The accuracy of the reference electrode potential is critical in electrochemical studies. This work studies the approach to calibrate reference electrodes experimentally to the reversible hydrogen electrode (RHE) scale in an acidic condition. Multiple working electrodes are used while varying rotation rates, scan ranges, and scan rates to demonstrate how the calibration process will affect the calibrated RHE values of reference electrodes. It is recommended to rotate the working electrode for RHE scale calibration. The cyclic voltammetry potential range is suggested to be within +/- 0.01 V from 0 V versus RHE to minimize errors in the analysis. The scan rate of cyclic voltammetry for RHE scale calibration is no more than 10 mV/s. This experimental practice aims to benefit the standardization of experimental reference electrode calibration in the electrochemical field.

Vanadium carbide nanoflakes were synthesized and investigated as catalysts for V3+/V2+ redox reactions. This work explored a simple and environmentally friendly synthesis process that involved in situ carburization of a metal precursor and a carbon material as the carbon source and support. The structure, composition, morphology, and thermal stability of the vanadium carbide nanoflakes were characterized by X-ray diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Vanadium carbide supported on Vulcan XC72 carbon black showed a smaller particle size than that on graphite. Electrochemical properties of vanadium carbide nanoflakes toward the V3+/V2+ redox reaction were characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results showed that vanadium carbide nanoflakes exhibited significantly enhanced catalytic activities and reversibility than graphite toward the V3+/V2+ redox reaction.

To develop a novel electrolyte with high proton conductivity under high temperature and low humidity for the cathode catalyst layer of high temperature proton exchange membrane fuel cells (HT-PEMFC), a multilayer structure inorganic material is synthesized with varying oxidation states transit metal complex by refluxing and hydrothermal methods. A fast proton transport pathway is established in the inorganic material by inserting H-bond ligands in the layered structure. With the preliminary tests, the electrolyte powders demonstrate a bulk conductivity of ~10-3 S cm-1 and a particles boundary conductivity of ~10-6 - 10-4 S cm-1 in the temperature range of 20 - 150 °C without humidification, as shown in Figure 1. The boundary conductivity increases with the increasing of testing temperature up to 110 °C then decreases rapidly; but the bulk conductivity barely changes within the testing temperature range. The thermal gravimetric analysis (TGA) indicates the material is stable up to 350 °C in nitrogen (N2) or helium (He). The properties and performance of the material will be further characterized and evaluated; and the structure and composition will be determined. The material will be integrated into the cathode catalyst layer of HT MEAs, and the MEA performance will be evaluated at 120 - 180 °C and low humidity. Figure 1. The proton conductivity of the inorganic particles at temperature of 20 - 150 °C Figure 1

Water electrolysis is one of the most promising ways for hydrogen production. Transition metal carbides are regarded as potential candidates to replace state-of-art but expensive platinum-group catalysts for hydrogen evolution reaction (HER). Considering the excellent electrochemical stability of TiC, a bimetallic VTiC with minor percentage of Ti would increase stability. Vanadium carbides were prepared from commercially available TiC as carbon sources and supports at 1000°C (denoted as VxTiC-1000°C) and 1100°C (denoted as VxTiC-1100°C). As shown in Figure 1a, VxTiC-1000°C and VxTiC-1100°C are a mixture of V8C7 and (Ti0.3V1-0.3)2O3 phases. While VxTiC-1000°C contains some unreacted TiC. Figure 1b shows numerous flakes grown on the particle surface of VxTiC that are expected to possess extremely large surface area. There is no phase change for VxTiC before and after treated in 3 M H2SO4 at 80 °C which means that VxTiC is acid resistant. Stability tests for VxTiC performed in 0.5 M H2SO4 up to 1.4 V exhibit excellent electrochemical stability and catalytic activity of VxTiC toward HER. Figure 1. (a) X-ray diffraction patterns and (b) scanning electron microscopy image of VxTiC. Acknowledgments Authors are grateful to the Office of Naval Research (award N00014-19-1-2159, N00014-120-1-2270). Figure 1

