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The degradation of the carbon supports and high platinum (Pt) loading significantly hinder the wide adoption of proton exchange membrane fuel cells. In conventional electrodes, the ionomer binders introduce an undesirable, high oxygen-transport resistance and cover the catalysts active sites. Herein, an advanced catalytic layer based on vertically aligned titanium nitride nanorod arrays (TiN NRs) is prepared, without additional ionomer or binders in the cathode. After supporting the thin-film platinum-palladium-cobalt (PtPdCo) catalyst (Pt loading: 66.9 μm cm−2) onto TiN NRs, the ordered electrodes were investigated as the cathode of a single cell without additional ionomer in the catalytic layer. With this electrode architecture, the as-synthesized electrode performs with a maximum power density of 390.5 mW cm−2 and cathode mass-specific power density of 5.84 W mgPt−1. The 2000 potential cycles accelerated degradation test shows that the PtPdCo-TiN electrode is more stable than the commercial gas diffusion electrode. [ABSTRACT FROM AUTHOR]

An oriented ultrathin catalyst layer (UTCL) has been prepared for fuel cells application based on the high electrical conductivity TiO 2 nanotube (TNTs). The electrical conductivity of TNTs was improved by the deposited C via a plasma enhanced chemical vapor deposition (PECVD) technique. Pt catalysts were deposited on the high electrical conductivitve TNTs by the radio frequency (RF) sputtering to form the oriented C-TNTs-Pt electrode. The mass activity of C-TNTs-Pt-1 at 0.85 V was about 0.44 A mg Pt −1 . The prepared oriented UTCL based on the C-TNTs-Pt electrode displayed a maximum power density of 206 and 305 mW cm −2 at an ultralow Pt loading resulting in a relatively high Pt utilization of 8.3 and 6.0 kW g −1 Pt . A 2D symmetry model based on the parameters of the oriented UTCL was established. In the model, the performance of fuel cell was improved along with the decreasing of CL thickness. Meanwhile, it is found that there is little effect on the cell performance when the electrical conductivity of CL is larger than 3 S cm −1 . The study in this work gave effectual evidence on the possibility of using the oriented UTCL for developing low cost fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: With Ni as the precursor, by using pulse electrodeposition technique, Pt nanoparticles were synthesized and deposited onto the high aspect ratio TiO2 nanotube arrays support for fuel cells. The influence of pulse electrodeposition parameters on the morphology of Ni nanoparticles was investigated, and the prepared Ni nanoparticles with diameter of about 30nm were advantageous to the deposition and dispersion of Pt catalysts within TiO2 nanotubes support. The modified electrode exhibited high activity at half cell test. Furthermore, the electrochemical surface area of this electrode had reduced by 28% after an accelerated durability test compared to 57% for commercial Pt/C (JM). In this work, a TiO2 nanotube arrays as catalyst support in was tested under single cell test condition. The maximum power density reached 557mWcm−2 when this novel electrode was used as the anode of fuel cells. [Copyright &y& Elsevier]

Abstract: This study correlates the post start cell performance and impedance with the cold start process in the subzero environment. The sequential failed cold starts are deliberately conducted as well as the start at small current density. Here the failed cold start means the cell voltage drops to or below zero within very short time during the start process. It is found that there are reversible performance losses for the sequential failed cold starts, while not obvious degradation and no recovery happen for the start at small current density. Using the thin film and agglomerate model, it is confirmed that this is due to the water blocking effect. Comparing the results from different start processes, a model with respect to the shifting of reactive region within the catalyst layer is applied to explain that the reversible performance loss is associated with the amount of the generated water or ice and the water location or distribution during cold start. The relationship of the cold start performance at high current density and the pore volume in the catalyst layer is also discussed. [Copyright &y& Elsevier]

