The Hydrogen and Fuel Cell Center

LOHC storage and transport concept (H₀LOHC: unloaded LOHC, H_nLOHC: loaded LOHC).

The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m(2) g(-1) and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 °C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support.

into chemical energy sources and raw materials, is the basis for securing a future sustainable "green" energy supply. Some weaknesses and inconsistencies in the practice of determining the electrocatalytic performance, which prevents a rational bottom-up catalyst design, are discussed. Large discrepancies in material properties as well as in electrocatalytic activity and stability become obvious when materials are tested under the conditions of their intended use as opposed to the usual laboratory conditions. They advocate for uniform activity/stability correlations under application-relevant conditions, and the need for a clear representation of electrocatalytic performance by contextualization in terms of functional investigation or progress towards application is emphasized.

reduction reaction, reported in the literature. However, almost none of them entered the stage of application yet. Likewise, the reports on process engineering inadequately address the utilization of these catalysts, as well as electrode and cell concepts, that might be suitable for the market. Evidently, a closer collaboration between chemists and engineers from industry and academia is desirable to speed up the development of these disruptive technologies. Herein, we elucidate the critical parameters and highlight the necessary aspects to accelerate the development of industrially relevant catalysts capable of fulfilling the forthcoming challenges related to energy conversion and storage. The aim of this Perspective, composed by industrial and academic partners, is to critically question current undertakings and to encourage researchers to strike interdisciplinary research pathways.

Abstract The EU Integrated Project Real‐SOFC aims at improving the understanding of degradation in SOFC stacks, and extending the durability of planar SOFC stacks to degradation rates suitable for stationary application. As part of the Real‐SOFC project, three series of SOFC stacks, each with two or four planar anode‐supported cells, were operated for durations of 3,000 h up to 10,000 h under varying fuel and electrical load conditions. The durability tests on these short stacks were conducted galvanostatically at 800 and 700 °C in dependence of current‐density (0.3, 0.5 or 0.7 A cm –2 ), of fuel composition (hydrogen: H 2 + 3–10% H 2 O or methane: CH 4 /H 2 O ( S/C = 2)) and of fuel utilisation (8, 40, 60 or 75%). A pronounced difference in degradation behaviour was observed between the stacks operated at different current densities. The degradation behaviour was, however, not influenced by the choice of fuel (hydrogen or methane) and was hardly influenced by the fuel utilisation. Lowest degradation rates of about 20 mΩ cm 2 kh –1 were determined for the tests of a short stack with cells with LSM cathodes operated at 800 °C and a current‐density of 0.3 A cm –2 and of a short stack with cells with LSCF cathodes operated at 700 °C and a current‐density of 0.5 A cm –2 . Post‐test characterisation of the cathode with respect to chromium poisoning was performed on cells from several stacks. No clear relationship between the degradation rate of the stacks and amount of Cr incorporated in the cathode could be established. The major difference was a change in microstructure of the cathode in the region near the electrolyte interface; in the stacks operated at lower current densities, the structurally changed zone was clearly thinner than in those stacks operated at higher currents.

In this paper, the optimization of a power management strategy of a fuel cell/battery/supercapacitor hybrid vehicular system is investigated, both offline and in real time. Two offline optimization algorithms, namely, dynamic programming and Pontryagin's minimum principle, are first compared. The offline optimum is used as a benchmark when designing a real-time strategy, which is an inevitable step since the offline optimum is not real-time capable and is oriented only toward minimizing hydrogen consumption, which may result in the unnecessary overloading of the battery. The design and optimization of the real-time strategy makes use of a multiobjective genetic algorithm while taking into account, apart from hydrogen consumption, other important factors, such as the slow dynamics of the fuel cell system and minimizing the battery power burden. As a result, the real-time strategy is found to consume slightly more hydrogen than the offline optimum; however, it dramatically improves system durability.

