An advanced sulfonated poly(ether ether ketone) (sPEEK)-based multi-layer composite membrane with high performance and durability is fabricated, which consists of a porous sPEEK base membrane, two transition layers (TLs) and two PFSA outer layers (PLs). These porous sPEEK base membranes with nanoscale pores are prepared first through a vapor induced phase inversion (VIPI) method. Owing to the higher porosity and the denser distribution of sulfonic acid clusters, the cell performance and physical properties of porous sPEEK membranes are superior to those of sPEEK membranes prepared by a solvent casting method. The multi-layer structure of this composite membrane results in reduced swelling and improved water uptake, and eventually brings about a high proton conductivity. Single cell tests indicate that the multi-layer composite membrane has a higher cell performance and more outstanding durability in comparison with sPEEK membranes. The growth rate of hydrogen crossover current density of this composite membrane is much lower than that of sPEEK membranes, proving the effectiveness of PLs in improving the chemical durability of sPEEK-base membranes. After long-term stability tests, the sPEEK multi-layer composite membrane still shows a good cell performance, especially at low relative humidity (RH).

A novel PEMFC electrode (E-U electrode) with ultralow platinum is prepared by electrospinning and underpotential deposition techniques. The platinum skin (Ptskin) is in situ deposited on the surface of Pd nanoparticle in the electrospun Pd/C catalyst layer. The energy-dispersive X-ray spectroscopy (EDS) mapping of the cross-section of a single fiber confirms that the distribution of Pd/C@Ptskin catalysts and Nafion® ionomer matches well in the E-U electrode. The high porosity and large electrochemical surface area (ECSA) of the E-U electrode mitigates the oxygen transfer resistance. The peak power density of the E-U electrode arrives at 0.62 W cm−2 with a Pt loading of 19 μg cm−2, which is higher than that of the conventional electrode (0.55 W cm−2) with a Pt loading of 100 μg cm−2. The degradation rate of peak power density of the E-U electrode is only 4.8% after accelerated stability test (AST) for 30000 cyclic voltammetry (CV) cycles, demonstrating a better durability than that of the conventional electrode. The enhanced durability of the E-U electrode is attributed to nanofiber structure and interaction between Pd and Pt in the Pd/C@Ptskin catalyst.

•An advanced multi-layer composite membrane with low-cost and high durability•TLs improve the interfacial compatibility between SPEEK and PLs, avoiding the delamination problem.•PLs formed by PFSA ionomer can protect the SPEEK base membrane against the chemical degradation.•Higher durability of this multi-layer composite membrane under accelerated open circuit voltage (OCV) tests is confirmed.Multi-layer composite membrane with low-cost and high durability is prepared via hot-spraying methods for proton exchange membrane fuel cell (PEMFC) applications, which consists of a mid layer of sulfonated poly(ether ether ketones) (SPEEK), two transition layers (TLs) and two PFSA outer layers (PLs). Here, PLs can protect SPEEK membrane against the chemical degradation from reactive oxygen species and endow the composite membrane with high chemical stability. TLs improve the interfacial compatibility between SPEEK membrane and PLs, avoiding the delamination problem. This multi-layer composite membrane exhibits a proper ion-exchange capacity (IEC) and higher proton conductivity compared with that of SPEEK membrane, and it also keeps a balance between water uptake and swelling ratio owing to the presence of the multi-layer structure. Besides, the lower cost of the composite membrane is confirmed due to the small content of Nafion. Single cell tests indicate that the multi-layer composite membrane has better cell performance than that of SPEEK membrane. The higher durability for the membrane under accelerated open circuit voltage (OCV) tests reveals the effectiveness of this multi-layer composite strategy in improving the chemical durability of the SPEEK membrane.

Arc ion plating (AIP) is applied to form Ti/(Ti,Cr)N/CrN multilayer coating on the surface of 316L stainless steel (SS316L) as bipolar plates for proton exchange membrane fuel cells (PEMFCs). The characterizations of the coating are analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Interfacial contact resistance (ICR) between the coated sample and carbon paper is 4.9 mΩ cm2 under 150 N/cm2, which is much lower than that of the SS316L substrate. Potentiodynamic and potentiostatic tests are performed in the simulated PEMFC working conditions to investigate the corrosion behaviors of the coated sample. Superior anticorrosion performance is observed for the coated sample, whose corrosion current density is 0.12 µA/cm2. Surface morphology results after corrosion tests indicate that the substrate is well protected by the multilayer coating. Performances of the single cell with the multilayer coated SS316L bipolar plate are improved significantly compared with that of the cell with the uncoated SS316L bipolar plate, presenting a great potential for PEMFC application.Download high-res image (112KB)Download full-size imageTi/(Ti,Cr)N/CrN multilayer coating was deposited on the surface of 316L stainless steel bipolar plate with interfacial contact resistance reduced and corrosion resistance improved.

