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This study presents an online algorithm capable to simultaneously estimate the state of charge and state of health of a vanadium redox flow battery. Starting from a general electrochemical model, some order reductions are carried out considering different conservation laws. Based on these low-order models, the observer is designed considering the terminal voltage of the battery. This observer is firstly analyzed using numerical tools. Secondly, an experimental validation is carried out with real data provided by a vanadium redox flow battery stack, consisting on current and voltage measurements., Peer Reviewed, Postprint (published version)

In the present research, the performance of three commercial graphite felts (a 6 mm thick Rayon-based Sigracell®, a 4.6 mm thick PAN-based Sigracell®, and a 6 mm thick PAN-based AvCarb®) used as electrodes in vanadium redox flow batteries (VRFBs) is analyzed before and after thermal activation. The thermal treatment of the electrodes at 500 °C for 1 h in a self-designed industrial furnace under a synthetic air atmosphere. XPS confirms that thermal activation provides with different C=O/Csingle bondO and sp2/sp3 ratios to the graphite electrodes depending on their carbon precursors, providing different catalitic behavior. T-GFD4.6-EA felt electrode was also oxidized by cycling in H2SO4 and in 0.4 M VOSO4 + 2 M H2SO4 solution. In the first case, the graphite electrode increased the current density 24.27 mA cm−2 for the VO2+ electrooxidation, however the cathodic current density (VO2+ reduction reaction) was decreased 36 mA cm−2. In the second case, the increase was of 21.27 mA cm−2, whereas the current density for the VO2+ reduction hardly changed. Thermally treated GFD4.6-EA graphite felt chemical composition also changed differently when exposed to different laboratory experiments which mimic the electrode behavior in a VRFB. XPS analysis confirmed that the chemical modification of the graphite surfaces can either improve or decrease the electrocatalytic activity of the electrodes depending on their carbon precursors.

This study presents a vanadium redox flow battery model that considers the most important variables that have a crucial role in the performance of the system. A complete model divided in an electrochemical, thermal, hydraulic and voltage submodels is presented. The analytic analysis of the model is carried out to reduce the system order according to some conservation laws. Based on this analysis, a subsequent calibration of the model parameters is developed using real experimental data. The validation is performed comparing the real measured voltage and the one estimated with the model. To calibrate the model an algorithm based on the implementation of a particle swarm optimizer is used. Results obtained in both short and long-term operation are presented, in order to compare and validate if the model can be used for both state of charge and state of health estimation.

Figure S1: Thermostated electrochemical reactor with a typical three-electrode configuration. Figure S2: Deconvoluted spectra of C1s peak for a) T-GFD4.6 (100 cycles in 2 M H2SO4), b) T-GFD4.6 (immersion 2 M H2SO4 0.4 M VOSO4) and c) T-GFD4.6 (100 cycles 2 M H2SO4 0.4 M VOSO4). Figure S3: Deconvoluted spectra of O1s peak for a) T-GFD4.6 (100 cycles in 2 M H2SO4), b) T-GFD4.6 (immersion 2 M H2SO4 0.4 M VOSO4) and c) T-GFD4.6 (100 cycles 2 M H2SO4 0.4 M VOSO4). Figure S4: Deconvoluted spectra of N1s peak for a) T-GFD4.6 electrode after being immersed 5 days in 2 M H2SO4 + 0.4 M VOSO4 electrolyte b) the T-GFD4.6 activated after 100 CV cycles in 2 M H2SO4. Figure S5: Tafel plots of the a) GFD4.6-EA, GFA6 and Avcarb6 and b) T-GFD4.6-EA, T-GFA6 and T-Avcarb6 obtained from the Linear Sweep Voltammetry curves. Figure S6: Linear relationship between the logarithm of the redox peak current and the logarithm of the scan rate for the thermal pre-treated electrodes; a)T-GFD4.6, b) T-AvCarb6 and c) T-GFA6. Table S1. Table S2. Table S3.

When fuel cells are used to power mobile applications, such a vehicles, hybridization with batteries is normally required. Depending on the electronic coupling between the energy sources the power plants can have passive or active configurations. Hybrid fuel cell-battery power plants with active power control flow have some advantages. For example, they can decrease the total energy losses, while improving the fuel cell performance, extending its lifetime. Power plants with DC/DC converters show low specific energy ratios, but with a superior energy management. In the present research, the hybrid power plant for an unmanned aquatic surface vehicle (USV) based on a PEM fuel cell and a Li-ion battery is developed. Active (with DC–DC converters) or passive architectures are analyzed by numerical simulations and experimental tests. Good results are obtained for the active power plant, where the peak power demands are managed by the battery pack while the fuel cell power remains constant thanks to the DC-converter control. The study shows that a simple control algorithm (no optimal) can help to extend the USV autonomy above 12 h in calm waters with a specific energy of 85.6 W h kg-1.