Abstract: Effect of catalytic ink on sub-freezing endurance of proton exchange membrane fuel cells (PEMFCs) was investigated in this paper. By direct spraying method, a catalyst-coated membrane (CCM) was fabricated with isopropyl alcohol as organic solvent (CCM-A), and CCM-B was fabricated with isopropyl alcohol and butyl acetate. The hydrophobicity of the two CCMs was similar proved by contact angle tests, and CCM-B showed larger pore volume demonstrated by mercury intrusion tests. Initial cell performance and relevant electrochemical characteristics of the two CCMs were measured and compared. CCM-B showed better performance and larger electrochemical active surface area (ECA). By analyzing the electrochemical impedance spectra (EIS) at low current densities, the ionic resistances of the catalyst layers were calculated. Results indicated that adding butyl acetate to the catalytic ink benefited the ionic resistance. Then, the fuel cells with the two CCMs were subzero stored at −20 °C with saturated residual water. After 20 freeze–thaw cycles, the CCM prepared with isopropyl alcohol and butyl acetate showed less degradation in terms of polarization curves and EIS. And the ionic resistances of the both CCMs decreased to a certain extent. [ABSTRACT FROM AUTHOR]

Abstract: In this study, a novel strategy is reported to improve the cold start performance of proton exchange membrane (PEM) fuel cells at subzero temperatures. Hydrophilic nano-oxide such as SiO2 is added into the catalyst layer (CL) of the cathode to increase its water storing capacity. To investigate the effect of nanosized SiO2 addition, the catalyst coated membranes (CCMs) with 5 wt.% and without nanosized SiO2 are fabricated. Although at normal operation conditions the cell performance with nanosized SiO2 was not so good as that without SiO2, cold start experiments at −8 °C showed that the former could start and run even at 100 mA cm−2 for about 25 min and latter failed very shortly. Even at −10 °C, the addition of SiO2 dramatically increased the running time before the cell voltage dropped to zero. These results further experimentally proved the cold start process was strongly related with the cathode water storage capacity. Also, the performance degradation during 8 cold start cycles was evaluated through polarization curves, cyclic voltammetry (CV) and electrochemical impedance spetra (EIS). Compared with the cell without SiO2 addition, the cell with 5 wt.% SiO2 indicated no obvious degradation on cell performance, electrochemical active surface area and charge transfer resistance after experiencing cold start cycles at −8 °C. [Copyright &y& Elsevier]

Abstract: A new hydrophobic thin film catalyst layer (CL) was prepared by the decal method in this work. Polytetrafluoroethylene (PTFE) was introduced to the catalyst ink with 1wt.% Nafion® ionomer as the hyperdispersant. Aluminum foil was adopted as the transferring medium which enabled the sintering process of PTFE. Then an appropriate amount of Nafion® ionomer was sprayed onto the CL for proton conduction. At last, the CL was transferred onto a Nafion® membrane and the catalyst-coated membrane (CCM) was formed. Contact angle measurement and mercury intrusion porosimetry test were conducted to characterize the hydrophobicity and porosity of the thin film CL. The results showed that PTFE addition favored the CL hydrophobicity and porosity. The optimal PTFE content was also deduced by comparing the fuel cell performance under different PTFE contents. Electrochemical analysis revealed that PTFE addition decreased the electrochemical active area (ECA) but enhanced the diffusion process in the CL. [Copyright &y& Elsevier]

Abstract: Hydrophilic nanosized SiO2 and sulfonated SiO2 particles were added to the cathode catalyst layer (CL) to improve the water wettability and the performance of a proton exchange membrane fuel cell (PEMFC) at low humidity. It was found that both nanosized SiO2 and sulfonated SiO2 additive improved the hydrophilicity of the cathode CL by the contact angle measurement. Contrary to nanosized SiO2, sulfonated SiO2 improved the conductivity of the cathode CL. Increased wettability of the cathode CL from SiO2 maintained fuel cell at hydration conditions. This phenomenon had a profound influence on electrode performance at low humidity. Since the sulfonic groups in sulfonated SiO2 improved the proton conductivity of the cathode CL, the cell with sulfonated SiO2 showed better performance. [Copyright &y& Elsevier]