A Fe–N–C catalyst, synthesized with porous carbon BP2000, the nitrogen source imidazole and iron source FeCl3, is developed for SO2 electrooxidation through a series of thermal and pyrolytic disposing processes. The electrochemical measurements of linear sweep voltammograms (LSV) and cyclic voltammograms (CV) are applied to investigate the SO2 oxidation performance of the catalyst. The results show that the half-wave oxidation potential of Fe–N–C is 283.8 mV lower than that of BP2000 meanwhile the onset oxidation potential reduces 58 mV as well, implying there is a highly improved SO2 oxidation performance of the catalyst. The structural and physical characteristics of the Fe–N–C catalyst are examined by the methods of TEM, XPS, XRD and Raman spectroscopy. The characterization proves the formation of graphitic carbon, iron carbides, single-layer graphene and defects as well as the existence of FeN/Fe2N, pyridinic N and Fe–N components on the prepared Fe–N–C catalyst, which are supposed to have significant effects on the SO2 electrooxidation performance.

•Nitrogen-doped graphite was fabricated via one-step pyrolysis of sugar and urea.•Nitrogen-doped graphite exhibited activity for electrooxidation of sulfur dioxide.•The electrocatalytic activity positively related to the pyrolysis temperature.•The electrooxidation reaction was irreversible and diffusion controlled.This work reports on the electrochemical oxidation of sulfur dioxide on nitrogen-doped graphite (NG) in acidic media. The NG samples were prepared via one-step pyrolysis of the mixtures of sugar and urea at 700–1000 °C in argon atmosphere. Mechanism analysis indicated that the electrochemical oxidation reaction of sulfur dioxide on NG was irreversible and diffusion controlled. Moreover, the influence of pyrolysis temperature on the electrocatalytic activity of NG was also investigated. The electrochemical measurement and physical characterization results revealed that elevating the pyrolysis temperature could enhance the electrocatalytic activity of NG, which might ascribe to the improved surface area, graphitization degree and electrical conductivity.

Antimony doped tin oxide (ATO), a kind of semiconducting nanocrystalline material, has excellent electrochemical stability but poor electrical conductivity. Herein, ATO nanocomposites with carbon coatings are prepared by immersing ATO nano-material into dopamine solution, and then thermal treatment to improve the electrical conductivity of the ATO material. The morphology and microstructure of ATO@C/N nanocomposites are characterized using a scanning electron microscope and transmission electron microscopy. The GDLs with the MPL prepared from ATO@C/N nanocomposites are characterized by through-plane resistance testing, mercury intrusion porosimetry and surface contact angle measurement. The results of the above show that ATO@C/N nanocomposites with a 2.16 nm thick carbon coating enhance the electrical conductivity of ATO nanocrystals and exhibit higher electrochemical stability. Further, the performance of MEA fabricated with ATO@C/N as the cathode MPL is evaluated. The maximum power density approaches 1000 mW cm−2, and a slight difference in cell performance is observed compared to XC-72.

•The GDL with in-situ grown CNTs on the fibrous carbon paper is fabricated.•A CNT/GDL with proper hydrophobicity and pore structure is obtained.•PEMFC with CNT/GDL shows better performance than the one with CB/GDL.The performance of proton exchange membrane fuel cell (PEMFC) is greatly influenced by the characteristics of gas diffusion layer (GDL). Herein, in situ grown carbon nanotubes (CNTs) on carbon paper as a gas diffusion layer (GDL) were fabricated by a plasma-enhanced chemical vapor deposition (PECVD) process. Fuel cells using CNT-based GDLs with nickel (II) nitrate loading of 1.6 mg cm−2 show better performance compared with the GDLs which employ Vulcan XC-72 as the MPL. The pore size distribution and the gas permeability results revealed that the increasing density of CNT layer had two main effects on the pore structure of GDL: firstly, the increasing density of CNT layer decreased the macro pore volume and the open through pore volume of CNT-based GDL; secondly, the increasing density of CNT layer decreased the micro pore diameter of CNT-based GDL. The data obtained from the vapor permeability and the fuel cell performance tests indicated that the water flooding can be reduced by applying CNT-based GDLs. The electrochemical impedance spectroscopy (EIS) confirmed that the CNT-based GDL can effectively promote the mass transfer in the FCs which was attributed to its suitable hydrophobicity and proper structure.

