity, leading to a better and more stable stack performance. In addition, it is found that the stack performance is significantly improved under the assisted-air-breathing condition. Moreover, the simulation results and the experimental data are basically consistent. It is suggested to adopt the average temperature over the cross-sectional flow region from simulation as fitting the simulation results and the measured data.

Removing excessive moisture from the ambient air by means of a selective membrane in the membrane-based dehumidifier has become a new emerging technology. The present study pertains to the experimental work on heat and mass transfer of a multi-stage planar membrane dehumidifier. Commercial Nafion 212 membranes are applied in this membrane dehumidification system because of the large selectivity. The operating conditions of inlet dry air are fixed to maintain at temperature of 27 degrees C and relative humidity of 0.1% while performing dehumidification tests. Attention is mainly paid to examining the effects of various temperature, relative humidity and flow rate of the wet side inlet air on performance indexes including the dehumidification rate (DR), dew point approach temperature (DPAT), pressure loss (Delta P), and pumping power (Omega) in planar membrane-based dehumidifiers. Measured results show that increasing inlet temperature, relative humidity and flow rate of humid air in the wet channel enhances performance indexes, that is, higher DR, DPAT, AP and n. In addition, the counter flow configuration in the dehumidifier provides better mass and heat transfer performance compared to parallel flow configuration. (C) 2019 Elsevier Ltd. All rights reserved.

The research and development of humidifiers is important to proton exchange membrane fuel cell systems. The water exchange membrane is a key component to the planar membrane humidifier. In this work, two types of low-cost membrane, the pervaperation (PV) membrane and the reverse osmosis (RO) membrane, are selected as the research targets. Their physical properties and humidification performance are tested and compared with the Nafion (R)-212 membrane. The ex-situ tests indicate that the order of air permeability is RO membrane > Nafion (R) 212 membrane > PV membrane, and the order of water vapor permeability is RO membrane similar to Nafion (R) 212 membrane > PV membrane. From the in-situ tests, the order of humidification performance is Nafion (R) 212 membrane > RO membrane > PV membrane at all air flow rates. The DPATs with the RO and PV membranes are roughly 1-2 degrees C and 2-3 degrees C higher than that with the Nafion (R) 212 membrane, respectively. The highest WRRs obtained at 30 L/min with the Nafion (R) membrane, RO membrane and the PV membrane are about 53%, 48% and 42%, respectively. The Nafion (R) membrane is most energy-efficient because it has the highest COP. Moreover, the PV and RO membranes are equally energy-efficient when considering both the water transfer performance and the power loss. (C) 2019 Elsevier Ltd. All rights reserved.

Applying metallic bipolar plates on high temperature proton exchange membrane fuel cells, which are practical for stationary applications, is a considerable option to reduce the cost and to improve the specific power of this type of fuel cell. To understand the life issue of the high temperature proton exchange membrane fuel cells with metallic bipolar plates, the performance degradation phenomena with graphite, uncoated 304 stainless steel, and gold coated 304 stainless steel bipolar plates are studied and compared. The experimental results show that the order of performance degradation rate is uncoated 304 stainless steel > gold coated 304 stainless steel graphite. The faster performance degradation of the high temperature proton exchange membrane fuel cells with uncoated 304 stainless steel bipolar plates can be attributed to the dramatic increase in the ohmic resistance, which is due to the formation of ferric oxide and iron phosphate on the metal surface. In addition, gold coating peels off from the stainless steel bipolar plate after a 432-hr operation. A coating layer with an improved life is still needed to further extend the operating life of this type of fuel cell. (C) 2019 Elsevier Ltd. All rights reserved.

The influence of channel dimension and altering dry air inlet conditions such as temperature and humidity on the humidification efficiency of a multi-stage plate-type membrane humidifier for kW-scale proton exchange membrane fuel cells is analyzed in terms of the dew point approach temperature, water recovery ratio, pressure loss, and the coefficient of performance, Investigating the effect of channel dimension reveals that the width and depth of the channel significantly affect the humidification performance. The results show that the increase of dry air inlet temperature and humidity leads to improving the dew point approach temperature, decreasing the water recovery ratio, slight increasing the pressure drop, and consequently decreasing the coefficient of performance. The minimum dew point approach temperature and maximum water recovery ratio occur at the flow rate of 30 L/min. The highest water recovery ratio, 73%, is achieved at the temperature of 50 degrees C and relative humidity of 40%. Moreover, the pressure loss increases with the increment of air flow rate and the coefficient of performance declines with the increase of air flow rate. Thus, it is recommended to select the minimum possible flow rate, dry air inlet temperature, and relative humidity as the efficient operating condition.

The objective of this work is to study a high-temperature proton exchange membrane fuel cell using CO- and methane-containing hydrogen-rich gases because of the advantages of high operating temperature and the growing feasibility of using natural gases or methane as the sources of hydrogen-rich reformate gases. According to the experimental results, it is suggested that the fuel cell be operated at 180 °C under reformate gases with high CO concentrations to avoid not only a significant decrease in performance, but also severe potential oscillations. In addition, the anode oxidation reaction is more sensitive to the temperature than the cathode reduction reaction under CO-containing H2. On the other hand, the effects of methane in the reformate gas on the fuel cell can be ignored because the existence of methane causes neither a decrease in the cell performance nor an increase in the anodic charge transfer resistance. Thus, the CO concentration and operating temperature are still the two dominant parameters with regard to the cell performance under CO- and methane-containing hydrogen-rich gases.