Flexible electrochemical energy sources with unconventional cell materials and topologies are becoming more and more popular because they present novel design possibilities that are currently being investigated. Adopting electronics manufacturing techniques to manufacture flexible electrochemical devices can provide advantages such as conformability, high power density, high specific power, and lower costs. This study examines the feasibility of printing metal current collectors (CCs) directly onto Gas Diffusion Medium (GDM) typically used in Proton Exchange Membrane Fuel Cells (PEMFCs). In this work, we print the metal CCs directly onto the GDM using different techniques such as screen printing and ink jet printing. We also investigate the effect of varying the metal CCs geometry (square shape vs. hexagonal), opening ratio (30%, 40% and 50%) and metal thicknesses (10 µm to 50 µm thick) on the overall single cell performance and cell ohmic resistances. Techniques used to understand cell performance include I-V polarization curves, electrochemical impedance spectroscopy (EIS), and thermal imaging. The performance of the cells tested with the embedded GDM/Metal CCs is compared to the performance of a standard cell.

Flexible electrochemical energy sources using non-traditional cell materials and topologies have attracted growing attention because they offer unique design opportunities that are still being explored. They also offer potential advantages such as conformability, high power density, high specific power, and low cost through the adoption of electronics manufacturing techniques. This study examines the feasibility of using flexible printed circuits boards (PCBs) as the anode and cathode current collectors (CCs) of single cell Proton Exchange Membrane Fuel Cell (PEMFCs). In this work, we determine the best anode and cathode interfaces at which to embed flexible CCs to obtain the highest power, as illustrated in Figure 1. The flexible anode and cathode CCs are embedded A) inside the PEM|Catalyst Layer (CL) interface, B) between the CL|Micro Porous Layer (MPL) interface and C) between the Gas Diffusion Layer (GDL)| Flow field (FF) interface. The performance of the single cell PEMFC with the embedded flexible anode and cathode CCs at the different interfaces described in Figure 1 is investigated by using I-V polarization curves, electrochemical impedance spectroscopy (EIS), and thermal imaging. The performance of the cells tested with the embedded flexible CCs is compared to the performance of a standard cell. This study also investigates the effect of varying the anode and cathode CC geometry (square shape vs. circular) and opening ratio (20%, 30%, 40%, 50% and 60%) on the cell performance. Figure 1

Proton exchange membrane fuel cell (PEMFC) water management and current density are highly sensitive to the gas diffusion media (GDM) used at both the anode and the cathode. As the gas and mass transport requirements vary at each of these electrodes, the optimal properties for the respective GDM contrast. Utilizing different GDM at the anode and cathode, in an asymmetric GDM pairing, maximizes current densities in a broad range of operating conditions compared to symmetric pairings comprising the same GDM at the anode and cathode. The optimal asymmetric GDM pairing features a highly permeable anode GDM with a high porosity and thick microporous layer (MPL, 80 µm) that is homogeneous in through-plane flux. Alternatively, the cathode GDM is less permeable and has a thinner and less porous MPL (20-45 µm) with a broad flux distribution. Net water drag measurements show that this asymmetric GDM pairing facilitates water retention at the anode and water expulsion from the cathode to realize lower oxygen transport resistance and up to 73% higher current density than PEMFCs with symmetric GDM pairings. Symmetric GDM pairings are insufficient at removing product water from the PEMFC cathode, resulting in greater cathode water saturation. As a result, more product water must back-diffuse across the membrane to be removed from the anode at the expense of significantly greater oxygen transport resistances and concomitantly lower current and power densities than the asymmetric GDM pairing. GDM are characterized by X-ray computed tomography (CT) and scanning electron microscopy (SEM) to reveal differences in MPL carbon type, average pore size, pore character, porosity, pore connectivity, tortuosity, and spatial flux distribution that govern PEMFC gas transport and water management.

Asymmetric gas diffusion media (GDM) pairing, which feature distinct GDM at the anode and cathode of the proton electrolyte membrane fuel cell (PEMFC), enhance water management compared to symmetric pairing of GDM (anode and cathode GDM are identical). An asymmetric pairing of Freudenberg GDM (H24C3 at anode and H23C2 at cathode) reduces ohmic resistances by up to 40% and oxygen transport resistances by 14% en route to 25% higher current density in dry gas flows. The asymmetric GDM pairing effectively hydrates the membrane electrode assembly (MEA) while minimizing liquid water saturation in the cathode compared to a commonly used symmetric GDM pairing of SGL 29BC at the anode and cathode. Superior water management observed with asymmetric GDM in flow-through mode is also realized in dead-ended anode (DEA) mode. Compared to the symmetric GDM pairing, the asymmetric GDM pairing with Freudenberg GDM increases cell voltage at all current densities, extends and stabilizes steady-state voltage behavior, slows voltage decay, and vastly reduces the frequency of anode purge events. These results support that the asymmetric Freudenberg GDM combination renders the PEMFC less prone to anode water saturation and performance loss from the anticipated increase in water back-diffusion during DEA mode operation.