In this research, the flow behavior through a commercial electrode used in Redox Flow Batteries (RFB) was characterized by means of Planar Laser Induced Fluoresce imaging (PLIF) for different cell configurations, without channels or with channels machined either in the back plate or in the electrode. Measurements of the pressure drop were obtained for each case, and the evolution of the electrode soaking process was quantified defining an electrode surface wetting rate. Using the pressure drop measurements, equivalent Darcy and intrinsic permeability coefficients were calculated for the different configurations. It was observed that the tight fitting of the electrode within its housing appears to be crucial for an adequate distribution of the electrolyte within the porous media. In general, when channels are available, the electrolyte tends to circulate along them, without crossing through the electrode felt, and lower pressure losses are accompanied by lower wetting rates. The flow field with serpentine channels in the back plate could be considered the most suitable configuration in terms of energy consumption, nearly 87% less than in a case without any channels, but this same percentage of electrolyte will exit the cell without traversing the electrode, and thus not contributing to the electrochemical reactions.

The Jarama River, due to its proximity to Madrid, has been a highly regulated and polluted for decades; we evaluated the effects of changing multi-pressures over time and along the fluvial continuum. Changes in macrobenthic composition and structure in response to alterations in river habitat have been analyzed from two macroinvertebrate sampling campaigns carried out 42 years apart at 11 locations along the Jarama River. Results show that the macrobenthic communities follow a similar pattern along the river continuum in both periods. Richness and diversity were higher at mountain reaches without pollution and unregulated. The minimum values are reached at San Fernando de Henares, although in the lower part of the river, after receiving all the pollution discharges from the Manzanares River, there are no macrobenthos since the Jarama bottoms are anoxic sludge. Comparing the communities at the same localities we have detected clear temporal changes. In the upper zone, the total number of taxa and diversity decreased, but the fauna richness is maintained. In the section just below large reservoirs we find an increase in macrobenthos richness. In all the medium sections there is a recovery in all the macrobenthos parameters, but this improvement does not reach good ecological status, due to the high concentrations of ammonia. In the lower section, no changes are detected because the accumulated sludge is still present.

In the present research, a commercial battery-powered pure electric vehicle was suitably modified to convert it into a hybrid one integrating a PEMFC stack. The hydrogen supply system to the stack included a passive recirculation system based on a Ventury-type ejector. Besides, in order to achieve an optimum operation of the PEMFC stack, a discrete state machine model was considered in its control system. The inclusion of a rehabilitation operating mode prevented the stack from possible failures, increasing its lifetime. It was verified that for the rated operating point when supplying power to the vehicle (2.5 kW) the hydrogen consumption decreased, and the actual efficiency (47.9%) PEMFC was increased close to 1%. Field tests performed demonstrate that the range of the hybrid electric vehicle was increased by 78% when compared to the one of the original battery electric car. Also, under the tested experimental conditions in hybrid mode, 34% of the total energy demanded by the electric machine of the vehicle was supplied by the PEMFC stack.

Fuel and oxidant starvation are amongst the most critical phenomena affecting fuel cell durability. Reactant starvation during proton exchange membrane fuel cell operation can cause serious irreversible damages. In the present research, the effect of a selective induced starvation of reactant gases on the performance and degradation of a high-temperature PEM fuel cell is studied. A specifically designed 5-cell stack is used, which enables varying the gas supplied to any of the individual cells. The particularity of selectively starving only one cell in a controlled manner is one of the novelties of this study. Two different tests are performed actuating on the central cell (cell 3). They are denoted as moderate and severe starvation, depending on the intensity of the limitation imposed to the gases flowrate. Some relevant and novel results are obtained. It is verified that the performance degradation caused by a moderate starvation of the reactant gases in a cell is reversible. On the contrary, the damages caused by an aggressive gas starvation, which is also maintained in time (30 min), are irreversible. However, the behavior of the rest of the cells is barely affected by the gas starvation to cell 3. Thus, the other major novelty of the present work is the evidence/proof of the ability of a stack with a starved and highly degraded cell, to continue operating, although with a drastic reduction in the total generated current.

The present research aims to assess the durability of a single cell formed by a commercial high-temperature membrane electrode assembly (MEA) and Al bipolar plates (Al-BPPs) coated with Ni-P. To this end, an accelerated degradation test based on voltage load cycles is carried out, and the effects of the degradation on the MEA and its impact on the Al-coated bipolar plates are analyzed. They are compared with the results obtained testing a similar cell formed by the same MEA with graphite plates. MEAs from both cells were analyzed by different characterization techniques before and after the degradation tests (XRD, SEM, TEM). The performance of the Al-based cell is initially better, but it suffers a faster deterioration mainly due to the degradation of the Ni-P surface coating. A green deposit is formed, probably due to the chemical reaction of the phosphoric acid leached from the MEA. These deposits cause an increase in the contact resistance of the plates, local channel blockages and, eventually, a larger degradation. This work proves that PBI membranes still need to be improved to ensure their long-term durability.