Membrane water content is of vital importance to the freezing durability of proton exchange membrane fuel cells (PEMFCs). Excessive water freezing could cause irreversible degradation to the cell components and deteriorate the cell performance and lifetime. However, there are few studies on the critical membrane water content, a threshold beyond which freezing damage occurs, for cold storage of PEMFCs. In this work, we first proposed a method for measuring membrane water content using membrane resistance extracted from measured high frequency resistance (HFR) based on the finding that the non-membrane resistance part of the measured HFR is constant within the range of membrane water content of 2.98 to 14.0. Then, freeze/thaw cycles were performed from −50 °C to 30 °C with well controlled membrane water content. After 30 cycles, cells with a membrane water content of 8.2 and 7.7 exhibited no performance degradation, while those higher than 8.2 showed significant performance decay. Electrochemical tests revealed that electrochemical surface area (ECSA) reduction and charge transfer resistance increase are the main reasons for the degradation. These results indicate that the critical membrane water content for successful cold storage at −50 °C is 8.2. [ABSTRACT FROM AUTHOR]

Alkaline anion exchange membrane fuel cells (AEMFCs) are attracting more and more attention due to the advantages of using non-platinum-group (NPG) metal catalysts and less expensive metal hardware at the high pH conditions. However, the studies of electrodes with the non-precious metal are still less and the performance of the AEMFC operated with the NPG metal catalysts need to improve. In this work, based on AEMFCs operated with the commercial non-precious metal ORR catalysts (Acta 4020), a two dimensional, two-phase flow and steady-state agglomerates model is developed, and the effects of operational conditions of the relative humidity and the structure of the catalyst layer on fuel cell performance are numerically studied and analyzed. The results demonstrate that the relative humidity directly impacts the water distribution and transport in the MEA, and the low relative humidity in the cathode can increase the water back diffusion from the anode to the cathode and improve the fuel cell performance. An increase in the catalyst loading has been found to have a positive effects on the fuel cell performance, but the improvement is limited when the catalyst loading increases to a certain value. In addition, the increase in the mass ratio of catalyst to ionomer results in a decrease in the thickness of the ionomer film, but the excessive mass ratio of the catalyst to the ionomer also leads to a decrease in ionic conductivity, thereby deteriorating the performance of fuel cell. At last, operating with the optimized conditions from the model, the AEMFC realized a good fuel cell performance, and the peak power density reached 566 mW cm−2 and 326 mW cm−2 for H 2 /O 2 and H 2 /Air (CO 2 -free) at 60 °C, respectively, and the results are higher than those reported in references. • An agglomerate model for AEMFC operated with non-noble metal catalyst is developed. • The effects of RHs on the water distribution and transport are analyzed in details. • The cell performance with non-noble metal catalyst reached 566 mW cm−2 at 60 °C. [ABSTRACT FROM AUTHOR]

Cell reversal has a significant impact on the durability of proton exchange membrane fuel cell (PEMFC). Oxygen evolution reaction (OER) catalysts are often introduced to serve as reversal tolerant materials. However, adding OER catalysts to the anode may lead to a reduction in performance as they could potentially cover the active Pt site. In this study, carbon nanotube (CNT) supported Pt-Ir bifunctional catalyst is used as the anode catalyst to balance the tradeoff between cell reversal resistance and power generation performance. The obtained Pt 3 Ir 1 /CNT catalyst exhibits a faster OER kinetic (83.8 mV dec−1) than the commercial Pt/C (151.8 mV dec−1) catalyst and the similar hydrogen oxidation reaction (HOR) activity with Pt/C. After the accelerated durability test, the electrochemical active surface area (ECSA) loss of Pt 3 Ir 1 /CNT is 19.6% while that of Pt/C is 54.7%. After 50 consecutive cell reversal tests, it was observed that the MEA with Pt 3 Ir 1 /CNT exhibits almost no degradation in cell voltage. In contrast, the MEA with Pt/C showed a degradation of 4.9% (@ 1000 mA cm−2) when subjected to the same conditions. The strategy of combing bifunctional catalysts with high-durability supports has been shown to improve the reversal tolerance of the cell without performance loss. • RTAs based on CNTs-supported bifunctional catalysts are proposed. • Pt 3 Ir 1 /CNT bifunctional catalyst shows a faster OER kinetic than Pt/C. • Pt 3 Ir 1 /CNT bifunctional catalyst exhibits a similar activity of HOR with Pt/C. • The oxidation degree of XC-72 is much more severe than CNT after the ADT. • The MEA with Pt 3 Ir 1 /CNT in the anode shows excellent cell reversal tolerance. [ABSTRACT FROM AUTHOR]