Low system complexity and high hydrogen utilization are important attributes for effective proton exchange membrane fuel cells (PEMFCs). Operating a PEMFC with a dead-ended anode (DEA) mode configuration is a simple and effective way to solve these two challenges 1, 2 . In comparison with the hydrogen flow-through and recirculation mode, in DEA mode the hydrogen supplied to the anode compartment is controlled by pressure regulation instead of a mass flow controller, where a pressure regulator is installed at the anode inlet and a normally closed solenoid valve blocks the outlet. Over time, accumulated water and nitrogen diffused from the cathode are removed by forced gas convection through intermittent opening of the solenoid valve. The anode and cathode gas diffusion media (GDM) play a role in PEMFC water management and have a significant impact on PEMFC performance. We compare an asymmetric GDM pairing with Freudenberg GDM (H24C3 at anode, H23C2 at cathode) to a symmetric GDM pairing frequently used in the open literature containing SGL 29BC at both the anode and cathode, to highlight the impact of the GDM water management on fuel cell operation in flow-through mode and DEA mode. We have previously shown in open-cathode fuel cells that an asymmetric GDM pairing featuring higher porosity in the anode GDM than the cathode significantly improves hydration and power production 3, 4 . The results at 25% relative humidity (RH) are shown in Figure 1. Consistent with our prior results 5 , in regular flow-through mode, Figure 1A shows the PEMFC with an asymmetric Freudenberg GDM pairing has significantly higher current densities vs. the PEMFC with symmetric SGL 29BC GDM at an operating cell voltage ≤ 0.60 V. The advantage of using asymmetric GDM observed in flow-through mode is maintained when the PEMFCs are operated in DEA mode (i.e. open symbols). There is only a marginal decrease in cell voltages during operation in DEA mode compared to flow-through mode probably due to the use of dry hydrogen on the anode side during testing in DEA mode. Figure 1B shows that the cell voltage decay is significantly different for a PEMFC containing the symmetric SGL 29BC GDM compared one with asymmetric Freudenberg GDM when tested in DEA mode configuration. The time between purge events is much greater for the asymmetric Freudenberg GDM pairing. The anode is purged with 99.999% H 2 when the cell voltage drops by 100 mV. The PEMFC tested with the asymmetric Freudenberg GDM pairing dwells longer at steady-state prior to voltage decay, and its periods of voltage decay are more gradual. The PEMFC containing the symmetric SGL 29BC pairing has a mean purge interval of about 2min 33s and a total of fourteen purge events are necessary over 80 minutes operation, compared to a mean purge interval of about 18min 29s and a total of four purge events are necessary for the PEMFC containing the asymmetric Freudenberg pairing. A longer purge duration is desirable in a fuel cell system because it increases H 2 utilization and reduces valve wear. The results show that the asymmetric GDM pairing improves water management in PEMFCs and improves both power density and system level performance. Acknowledgements: The authors are grateful to the Office of Naval Research for support of this research. References I.-S. Han, J. Jeong and H. K. Shin, Int. J. Hydrogen Energy , 38 , 11996 (2013). K. Nikiforow, H. Karimäki, T. M. Keränen and J. Ihonen, J. Power Sources , 238 , 336 (2013). R. W. Atkinson, M. W. Hazard, J. A. Rodgers, R. O. Stroman and B. D. Gould, J. Electrochem. Soc. , 166 , F926 (2019). R. W. Atkinson, J. A. Rodgers, M. W. Hazard, R. O. Stroman and B. D. Gould, J. Electrochem. Soc. , 165 , F1002 (2018). R. W. Atkinson, Y. Garsany, B. D. Gould, K. E. Swider-Lyons and I. V. Zenyuk, ACS Appl. Energy Mater. , 1 , 191 (2018) Figure 1. (A) Comparison of I-V polarization curves measured for a PEMFC containing a typical symmetric SGL 29BC GDM pairing on the anode and cathode side and a PEMFC containing an asymmetric Freudenberg GDM pairing . Polarization curves are measured in DEA mode and flow-through mode at 25 % RH inlet cathode. In all cases the cell temperature is 65 °C, in H 2 |air, with air supplied to the cathode a stoichiometric ratio of 2 at atmospheric pressure. During DEA mode, dry H 2 is supplied to the anode at 2 psi. (B) Time evolution of the cell voltage obtained at a current density of 1200 mA cm -2 for an H 2 inlet pressure of 2 psi and 25 % RH inlet cathode. Figure 1

