The US Department of Energy’s (DOE’s) Fuel Cell Technologies Office (FCTO) has issued a request for information (RFI) (DE-FOA-0001596) to obtain feedback and input from stakeholders on strategies and potential pathways for cost reduction and performance improvements of composite overwrapped pressure vessel (COPV) systems for compressed hydrogen storage for onboard vehicle applications. The purpose of the RFI is to identify future strategic research and development pathways for the DOE to pursue with potential to meet future system cost targets.
Currently, carbon fiber (CF) reinforced polymer (CFRP) composites are used to make COPVs. Type III COPVs have a metallic liner and Type IV COPVs have non-metallic liners. COPVs designed to store hydrogen gas at pressures up to 700 bar are being deployed in fuel cell electric vehicles (FCEVs) currently available on the market.
While 700 bar compressed hydrogen storage provides a near-term commercialization pathway, the performance of this storage technology falls short of the DOE onboard FCEV hydrogen storage targets, particularly for volumetric hydrogen energy density and system cost. That high cost is a barrier for widespread commercial deployment of light-duty FCEVs.
Although improvements in compressed hydrogen storage volumetric density are limited by real gas compression physics, DOE suggests that there may be paths forward for significant system cost reductions to address DOE FCTO’s technical targets.
While DOE recognizes the impact of balance of plant (BOP) on the overall system cost, the RFI is focused primarily on the COPV as it is believed that industry will be the primary driver in designing their own specific hydrogen storage system BOP. Improved designs, such as conformable designs, have potential to reduce costs by reducing the need for multi-tank systems. However, in order to achieve a significant cost reduction of onboard compressed hydrogen storage systems, the primary focus needs to be on the composite materials used in these systems.
A primary cost driver of the composite materials and processing is the synthesis and conversion of precursor polymer into CF. Polyacrylonitrile (PAN) is the current state of the art precursor material that is converted to high-strength CF. Pitch-based CF is a lower cost alternative to PAN based CF; however, pitch-based CF has not been demonstrated to meet the strength and durability quality needed to meet 700 bar compressed hydrogen storage system performance.
The current synthesis and production of high-quality, high PAN content precursor fiber is expensive, representing approximately 50% of the cost of the CF. The conversion process of PAN precursor to CF is also energy intensive. Furthermore, the CF mass yield is approximately 50% relative to the PAN input mass.
Therefore alternative precursor materials that can lead to lower cost CF through lower cost materials, lower cost and less energy intensive processing, and/or higher CF output yields are of interest.
Another cost driver is the polymer resin. COPVs are typically made using epoxy type resins. The resin is critical for the distribution of shear stresses during hydrogen gas pressure loading to the CFs, which are the main structural elements of the tanks. Epoxy resins can be expensive and have high density, which is detrimental to system cost and gravimetric density.
DOE is requesting information on technology strategies and pathways to reduce the cost of components of Type III and Type IV COPVs, including but not limited to the composite materials such as CF precursors, lower cost conversion processes for CF production, alternative fibers to CF, lower cost polymer resins, resin additives, etc., and other components such as liner and boss materials.
In addition to strategies to reduce cost, DOE is also requesting information on technology strategies to improve system performance to reduce the amount of high cost composites required, designs for enhanced conformability and improved packaging, and design improvements with potential to lower cost of operation and improve performance of the refueling infrastructure (e.g., eliminate need for hydrogen pre-cooling).
This RFI is focused on COPVs which require high-strength fiber reinforced composites and is therefore differentiated by activities carried out through the EERE Vehicle Technology and Advanced Manufacturing Offices for vehicle lightweighting, which are focused on lower strength fiber reinforce composites.
RFI responses must be received no later than 5 pm Eastern Daylight Time on 30 June 2016.