An electrochemical reactor, with a membrane-electrode-assembly technology, has been developed for the electrochemical reduction of CO in gas phase. The reactor was carefully designed to prevent the strong corrosion by the high overpotentials required for addressing CO reduction. In addition, electrodes based on Fe and Pt supported on Vulcan XC-72R (the commercial carbon black often used for electrochemical applications) were used as cathode. These electrodes favor the CO confinement in the nanoporous structure of the carbon support, resulting in higher pressures at the electrocatalytic surface, and consequently, enhancing the performance. The behavior of the electrodes for CO reduction was studied in both acid media (0.5 M HSO) and in gas phase using the designed reactor in order to establish a correlation of the results. A higher current density was developed for the Pt-based electrode due to a significant formation of H by the water reduction, whereas the CO conversion could be favored on the Fe electrode, in both acid media and gas phase.

In the present research, the energy demanded by the wastewater treatment plant of a winery and the pumping station of the irrigation system of a vineyard is supplied by a stand-alone renewable energy system formed by three photovoltaic arrays connected to a microgrid. A relatively small battery maintains the stability and quality of the energy supply acting as a short-term energy storage. Hydrogen is generated in a production and refueling plant specifically designed for this project, and it is eventually used in a plug-in BEV properly modified as a hybrid vehicle by adding a PEM fuel cell. On the one hand, the technical and economic feasibility of the on-site electricity production for the winery and vineyard, compared to the commercial electricity from the grid and diesel gensets, is demonstrated. On the other hand, the diesel savings by the hydrogen generated on site are assessed. The electricity (72 MWh) and hydrogen (1214 m3) produced in the first year have saved the emission of around 27 tons of equivalent CO2.

Several tagging methods have been tested to assess important aspects on ecology, such as population dynamic, movement pattern, and behavioral studies. The use of external and internal tags has been extensively used for individual identification in sea urchins. Different types of tags have been used in Echinometra lucunter, considered the most common sea urchin in the Caribbean. We evaluated whether PIT-tags and S-tags may affect retention, survival and growth rates under laboratory conditions, using the sea urchin E. lucunter as a model. The type of tag was critical in terms of retention rates, with significant differences between PIT-tag and S-tags groups (Kruskal–Wallis, H = 5.33, p = 0.021), and mortality exhibited similar rates among treatments. No significant association was detected between initial maximum test diameter and the number of weeks the individuals retained neither the PIT-tag (r = −0.09, p = 0.620), nor the S-tag (r = −0.175, p = 0.413), and no significant differences in growth rate were detected among treatments (F = 1.66, df = 2, p = 0.401). We do not recommend the use of S-tag due to low retention; but we support the use of PIT-tags in E. lucunter for their positive performance displayed in terms of retention and survival but with caution, particularly in those studies requiring 80% or higher retention.

Development of new materials for polymer electrolyte membranes has allowed increasing the operational temperature of PEM fuel cell stacks above 120 °C. The present paper summarizes the main results obtained in a research devoted to the design, fabrication and operational tests performed on a high-temperature PEMFC prototype. A 5-cell stack has been assembled with commercial Celtec P-1000 high-temperature MEAs from BASF Fuel Cells, but the rest of elements and processes have been developed at LIFTEC research facilities. The stack includes different novelties, such as the way in which reactant gases are supplied to the flowfield, the design of the flowfield geometry for both anode and cathode plates, the concept of block that eases the assembling and maintenance processes, and the heating strategy for a very fast start-up. The different procedures comprising the assembly, closing and conditioning stages are also widely described and discussed. Results obtained in the preliminary operational tests performed are very promising, and it is expected that the 30-cells HT-PEMFC stack will deliver an electric power 2.3 times larger than the one initially predicted.

The Iberian Symposium on Hydrogen, Fuel Cells and Advanced Batteries (Hyceltec) emerged from the Spanish Network of Fuel Cells, Hydrogen and Advanced Batteries (REPICOBA), created in 2001 as an initiative of the Spanish National Research Council (CSIC) and also joined by a significant number of research teams from different Spanish Universities. An annual workshop was regularly organized from 2002 to 2006 and, due to its fast growth and success, in 2007 the Organizing Committee of REPICOBA decided to extend the participation to research teams and industrial companies in the Iberian Peninsula and Latin-American Countries, turning the Network into Hyceltec.