•Local current firstly degrades at anode outlet region, then proceeds to the inlet.•The fuel starvation leads to a high cathode potential and carbon corrosion.•SEM images reveal thickness reduction and porous structure collapse.•The dominant factor, leading to the performance decay, is the nitrogen crossover.Proton exchange membrane fuel cells (PEMFCs) with a dead-ended anode (DEA) can obtain high hydrogen utilization by a comparatively simple system. Nevertheless, the accumulation of the nitrogen and the water in the anode channels can lead to a local fuel starvation, which degrades the performance and durability of PEMFCs. In this paper, the behaviors of PEMFCs with a DEA are explored experimentally by detecting the current distribution and the local potentials. The results indicate that the current distribution is uneven during the DEA operation. The local current firstly decreases at the region near the anode outlet, and then extends to the inlet region along the channels with time. The complete fuel starvation near the anode outlet leads to a high local potential and carbon corrosion on the cathode side. The SEM images of the cathode electrode reveal that the significant thickness reduction and the collapse of the electrode's porous structure happen in the cathode catalyst layer, leading to the irreversible decline of the performance. The comparison of the experiments with different oxidants and fuels reveals that the nitrogen crossover from cathode to anode is the dominant factor on the performance decline under the DEA operations.

Tin oxide nanocluster (SnO2) with parallel nanorods was synthesized via a hard template method and explored as the anode catalyst support for proton exchange membrane fuel cells (PEMFCs). Single cell test demonstrated that SnO2 supported Pt catalyst (Pt/SnO2) exhibited comparable anode performance with conventional Pt/C. Electrochemical measurements showed that Pt/SnO2 exhibited significantly enhanced electrochemical stability than Pt/C under high potential electro-oxidation and potential cycling. The Pt/SnO2 catalyst reserved most of its electrochemically active surface area (ECA) under 10 h potential hold at 1.6 V while its ECA degradation rate was one order of magnitude lower than Pt/C under potential cycling between 0.6 and 1.2 V. Therefore, SnO2 nanocluster can be considered as a promising alternative anode catalyst support for PEMFCs.

CrN/Cr multilayer coating is prepared on 316L stainless steel as bipolar plates for proton exchange membrane fuel cell (PEMFC) by pulsed bias arc ion plating (PBAIP). Interfacial conductivity of the bipolar plate with CrN/Cr multilayer is improved obviously, presenting an interfacial contact resistance (ICR) of 8.4 mΩ cm−2 under 1.4 MPa. The results tested by potentiodynamic and potentiostatic measures in simulated PEMFC environments show that the bipolar plate with CrN/Cr multilayer has good anticorrosion performance. The corrosion current density of the bipolar plate with CrN/Cr multilayer is approximately 10−8.0 A cm−2 at 0.6 V (vs. SCE) in a 0.5 M H2SO4 + 5 ppm F− solution at 70 °C with pressured air purging. The results of SEM and ICR before and after corrosion tests indicate that the bipolar plate with CrN/Cr multilayer is considerably stable electrochemically. The bipolar plate with CrN/Cr multilayer combined the prominent interfacial conductivity and the excellent corrosion resistance, showing great potential of application in PEMFC.Highlights► The structure of CrN/Cr multilayer was designed to improve the anticorrosion and yields good results as anticipated. ► The bipolar plate with CrN/Cr multilayer exhibits prominent interfacial conductivity and excellent corrosion resistance. ► The results of SEM and ICR before and after corrosion tests indicate that the bipolar plate with CrN/Cr multilayer is considerably stable electrochemically.

SO2, a pollutant in air, can cause a serious degradation of the proton exchange membrane fuel cell (PEMFC) performance. After direct exposure to 1 ppm SO2-air for 50 h, the cell voltage degraded by 28%. In order to cope with this problem, an electrochemical filter was fabricated and used for SO2 removal on-board in this study. The modified carbon felt was used as the filter anode. The effect of the applied voltages on the SO2 removal was investigated, and the cell performance was further tested both with and without the filter. When an external voltage of 0.5 V was applied across the filter, the cell voltage had no obvious decrease during the 240 h test, and cycle voltammery (CV) measurements showed that SO2 was not adsorbed on the cell cathode. The electrochemical filter successfully protected a single cell from being poisoned by 1 ppm SO2-air for more than 240 h.Highlights► An electrochemical filter is designed and fabricated for the PEMFC application. ► The mechanism of SO2 removal at the filter anode is investigated with linear sweep operations. ► The filter successfully protects a single cell from being poisoned by 1 ppm SO2-air for more than 240 h.