In this work, a high temperature proton exchange membrane fuel cell (HT-PEMFC) with stamped SS304 bipolar plates is successfully developed. Its performance was evaluated under two types of gaskets at different assembly torques and air stoichiometric ratios. The rates of pressure loss at a torque of 7 N-m with 50 Shore A hardness gaskets was 2.0 x 10(-3) MPa min(-1), which is acceptable. The best performance of the developed HT-PEMFC with stamped SS304 bipolar plates was 228.33 mW cm(-2), which approaches the performance of HT-PEMFCs with graphite bipolar plates. The optimal air stoichiometric ratio for the HT-PEMFC with stamped SS304 bipolar plates was 4.0, which is higher than that for proton exchange membrane fuel cells with CNC milled graphite bipolar plates. This is probably because of the deformation of the flow channels under the assembly compression force, which causes an elevated gas-diffusion drag in the flow channels. After the test, it was observed that some products of corrosion reaction formed on the surface of the SS304 bipolar plate. This phenomenon may lead to a decrease in the operating life of the HT-PEMFC. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

In this work, a proton exchange membrane fuel cell with stamped 304 stainless steel bipolar plates is successfully assembled, The total weight of the bipolar plates, membrane electrode assembly and gaskets in the fuel cell is reduced by 37% when replacing milled graphite plates by the stamped 304 stainless steel plates. Moreover, the gas leaking rates and electrochemical characteristics of the fuel cell at different assembly torques are studied. It is found that increasing the torque increases the sealing performance. However, an excess torque (>6 N-m) decreases the power due to a decrease in the porosity and hydrophobicity of the gas diffusion layer, and a deformation of the flow channels in the metallic plate. The pressure loss rate declines by 56% as the torque increases from 2 N-m to 7 N-m. The best performance is obtained at 6 N-m. The cell performance increases by about 21% as the torque increases from 2 N-m to 6 N-m. However, the performance decreases by about 11% as the torque further increases from 6 N-m to 7 N-m. The suspected reason for the above phenomenon is verified via the electrochemical impedance spectroscopies and the microscopic images of the gas diffusion layer. (C) 2018 Elsevier Ltd. All rights reserved.

The proton exchange membrane fuel cell (PEMFC) becomes more important as an alternative energy source recently. Maintaining proper water content in the membrane is one of the key requirements for optimizing the PEMFC performance. The planar membrane humidifier has the advantages of simple structure, low cost, low pressure drop, light weight, reliable performance and good gas separability. Thus, it is a common external humidifier for PEMFCs. In this work, a planar membrane humidifier for kW-scale PEMFCs is developed successfully. The heat and mass transfer of humidifier is discussed and its performance is analyzed in term of dew point approach temperature (DPAT), water vapor transfer rate (WVTR) and water recovery ratio (WRR). The DPAT of the humidifier with the counter flow approach reaches about 6 degrees C under inlet dry air of 50 degrees C and 60% RH and inlet humid air of 70 degrees C and 100% RH. The rate of pressure loss of the humidifier is 5.0 x 10(2) Pa/min at the torque of 7 N m, which reaches the standard of commercial planar membrane humidifiers. From the tests, it is found that increasing the air flow rate increases the WVTR. However, the DPAT and the WRR are not improved by increasing the WVTR as the air flow rate is higher than the optimal value. In addition, increasing the inlet temperature or the humidity of dry air decreases the WVTR and the WRR. Nevertheless, the DPAT is improved at elevated inlet temperatures or humidities of dry air. Furthermore, the performance of the humidifier with the counter flow approach is better than that with the parallel flow approach. The DPAT difference between the two flow approaches reaches up to 8 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.

In the study, a self-made kW-class 40-cell proton exchange membrane fuel cell (PEMFC) stack, with an active area of 112.85 cm(2) for each membrane electrode assembly and with the anodic Pt-Ru catalyst, was tested under different simulated reformate gases of different CO concentrations and different hydrogen concentrations. The performances and the transient voltages of the stack and the individual cells under different CO/N-2/H-2 mixtures were studied. The results show that increasing the CO concentration or decreasing the H-2 concentration of the CO-contained reformate gas negatively affects the performance of the PEMFC stack. Moreover, the PEMFC stack with the Pt-Ru anodic catalyst can tolerate a CO concentration of up to 50 ppm under non-diluted H-2. However, it can only tolerate 10 ppm CO under diluted H-2. The CO tolerance decreases dramatically with an increase in the H-2 dilution level. In addition, increasing the CO concentration in diluted H-2 or decreasing the H-2 concentration in CO-contained H-2 accelerates the occurrence of potential oscillation. The potential oscillation is owing to the interactions of CO electro-oxidation and adsorption reactions on the catalyst. This work is also the first to report that the potential oscillation phenomenon initially occurs at the upstream cells of the stack. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Although an air-cooled proton exchange membrane fuel cell stack is usually designed below 1 kW because of the cooling capacity limit, development of a high power air-cooled stack is still necessary. In this work, an air-cooled proton exchange membrane fuel cell stack with the maximum power of 2.55 kW is successfully developed. The efficiency of the fuel cell stack is 43.1% at the maximum output power. The maximum heat flux through the cooling channel of the stack is estimated to be 2.61 x 10(3) W m(-2) and the average rate of heat transfer through an individual cooling channel is 1.5 W. The performance tests at different stoichiometric ratios and the electrochemical impedance spectroscopy measurement at various stack temperatures and dew point temperatures were carried out. A synchronous measurement of the electrochemical impedance spectroscopy (EIS) of all 40 cells was also carried out to understand the EIS distribution throughout the stack. The experimental results show that an appropriate combination of operational parameters can avoid a high stack resistance and a non-uniform resistance distribution throughout the stack. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.