Response to the comments on “Experimental study of the pressure drop in the cathode side of air-forced open-cathode proton exchange membrane fuel cells” by Dejan Brkic

The electrical and corrosion properties of CrN-coated aluminium alloy Magnal-45 (Al-5083) probes have been evaluated, in order to assess their viability to be used as bipolar plates in polymer electrolyte fuel cells. To this end, ceramic micro-layers of chromium nitride (CrN) with different thicknesses (3, 4. and 5 mu m) have been deposited on the surface of the Al alloy (Al-5083) using the physical vapour deposition (PVD) technique. A decrease in 2 orders of magnitude of I(corr) values for the coated Al has been observed compared to the as-received Al-alloy when the probes have been exposed to simulated anodic conditions in a micro-reactor. On the other hand, when subjected to a cathodic-simulated environment, the Al-CrN probes with 3 mu m and 4 mu m coatings have shown a decrease in I(corr) of one order of magnitude, while a variation of two orders of magnitude has also been obtained for the 5 mu m coating. (C) 2010 Elsevier B.V. All rights reserved.

The present work is devoted to determine the magnitude of the main parameters that yield the optimum results for twin-fluid nozzles with an internal mixing chamber. The focus is placed on the study of the interaction of both air and liquid flows at the internal chamber and its effects on the resulting spray. To this end, some experiments have been performed for different air central channel diameters and liquid ports, as well as for several experimental conditions (air and liquid mass flow rates), in order to understand the influence of the flow conditions at the mixing chamber on the size of the droplets produced. It has been demonstrated that under certain experimental conditions the atomizing fluid discharged to the internal chamber is choked. The sonic condition is achieved for different air and liquid mass flow rates as a function of the air central channel diameter. It has also been obtained that to achieve the best results with moderate atomizing fluid flow rates, it is convenient to operate in choked conditions. This is an important result that will help in the optimum design of this type of nozzles. © 2008 Elsevier B.V. All rights reserved.

After studying the velocity and pressure fields inside bipolar plates with different geometries, the analysis has been extended to include the gas passage across the backing or gas diffusion layer (GDL). The gas flow emerging from the porous layer has been monitored using acetone vapor laser-induced fluorescence. The different configurations tested are a parallel commercial case, a set of parallel diagonal channels, a branching cascade-type, and a serpentine distribution of parallel channel blocks. The experimental results have been compared with the predictions obtained from a computational numerical simulation. This study has served to determine the most suitable topology among the tested ones, and has also revealed that knowing the velocity map inside the bipolar plate may not be sufficient to decide if the gas distribution over the catalyst is going to be homogeneous and if a fuel cell is going to operate in an efficient way.

This experimental research studies some aspects of water formation and management in polymer electrolyte membrane fuel cells (PEMFCs). To this end, two different single cells of 49 cm2 active area have been tested, the first one with a serpentine-parallel geometry and the second with a cascade-type flow-field topology. In order to visualize the processes, flow-field channels have been machined on transparent plastic. Experiments have consisted in both image acquisition using a CCD camera, and simultaneous measurements of pressure drop in both hydrogen and oxygen gas flow paths. It has been observed that with the cascade-type flow-field geometry, water produced in the cathode does not flood the gas flow channels and, consequently, can be drained in an easy way. On the other hand, it has also been verified that saturated condition for the hydrogen gas flow at the anode side produces water condensation and channel flooding for the serpentine-parallel flow-field topology. Time fluctuations in the pressure drop of the gas flow have been detected and are associated to some transient process inherent to water formation and management. © 2008 Elsevier B.V. All rights reserved.

The flow of air to feed oxygen to the cathode of each plate in a proton exchange membrane fuel cell (PEMFC) is studied for a 300 W stack in a realistic 3D configuration. Two configurations for gas income are solved, a "U" shape, where both the inlet and outlet of the air collectors are at the same end plate, and a "Z" shape, where inlet and outlet are at opposite sides of the stack. Under a simplified assumption for the flow of oxygen entering the gas diffusion layer of each cell, detailed mass flow and pressure distributions are shown, including the possibility of a turbulent flow inside the main collectors. © 2008 Elsevier B.V. All rights reserved.

The flow distribution obtained with three different bipolar plate geometries has been studied, analyzing their fluid dynamic performance. Three plate topologies have been selected in some way representative of different design models commonly used. The configurations tested are a set of parallel diagonal channels, a branching cascade type, and a serpentine distribution of parallel channel blocks. The flow distribution across the plates has been first simulated numerically. To visualize the flow pattern at the plate channels plane, a laser-induced fluorescence (LIF) trace tracking technique has been applied. From experimental and numerical simulations it is concluded that the diagonal topology distributes the flow in a non-uniform way. On the other hand, an inadequately large pressure drop is established along the serpentine-parallel plate. In the cascade case, both velocity and pressure fields are very uniform, and it can be expected to produce a very homogeneous distribution of reactants over the catalyst layer.