As one of the most deleterious impurities to proton exchange membrane fuel cells (PEMFCs), sulfur dioxide (SO2) in air can pass through the membrane from the cathode to the anode and poison the catalyst of the two electrodes. The phenomenon of SO2 crossover is investigated electrochemically in this paper. The influences of SO2 concentration, relative humidity, gas pressure and current density on SO2 crossover are discussed. Experimental results reveal that the anode tends to be poisoned heavily with the increasing concentration of SO2 in the cathode. The coverage of the anode catalyst by SO2 permeating from the cathode enlarges with the decreasing relative humidity in the anode. The rate of SO2 crossover from the anode to the cathode is promoted at high current density when SO2 is directly introduced into the anode side instead of the cathode side, which can be ascribed to the electro-osmotic drag effect. Gas pressures show no obvious effects on SO2 crossover. A co-permeation mechanism of SO2 with water is deduced based on the overall analysis.Research highlights▶ The phenomenon of SO2 crossover in PEMFCs is investigated electrochemically. ▶ The influences of SO2 concentration, relative humidity, gas pressure and current density on SO2 crossover are discussed. ▶ A co-permeation mechanism of SO2 with water is deduced based on the overall analysis.

Durability is an important issue in proton exchange membrane fuel cells (PEMFCs) currently. Reactant starvation could be one of the reasons for PEMFC degradation. In this research, the oxidant starvation phenomena in a single cell are investigated. The local interfacial potential, current and temperature distribution are detected in situ with a specially constructed segmented cell. Experimental results show that during the cell reversal process due to oxidant starvation, the local interfacial potential in the oxidant inlet keeps positive while that of the middle and outlet regions become negative, which illustrates that oxygen and proton reduction reactions could occur simultaneously in different regions at the cathode. The current distribution would be more uneven with decreasing air stoichiometry before cell reversal. When cell reversal occurs, the current will redistribute and the current distribution tends more uniform. At the critical point of cell reversal, the most significant inhomogeneity in the current distribution can be observed. The temperature distribution in the cell is also monitored on-line. The local hot spot exists in the cell when cell reversal occurs. The study of the critical reversal air stoichiometry under different loads shows that the critical reversal air stoichiometry increases with the rising loads.Research highlights▶ The in situ measurement of local interfacial potentials has been utilized to study the cell reversal process during oxidant starvation. ▶ The negative interfacial potential is observed near the outlet of cathode and the current distribution appears inhomogeneous when the oxidant starvation occurs. ▶ The local hot spots appear at the cathode air inlet when the cell reversal takes place, which could be one of the reasons for MEA degradation.

Durability is an important issue in proton exchange membrane fuel cells (PEMFCs) currently. Fuel starvation could be one of the reasons for PEMFC degradation. In this research, the fuel starvation conditions of a unit cell in a stack are simulated experimentally. Cell voltage, current distribution and localized interfacial potentials are detected in situ to explore their behaviors under different hydrogen stoichiometries. Results show that the localized fuel starvation occurs in different sections at anode under different hydrogen stoichiometries when the given hydrogen is inadequate. This could be attributed to the “vacuum effect” that withdraws fuel from the manifold into anode. Behaviors of current distribution show that the current will redistribute and the position of the lowest current shifts close to the anode inlet with decreasing hydrogen stoichiometry, which indicates that the position of the localized fuel starvation would move towards the inlet of the cell. It is useful to understand the real position of the degradation of MEA.Highlights► The effect of manifold on the single cell suffered from fuel starvation in a stack is studied. ► The actual hydrogen stoichiometry is almost 1 even though the fed hydrogen is not sufficient due to the “vacuum effect”. ► The position where localized fuel starvation occurs firstly gets closer to the anode inlet (not always outlet) with the decrease of hydrogen stoichiometry.

