Hydrogen Storage Engineering Center Of Excellence Research Articles

Engineering Challenges of Solution and Slurry-Phase Chemical Hydrogen Storage Materials for Automotive Fuel Cell Applications.

We present the research findings of the DOE-funded Hydrogen Storage Engineering Center of Excellence (HSECoE) related to liquid-phase and slurry-phase chemical hydrogen storage media and their potential as future hydrogen storage media for automotive applications. Chemical hydrogen storage media other than neat liquid compositions will prove difficult to meet the DOE system level targets. Solid- and slurry-phase chemical hydrogen storage media requiring off-board regeneration are impractical and highly unlikely to be implemented for automotive applications because of the formidable task of developing solid- or slurry-phase transport systems that are commercially reliable and economical throughout the entire life cycle of the fuel. Additionally, the regeneration cost and efficiency of chemical hydrogen storage media is currently the single most prohibitive barrier to implementing chemical hydrogen storage media. Ideally, neat liquid-phase chemical hydrogen storage media with net-usable gravimetric hydrogen capacities of greater than 7.8 wt% are projected to meet the 2017 DOE system level gravimetric and volumetric targets. The research presented herein is a collection of research findings that do not in and of themselves warrant a dedicated manuscript. However, the collection of results do, in fact, highlight the engineering challenges and short-comings in scaling up and demonstrating fluid-phase ammonia borane and alane compositions that all future materials researchers working in hydrogen storage should be aware of.

Specific heat capacities of MOF-5, Cu-BTC, Fe-BTC, MOF-177 and MIL-53 (Al) over wide temperature ranges: Measurements and application of empirical group contribution method

Specific heat capacities of five MOFs: MOF-5, Cu-BTC, Fe-BTC, MIL-53 (Al) and MOF-177 are reported over wide temperature ranges. For MOF-5, which is the primary candidate material down selected by the Hydrogen Storage Engineering Center of Excellence (HSECoE) for cyro-adsorptive vehicular hydrogen storage, specific heat capacity in the range 2–300 K is obtained by combining the measurements using a Calvet calorimeter and a direct adiabatic relaxation calorimeter while for remaining MOFs, Cps are measured in the temperature range 80–320 K using the Calvet calorimeter alone. All MOFs exhibit monotonically increasing specific heat capacities with no visible thermal anomalies implying the absence of any temperature-induced phase transitions in the temperature range considered. A simple ion-based group contribution approach is applied to empirically predict the specific heat capacities of all MOFs at 323 K.

Development and validation of a slurry model for chemical hydrogen storage in fuel cell vehicle applications

The U.S. Department of Energy's (DOE) Hydrogen Storage Engineering Center of Excellence (HSECoE) is developing models for hydrogen storage systems for fuel cell-based light duty vehicle applications for a variety of promising materials. These transient models simulate the performance of the storage system for comparison to the DOE's Technical Targets and a set of four drive cycles. PNNL developed models to simulate the performance and suitability of slurry-based chemical hydrogen storage materials. The storage systems of both a representative exothermic system based on ammonia borane and an endothermic system based on alane were developed and modeled in Simulink®. Once complete, the reactor and radiator components of the model were validated with experimental data. The system design parameters were adjusted to allow the model to successfully meet a highway cycle, an aggressive cycle, a cold–start cycle, and a hot drive cycle. Finally, a sensitivity analysis was performed to identify the range of material properties where these DOE targets and drive cycles could be met. Materials with a heat of reaction >11 kJ mol−1 H2 generated and a slurry hydrogen capacity of >11.4% will meet the on-board efficiency and gravimetric capacity targets, respectively.

Systems modeling, simulation and material operating requirements for chemical hydride based hydrogen storage

Research on ammonia borane (AB, NH 3BH 3) has shown it to be a promising material for chemical hydride based hydrogen storage. AB was selected by DOE’s Hydrogen Storage Engineering Center of Excellence (HSECoE) as the initial chemical hydride of study because of its high hydrogen storage capacity (up to ∼16% by weight for the release of ∼2.5 M equivalents of hydrogen gas) and its stability under typical ambient conditions. Another promising candidate is alane, AlH 3 (10.1% by weight). Materials operating requirements to use chemical hydrides for vehicle onboard storage are discussed. A flow-through system concept based on augers, ballast tank, hydrogen heat exchanger and H 2 burner was designed and implemented in simulation. In this design, the chemical hydride material was assumed to produce H 2 in the auger itself, thus minimizing the size of ballast tank and reactor. One dimensional models based on conservation of mass, species and energy were used to predict important state variables such as reactant and product concentrations, temperatures of various components, flow rates, along with pressure, in various components of the storage system. Various subsystem components in the models were coded as ‘C’ language S-functions and implemented in Matlab/Simulink. Steady state simulation results for all the three candidate materials (solid AB, liquid AB and alane) were presented to show the proof of concept, whereas the drive cycle simulations were discussed only for solid AB using the fuel cell H 2 demand for four different US drive cycles. Conditional logic based controllers that control the material flow rate into the reactor and to control the H 2 fed to the burner were developed and implemented in drive cycle simulations. Simulation results show that the proposed system meets most of the 2010 DOE targets, and is well above the required > 40% of the DOE targets for fill time, well-to-powerplant efficiency, and volumetric and gravimetric density.

Dynamic Modeling and Simulation Based Analysis of an Ammonia Borane (AB) Reactor System for Hydrogen Storage

Research on ammonia borane (AB, NH3BH3) has shown it to be a promising material for chemical hydrogen storage in PEM fuel cell applications. AB was selected by DOE's Hydrogen Storage Engineering Center of Excellence (HSECoE) as the initial chemical hydride of study because of its high hydrogen storage capacity (up to 19.6% by weight for the release of three molar equivalents of hydrogen gas) and its stability under typical ambient conditions. A model of a bead reactor system which includes feed and product tanks, hot and cold augers, a ballast tank/reactor, a H2 burner and a radiator was developed to study AB system performance in an automotive application and estimate the energy, mass, and volume requirements for this off-board regenerable hydrogen storage material. Preliminary system simulation results for a start-up case and for a transient drive cycle indicate appropriate trends in the reactor system dynamics. A new controller was developed and validated in simulation for a couple of H2 demand cases.