FUEL CELL TECHNOLOGIES OFFICE

Hydrogen Storage Figure 2: A schematic of a Compact, reliable, safe, and cost- Type-IV Composite effective storage of hydrogen is a Overwrapped Pressure Vessel key challenge to the widespread (COPV) designed for commercialization of fuel cell electric compressed hydrogen vehicles (FCEVs) and other hydrogen storage on-board Fuel fuel cell applications. While some light- Cell Electric Vehicles (FCEVs) duty FCEVs with a driving range of over 300 miles are emerging in limited (Credit: Process Modeling Group, markets, affordable onboard hydrogen Nuclear Engineering TPRD=Thermally Activated storage still remains as a key roadblock. Pressure Relief Device Division. Argonne National Lab (ANL)) Hydrogen has a low energy density. While the energy per mass of hydrogen Near-term hydrogen on developing lower cost precursor is substantially greater than most other storage solutions and fibers, however cost reduction strategies for conversion processes are also being fuels, as can be seen in Figure 1, its research needs energy by volume is much less than considered. Other cost reduction efforts The first generation of FCEVs use 700 liquid fuels like gasoline. For a 300 mile for compressed hydrogen storage bar Type IV pressure vessels to store driving range, an FCEV will need about systems include developing alternative hydrogen. Type IV pressure vessels, as 5 kg of hydrogen. At 700 bar (~10,000 lower cost and high performance shown in Figure 2, have a plastic liner psi) a storage system would have a fiber and resin materials, composite overwrapped by expensive carbon-fiber volume of about 200 liters or 3-4 times additives for improved performance, composite material to provide strength. the volume of gasoline tanks typically and alternative pressure vessel The use of carbon fiber composites found in cars today. A key challenge, manufacturing processes and identifying result in significantly lower weight therefore, is how to store sufficient alternative materials for balance-of- than all metal pressure vessels would quantities of hydrogen onboard without plant components. Analysis of 700 bar have. The use of Type IV pressure sacrificing passenger and cargo space. in 2015 projected a 12% reduction in vessels, however, increases the cost of the cost of Type IV onboard systems Much of the effort of the Hydrogen storing hydrogen in FCEVs, primarily compared to the 2013 baseline system Storage program is focused on due to the high cost of the carbon fiber cost.1 developing cost-effective hydrogen composite material, as can be seen in Figure 3. storage technologies with improved Long-term research energy density. Research and The cost of high-strength carbon fiber development efforts include high- directions comes almost equally from the cost of pressure compressed storage and Longer-term research focuses on the precursor fiber and the conversion materials-based storage technologies. developing advanced hydrogen of the precursor fiber to carbon fiber. storage technologies that can meet the To reduce the cost of high-strength challenging performance levels required carbon fiber, the program has focused

Figure 1: Gravimetric and volumetric energy densities Figure 3: Potential strategy to meet cost target (700 bar cH2). To meet the ultimate cost of common fuels based on lower heating values target for 700 bar systems, the bulk of cost reductions must come from reducing the calculated for ambient temperature conditions. amount and costs of carbon fiber composite materials and Balance-of-Plant (BOP) FUEL CELL TECHNOLOGIES OFFICE

for FCEVs while providing greater the surface of porous solids, providing storage materials. The program has energy density than 700 bar compressed the potential for higher storage densities recently launched the Hydrogen hydrogen at competitive cost. There are at significantly lower pressures. Two Materials-Advanced Research two key approaches being pursued: 1) types of metal hydrides investigated Consortium (HyMARC) to bridge use of sub-ambient storage temperatures as reversible (or rechargeable) storage many of these gaps by coordinating and 2) materials-based hydrogen storage materials include a) intermetallic (or newer synthetic and characterization technologies. interstitial) hydrides where hydrogen techniques with advanced multi- occupies interstitial spaces within scale modeling capabilities. New As shown in Figure 4, higher hydrogen metal alloys (e.g., LaNi5H6), and b) materials development projects are densities can be obtained through complex hydrides where hydrogen being incorporated into HyMARC in use of lower temperatures. Cold and covalently bonds to a metal to form an effort to accelerate the discovery cryogenic-compressed hydrogen a multi-element anion that combines of breakthrough storage materials. systems allow designers to store the with another metal(s) through ionic In addition, existing characterization same quantity of hydrogen either in interactions (e.g., Na(AlH4)). In and validation activities have been smaller volumes at the same pressure, or chemical hydrogen storage materials, consolidated into the Hydrogen Storage in the same volume at lower pressures. also known as off-board regenerable Characterization Optimization Research The program supports efforts to develop materials, the hydrogen typically Effort (HySCORE) to support the and evaluate insulated system designs bonds to other elements through either program’s entire materials based storage that minimize heat leakage into the covalent bonds (e.g., NH3BH3) or development project portfolio. vessels so that the hydrogen can be ionic interactions (e.g., CaH2). The stored for extended periods of time hydrogen is released from chemical In addition to developing hydrogen without the need for venting. Efforts hydrogen storage materials through storage materials, understanding how also support a better understanding non-equilibrium processes so the the materials would function in a of material performance under these now-depleted materials have to be complete system is critical. System temperature and pressure conditions. removed and chemically processed design needs to account for factors such to regenerate the original hydrogen as a) how the material is packaged, b) Hydrogen can also be densely stored containing material. Hydrogen sorbents how hydrogen flows into and through in materials at low pressures. Atomic are high-surface area, micro-porous the system and c) how heat associated hydrogen can bind with other elements solids (e.g., activated carbons or with the charge and discharge of to form compounds or solid solutions metal-organic frameworks (MOFs)) hydrogen is moved into and out of and molecular hydrogen can adsorb onto where the diatomic hydrogen molecule the systems, all while meeting safety adsorbs onto the surface through van requirements. The program has der Waals interactions. The challenge supported another Center of Excellence for all hydrogen storage material to investigate engineering aspects development efforts is to develop cost- of materials-based hydrogen storage effective materials with high hydrogen systems for FCEVs. This effort has density by volume and mass. Moreover, produced and made available complete these materials must be capable of system models that allow researchers fast charge/discharge rates within the to predict how their materials would temperature and pressure ranges of fuel perform when incorporated into a 2 cell operation and be able to undergo system. The models also provide the sufficient charge/ discharge cycles to opportunity to “reverse” engineer from last the lifetime of the FCEV. system level performance to material properties to better guide researchers The program has supported three in developing materials that meet multi-partner programs (Centers of the challenging hydrogen storage Excellence) and independent projects requirements. investigating hydrogen storage 1 https://www.hydrogen.energy.gov/ materials, but gaps still remain in Figure 4: Cold or Cryogenic-compressed pdfs/15013_onboard_storage_performance_ hydrogen storage leads to higher on-board the foundational understanding of cost.pdf hydrogen storage hydrogen densities the interaction of hydrogen with 2 http://hsecoe.org/models.php

For more information, visit: hydrogenandfuelcells.energy.gov

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