In this work, we use a method to separate the total oxygen mass transport coefficient into molecular, Knudsen, and ionomer contributions. Therefore, limiting current density measurements are carried out as a function of the diluent gas (He, N2, CO2), temperature (30, 50, 80°C), relative humidity (50, 75, 100%), and oxygen concentration (1, 3, 5, 7%) using state of the art membrane electrode assemblies with three platinum loadings (0.05, 0.1, 0.15 mg/cm2). As expected, the molecular diffusion coefficient is independent of the platinum loading, but increases with temperature to a varying degree depending on the humidity level. On the other hand, the Knudsen diffusion coefficient increases with increasing electrochemical active surface area and temperature, and with decreasing relative humidity. The separation procedure includes a novel feature to isolate the ionomer mass transport resistance. Its interpretation as well as the method’s reliability are critically questioned using operating condition dependencies.

Several experimental methods were used to identify the cause of the concurrent increase in kinetic and mass transfer overpotentials during the contamination of proton exchange membrane fuel cells outfitted with a commercially relevant cathode catalyst loading of 0.1 mg Pt per cm(2). Neutron images demonstrated that the transport of liquid water through gas diffusion electrode materials was subtly affected by the presence of propene and methyl methacrylate in air at ppm levels (25 to 100 ppm propene, 12.5 to 50 ppm methyl methacrylate). Multioxidant polarization curves were obtained to isolate overpotentials (O-2, 21% O-2 + 79% He, and air). For all cases, neat air, 50 ppm propene in air, and 25 ppm methyl methacrylate in air, only kinetic and mass transfer overpotentials increased (O-2 reduction on a Pt supported on C catalyst, O-2 diffusion through the catalyst layer ionomer). Also, only the O-2 mass transfer coefficient associated with diffusion in the catalyst layer ionomer increased in the presence of 50 ppm propene and 25 ppm methyl methacrylate. Contaminant species adsorbed on the catalyst decrease the active surface area and increase both the real current density and the O-2 reduction kinetic overpotential. The smaller active surface area also brings the real current density closer to the limiting value, inducing an increase of the mass transfer overpotential connected with O-2 movement in the ionomer layer covering the catalyst. This mechanism was supported by a mathematical contamination model focused on contaminant and O-2 processes on the catalyst surface (adsorption, reaction, desorption).

Proton exchange membrane fuel cell (PEMFC) power production is highly influenced by the properties of the gas diffusion media (GDM). The GDM typically comprise a mesoporous carbon layer (MPL) on top of a porous carbon-fiber gas diffusion layer (GDL) which are both wetted with polytetrafluoroethylene (PTFE) to modify their water retention. In a PEMFC, the GDM are compressed to either side of the catalyst coated membrane. The GDM are active in the fuel cell transport processes including electron and heat conduction, water removal, and distributing reactant gases to the catalyst layers, which affects the electrochemistry in the catalyst layers. These transport phenomena rely on both the properties of the GDM solid phase and its voids, making optimization of GDM material properties challenging. The majority of reports in the PEMFC literature addressing GDM focus solely on the cathode, since water is produced at this electrode and its ineffective removal can block active sites and occlude O2 diffusion. Most research reports use symmetrical anode and cathode GDM. To date, there has been less discussion on the role of the anode GDM or how anode and cathode GDM properties can be selected in concert to increase fuel cell power output, despite that a significant amount of water in a fuel cell is rejected to the anode. We consider that anode and cathode GDM properties, such as air permeability, must be chosen in unison to improve cell water management. In our previous work, we used X-ray computed tomography to observe that dry-laid, non-woven, Freudenberg GDM maintain large void volume while permitting high compressive stress, ultimately resulting in lower contact and ohmic resistances and better mass transport compared to another distinct class of GDM (wet-laid, SGL).1 In this work, we make a range of PEMFCs using a suite of Freudenberg GDM to study the influence of anode and cathode GDM air permeability and how these properties may be paired to improve cell hydration and increase fuel cell power production in a broad range of operating conditions. Fuel cells are characterized with cyclic voltammetry, electrochemical impedance spectroscopy (EIS), gravimetric analysis, and limiting current measurements to quantify the sources of mass transport resistance. Gradients of GDM material properties from anode to cathode improve cell hydration and facilitate water removal to reduce mass transport resistances and enable higher power operation. 1. “The Role of Compressive Stress on Gas Diffusion Media Morphology and Fuel Cell Performance,” R. W. Atkinson III, Y. Garsany, B. D. Gould, K. E. Swider-Lyons, I. V Zenyuk, ACS Applied Energy Materials, 2017, 1 (1), 191–201.