Titanium with excellent corrosion resistance, good mechanical strength and lightweight is an ideal BPP material for unitized regenerative fuel cell (URFC), but the easy-passivation property accordingly results in poor cell performance. Surface modification is needed to improve the interfacial conductivity. In this study, Ti–Ag film is prepared on TA1 titanium as bipolar plates for URFC by pulsed bias arc ion plating (PBAIP). Interfacial conductivity of Ti–Ag/Ti is improved obviously, presenting an interfacial contact resistance of 4.3 mΩ cm2 under 1.4 MPa. The results tested by potentiodynamic, potentiostatic and stepwise potentiostatic measures in simulated URFC environments show that Ti–Ag/Ti has good anticorrosion performance, especially at high potential. The corrosion current density of Ti–Ag/Ti is approximately 10−5.0 A cm−2, similar to that of uncoated titanium, at 2.00 V (vs. NHE) in a 0.5 M H2SO4 + 5 ppm F− solution at 70 °C with pressured air purging. Ti–Ag/Ti sample also has low surface energy. The contact angle of the sample with water is 102.7°, which is beneficial for water management in URFC. The bipolar plate with cost-effective Ti–Ag film combines the prominent interfacial conductivity with the excellent corrosion resistance at high potential, showing great potential of application in URFC.

In this research, the fuel starvation phenomena in a single proton exchange membrane fuel cell (PEMFC) are investigated experimentally. The response characteristics of a single cell under the different degrees of fuel starvation are explored. The key parameters (cell voltage, current distribution, cathode and anode potentials, and local interfacial potentials between anode and membrane, etc.) are measured in situ with a specially constructed segmented fuel cell. Experimental results show that during the cell reversal process due to the fuel starvation, the current distribution is extremely uneven, the local high interfacial potential is suffered near the anode outlet, hydrogen and water are oxidized simultaneously in the different regions at the anode, and the carbon corrosion is proved to occur at the anode by analyzing the anode exhaust gas. When the fuel starvation becomes severer, the water electrolysis current gets larger, the local interfacial potential turns higher, and the carbon corrosion near the anode outlet gets more significant. The local interfacial potential near the anode outlet increases from ca. 1.8 to 2.6 V when the hydrogen stoichiometry decreases from 0.91 to 0.55. The producing rate of the carbon dioxide also increases from 18 to 20 ml min−1.

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to investigate changes in the cathode after the introduction of SO2. The decay in performance of the proton exchange membrane fuel cell (PEMFC) was ascribed to the increasing of the charge transfer resistance (Rct) caused by the loss of the electrochemical surface area (ECA). The results show that the oxidation and adsorption behaviors of SO2 depended closely on the potential. Adsorbed sulfur began to be oxidized over 0.9 V and could be oxidized completely with CV maximum potentials up to 1.05 V or higher. At about 0.65 V, the adsorbed SO2 was probably in a molecular state, which could be reduced in the range of 0.65–0.05 V. Some SO2 molecules occupied initially two Pt sites through S and O. One of the two sites could be released after the reduction. The increasing of ECA due to reduction could lessen the impact of SO2 on the PEMFC performance at voltages below 0.65 V.

Several different start-up and shutdown processes of a fuel cell were investigated in this paper by measuring cathode, anode and membrane potentials respectively versus reference hydrogen electrode (RHE). The membrane potential was measured by using thin copper wire sandwiched between two membranes. During the formation of hydrogen/air boundary at the anode caused by unprotected start-up and shutdown, the in-plane potential difference between membrane inlet and outlet was measured to be as high as 0.8 V, and the interfacial potential difference between cathode and membrane outlet increased to about 1.6 V, which in turn would cause carbon corrosion. Appropriate start-up and shutdown processes were suggested to avoid the formation of hydrogen/air boundary.

Pulsed bias arc ion plating was used to form Cr-nitride films on stainless steel as bipolar plate of proton exchange membrane fuel cell. Surface micrograph, film thickness, film composition, corrosion resistance, interfacial conductivity and contact angle with water of the sample obtained at the optimal flow rate of N2 were investigated. The atomic ratio of Cr to N was close to 2:1 and the CrN phase with crystal planes of (111), (200), (220) and (311) was found in the film. Potentiodynamic and potentiostatic tests showed that the corrosion resistance of the bipolar plate sample was greatly enhanced. The contact resistance between the bipolar plate sample and Toray carbon paper was about two orders of magnitude lower than that of 316L stainless steel. The contact angle of the sample with water was 95°, which is beneficial for water management in fuel cells.