Abstract Gas crossover is an unavoidable phenomenon in proton exchange fuel cell membranes. Nitrogen and oxygen from the cathode pass through the membrane to the anode, while hydrogen crosses from the anode to the cathode. The hydrogen crossover leads to a reduction in efficiency due to parasitic hydrogen consumption and mixed potentials on the cathode electrode. Furthermore it causes degradation effects and pinhole formation. Hence the hydrogen crossover represents a fundamental factor for the lifetime of a fuel cell and quantification of the crossover is a key factor for membrane qualification. In this article two in situ electrochemical techniques to evaluate the hydrogen crossover are described, cyclic voltammetry and potential step method. Both methods and the achieved results are compared to each other. Finally the potential step method is applied to evaluate the hydrogen crossover as a function of the anode pressure and the hydrogen permeability coefficients are determined.

Celtec-V is a proton exchange membrane based on polybenzimidazole (PBI) comprising an interpenetrating network of polyvinylphosphonic acid designed for application in the direct methanol fuel cell. The properties and fuel cell performance of Celtec-V are investigated and compared against a Nafion 117 standard. It is shown that with the PBI-based membrane, fuel cell performance can be sustained to higher methanol feed concentration at around half the methanol crossover rate. Above 1.0 M methanol, Celtec-V outperforms Nafion 117. Furthermore, lower water permeation is observed, with Celtec-V having an electro-osmotic drag coefficient of around 1 compared to a value of 4-5 for Nafion 117. Room for improvement is identified in the ohmic resistance of the membrane and the cathode-membrane interface, where higher losses are observed at increasing current density.

ABSTRACT: The CAPP2 trial investigated the long-term effects of aspirin and resistant starch on cancer incidence in patients with Lynch syndrome (LS). Participants with LS were randomized double-blind to 30 g resistant starch (RS) daily or placebo for up to 4 years. We present long-term cancer outcomes based on the planned 10-year follow-up from recruitment, supplemented by National Cancer Registry data to 20 years in England, Wales, and Finland. Overall, 463 participants received RS and 455 participants received placebo. After up to 20 years follow-up, there was no difference in colorectal cancer incidence (n = 52 diagnosed with colorectal cancer among those randomized to RS against n = 53 on placebo) but fewer participants had non-colorectal LS cancers in those randomized to RS (n = 27) compared with placebo (n = 48); intention-to-treat (ITT) analysis [HR, 0.54; 95% confidence interval (CI), 0.33-0.86; P = 0.010]. In ITT analysis, allowing for multiple primary cancer diagnoses among participants by calculating incidence rate ratios (IRR) confirmed the protective effect of RS against non-colorectal cancer LS cancers (IRR, 0.52; 95% CI, 0.32-0.84; P = 0.0075). These effects are particularly pronounced for cancers of the upper GI tract; 5 diagnoses in those on RS versus 21 diagnoses on placebo. The reduction in non-colorectal cancer LS cancers was detectable in the first 10 years and continued in the next decade. For colorectal cancer, ITT analysis showed no effect of RS on colorectal cancer risk (HR, 0.92; 95% CI, 0.62-1.34; P = 0.63). There was no interaction between aspirin and RS treatments. In conclusion, 30 g daily RS appears to have a substantial protective effect against non-colorectal cancer cancers for patients with LS. PREVENTION RELEVANCE: Regular bowel screening and aspirin reduce colorectal cancer among patients with LS but extracolonic cancers are difficult to detect and manage. This study suggests that RS reduces morbidity associated with extracolonic cancers. See related Spotlight, p. 557.

The integration of cross-sectoral energy hubs into large-scale wind farms opens up existing structures to new applications and contributes to achieving renewable energy systems and climate protection targets. The offshore energy hub concept consists in establishing an artificially constructed energy conversion and distribution hub that addresses two energy-related markets by power supply to public grids and by potentially enabling the conversion of renewable electricity into hydrogen or ammonia and supplying it ashore. Hence, the energy hub concept enables smart integration of offshore wind power into gas grids. Power generation on demand from stored green gas is able to cover residual power loads at low carbon intensity. Electrofuel production provides also the opportunity to export renewable fuels for sectors with traditionally high greenhouse gas emissions, e.g., agriculture or transportation. In this contribution an energy hub system in the North Sea is modeled and simulated to determine production quantities and efficiencies of electricity, hydrogen and ammonia. When comparing the efficiencies of production, storage, and transport values of 45.1–65% for hydrogen and values of 52–52.3% for ammonia were determined. Re-conversion to electricity with fuel cells of both hydrogen and ammonia is less efficient and cost worthly than their use in electrofuel applications. Because of emerging and potential cost reductions a sensitivity analysis is performed where lower capital costs (50%) lead to cost reductions in hydrogen (42–45%) and ammonia production (40–42%). Results show that energy hubs can become sustainable pillars in future energy systems through improving cost-competitiveness of wind power.