Cathode catalyst layer (CL) design is important for improved performance, durability and stability of proton exchange membrane fuel cells (PEMFCs). An effective cathode CL must serve multiple functions simultaneously: electron and H+ conduction, O2 or H2 supply, and effective water management. The reaction in the CL requires three-phase boundaries (or interfaces) among ionomer (for proton transfer), platinum (for catalysis), and carbon (for electron transfer), as well as voids (reactant diffusion); an optimized cathode CL structure should have micropores and mesopores to balance water egress and O2 diffusion. Our previous research showed that increasing microporosity in the cathode CL increases the power production of the PEMFCs [1]. Modeling indicates that high CL microporosity enhances water evaporation, which reduces mass transport resistances to enable higher power production [2]. Meanwhile, low microporosity encourages liquid water retention. It is known that catalyst support type has a profound effect on electrode porosity, influencing both micro- and mesoporosity [3, 4]. By constructing electrodes with layers of different carbon supported catalyst types, we demonstrate that we can create porosity gradients in the CLs that vary the electrode water management properties and the power of the PEMFC. Two different types of commercial platinum/carbon electrocatalysts are used in dual cathode CLs – 40 wt. % Pt on Vulcan carbon (Pt/VC) having low micropores and low porosity and 40 wt. % Pt on Ketjen black (Pt/KB) having large micropores and high porosity. CLs are created with both homogeneous porosity in the Z direction (Figure 1a), and compared to ones with non-uniform porosity across the Z-direction (Figure 1b). The microstructure of these cathode CLs is characterized using N2-sorption porosimetry. The CLs are assembled into PEMFCs and probed with polarization curves (at 100, 50 and 25% RH), cyclic voltammetry, O2 gain, electrochemical impedance spectroscopy, and limiting current measurements to quantify the sources of mass transport resistance. The results indicate that the regions with low microporosity encourage liquid water retention, while high microporosity encourages water evaporation. These countering actions are balanced for high CL hydration and gas diffusion, and better PEMFC performance. References [1] Y. Garsany, R.W. Atkinson, M.B. Sassin, R.M.E. Hjelm, B.D. Gould, K.E. Swider-Lyons, J. Electrochem. Soc., 165 (2018) F381-F391. [2] M. Eikerling, J. Electrochem. Soc., 153 (2006) E58-E70. [3] T. Soboleva, K. Malek, Z. Xie, T. Navessin, S. Holdcroft, ACS Appl. Mater. Interfaces, 3 (2011) 1827-1837. [4] Y.-C. Park, H. Tokiwa, K. Kakinuma, M. Watanabe, M. Uchida, Journal of Power Sources, 315 (2016) 179-191. Figure 1