Carbon-based films on 316L stainless steel were prepared as bipolar plates for proton exchange membrane fuel cells (PEMFCs) by pulsed bias arc ion plating. Three kinds of films were formed including the pure C film, the C–Cr composite film and the C–Cr–N composite film. Interfacial conductivity of the bipolar plate with C–Cr film was the highest, which showed great potential of application. Corrosion tests in simulated PEMFC environments revealed that the C–Cr film coated sample always showed better anticorrosive performance than 316L stainless steel either in reducing or oxidizing environments. The C–Cr film coated bipolar plate sample also had high surface energy. The contact angle of the C–Cr film coated sample with water was 92°, which is beneficial for water management in a fuel cell.

Flexible graphite can be stamped into gas channels for proton exchange membrane fuel cells attributing to its good conductivity, corrosion resistance and flexibility. However, the electrical resistance of the bipolar plate consisting of a coated metal foil and the stamped flexible graphite flowfield plate should be investigated, for the internal resistance would affect the output power of the fuel cell greatly. The influences of various parameters, such as compacting pressure, temperature, effective area of the coating and the water content of the flexible graphite on the electrical resistance were studied. The electrical resistance decreases with the increment of compacting pressure exponentially. The temperature and the effective area of metal foil coating both have linear relations with the electrical resistance. And the water content of the flexible graphite has a very complex relation with the electrical resistance; it is the most important influencing factor. At last, an empirical equation for the electrical resistance, giving a good fit to the test data, was determined.

Three different kinds of CrxN films on 316L stainless steels were prepared by pulsed bias arc ion plating as bipolar plates for proton exchange membrane fuel cell (PEMFC). The interfacial contact resistance, corrosion resistance and surface energy of the bipolar plate samples were investigated. Among the three samples, the 316L stainless steel coated with Cr0.49N0.51 → Cr0.43N0.57 gradient film (sample 2) exhibited the best-integrated performance. The contact resistance between sample 2 and Toray carbon paper was 6.9–10.0 mΩ cm2 under 0.8–1.2 MPa. The bipolar plate sample also showed improved corrosion resistance in simulated PEMFC environments. Either in the reduction environment or in the oxidation environment 25 °C and 70 °C, the corrosion current densities of sample 2 were about one to two orders of magnitude lower than those of the base metal. In addition, the open circuit corrosion potential of sample 2 was also the highest in 0.5 M H2SO4 + 5 ppm F− solution at 25 °C. The treated bipolar plate had high surface energy; and the contact angle of sample 2 with water was about 90°, which is beneficial for water management in fuel cell.

In this paper, voltage sensors were developed to explore the voltage distribution characteristics inside the fuel cell under both steady and transient states. The effects of air stoichiometry and current density on the voltage distribution under steady state were discussed, and the dynamic voltage response due to the load change under transient state was also investigated. Results showed that under transient state, the fuel cell would experience a temporary voltage fluctuation due to the air starvation. Thus could probably lead to the degradation of materials, such as the catalyst, membrane, etc. To lessen the degree of air starvation, a method of pre-supplying certain amount of air before loading was adopted. The relationship between the voltage response at the loading transient and the amount of pre-supplied air was also studied, and a minimum value of the pre-supplied air was obtained. The experimental results of this paper could be applied to the optimization of vehicular fuel cell system.

Forming a coating on metals by surface treatment is a good way to get high performance bipolar plate of proton exchange membrane fuel cell (PEMFC). In our research, Ag–polytetrafluoroethylene (PTFE) composite film was electrodeposited with silver-gilt solution of nicotinic acid by a bi-pulse electroplating power supply on 316 L stainless steel bipolar plate of PEMFC. Surface topography, contact angle, interfacial conductivity and corrosion resistance of the bipolar plate samples were investigated. Results showed that the defects on the Ag–PTFE composite coating are greatly reduced compared with those on the pure Ag coating fabricated under the same condition; and the contact angle of the Ag–PTFE composite coating with water is 114°, which is much bigger than that of the pure Ag coating (73°). In addition, the interfacial contact resistance of the composite coating stays as low as the pure Ag coating; and the bipolar plate sample with composite coating shows a close corrosion resistance to the pure Ag coating sample in potentiodynamic and potentiostatic tests. Coated 316 L stainless steel plate with Ag–PTFE composite coating exhibits well hydrophobic characteristic, less defects, high interfacial conductivity and good corrosion resistance, which shows a great potential of the application in PEMFC.