A 9-cell proton exchange membrane (PEM) water electrolysis stack is developed and tested for 7800 h. The average degradation rate of 35.5 μV h −1 per cell is measured. The 4th MEA of the stack is offline investigated and characterized. The electrochemical impedance spectroscopy (EIS) shows that the charge transfer resistance and ionic resistance of the cell both increase. The linear sweep scan (LSV) shows the hydrogen crossover rate of the membrane has slight increase. The electron probe X-ray microanalyze (EPMA) illustrates further that Ca, Cu and Fe elements distribute in the membrane and catalyst layers of the catalyst-coated membranes (CCMs). The cations occupy the ion exchange sites of the Nafion polymer electrolyte in the catalyst layers and membrane, which results in the increase in the anode and the cathode overpotentials. The metallic impurities originate mainly from the feed water and the components of the electrolysis unit. Fortunately, the degradation was reversible and can be almost recovered to the initial performance by using 0.5 M H 2 SO 4. This indicates the performance degradation of the stack running 7800 h is mainly caused by a recoverable contamination. [ABSTRACT FROM AUTHOR]

Abstract: The quaternary ammonia polysulfone (QAPS) alkaline anion exchange membrane (AAEM) was previously prepared successfully. The QAPS membrane showed good ionic conductivity but poor mechanical strength and high swelling ratio. This study focused on membrane mechanical strength and dimensional stability by PTFE membrane enhancement, which increases the mechanical strength by five times and decreases the swelling ratio by 50%. The fuel cell with the resulted thinner QAPS/PTFE composite membrane with catalyst coated membrane (CCM) as the electrode showed a high power output, and the peak power density of 315 mW cm−2 was achieved at 50 °C. [Copyright &y& Elsevier]

Abstract: IrO2 nanoparticles coated TiO2 nanopore arrays (IrO2/TNPs) electrode has been successfully synthesized by depositing IrO2 on the surface of size-controllable TiO2 nanopore arrays (TNPs), which were fabricated by using anodic oxidation of pure titanium meshes in electrolyte solutions. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), liner sweep voltammetry (LSV), SPE cell polarization curves and electrochemistry impedance spectroscopy (EIS) were adopted to characterize their structures, properties and performances. The IrO2/TNPs electrode has ordered microstructure and more porous surface morphology than that of IrO2/Ti electrode. The electrochemical tests showed that IrO2/TNPs electrode exhibited higher catalytic activity than IrO2/Ti electrode. And the cell voltage can be as low as 1.16V at 1000mAcm−2 and 70°C, which is 90mV lower than that of the cell with IrO2/Ti electrode (1.25V). The increase in performance is attributed to the ordered microstructure and porous surface which decrease the interface contact resistance and charge transfer resistance. [Copyright &y& Elsevier]

Abstract: With electrochemical impedance spectroscopy (EIS), the ionic resistances of the catalyst layer (CL) were measured at different current densities after the proton exchange membrane (PEM) fuel cell suffered the subfreezing temperature. Compared with those of the CL before being frozen, the ionic resistances unexpectedly decreased a little, which accorded well with the polarization results. Considering that the frequency-dependent penetration depth was small in the high frequency region, a semi-quantitative method based on the finite transmission-line equivalent circuit was followed to investigate the ionic resistance profile across the whole CL. The results indicated that the change of the ionic resistance profile was not uniform across the CL after the cell experienced freeze/thaw cycles, which was more evident at the higher current densities. [Copyright &y& Elsevier]