Fuel cell vehicles have recently entered the market place (1). Future increases in technology adoption are dependent on concurrent cost reduction and improved durability (2). This is a major challenge because membrane/electrode assemblies based on low platinum catalyst loadings have shown inferior durability (3). Many processes limit the proton exchange membrane fuel cell (PEMFC) durability including the presence of contaminants in ambient air. Although a filter is added at the air intake to remove particulates and undesirable gaseous species, contaminant slippage, missed replacements after the filter has reached its end of life and other failures increase fuel cell exposure risks. A strategy relying on the understanding of contamination mechanisms is expected to result in a more robust system with the development of mitigation, recovery and maintenance procedures that supplement the air filter. Such a strategy is necessary because the impact of many contaminants is still unknown (4). Furthermore, relatively little contaminant related information is available for low platinum catalyst loadings (5-7). In this tutorial, focus will be given to recent contamination results and fundamental understanding obtained with a low cathode platinum loading of 0.1 mg cm-2, a value consistent with the United States Department of Energy 2020 target of 0.125 mg cm-2 for the sum of anode and cathode catalyst loadings. All tested contaminants are organic and representative of alcohols (iso-propanol), alkenes (propene), alkynes (acetylene), esters (methyl methacrylate), halocarbons (bromomethane), nitriles (acetonitrile), and polycyclic aromatics (naphthalene). The impact of catalyst loading and contaminant on cell performance, contaminant hydrophobicity on liquid water transport, a long duration contaminant exposure on degradation, a fuel cell stack compatible recovery procedure on cell voltage losses sustained during contamination, and a contaminant mixture on the synergy between species and cell performance will be discussed and contextualized with the relevant literature. All these contamination aspects have either not been explored or been insufficiently documented. Acknowledgments Authors are grateful to the Office of Naval Research (award N00014-13-1-0463), the Department of Energy (award DE-EE0000467), the National Institute of Standards and Technology (neutron imaging beam time), and the Hawaiian Electric Company for their ongoing support to the operations of the Hawaii Sustainable Energy Research Facility. References 1. T. Yoshida and K. Kojima, Electrochem. Soc. Interf., 24(2), 45 (2015). 2. E. L. Miller, D. Papageorgopoulos, N. Stetson, K. Randolph, D. Peterson, K. Cierpik-Gold, A. Wilson, V. Trejos, J. C. Gumez, N. Rustagi, and S. Satyapal, MRS Adv., 1, 2839 (2016). 3. G. P. Keeley, S. Cherevko, and K. J. J. Mayrhofer, ChemElectroChem, 3, 51 (2016). 4. J. St-Pierre, Y. Zhai, and M. S. Angelo, J. Electrochem. Soc., 161, F280 (2014) and 162, X7 (2015). 5. Y. Hashimasa, Y. Matsuda, D. Imamura, and M. Akai, Electrochemistry, 79, 343 (2011). 6. Z. Noda, K. Hirata, A. Hayashi, S. Taniguchi, N. Nakazato, A. Seo, I. Yasuda, S. Ariura, H. Shinkai, and K. Sasaki, Int. J. Hydrogen Energy, 37, 16256 (2012). 7. Z. Noda, K. Hirata, A. Hayashi, T. Takahashi, N. Nakazato, K. Saigusa, A. Seo, K. Suzuki, S. Ariura, H. Shinkai, and K. Sasaki, Int. J. Hydrogen Energy, 42, 3281 (2017).

A novel device called the Environmental Sensor System has been designed and demonstrated to provide real time environmental air contaminant analysis and monitoring to allow fuel cell control systems to protect the integrity of the fuel cell from environmental contaminants. This is accomplished through continuous sampling of the ambient air used to provide oxygen to the fuel cell. Electrochemical sensors are used in this prototype device to monitor hydrogen sulfide, sulfur dioxide, nitric oxide, nitrogen dioxide and volatile organic compounds. The air is monitored before and after the air filter to allow for preventative maintenance and emergency protection. The integration of this ancillary device will allow fuel cell systems to safely and reliably operate in high air contaminant conditions which previously would have resulted in stack poisoning from air contaminants. Preliminary demonstration of this technology to protect the stack on a fuel cell electric bus is reported.

