WHAT ARE SOME OF THE PROBLEMS TO BE SOLVED?
COST REDUCTIONS: There are many technical hurdles remaining before hydrogen becomes economically viable as an energy source, and to succeed in the transportation market, hydrogen must be cost-competitive with conventional fuels and technologies on a per-mile basis.  The following table spotlights costs associated with several selected hydrogen production methods:
Source: Congressional Research Service, 2020
IMPROVED PRODUCTION TECHNOLOGIES:
Government and industry researchers are working to determine which mix of hydrogen production methods and feedstocks will best serve the needs of the USA and the world - both economically and environmentally. Each hydrogen production method has its own challenges:
- Natural Gas Reforming: This process is an advanced and mature production process that builds on the existing natural gas pipeline delivery infrastructure. Reforming low-cost natural gas can provide hydrogen for fuel cell electric vehicles and other applications. DOE expects that hydrogen production from natural gas will be augmented with production from renewable, nuclear, coal, and other low-carbon, domestic energy resources.
- Biomass Gasification: This process uses heat, steam, and oxygen to convert biomass to hydrogen and other products, without combustion. Key challenges involve reducing costs associated with capital equipment and biomass feedstocks, including replacing the cryogenic process currently used, developing new membrane technologies, combining steps of the process, and improved agricultural practices to result in low and stable feedstock costs.
- Electrolysis: More research is needed to reduce the capital cost of the electrolyzer unit and the balance of the system and improve energy efficiency for converting electricity to hydrogen. Also, integrating compression into the electrolyzer to avoid the cost of a separate hydrogen compressor is needed to increase pressure for hydrogen storage. Today’s grid electricity is not the ideal source of electricity for electrolysis because most of it is generated using technologies that produce greenhouse gases and are energy intensive. Electricity from renewable or nuclear energy could be a viable option.
- Biomass-Derived Liquid Reforming: Reforming biomass-derived liquids is a process very similar to reforming natural gas, except biomass-derived liquids are composed of larger molecules with more carbon atoms than natural gas, making them more difficult to reform. Future research needs to identify better catalysts to improve yields and selectivity. Other challenges include: Reducing the cost of biomass-derived liquids; and reducing capital equipment costs, as well as operation and maintenance costs, and improving process efficiency.
- Fermentation: Key areas of research and development include: Improving the rates and yields of hydrogen production from fermentation processes through a number of methods such as microbial strain improvements, reactor system optimization, and identifying feedstock sources and processing methods with the highest yields; and developing MEC systems that can be scaled up to commercially relevant sizes while maintaining the production rates and system efficiencies seen at the bench scale and minimizing the costs of the reactor components.
- Thermochemical Water Splitting: While exciting progress continues, leveraging synergies with concentrated solar power technologies, and with emerging solar-fuel production technologies, the efficiency and durability of reactant materials for thermochemical cycling need to be improved; and efficient and robust reactor designs compatible with high temperatures and heat cycling need to be developed. For solar thermochemical (STCH) systems, the cost of the concentrating mirror systems needs to be reduced.
- Photobiological Water Splitting: Further research is needed to: improve the activity of the enzymes that produce the hydrogen, as well as the metabolic pathways needed for the reactions, to increase the hydrogen production rates; develop strains that can efficiently use the sunlight and other inputs to increase the hydrogen yields; and develop strains and reactor configurations that can ultimately be used at large scales for commercial hydrogen production.
- Photoelectrochemical Water Splitting: Continued improvements in efficiency, durability, and cost are needed for market viability, but ongoing R&D of PEC materials, devices, and systems is making important strides and hydrogen production costs are being lowered through reduced materials and materials processing costs. Efficiencies are being improved through enhanced sunlight absorption and better surface catalysis. The durability and lifetime are being improved with more rugged materials and protective surfaces.
ADVANCED DELIVERY TECHNOLOGIES: Key challenges to hydrogen delivery include reducing cost, increasing energy efficiency, maintaining hydrogen purity, and minimizing hydrogen leakage. Further research is needed to analyze the trade-offs between hydrogen production and delivery. Research is being conducted to: improve the reliability and lower the cost of hydrogen compression; to reduce the cost and footprint of hydrogen storage; develop improved, lower cost materials for pipelines; discover new approaches to hydrogen liquefaction; develop lighter weight, stronger materials and structures for high pressure hydrogen storage and transport; and develop novel low pressure solid and liquid carrier systems for delivery and storage.
MORE COMPACT STORAGE: Hydrogen can be stored in a variety of ways, but to be a competitive fuel for vehicles, researchers still need to develop technology for storing enough hydrogen on-board a vehicle to achieve a driving range of greater than 300 miles - a comparable distance to conventional hydrocarbon-fueled vehicles. While some light-duty hydrogen fuel cell electric vehicles capable of this range have emerged onto the market, they rely on compressed gas onboard storage using large-volume, high-pressure composite vessels. This may work for larger vehicles but providing sufficient hydrogen storage across all light-duty platforms remains a challenge, so most research in this area is centered on the storage of hydrogen in a lightweight, compact manner suitable to the smaller mobile applications. Current research for storage of hydrogen has resulted in hydrides (both simple and complex), carbon nanotubes, and metal organic frameworks. These are in various stages of research and commercialization. The U.S. Department of Energy’s Fuel Cell Technologies Office (FCTO) has a goal to develop, by 2020, these hydrogen storage targets for onboard light-duty vehicle, material-handling equipment, and portable power applications, that will allow these hydrogen-fueled platforms to meet customer performance expectations for range, passenger and cargo space, refueling time, and overall vehicle performance:
- 1.5 kWh/kg system (4.5 wt.% hydrogen)
- 1.0 kWh/L system (0.030 kg hydrogen/L)
- $10/kWh ($333/kg stored hydrogen capacity)
In September 2018, at the International Hydrogen Infrastructure Workshop in Boston, MA, the DOE Fuel Cell Technologies Office described the status and growth of the U.S. hydrogen fueling network in its presentation: Overview of Status of Hydrogen Fueling Infrastructure in U.S. One of the challenges discussed is hydrogen fueling station reliability.
Source: U.S. Department of Energy, 2018
Updated June 2022 by Erin Bennett
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