Abstract: The effects of the residual water in the PEM fuel cell after cold start on the performance, electrode electrochemical characteristics, and cell components were investigated by controlling the cold-start processes of three cells at . Neither the cell performance loss nor the cell resistance increase with the start number was observed. There was no change in the electrochemical active surface area (ECA) and charge transfer resistance at low current density. The correlation between the amount of the residual water and the ohmic polarization and cell resistance showed mass-transport process slightly changed with the water amount in the cell. This trend correlated well with the charge transfer resistance at high current density. The change of mass-transport process came from the gas diffusion layer by the analysis of ECA. It was found that hydrogen crossover rate of the membrane at the three hydrated states did not change through eight start-ups at . Based on the analysis of SEM and water-storage capacity, it was believed that less water was stored in the catalyst layer even though much water resided in the cell. [Copyright &y& Elsevier]

The speed of the subzero start-up of proton exchange membrane fuel cells is a hot research topic. However, the cost of the start-up of proton exchange membrane fuel cell is an important factor that affects their commercialization. In this paper, a reused gas cold-start method is developed. Hydrogen–air mixture is introduced to the anode of the fuel cell, and the exhausted gas from the anode is introduced to the cathode. Thermal equilibrium at −20 °C start-up of the fuel cell is calculated. The best gas ratio is confirmed by the start-up process at −20 °C.The fuel consumption and hydrogen utilization of the reused gas cold start and the conventional catalytic reaction cold start are compared. 1/4 is the optimal ration of air/hydrogen. The catalytic reactions take place simultaneously in the anode and the cathode of the fuel cell in there used gas cold-start method, thereby saving energy and time during start up. With this method, the fuel cell can start-up at−40 °C, and the performance of the fuel cell does not seem to change after the cold-start process. • Thermal equilibrium at −20 °C start-up of the fuel cell was calculated. • The catalytic reaction method using exhaust gas can fully utilize the un-reacted mixed gas. • With this method, PEMFC can start-up at −40 °C within 67s. [ABSTRACT FROM AUTHOR]

A cost-effective nanoporous ultrathin film (NPUF) electrode based on nanoporous gold (NPG)/IrO 2 composite has been constructed for proton exchange membrane (PEM) water electrolysis. The electrode was fabricated by integrating IrO 2 nanoparticles into NPG through a facile dealloying and thermal decomposition method. The NPUF electrode is featured in its 3D interconnected nanoporosity and ultrathin thickness. The nanoporous ultrathin architecture is binder-free and beneficial for improving electrochemical active surface area, enhancing mass transport and facilitating releasing of oxygen produced during water electrolysis. Serving as anode, a single cell performance of 1.728 V (@ 2 A cm −2 ) has been achieved by NPUF electrode with a loading of IrO 2 and Au at 86.43 and 100.0 μg cm −2 respectively, the electrolysis voltage is 58 mV lower than that of conventional electrode with an Ir loading an order of magnitude higher. The electrolysis voltage kept relatively constant up to 300 h (@250 mA cm −2 ) during the course of durability test, manifesting that NPUF electrode is promising for gas evolution. [ABSTRACT FROM AUTHOR]

The degradation of carbon supports significantly influences the performance of proton exchange membrane fuel cells (PEMFCs), particularly in the cathode, which must be overcome for the wide application of fuel cells. In this study, advanced catalytic layer with electronic conductive polymer–polypyrrole (PPy) nanowire as ordered catalyst supports for PEMFCs is prepared. A platinum–palladium (PtPd) catalyst thin layer with whiskerette shapes forms along the long axis of the PPy nanowires. The resulting arrays are hot-pressed on both sides of a Nafion ® membrane to construct a membrane electrode assembly (without additional ionomer). The ordered thin catalyst layer (approximately 1.1 μm) is applied in a single cell as the anode and the cathode without additional Nafion ® ionomer. The single cell yields a maximum performance of 762.1 mW cm −2 with a low Pt loading (0.241 mg Pt cm −2 , anode + cathode). The advanced catalyst layer indicates better mass transfer in high current density than that of commercial Pt/C-based electrode. The mass activity is 1.08-fold greater than that of DOE 2017 target. Thus, the as-prepared electrodes have the potential for application in fuel cells. [ABSTRACT FROM AUTHOR]