This work evaluated the ability of 1-ethyl-3-methylimidazolium acetate ionic liquid and potassium hydroxide loaded activated carbon sorbents to remove SO2 and NO2 under simulated atmospheric conditions containing <= 10 ppm of gas contaminants in air at 25 degrees C and relative humidity of 50%. The studies indicate the 1-ethyl-3-methylimidazolium acetate loaded activated carbon, [C(2)mim] [Ac] sorbent, has superior sorption performance for SO2, with breakthrough times greater than pure activated carbon, pelletized KOH activated carbon and granulated KOH loaded activated carbon. The pelletized KOH loaded activated carbon had lowest performance indicating pelletized sorbents are not ideal for use in high flow rate applications such as fuel cells. The SO2 concentration significantly impacted the breakthrough times of the [C(2)mim] [Ac] sorbent, low SO2 concentration resulted in the longest break through times but lowest sorption capacities. The granulated KOH activated carbon and pure activated carbon had highest NO2 break through times compared to [C(2)mim] [Ac] sorbents. The simultaneous SO2 and NO2 sorption studies indicated that the [C(2)mim] [Ac] sorbent had greater selectivity for SO2 than NO2 compared to the KOH sorbents, as evidenced by high breakthrough times for SO2 compared to NO2. Theoretical studies using DFT-B3LYP were performed to elucidate the favored binding interactions of the [C(2)mim] [Ac] with acidic gas contaminants. Theory indicates acidic gas contaminants preferentially interact strongly with the oxygen atoms of the acetate anion compared to the imidazole cation. The computational work also confirmed experiments showing high selectivity of the 1-ethyl-3-methylimidazolium acetate ionic liquid sorbent for SO2 compared to NO2.

Elements constituting a fuel cell laboratory are succinctly discussed using the experience developed at the Hawaii Sustainable Energy Research Facility. The information is expected to be useful to organizations with a desire to create or improve a fuel cell laboratory in view of the recent and anticipated fuel cell commercialization activities. Topics discussed cover a wide range with an emphasis on differentiating aspects from other types of laboratories including safety, fuel cell and test equipment, and methods used to characterize fuel cells. The use of hydrogen, oxygen and specifically introduced chemical species, and the presence of high voltages and electrical short risks constitute the most prominent hazards. Reactant purity, cleaning, test station control including data acquisition, and calibration are the most important considerations to ensure fuel cell characterization data quality. Cleanliness is also an important consideration for the fuel cell assembly and integration into the test station. The fuel cell assembly also needs to be verified for faults. Fuel cells need to be conditioned for optimum performance before a purposefully designed test plan is implemented. Many fuel cell diagnostic methods are available but novel techniques are still needed in many areas including through plane temperature distribution, stack diagnostics and mass transfer properties. The emphasis is given to commonly and sparingly used electrochemical techniques. In situ techniques include polarization, impedance spectroscopy, voltammetry and current distribution over the active area. Ex situ techniques include the rotating ring- disc electrode and the membrane conductivity cell. Other nonelectrochemical techniques are also useful to understand fuel cell behavior and include the analysis of reactant streams and condensed water, and spectroscopic measurements in combination with electrochemical cells (spectroelectrochemical cells).

A diagnostic method for the performance degradation of low temperature proton exchange membrane fuel cells is proposed. The method is based on the analysis of the cell electrochemical noise. Experimental noise data were collected for a range of air relative humidities and stoichiometries including conditions leading to water flooding, membrane dehydration and air starvation failure modes. Data were converted with a Fourier transform (frequency window averaging of the amplitude) and a wavelet transform (coefficients standard deviation). Data were compared to impedance spectroscopy results. The method based on the wavelet transform was more sensitive. Cell states labeled by their air relative humidity and stoichiometry were correctly identified using a brute force algorithm by minimizing the Chebyshev distance between the actual and the calculated states. Independent and uniformly distributed random variations were added to experimental wavelet coefficients' standard deviations to define the calculated states.

As progress toward the commercial deployment of wave energy converters accelerates, it is important to ensure that these renewable energy systems do not have unintended, adverse environmental consequences. While the sound from wave energy converters is unlikely to cause acoustic injury to marine animals, it may affect their behavior. Here, we present measurements from a point-absorber wave energy converter at the U.S. Navy Wave Energy Test Site in Kaneohe Bay, HI. Measurements of wave converter sound are obtained for a range of sea states using a combination of free-drifting near-surface measurements and stationary bottom packages. The relative effectiveness of these systems are contrasted and the unique challenges associated with acoustic measurements at energetic sites discussed. For example, fixed measurements are found to be substantially contaminated by flow-noise (non-propagating sound) during long-period ocean swell, while free-drifting measurements require significant post-processing to avoid convolving flow-noise or self-noise with wave converter sound. Preliminary results of parabolic equation modeling is also presented and used to interpret spatially distributed measurements.