The operations of fuel cell stacks in fuel cell vehicle are dynamic. During dynamic loading, the oxidant starvation often occurs, due to the gas response rate lagging the loading rate. To study the transient behavior of the fuel cell stack at load changes, the measuring methods of current and temperature distribution are developed. In this paper, the current distribution and temperature distribution as well as their dynamic changes in fuel cell stack have been evaluated in situ. The experimental results show that the local current and temperature rise when load rapidly. The extent of temperature fluctuation during dynamic loading is significantly influenced by air stoichiometries, loading rates, and air relative humidities. When air stoichiometry is very low, the temperature of cathode inlet rises sharply. The quicker the loading rate is, the bigger the extent of temperature fluctuation is. With increasing air relative humidity, the transient temperature of cathode inlet rises, while the transient temperature of cathode outlet decreases. This paper will provide reference for durability researches on fuel cell vehicles (FCVs).

A simple and effective method for reactivation of H2S poisoned Pt-anodes is described and the feasibility of the method was examined by single cell tests and 1 kW stack tests. The performance of the H2S poisoned Pt-anode can be basically recovered by applying a high voltage pulse (1.5 V for 20 s) followed by a low voltage pulse (0.2 V for 20 s) in a single cell. During the 10 poisoning–recovery cycles, the ohmic resistance and electrochemical surface area did not change significantly. The 1 kW stack tests show that the stack performance decayed severely and the maximum power decreased to 0.366 kW (32% of the original value) after exposure to 18 ppm H2S/H2 for 2 h at 600 mA cm−2. The stack performance can be significantly recovered by applying a high voltage pulse (1.5 V for 2 min) followed by a low voltage pulse (0.2 V for 2 min) to each cell. The maximum power recovered to 1.095 kW (97.5% of the original value).

The endplate is a crucial component in a proton exchange membrane fuel cell (PEMFC) stack. It can provide the necessary rigidity and strength for the stack. An aluminium alloy is one of the ideal materials for PEMFC endplates because of its low density and high rigidity. But it does not meet the requirements of corrosion resistance and electrical insulation in PEMFC environments. In this work, methods of sealing treatments and the conditions of aluminium alloy anodization were investigated. Corrosion resistances of the samples prepared by different technologies were evaluated in simulated PEMFC environments. The results showed that the corrosion resistance of the samples sealed by epoxy resin was greatly improved compared with those sealed in boiling water, and the samples anodized at a constant current density performed better than those anodized at a constant voltage. By insulation measurements, all of the samples showed good electrical insulation. The aluminium alloy endplate anodized at a constant current density and sealed with thermosetting bisphenol-A epoxy resin exhibited promising potential for practical applications by assembling it in a PEMFC stack and applying a life test.

A novel proton exchange membrane fuel cell (PEMFC) anode which can facilitate the CO oxidation by air bleeding and reduce the direct combustion of hydrogen with oxygen within the electrode is described. This novel anode consists of placing Pt or Au particles in the diffusion layer which is called Pt- or Au-refined diffusion layer. Thus, the chemical oxidation of CO occurs at Pt or Au particles before it reaches the electrochemical catalyst layer when trace amount of oxygen is injected into the anode. All membrane electrode assemblies (MEAs) composed of Pt- or Au-refined diffusion layer do perform better than the traditionary MEA when 100 ppm CO/H2 and 2% air are fed and have the performance as excellent as the traditionary MEA with neat hydrogen. Furthermore, CO tolerance of the MEAs composed of Au-refined diffusion layer was also assessed without oxygen injection. When 100 ppm CO/H2 is fed, MEAs composed of Au-refined diffusion layer have the slightly better performance than traditionary MEA do because Au particles in the diffusion layer have activity in the water gas shift (WGS) reaction at low temperature.

The effect of hydrogen sulfide on proton exchange membrane fuel cell (PEMFC) anodes was studied by cyclic voltammetry (CV), potential steps and electrochemical impedance spectroscopy (EIS). The severity of the effect of H2S varies depending on the H2S concentration, current density and the cell temperature. The anode humidification does not impact the poisoning rate much when the anode is exposed to H2S. The adsorption of H2S on the anode is dissociative and this dissociation can produce adsorbed sulfur. The dissociation potential of H2S was studied by potential steps, and the values of the dissociation potential are about 0.4 V at 90 °C, 0.5 V at 60 °C and 0.6 V at 30 °C, respectively. The adsorbed sulfur can be oxidized at a higher potential. During CV scans, two oxidation peaks for the adsorbed sulfur at 1.07 and 1.2 V were observed at 90 °C, however a single oxidation peak could be observed at 1.2 V at 60 °C and at 1.27 V at 30 °C. Application of EIS to a H2S|H2 half-cell shows that the charge transfer resistance increases when the anode is exposed to H2S because of H2S adsorption.