Carbon-coated titanium dioxide (TiO 2 –C) has received much attention as a catalyst support in proton exchange membrane fuel cells. In this study, TiO 2 nanorod arrays (NRs) are hydrothermally grown on carbon paper and converted into TiO 2 –C NRs by heat treatment at 900 °C under methane atmosphere. Then, platinum nanoparticles are sputtered onto the TiO 2 NRs by physical vapor deposition to produce Pt–TiO 2 –C. The as-prepared Pt–TiO 2 –C exhibits high stability during accelerated durability tests. As compared with the commercial gas diffusion electrode (GDE, 34.4% decrease), a minor reduction in the electrochemically active surface area of the Pt–TiO 2 –C electrode after 1500 cycles (10.6% decrease) is observed. When the as-prepared electrode with ultra-low platinum content (Pt loading: 28.67 μg cm −2 ) is employed as the cathode of a single cell, the electrode generates power that is 4.84 × that of the commercial GDE (Pt loading: 400 μg cm −2 ). An electrode that generates power of 11.9 kW g Pt −1 (as the cathode) is proposed. The fabricated Pt–TiO 2 –C electrode can be used in proton exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells suffer from cell reversal due to hydrogen starvation, which can be exacerbated by hydrogen channel blockage after extensive ice formation under freezing conditions. The cell reversal degradation of conventional anodes and reversal-tolerant anodes (RTAs) at sub-zero temperature (−30 °C to −5 °C) is investigated. During freezing cell reversal, a water electrolysis plateau is observed with a low reversal voltage, but the typical subsequent carbon corrosion plateau usually observed at above-zero temperature is absent. Reversal tests indicate that the reversal time of RTAs at freezing temperature is significantly shorter than that at above-zero temperature. Local water starvation can occur in freezing cell reversal, as evidenced by the consistent changing trend of the reversal voltage and internal resistance because of the reduced water diffusion capacity in the proton exchange membrane. The 300 min accumulated long-term cyclic freezing reversal of RTAs reveals a low degradation rate. The suppression of the sub-zero temperature on the oxidation of the carbon support and the platinum–carbon catalyst and the influence of the water content in the catalyst layer on cell reversal explain the low degradation rate in freezing cell reversal. • No evident carbon corrosion plateau is observed in freezing cell reversal. • The cell reversal voltage and internal resistance have the same change trend. • The freezing cell reversal has a much lower degradation rate. • Low relative humidity and freezing temperature suppress carbon corrosion. [ABSTRACT FROM AUTHOR]

A rapid and safe cold start is essential for the commercialisation of proton exchange membrane fuel cell (PEMFC) vehicles, and self-start is considered as the optimal way to fulfil this expectation. In this study, the self-start of large-area PEMFCs is investigated. It is found that there exists a severe temperature distribution nonuniformity along the flow direction during one-way air-supply self-start, and the cold-start capability is limited by the fact that most of the heat is concentrated in the inlet area, while less heat is in the outlet area, which makes it difficult to start at −15 °C. To solve this issue, an alternating air-supply strategy is suggested. By applying this strategy, temperature distribution uniformity and cold-start performance are significantly improved. Self-start from −15 °C and −20 °C can be achieved in 165 s and 142 s with starting voltages of 0.8 V and 0.6 V, respectively. The alternating interval has a negligible impact on start-up time but will affect the temperature distribution and fluctuation. The advantages of alternate air supply are analyzed based on the calculation of heat generation and water production. A performance degradation test indicates that cell performance is well preserved after 20 cold starts [Display omitted] [ABSTRACT FROM AUTHOR]