Abstract It is known that traffic related air contaminants cause power loss, decreasing lifetime or a complete failure of proton exchange membrane fuel cell (PEMFC). Therefore, the present study aims for a better understanding and the development of a data basis for further decisions in dealing with air contaminants for automobile applications. The first section provides an overview of scientific literature about the influence of important air contaminants on proton exchange membrane fuel cells (PEMFC). The second section describes an extensive study of air contaminants at possible automotive operating conditions using a full factorial matrix test. The specific variation of temperature, cell potential and harmful gas concentration resulted in 27 operating points for each used air contaminant. The gases NO, NO 2 , SO 2 , NH 3 , toluene and ethane were used. The results indicate significant degradation but as well the possibility of regeneration. The degradation caused by different harmful gases is both, dependent on temperature and potential. Furthermore, a clear difference of the influence of NO and NO 2 at low concentrations could be shown. The experiments give an overview of the cathode harming potential of relevant air contaminants. Hence, the work provides a basis for the development of cathode air filter and regeneration techniques for automotive applications.

Abstract High-power, nanosecond, pulsed-laser ablation in liquids enables the continuous synthesis of highly pure colloidal nanoparticles (NPs) at an application-relevant scale. The gained mass-weighted particle size distribution is however often reported to be broad, requiring post treatment like centrifugation to remove undesired particle size fractions. To date, available centrifugation techniques are generally discontinuous, limiting the throughput and hindering economic upscaling. Hence, throughout this paper, a scalable, continuously operating centrifugation of laser-generated platinum NPs in a tubular bowl centrifuge is reported for the first time. To that end, using a 121 W ns-laser, the continuous production of a colloidal suspension of NPs, yet with broad particle size distribution has been employed, yielding productivities of 1–2 g h −1 for gold, silver, and platinum. The power-specific productivities (Au: 18 mg h −1 W −1 , Pt: 13 mg h −1 W −1 , Ag: 8 mg h −1 W −1 , Ni: 6 mg h −1 W −1 ) are far higher than reported before. Subsequent downstream integration of a continuously operating tubular bowl centrifuge was successfully achieved for Pt NPs allowing the removal of undesired particle size with high throughput. By means of a systematic study of relevant centrifugation parameters involved, effective size optimization and respective size sharpness parameters for a maximum Pt NP diameter of 10 nm are reported. The results of the experimental centrifugation of laser-generated Pt NPs were in excellent agreement with the theoretically calculated cut-off diameter. After centrifugation with optimized parameters (residence time of 5 min; g-force of 38,454 g), the polydispersity indices of the Pt NPs size distributions were reduced by a factor of six, and high monodispersity was observed.

Abstract A hydrogen storage tank based on the metal hydride sodium alanate is coupled with a high temperature PEM fuel cell (HT‐PEM). The waste heat of the fuel cell is used for desorbing hydrogen from the storage tank that in return feeds the fuel cell. ZBT has developed the HT‐PEM fuel cell, Max‐Planck‐Institut für Kohlenforschung the sodium alanate, and IUTA the hydrogen storage tank. During the experiments of the system the fuel cell was operated by load cycling from 165 up to 240 W. Approximately 60 g of hydrogen were delivered from the tank, which was charged with 2676.8 g of sodium alanate doped with 4 mol.% of TiCl 3 . This amount of hydrogen was desorbed in 3 h and generated a cumulated electrical energy of 660 Wh. In the first cycle 81.5 g of hydrogen were supplied during 3.69 h to the HT‐PEM fuel cell, which was operated nearly constant at 260 W. In the latter case the cumulated electrical energy was 941 Wh.