Proton exchange membrane fuel cells (PEMFCs) most likely will use reformed fuel as the primary source for the anode feed which always contains carbon dioxide (CO) and hydrogen sulfide (H2S). Trace amount of CO and H2S can cause considerable cell performance losses. A comparison between the effect of CO and that of H2S on PEMFC performance was made in this paper. Under the same conditions, the H2S poisoning rate is much higher than CO because of different adsorption intensity. When the fuel stream contains the gas mixture (25 ppm CO and 25 ppm H2S), the fuel cell performance deteriorates more quickly than 50 ppm CO but slowly than 50 ppm H2S and can be only partially recovered by reintroducing neat H2. The resulting effects of the mixtures can be divided into two parts roughly: during the inception phase, the cell voltage drops quickly and the actual values of anode overvoltage are bigger than the corresponding calculated values; then the deterioration rate of the cell performance decreases gradually.

This paper mainly presents the AC impedance characteristics of a 2 kW PEMFC stack under different operating conditions and load changes. The AC impedances of the fuel cell stack are examined by a fuel cell impedance meter. Air stoichiometry, air humidity, and operation temperature are shown to have significant effects on the AC impedance of stack. When air stoichiometry decreases, the mass transfer resistance of stack increases obviously, but the influences on other resistances are very slight. The air humidity and operation temperature mainly influence the charge transfer resistance of stack. The influences of load changes on the AC impedance of stack are also investigated, and the results of which show that it is quite necessary to adjust the humidity of reactant gas according to the fuel cell load changes during fuel cell running. The AC impedance diagnosis of stack can provide some useful information for the running of fuel cell stack.

Sn-doped TiO2 nanoparticles with high surface area of 125.7 m2·g−1 are synthesized via a simple one-step hydrothermal method and explored as the cathode catalyst support for proton exchange membrane fuel cells. The synthesized support materials are studied by X-ray diffraction analysis, energy dispersive X-ray spectroscopy and transmission electron microscopy. It is found that the conductivity has been greatly improved by the addition of 30 mol% Sn and Pt nanoparticles are well dispersed on Ti0.7Sn0.3O2 support with an average size of 2.44 nm. Electrochemical studies show that the Ti0.7Sn0.3O2 nanoparticles have excellent electrochemical stability under a high potential compared to Vulcan XC-72. The as-synthesized Pt/Ti0.7Sn0.3O2 exhibits high and stable electrocatalytic activity for the oxygen reduction reaction. The Pt/Ti0.7Sn0.3O2 catalyst reserves most of its electrochemically active surface area (ECA), and its half wave potential difference is 11 mV, which is lower than that of Pt/XC-72 (36 mV) under 10 h potential hold at 1.4 V vs. NHE. In addition, the ECA degradation of Pt/Ti0.7Sn0.3O2 is 1.9 times lower than commercial Pt/XC-72 under 500 potential cycles between 0.6 V and 1.2 V vs. NHE. Therefore, the as synthesized Pt/Ti0.7Sn0.3O2 can be considered as a promising alternative cathode catalyst for proton exchange membrane fuel cells.Ti0.7Sn0.3O2 nanoparticles with high surface area are used as Pt catalyst supports for the oxygen reduction reaction. Pt/Ti0.7Sn0.3O2 exhibits excellent electrochemical stability compared to Pt/XC-72 under high potential electrooxidation and potential cycling.Download full-size image

Pt/WO3/C nanocomposites with parallel WO3 nanorods were synthesized and applied as the cathode catalyst for proton exchange membrane fuel cells (PEMFCs). Electrochemical results and single cell tests show that an enhanced activity for the oxygen reduction reaction (ORR) is obtained for the Pt/WO3/C catalyst compared with Pt/C. The higher catalytic activity might be ascribed to the improved Pt dispersion with smaller particle sizes. The Pt/WO3/C catalyst also exhibits a good electrochemical stability under potential cycling. Thus, the Pt/WO3/C catalyst can be used as a potential PEMFC cathode catalyst.Pt/WO3/C nanocomposites with parallel WO3 nanorods were prepared as ORR catalyst, and show enhanced electrochemical activity and stability compared with Pt/C.Download full-size image