Abstract The polymer electrolyte membrane (PEM) fuel cell model of a commercial software package is presented. The basic performance model is extended by two chemical degradation effects: ionomer degradation and carbon corrosion including platinum oxidation. The ionomer degradation model describes the ionomer mass loss due to hydrogen peroxide formation and subsequent attack of the ionomer by radicals. The carbon corrosion model calculates the carbon mass loss caused by carbon oxidation and the active area reduction due to platinum oxidation. The degradation models are coupled with an agglomerate model of the catalyst layer. The model is validated against measurements on an industrial cell. For these measurements, the cell is equipped with a segmented measuring board, which is used to measure the current density distribution and high frequency resistance of every segment. In order to test the predictability of the model under different operating conditions, measurements for stoichiometry and pressure variations are carried out. Calculated and measured current density distributions of the cell, aged by an accelerated stress test, are compared for the validation of the degradation model. Moreover, 3D simulation results of the fresh and aged cells are analyzed in detail and the influence of operating conditions on fuel cell aging is pointed out.

A single-channel DMFC is constructed that allows for flow measurements at the anode side as well as detailed time–resolved cell-voltage measurement. The coherence between flow and bubble clogging and slug movement can be investigated without parasitic effects like flow shortcuts through the gas diffusion layer (GDL) between neighbouring channels, as in serpentine or parallel-channel configurations. Optical access is granted to the anode side by a transparent foil, which is necessary for the application of the laser-optical velocity measurement technique (micro–particle image velocimetry, μPIV). Small fluorescent particles are added to the fluid, which are illuminated by a laser. The particle movement can be optically detected using a microscope, and transferred to a planar velocity field. Hence, the appearance and evolution of CO2 bubbles can be qualitatively and quantitatively investigated. The analysis of the velocity structure around a CO2 bubble or a moving slug allows a deeper understanding of the coherence of fluid motion, channel blockage, and cell performance. In addition to the flow analysis, a time-resolved measurement of the cell voltage is performed. The results clearly indicate that the cell power increases when huge bubbles reduce the free cross-section area of the channel. Methanol is forced into the GDL, i.e. methanol is continuously convected to the catalyst layer and is oxidised to CO2. Hence, the fuel consumption increases and the cell performance rises. When the huge bubble is released from the GDL and forms a moving slug, the moving slug effectively cleans the channel from CO2 bubbles on its way downstream. Since the channel cross-section is not severely diminished by the bubbles at this stage, the methanol flow is no longer forced into the GDL. The remaining amount of methanol in the GDL is oxidised. The cell power decreases until enough CO2 is produced to eventually form bubbles again that significantly reduce the free cross-section of the channel, and the process starts again.

PtPd catalysts are state-of-the-art for automotive diesel exhaust gas treatment. Although wet-chemical preparation of PtPd nanoparticles below 3 nm and kg-scale synthesis of supported PtPd/Al2O3 are already established, the partial segregation of the bimetallic nanoparticles remains an issue that adversely affects catalytic performance. As a promising alternative, laser-based catalyst preparation allows the continuous synthesis of surfactant-free, solid-solution alloy nanoparticles at the g/h-scale. However, the required productivity of the catalytically relevant size fraction <10 nm has yet to be met. In this work, by optimization of ablation and fragmentation conditions, the continuous flow synthesis of nanoparticles with a productivity of the catalytically relevant size fraction <10 nm of >1 g/h is presented via an in-process size tuning strategy. After the laser-based preparation of hectoliters of colloid and more than 2 kg of PtPd/Al2O3 wash coat, the laser-generated catalysts were benchmarked against an industry-relevant reference catalyst. The conversion of CO by laser-generated catalysts was found to be equivalent to the reference, while improved activity during NO oxidation was achieved. Finally, the present study validates that laser-generated catalysts meet the size and productivity requirements for industrial standard operating procedures. Hence, laser-based catalyst synthesis appears to be a promising alternative to chemical-based preparation of alloy nanoparticles for developing industrial catalysts, such as those needed in the treatment of exhaust gases.

Cyclic voltammetry, electrochemical impedance spectroscopy and current distribution measurements are employed at single cells and a fuel cell stack to reveal the differences and interrelations of ammonia, nitrogen oxide and nitrogen dioxide. It is shown that both nitrogen oxides are adsorbed at the catalyst as NO. The adsorption of NO2 is weaker and therefore leads to a lower and slower degradation. Moreover, all gases cause inhomogeneous stress of the MEA, which can lead to an accelerated degradation of the fuel cell. NH3 shows a combined reaction by partly being adsorbed as a nitric oxide and partly reacting with the perfluorosulfonic acid groups of the ionomer.

In a scenario characterized by an increasing penetration of non-dispatchable renewable energy sources and the need of fast-ramping grid-balancing power plants, the EU project GRASSHOPPER aims to setup and demonstrate a highly flexible PEMFC Power Plant, hydrogen fueled and scalable to MW-size, designed to provide grid support. In this work, different layouts proposed for the innovative MW-scale plant are simulated to optimize design and off-design operation. The simulation model details the main BoP components performances and includes a customized PEMFC model, validated through dedicated experiments. The system may operate at atmospheric or mild pressurized conditions: pressurization to 0.7 barg allows significantly higher net system efficiency, despite the increasing BoP consumptions. The additional energy recovery from the cathode exhaust with an expander gives higher net power and net efficiency, adding up to 2%pt and reaching values between 47%LHV and 55%LHV for currents between 100% and 20% of the nominal value.

Abstract The oxygen evolution reaction (OER) as one half‐cell reaction of electrochemical water splitting has a fundamental impact on water splitting efficiency and thus on the competitiveness of electrochemically generated hydrogen in the energy market. Nickel‐iron layered double hydroxides (NiFe LDH) are among the most promising electrocatalysts for efficient OER under alkaline conditions. Despite intensive research, correlations of the material properties and the resulting kinetically limiting surface processes are poorly investigated. This work focuses on the kinetic behavior of NiFe LDH catalysts containing different anions in the basal spacing in alkaline OER. Steady‐state Tafel plots, impedance measurements as well as reaction order plots were used to elucidate differences in the catalytic performance. All catalysts showed a dual Tafel behavior and fractional reaction orders. For kinetic modelling, the physisorbed hydrogen peroxide mechanism and Temkin adsorption model were adopted to fit experimental data. Our study showed that the intercalated anions affect the kinetics of rate determining steps. The hypophosphite intercalated LDH possessed the highest OER activity and the first step as rate determining. While for both carbonate and borate intercalated NiFe LDH, the second step proved to be rate determining in the low Tafel region, while the first step was found to be rate‐limiting in the high Tafel region.

Catalyst layers (CL), as an active component of the catalyst coated membrane (CCM), form the heart of the polymer electrolyte membrane fuel cell (PEMFC). For optimum performance of the fuel cell, obtaining suitable structural and functional characteristics for the CL is crucial. Direct tuning of the microstructure and morphology of the CL is non-trivial; hence catalyst inks as CL precursors need to be modulated, which are then applied onto a membrane to form the CCM. Obtaining favorable dispersion characteristics forms an important prerequisite in engineering catalyst inks for large scale manufacturing. In order to facilitate a knowledge-based approach for developing fuel cell inks, this work introduces new tools and methods to study both the dispersion state and stability characteristics, simultaneously. Catalyst inks were prepared using different processing methods, which include stirring and ultrasonication. The proposed tools are used to characterize and elucidate the effects of the processing method. Structural characterization of the dispersed particles and their assemblages was carried out by means of transmission electron microscopy. Analytical centrifugation (AC) was used to study the state and stability of the inks. Herein, we introduce new concepts, S score, and stability trajectory, for a time-resolved assessment of inks in their native state using AC. The findings were validated and rationalized using transmittograms as a direct visualization technique. The flowability of inks was investigated by rheological measurements. It was found that probe sonication only up to an optimum amplitude leads to a highly stable colloidal ink.